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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='extendpoky'>

<title>Common Tasks</title>
    <para>
        This chapter describes fundamental procedures such as creating layers,
        adding new software packages, extending or customizing images,
        porting work to new hardware (adding a new machine), and so forth.
        You will find that the procedures documented here occur often in the
        development cycle using the Yocto Project.
    </para>

    <section id="understanding-and-creating-layers">
        <title>Understanding and Creating Layers</title>

        <para>
            The OpenEmbedded build system supports organizing
            <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink> into
            multiple layers.
            Layers allow you to isolate different types of customizations from
            each other.
            For introductory information on the Yocto Project Layer Model,
            see the
            "<ulink url='&YOCTO_DOCS_OM_URL;#the-yocto-project-layer-model'>The Yocto Project Layer Model</ulink>"
            section in the Yocto Project Overview and Concepts Manual.
        </para>

        <section id='creating-your-own-layer'>
            <title>Creating Your Own Layer</title>

            <para>
                It is very easy to create your own layers to use with the
                OpenEmbedded build system.
                The Yocto Project ships with tools that speed up creating
                layers.
                This section describes the steps you perform by hand to create
                layers so that you can better understand them.
                For information about the layer-creation tools, see the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-bitbake-layers-script'>Creating a New BSP Layer Using the <filename>bitbake-layers</filename> Script</ulink>"
                section in the Yocto Project Board Support Package (BSP)
                Developer's Guide and the
                "<link linkend='creating-a-general-layer-using-the-bitbake-layers-script'>Creating a General Layer Using the <filename>bitbake-layers</filename> Script</link>"
                section further down in this manual.
            </para>

            <para>
                Follow these general steps to create your layer without using
                tools:
                <orderedlist>
                    <listitem><para>
                        <emphasis>Check Existing Layers:</emphasis>
                        Before creating a new layer, you should be sure someone
                        has not already created a layer containing the Metadata
                        you need.
                        You can see the
                        <ulink url='http://layers.openembedded.org/layerindex/layers/'>OpenEmbedded Metadata Index</ulink>
                        for a list of layers from the OpenEmbedded community
                        that can be used in the Yocto Project.
                        You could find a layer that is identical or close to
                        what you need.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Create a Directory:</emphasis>
                        Create the directory for your layer.
                        When you create the layer, be sure to create the
                        directory in an area not associated with the
                        Yocto Project
                        <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                        (e.g. the cloned <filename>poky</filename> repository).
                        </para>

                        <para>While not strictly required, prepend the name of
                        the directory with the string "meta-".
                        For example:
                        <literallayout class='monospaced'>
     meta-mylayer
     meta-GUI_xyz
     meta-mymachine
                        </literallayout>
                        With rare exceptions, a layer's name follows this
                        form:
                        <literallayout class='monospaced'>
     meta-<replaceable>root_name</replaceable>
                        </literallayout>
                        Following this layer naming convention can
                        save you trouble later when tools, components, or
                        variables "assume" your layer name begins with "meta-".
                        A notable example is in configuration files as
                        shown in the following step where layer names without
                        the "meta-" string are appended
                        to several variables used in the configuration.
                        </para></listitem>
                    <listitem><para id='dev-layer-config-file-description'>
                        <emphasis>Create a Layer Configuration File:</emphasis>
                        Inside your new layer folder, you need to create a
                        <filename>conf/layer.conf</filename> file.
                        It is easiest to take an existing layer configuration
                        file and copy that to your layer's
                        <filename>conf</filename> directory and then modify the
                        file as needed.</para>

                        <para>The
                        <filename>meta-yocto-bsp/conf/layer.conf</filename> file
                        in the Yocto Project
                        <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta-yocto-bsp/conf'>Source Repositories</ulink>
                        demonstrates the required syntax.
                        For your layer, you need to replace "yoctobsp" with
                        a unique identifier for your layer (e.g. "machinexyz"
                        for a layer named "meta-machinexyz"):
                        <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

     # We have recipes-* directories, add to BBFILES
     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"

     BBFILE_COLLECTIONS += "yoctobsp"
     BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
     BBFILE_PRIORITY_yoctobsp = "5"
     LAYERVERSION_yoctobsp = "4"
     LAYERSERIES_COMPAT_yoctobsp = "&DISTRO_NAME_NO_CAP;"
                        </literallayout>
                        Following is an explanation of the layer configuration
                        file:
                        <itemizedlist>
                            <listitem><para>
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>:
                                Adds the layer's root directory to BitBake's
                                search path.
                                Through the use of the
                                <filename>BBPATH</filename> variable, BitBake
                                locates class files
                                (<filename>.bbclass</filename>),
                                configuration files, and files that are
                                included with <filename>include</filename> and
                                <filename>require</filename> statements.
                                For these cases, BitBake uses the first file
                                that matches the name found in
                                <filename>BBPATH</filename>.
                                This is similar to the way the
                                <filename>PATH</filename> variable is used for
                                binaries.
                                It is recommended, therefore, that you use
                                unique class and configuration filenames in
                                your custom layer.
                                </para></listitem>
                            <listitem><para>
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'><filename>BBFILES</filename></ulink>:
                                Defines the location for all recipes in the
                                layer.
                                </para></listitem>
                            <listitem><para>
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_COLLECTIONS'><filename>BBFILE_COLLECTIONS</filename></ulink>:
                                Establishes the current layer through a
                                unique identifier that is used throughout the
                                OpenEmbedded build system to refer to the layer.
                                In this example, the identifier "yoctobsp" is
                                the representation for the container layer
                                named "meta-yocto-bsp".
                                </para></listitem>
                            <listitem><para>
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PATTERN'><filename>BBFILE_PATTERN</filename></ulink>:
                                Expands immediately during parsing to
                                provide the directory of the layer.
                                </para></listitem>
                            <listitem><para>
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>:
                                Establishes a priority to use for
                                recipes in the layer when the OpenEmbedded build
                                finds recipes of the same name in different
                                layers.
                                </para></listitem>
                            <listitem><para>
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERVERSION'><filename>LAYERVERSION</filename></ulink>:
                                Establishes a version number for the layer.
                                You can use this version number to specify this
                                exact version of the layer as a dependency when
                                using the
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDEPENDS'><filename>LAYERDEPENDS</filename></ulink>
                                variable.
                                </para></listitem>
                            <listitem><para>
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDEPENDS'><filename>LAYERDEPENDS</filename></ulink>:
                                Lists all layers on which this layer depends (if any).
                                </para></listitem>
                            <listitem><para>
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERSERIES_COMPAT'><filename>LAYERSERIES_COMPAT</filename></ulink>:
                                Lists the
                                <ulink url='&YOCTO_WIKI_URL;/wiki/Releases'>Yocto Project</ulink>
                                releases for which the current version is
                                compatible.
                                This variable is a good way to indicate if
                                your particular layer is current.
                                </para></listitem>
                        </itemizedlist>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Add Content:</emphasis>
                        Depending on the type of layer, add the content.
                        If the layer adds support for a machine, add the machine
                        configuration in a <filename>conf/machine/</filename>
                        file within the layer.
                        If the layer adds distro policy, add the distro
                        configuration in a <filename>conf/distro/</filename>
                        file within the layer.
                        If the layer introduces new recipes, put the recipes
                        you need in <filename>recipes-*</filename>
                        subdirectories within the layer.
                        <note>
                            For an explanation of layer hierarchy that
                            is compliant with the Yocto Project, see
                            the
                            "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout'>Example Filesystem Layout</ulink>"
                            section in the Yocto Project Board
                            Support Package (BSP) Developer's Guide.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Optionally Test for Compatibility:</emphasis>
                        If you want permission to use the Yocto Project
                        Compatibility logo with your layer or application that
                        uses your layer, perform the steps to apply for
                        compatibility.
                        See the
                        "<link linkend='making-sure-your-layer-is-compatible-with-yocto-project'>Making Sure Your Layer is Compatible With Yocto Project</link>"
                        section for more information.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='best-practices-to-follow-when-creating-layers'>
            <title>Following Best Practices When Creating Layers</title>

            <para>
                To create layers that are easier to maintain and that will
                not impact builds for other machines, you should consider the
                information in the following list:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Avoid "Overlaying" Entire Recipes from Other Layers in Your Configuration:</emphasis>
                        In other words, do not copy an entire recipe into your
                        layer and then modify it.
                        Rather, use an append file
                        (<filename>.bbappend</filename>) to override only those
                        parts of the original recipe you need to modify.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Avoid Duplicating Include Files:</emphasis>
                        Use append files (<filename>.bbappend</filename>)
                        for each recipe that uses an include file.
                        Or, if you are introducing a new recipe that requires
                        the included file, use the path relative to the
                        original layer directory to refer to the file.
                        For example, use
                        <filename>require recipes-core/</filename><replaceable>package</replaceable><filename>/</filename><replaceable>file</replaceable><filename>.inc</filename>
                        instead of
                        <filename>require </filename><replaceable>file</replaceable><filename>.inc</filename>.
                        If you're finding you have to overlay the include file,
                        it could indicate a deficiency in the include file in
                        the layer to which it originally belongs.
                        If this is the case, you should try to address that
                        deficiency instead of overlaying the include file.
                        For example, you could address this by getting the
                        maintainer of the include file to add a variable or
                        variables to make it easy to override the parts needing
                        to be overridden.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Structure Your Layers:</emphasis>
                        Proper use of overrides within append files and
                        placement of machine-specific files within your layer
                        can ensure that a build is not using the wrong Metadata
                        and negatively impacting a build for a different
                        machine.
                        Following are some examples:
                        <itemizedlist>
                            <listitem><para>
                                <emphasis>Modify Variables to Support a
                                Different Machine:</emphasis>
                                Suppose you have a layer named
                                <filename>meta-one</filename> that adds support
                                for building machine "one".
                                To do so, you use an append file named
                                <filename>base-files.bbappend</filename> and
                                create a dependency on "foo" by altering the
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                                variable:
                                <literallayout class='monospaced'>
     DEPENDS = "foo"
                                </literallayout>
                                The dependency is created during any build that
                                includes the layer
                                <filename>meta-one</filename>.
                                However, you might not want this dependency
                                for all machines.
                                For example, suppose you are building for
                                machine "two" but your
                                <filename>bblayers.conf</filename> file has the
                                <filename>meta-one</filename> layer included.
                                During the build, the
                                <filename>base-files</filename> for machine
                                "two" will also have the dependency on
                                <filename>foo</filename>.</para>
                                <para>To make sure your changes apply only when
                                building machine "one", use a machine override
                                with the <filename>DEPENDS</filename> statement:
                                <literallayout class='monospaced'>
     DEPENDS_one = "foo"
                                </literallayout>
                                You should follow the same strategy when using
                                <filename>_append</filename> and
                                <filename>_prepend</filename> operations:
                                <literallayout class='monospaced'>
     DEPENDS_append_one = " foo"
     DEPENDS_prepend_one = "foo "
                                </literallayout>
                                As an actual example, here's a snippet from the
                                generic kernel include file
                                <filename>linux-yocto.inc</filename>,
                                wherein the kernel compile and link options are
                                adjusted in the case of a subset of the supported
                                architectures:
                                <literallayout class='monospaced'>
     DEPENDS_append_aarch64 = " libgcc"
     KERNEL_CC_append_aarch64 = " ${TOOLCHAIN_OPTIONS}"
     KERNEL_LD_append_aarch64 = " ${TOOLCHAIN_OPTIONS}"

     DEPENDS_append_nios2 = " libgcc"
     KERNEL_CC_append_nios2 = " ${TOOLCHAIN_OPTIONS}"
     KERNEL_LD_append_nios2 = " ${TOOLCHAIN_OPTIONS}"

     DEPENDS_append_arc = " libgcc"
     KERNEL_CC_append_arc = " ${TOOLCHAIN_OPTIONS}"
     KERNEL_LD_append_arc = " ${TOOLCHAIN_OPTIONS}"

     KERNEL_FEATURES_append_qemuall=" features/debug/printk.scc"
                                </literallayout>
                                <note>
                                    Avoiding "+=" and "=+" and using
                                    machine-specific
                                    <filename>_append</filename>
                                    and <filename>_prepend</filename> operations
                                    is recommended as well.
                                </note>
                                </para></listitem>
                            <listitem><para>
                                <emphasis>Place Machine-Specific Files in
                                Machine-Specific Locations:</emphasis>
                                When you have a base recipe, such as
                                <filename>base-files.bb</filename>, that
                                contains a
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                                statement to a file, you can use an append file
                                to cause the build to use your own version of
                                the file.
                                For example, an append file in your layer at
                                <filename>meta-one/recipes-core/base-files/base-files.bbappend</filename>
                                could extend
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                                using
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                                as follows:
                                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"
                                </literallayout>
                                The build for machine "one" will pick up your
                                machine-specific file as long as you have the
                                file in
                                <filename>meta-one/recipes-core/base-files/base-files/</filename>.
                                However, if you are building for a different
                                machine and the
                                <filename>bblayers.conf</filename> file includes
                                the <filename>meta-one</filename> layer and
                                the location of your machine-specific file is
                                the first location where that file is found
                                according to <filename>FILESPATH</filename>,
                                builds for all machines will also use that
                                machine-specific file.</para>
                                <para>You can make sure that a machine-specific
                                file is used for a particular machine by putting
                                the file in a subdirectory specific to the
                                machine.
                                For example, rather than placing the file in
                                <filename>meta-one/recipes-core/base-files/base-files/</filename>
                                as shown above, put it in
                                <filename>meta-one/recipes-core/base-files/base-files/one/</filename>.
                                Not only does this make sure the file is used
                                only when building for machine "one", but the
                                build process locates the file more quickly.</para>
                                <para>In summary, you need to place all files
                                referenced from <filename>SRC_URI</filename>
                                in a machine-specific subdirectory within the
                                layer in order to restrict those files to
                                machine-specific builds.
                                </para></listitem>
                        </itemizedlist>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Perform Steps to Apply for Yocto Project Compatibility:</emphasis>
                        If you want permission to use the
                        Yocto Project Compatibility logo with your layer
                        or application that uses your layer, perform the
                        steps to apply for compatibility.
                        See the
                        "<link linkend='making-sure-your-layer-is-compatible-with-yocto-project'>Making Sure Your Layer is Compatible With Yocto Project</link>"
                        section for more information.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Follow the Layer Naming Convention:</emphasis>
                        Store custom layers in a Git repository that use the
                        <filename>meta-<replaceable>layer_name</replaceable></filename>
                        format.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Group Your Layers Locally:</emphasis>
                        Clone your repository alongside other cloned
                        <filename>meta</filename> directories from the
                        <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='making-sure-your-layer-is-compatible-with-yocto-project'>
            <title>Making Sure Your Layer is Compatible With Yocto Project</title>

            <para>
                When you create a layer used with the Yocto Project, it is
                advantageous to make sure that the layer interacts well with
                existing Yocto Project layers (i.e. the layer is compatible
                with the Yocto Project).
                Ensuring compatibility makes the layer easy to be consumed
                by others in the Yocto Project community and could allow you
                permission to use the Yocto Project Compatible Logo.
                <note>
                    Only Yocto Project member organizations are permitted to
                    use the Yocto Project Compatible Logo.
                    The logo is not available for general use.
                    For information on how to become a Yocto Project member
                    organization, see the
                    <ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink>.
                </note>
            </para>

            <para>
                The Yocto Project Compatibility Program consists of a layer
                application process that requests permission to use the Yocto
                Project Compatibility Logo for your layer and application.
                The process consists of two parts:
                <orderedlist>
                    <listitem><para>
                        Successfully passing a script
                        (<filename>yocto-check-layer</filename>) that
                        when run against your layer, tests it against
                        constraints based on experiences of how layers have
                        worked in the real world and where pitfalls have been
                        found.
                        Getting a "PASS" result from the script is required for
                        successful compatibility registration.
                        </para></listitem>
                    <listitem><para>
                        Completion of an application acceptance form, which
                        you can find at
                        <ulink url='https://www.yoctoproject.org/webform/yocto-project-compatible-registration'></ulink>.
                        </para></listitem>
                </orderedlist>
            </para>

            <para>
                To be granted permission to use the logo, you need to satisfy
                the following:
                <itemizedlist>
                    <listitem><para>
                        Be able to check the box indicating that you
                        got a "PASS" when running the script against your
                        layer.
                        </para></listitem>
                    <listitem><para>
                        Answer "Yes" to the questions on the form or have an
                        acceptable explanation for any questions answered "No".
                        </para></listitem>
                    <listitem><para>
                        Be a Yocto Project Member Organization.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                The remainder of this section presents information on the
                registration form and on the
                <filename>yocto-check-layer</filename> script.
            </para>

            <section id='yocto-project-compatible-program-application'>
                <title>Yocto Project Compatible Program Application</title>

                <para>
                    Use the form to apply for your layer's approval.
                    Upon successful application, you can use the Yocto
                    Project Compatibility Logo with your layer and the
                    application that uses your layer.
                </para>

                <para>
                    To access the form, use this link:
                    <ulink url='https://www.yoctoproject.org/webform/yocto-project-compatible-registration'></ulink>.
                    Follow the instructions on the form to complete your
                    application.
                </para>

                <para>
                    The application consists of the following sections:
                    <itemizedlist>
                        <listitem><para>
                            <emphasis>Contact Information:</emphasis>
                            Provide your contact information as the fields
                            require.
                            Along with your information, provide the
                            released versions of the Yocto Project for which
                            your layer is compatible.
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Acceptance Criteria:</emphasis>
                            Provide "Yes" or "No" answers for each of the
                            items in the checklist.
                            Space exists at the bottom of the form for any
                            explanations for items for which you answered "No".
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Recommendations:</emphasis>
                            Provide answers for the questions regarding Linux
                            kernel use and build success.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='yocto-check-layer-script'>
                <title><filename>yocto-check-layer</filename> Script</title>

                <para>
                    The <filename>yocto-check-layer</filename> script
                    provides you a way to assess how compatible your layer is
                    with the Yocto Project.
                    You should run this script prior to using the form to
                    apply for compatibility as described in the previous
                    section.
                    You need to achieve a "PASS" result in order to have
                    your application form successfully processed.
                </para>

                <para>
                    The script divides tests into three areas: COMMON, BSP,
                    and DISTRO.
                    For example, given a distribution layer (DISTRO), the
                    layer must pass both the COMMON and DISTRO related tests.
                    Furthermore, if your layer is a BSP layer, the layer must
                    pass the COMMON and BSP set of tests.
                </para>

                <para>
                    To execute the script, enter the following commands from
                    your build directory:
                    <literallayout class='monospaced'>
     $ source oe-init-build-env
     $ yocto-check-layer <replaceable>your_layer_directory</replaceable>
                    </literallayout>
                    Be sure to provide the actual directory for your layer
                    as part of the command.
                </para>

                <para>
                    Entering the command causes the script to determine the
                    type of layer and then to execute a set of specific
                    tests against the layer.
                    The following list overviews the test:
                    <itemizedlist>
                        <listitem><para>
                            <filename>common.test_readme</filename>:
                            Tests if a <filename>README</filename> file
                            exists in the layer and the file is not empty.
                            </para></listitem>
                        <listitem><para>
                            <filename>common.test_parse</filename>:
                            Tests to make sure that BitBake can parse the
                            files without error (i.e.
                            <filename>bitbake -p</filename>).
                            </para></listitem>
                        <listitem><para>
                            <filename>common.test_show_environment</filename>:
                            Tests that the global or per-recipe environment
                            is in order without errors (i.e.
                            <filename>bitbake -e</filename>).
                            </para></listitem>
                        <listitem><para>
                            <filename>common.test_world</filename>:
                            Verifies that <filename>bitbake world</filename> works.
                            </para></listitem>
                        <listitem><para>
                            <filename>common.test_signatures</filename>:
                            Tests to be sure that BSP and DISTRO layers do not
                            come with recipes that change signatures.
                            </para></listitem>
                        <listitem><para>
                            <filename>common.test_layerseries_compat</filename>:
                            Verifies layer compatibility is set properly.
                            </para></listitem>
                        <listitem><para>
                            <filename>bsp.test_bsp_defines_machines</filename>:
                            Tests if a BSP layer has machine configurations.
                            </para></listitem>
                        <listitem><para>
                            <filename>bsp.test_bsp_no_set_machine</filename>:
                            Tests to ensure a BSP layer does not set the
                            machine when the layer is added.
                            </para></listitem>
                        <listitem><para>
                            <filename>bsp.test_machine_world</filename>:
                            Verifies that <filename>bitbake world</filename>
                            works regardless of which machine is selected.
                            </para></listitem>
                        <listitem><para>
                            <filename>bsp.test_machine_signatures</filename>:
                            Verifies that building for a particular machine
                            affects only the signature of tasks specific to that
                            machine.
                            </para></listitem>
                        <listitem><para>
                            <filename>distro.test_distro_defines_distros</filename>:
                            Tests if a DISTRO layer has distro configurations.
                            </para></listitem>
                        <listitem><para>
                            <filename>distro.test_distro_no_set_distros</filename>:
                            Tests to ensure a DISTRO layer does not set the
                            distribution when the layer is added.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='enabling-your-layer'>
            <title>Enabling Your Layer</title>

            <para>
                Before the OpenEmbedded build system can use your new layer,
                you need to enable it.
                To enable your layer, simply add your layer's path to the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'>BBLAYERS</ulink></filename>
                variable in your <filename>conf/bblayers.conf</filename> file,
                which is found in the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                The following example shows how to enable a layer named
                <filename>meta-mylayer</filename>:
                <literallayout class='monospaced'>
     # POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf
     # changes incompatibly
     POKY_BBLAYERS_CONF_VERSION = "2"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       /home/<replaceable>user</replaceable>/poky/meta \
       /home/<replaceable>user</replaceable>/poky/meta-poky \
       /home/<replaceable>user</replaceable>/poky/meta-yocto-bsp \
       /home/<replaceable>user</replaceable>/poky/meta-mylayer \
       "
                </literallayout>
            </para>

            <para>
                BitBake parses each <filename>conf/layer.conf</filename> file
                from the top down as specified in the
                <filename>BBLAYERS</filename> variable
                within the <filename>conf/bblayers.conf</filename> file.
                During the processing of each
                <filename>conf/layer.conf</filename> file, BitBake adds the
                recipes, classes and configurations contained within the
                particular layer to the source directory.
            </para>
        </section>

        <section id='using-bbappend-files'>
            <title>Using .bbappend Files in Your Layer</title>

            <para>
                A recipe that appends Metadata to another recipe is called a
                BitBake append file.
                A BitBake append file uses the <filename>.bbappend</filename>
                file type suffix, while the corresponding recipe to which
                Metadata is being appended uses the <filename>.bb</filename>
                file type suffix.
            </para>

            <para>
                You can use a <filename>.bbappend</filename> file in your
                layer to make additions or changes to the content of another
                layer's recipe without having to copy the other layer's
                recipe into your layer.
                Your <filename>.bbappend</filename> file resides in your layer,
                while the main <filename>.bb</filename> recipe file to
                which you are appending Metadata resides in a different layer.
            </para>

            <para>
                Being able to append information to an existing recipe not only
                avoids duplication, but also automatically applies recipe
                changes from a different layer into your layer.
                If you were copying recipes, you would have to manually merge
                changes as they occur.
            </para>

            <para>
                When you create an append file, you must use the same root
                name as the corresponding recipe file.
                For example, the append file
                <filename>someapp_&DISTRO;.bbappend</filename> must apply to
                <filename>someapp_&DISTRO;.bb</filename>.
                This means the original recipe and append file names are
                version number-specific.
                If the corresponding recipe is renamed to update to a newer
                version, you must also rename and possibly update
                the corresponding <filename>.bbappend</filename> as well.
                During the build process, BitBake displays an error on starting
                if it detects a <filename>.bbappend</filename> file that does
                not have a corresponding recipe with a matching name.
                See the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_DANGLINGAPPENDS_WARNONLY'><filename>BB_DANGLINGAPPENDS_WARNONLY</filename></ulink>
                variable for information on how to handle this error.
            </para>

            <para>
                As an example, consider the main formfactor recipe and a
                corresponding formfactor append file both from the
                <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
                Here is the main formfactor recipe, which is named
                <filename>formfactor_0.0.bb</filename> and located in the
                "meta" layer at
                <filename>meta/recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     SUMMARY = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r45"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
	     # Install file only if it has contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
	     if [ -s "${S}/machconfig" ]; then
	             install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
	     fi
     }                </literallayout>
                In the main recipe, note the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                variable, which tells the OpenEmbedded build system where to
                find files during the build.
            </para>

            <para>
                Following is the append file, which is named
                <filename>formfactor_0.0.bbappend</filename> and is from the
                Raspberry Pi BSP Layer named
                <filename>meta-raspberrypi</filename>.
                The file is in the layer at
                <filename>recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
                </literallayout>
            </para>

            <para>
                By default, the build system uses the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                variable to locate files.
                This append file extends the locations by setting the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                variable.
                Setting this variable in the <filename>.bbappend</filename>
                file is the most reliable and recommended method for adding
                directories to the search path used by the build system
                to find files.
            </para>

            <para>
                The statement in this example extends the directories to
                include
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-THISDIR'><filename>THISDIR</filename></ulink><filename>}/${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>,
                which resolves to a directory named
                <filename>formfactor</filename> in the same directory
                in which the append file resides (i.e.
                <filename>meta-raspberrypi/recipes-bsp/formfactor</filename>.
                This implies that you must have the supporting directory
                structure set up that will contain any files or patches you
                will be including from the layer.
            </para>

            <para>
                Using the immediate expansion assignment operator
                <filename>:=</filename> is important because of the reference
                to <filename>THISDIR</filename>.
                The trailing colon character is important as it ensures that
                items in the list remain colon-separated.
                <note>
                    <para>
                        BitBake automatically defines the
                        <filename>THISDIR</filename> variable.
                        You should never set this variable yourself.
                        Using "_prepend" as part of the
                        <filename>FILESEXTRAPATHS</filename> ensures your path
                        will be searched prior to other paths in the final
                        list.
                    </para>

                    <para>
                        Also, not all append files add extra files.
                        Many append files simply exist to add build options
                        (e.g. <filename>systemd</filename>).
                        For these cases, your append file would not even
                        use the <filename>FILESEXTRAPATHS</filename> statement.
                    </para>
                </note>
            </para>
        </section>

        <section id='prioritizing-your-layer'>
            <title>Prioritizing Your Layer</title>

            <para>
                Each layer is assigned a priority value.
                Priority values control which layer takes precedence if there
                are recipe files with the same name in multiple layers.
                For these cases, the recipe file from the layer with a higher
                priority number takes precedence.
                Priority values also affect the order in which multiple
                <filename>.bbappend</filename> files for the same recipe are
                applied.
                You can either specify the priority manually, or allow the
                build system to calculate it based on the layer's dependencies.
            </para>

            <para>
                To specify the layer's priority manually, use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>
                variable and append the layer's root name:
                <literallayout class='monospaced'>
     BBFILE_PRIORITY_mylayer = "1"
                </literallayout>
            </para>

            <note>
                <para>It is possible for a recipe with a lower version number
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                in a layer that has a higher priority to take precedence.</para>
                <para>Also, the layer priority does not currently affect the
                precedence order of <filename>.conf</filename>
                or <filename>.bbclass</filename> files.
                Future versions of BitBake might address this.</para>
            </note>
        </section>

        <section id='managing-layers'>
            <title>Managing Layers</title>

            <para>
                You can use the BitBake layer management tool
                <filename>bitbake-layers</filename> to provide a view
                into the structure of recipes across a multi-layer project.
                Being able to generate output that reports on configured layers
                with their paths and priorities and on
                <filename>.bbappend</filename> files and their applicable
                recipes can help to reveal potential problems.
            </para>

            <para>
                For help on the BitBake layer management tool, use the
                following command:
                <literallayout class='monospaced'>
     $ bitbake-layers --help
     NOTE: Starting bitbake server...
     usage: bitbake-layers [-d] [-q] [-F] [--color COLOR] [-h] &lt;subcommand&gt; ...

     BitBake layers utility

     optional arguments:
       -d, --debug           Enable debug output
       -q, --quiet           Print only errors
       -F, --force           Force add without recipe parse verification
       --color COLOR         Colorize output (where COLOR is auto, always, never)
       -h, --help            show this help message and exit

     subcommands:
       &lt;subcommand&gt;
         show-layers         show current configured layers.
         show-overlayed      list overlayed recipes (where the same recipe exists
                             in another layer)
         show-recipes        list available recipes, showing the layer they are
                             provided by
         show-appends        list bbappend files and recipe files they apply to
         show-cross-depends  Show dependencies between recipes that cross layer
                             boundaries.
         add-layer           Add one or more layers to bblayers.conf.
         remove-layer        Remove one or more layers from bblayers.conf.
         flatten             flatten layer configuration into a separate output
                             directory.
         layerindex-fetch    Fetches a layer from a layer index along with its
                             dependent layers, and adds them to conf/bblayers.conf.
         layerindex-show-depends
                             Find layer dependencies from layer index.
         create-layer        Create a basic layer

     Use bitbake-layers &lt;subcommand&gt; --help to get help on a specific command
                </literallayout>
            </para>

            <para>
                The following list describes the available commands:
                <itemizedlist>
                    <listitem><para>
                        <emphasis><filename>help:</filename></emphasis>
                        Displays general help or help on a specified command.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>show-layers:</filename></emphasis>
                        Shows the current configured layers.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>show-overlayed:</filename></emphasis>
                        Lists overlayed recipes.
                        A recipe is overlayed when a recipe with the same name
                        exists in another layer that has a higher layer
                        priority.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>show-recipes:</filename></emphasis>
                        Lists available recipes and the layers that provide them.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>show-appends:</filename></emphasis>
                        Lists <filename>.bbappend</filename> files and the
                        recipe files to which they apply.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>show-cross-depends:</filename></emphasis>
                        Lists dependency relationships between recipes that
                        cross layer boundaries.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>add-layer:</filename></emphasis>
                        Adds a layer to <filename>bblayers.conf</filename>.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>remove-layer:</filename></emphasis>
                        Removes a layer from <filename>bblayers.conf</filename>
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>flatten:</filename></emphasis>
                        Flattens the layer configuration into a separate output
                        directory.
                        Flattening your layer configuration builds a "flattened"
                        directory that contains the contents of all layers,
                        with any overlayed recipes removed and any
                        <filename>.bbappend</filename> files appended to the
                        corresponding recipes.
                        You might have to perform some manual cleanup of the
                        flattened layer as follows:
                        <itemizedlist>
                            <listitem><para>
                                Non-recipe files (such as patches)
                                are overwritten.
                                The flatten command shows a warning for these
                                files.
                                </para></listitem>
                            <listitem><para>
                                Anything beyond the normal layer
                                setup has been added to the
                                <filename>layer.conf</filename> file.
                                Only the lowest priority layer's
                                <filename>layer.conf</filename> is used.
                                </para></listitem>
                            <listitem><para>
                                Overridden and appended items from
                                <filename>.bbappend</filename> files need to be
                                cleaned up.
                                The contents of each
                                <filename>.bbappend</filename> end up in the
                                flattened recipe.
                                However, if there are appended or changed
                                variable values, you need to tidy these up
                                yourself.
                                Consider the following example.
                                Here, the <filename>bitbake-layers</filename>
                                command adds the line
                                <filename>#### bbappended ...</filename> so that
                                you know where the following lines originate:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "A useful utility"
     ...
     EXTRA_OECONF = "--enable-something"
     ...

     #### bbappended from meta-anotherlayer ####

     DESCRIPTION = "Customized utility"
     EXTRA_OECONF += "--enable-somethingelse"
                                </literallayout>
                                Ideally, you would tidy up these utilities as
                                follows:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "Customized utility"
     ...
     EXTRA_OECONF = "--enable-something --enable-somethingelse"
     ...
                                </literallayout>
                                </para></listitem>
                        </itemizedlist>
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>layerindex-fetch</filename>:</emphasis>
                        Fetches a layer from a layer index, along with its
                        dependent layers, and adds the layers to the
                        <filename>conf/bblayers.conf</filename> file.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>layerindex-show-depends</filename>:</emphasis>
                        Finds layer dependencies from the layer index.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>create-layer</filename>:</emphasis>
                        Creates a basic layer.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='creating-a-general-layer-using-the-bitbake-layers-script'>
            <title>Creating a General Layer Using the <filename>bitbake-layers</filename> Script</title>

            <para>
                The <filename>bitbake-layers</filename> script with the
                <filename>create-layer</filename> subcommand simplifies
                creating a new general layer.
                <note><title>Notes</title>
                    <itemizedlist>
                        <listitem><para>
                            For information on BSP layers, see the
                            "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                            section in the Yocto Project Board Specific (BSP)
                            Developer's Guide.
                            </para></listitem>
                        <listitem><para>
                            In order to use a layer with the OpenEmbedded
                            build system, you need to add the layer to your
                            <filename>bblayers.conf</filename> configuration
                            file.
                            See the
                            "<link linkend='adding-a-layer-using-the-bitbake-layers-script'>Adding a Layer Using the <filename>bitbake-layers</filename> Script</link>"
                            section for more information.
                            </para></listitem>
                    </itemizedlist>
                </note>
                The default mode of the script's operation with this
                subcommand is to create a layer with the following:
                <itemizedlist>
                    <listitem><para>A layer priority of 6.
                        </para></listitem>
                    <listitem><para>A <filename>conf</filename>
                        subdirectory that contains a
                        <filename>layer.conf</filename> file.
                        </para></listitem>
                    <listitem><para>
                        A <filename>recipes-example</filename> subdirectory
                        that contains a further subdirectory named
                        <filename>example</filename>, which contains
                        an <filename>example.bb</filename> recipe file.
                        </para></listitem>
                    <listitem><para>A <filename >COPYING.MIT</filename>,
                        which is the license statement for the layer.
                        The script assumes you want to use the MIT license,
                        which is typical for most layers, for the contents of
                        the layer itself.
                        </para></listitem>
                    <listitem><para>
                        A <filename>README</filename> file, which is a file
                        describing the contents of your new layer.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                In its simplest form, you can use the following command form
                to create a layer.
                The command creates a layer whose name corresponds to
                <replaceable>your_layer_name</replaceable> in the current
                directory:
                <literallayout class='monospaced'>
     $ bitbake-layers create-layer <replaceable>your_layer_name</replaceable>
                </literallayout>
                As an example, the following command creates a layer named
                <filename>meta-scottrif</filename> in your home directory:
                <literallayout class='monospaced'>
     $ cd /usr/home
     $ bitbake-layers create-layer meta-scottrif
     NOTE: Starting bitbake server...
     Add your new layer with 'bitbake-layers add-layer meta-scottrif'
                </literallayout>
            </para>

            <para>
                If you want to set the priority of the layer to other than the
                default value of "6", you can either use the
                <filename>&dash;&dash;priority</filename> option or you can
                edit the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>
                value in the <filename>conf/layer.conf</filename> after the
                script creates it.
                Furthermore, if you want to give the example recipe file
                some name other than the default, you can
                use the
                <filename>&dash;&dash;example-recipe-name</filename> option.
            </para>

            <para>
                The easiest way to see how the
                <filename>bitbake-layers create-layer</filename> command
                works is to experiment with the script.
                You can also read the usage information by entering the
                following:
                <literallayout class='monospaced'>
     $ bitbake-layers create-layer --help
     NOTE: Starting bitbake server...
     usage: bitbake-layers create-layer [-h] [--priority PRIORITY]
                                        [--example-recipe-name EXAMPLERECIPE]
                                        layerdir

     Create a basic layer

     positional arguments:
       layerdir              Layer directory to create

     optional arguments:
       -h, --help            show this help message and exit
       --priority PRIORITY, -p PRIORITY
                             Layer directory to create
       --example-recipe-name EXAMPLERECIPE, -e EXAMPLERECIPE
                             Filename of the example recipe
                </literallayout>
            </para>
        </section>

        <section id='adding-a-layer-using-the-bitbake-layers-script'>
            <title>Adding a Layer Using the <filename>bitbake-layers</filename> Script</title>

            <para>
                Once you create your general layer, you must add it to your
                <filename>bblayers.conf</filename> file.
                Adding the layer to this configuration file makes the
                OpenEmbedded build system aware of your layer so that it can
                search it for metadata.
            </para>

            <para>
                Add your layer by using the
                <filename>bitbake-layers add-layer</filename> command:
                <literallayout class='monospaced'>
     $ bitbake-layers add-layer <replaceable>your_layer_name</replaceable>
                </literallayout>
                Here is an example that adds a layer named
                <filename>meta-scottrif</filename> to the configuration file.
                Following the command that adds the layer is another
                <filename>bitbake-layers</filename> command that shows the
                layers that are in your <filename>bblayers.conf</filename>
                file:
                <literallayout class='monospaced'>
     $ bitbake-layers add-layer meta-scottrif
     NOTE: Starting bitbake server...
     Parsing recipes: 100% |##########################################################| Time: 0:00:49
     Parsing of 1441 .bb files complete (0 cached, 1441 parsed). 2055 targets, 56 skipped, 0 masked, 0 errors.
     $ bitbake-layers show-layers
     NOTE: Starting bitbake server...
     layer                 path                                      priority
     ==========================================================================
     meta                  /home/scottrif/poky/meta                  5
     meta-poky             /home/scottrif/poky/meta-poky             5
     meta-yocto-bsp        /home/scottrif/poky/meta-yocto-bsp        5
     workspace             /home/scottrif/poky/build/workspace       99
     meta-scottrif         /home/scottrif/poky/build/meta-scottrif   6
                </literallayout>
                Adding the layer to this file enables the build system to
                locate the layer during the build.
                <note>
                    During a build, the OpenEmbedded build system looks in
                    the layers from the top of the list down to the bottom
                    in that order.
                </note>
                </para>
        </section>
    </section>

    <section id='usingpoky-extend-customimage'>
        <title>Customizing Images</title>

        <para>
            You can customize images to satisfy particular requirements.
            This section describes several methods and provides guidelines for each.
        </para>

        <section id='usingpoky-extend-customimage-localconf'>
            <title>Customizing Images Using <filename>local.conf</filename></title>

            <para>
                Probably the easiest way to customize an image is to add a
                package by way of the <filename>local.conf</filename>
                configuration file.
                Because it is limited to local use, this method generally only
                allows you to add packages and is not as flexible as creating
                your own customized image.
                When you add packages using local variables this way, you need
                to realize that these variable changes are in effect for every
                build and consequently affect all images, which might not
                be what you require.
            </para>

            <para>
                To add a package to your image using the local configuration
                file, use the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable with the <filename>_append</filename> operator:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append = " strace"
                </literallayout>
                Use of the syntax is important - specifically, the space between
                the quote and the package name, which is
                <filename>strace</filename> in this example.
                This space is required since the <filename>_append</filename>
                operator does not add the space.
            </para>

            <para>
                Furthermore, you must use <filename>_append</filename> instead
                of the <filename>+=</filename> operator if you want to avoid
                ordering issues.
                The reason for this is because doing so unconditionally appends
                to the variable and avoids ordering problems due to the
                variable being set in image recipes and
                <filename>.bbclass</filename> files with operators like
                <filename>?=</filename>.
                Using <filename>_append</filename> ensures the operation takes
                affect.
            </para>

            <para>
                As shown in its simplest use,
                <filename>IMAGE_INSTALL_append</filename> affects all images.
                It is possible to extend the syntax so that the variable
                applies to a specific image only.
                Here is an example:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                </literallayout>
                This example adds <filename>strace</filename> to the
                <filename>core-image-minimal</filename> image only.
            </para>

            <para>
                You can add packages using a similar approach through the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CORE_IMAGE_EXTRA_INSTALL'>CORE_IMAGE_EXTRA_INSTALL</ulink></filename>
                variable.
                If you use this variable, only
                <filename>core-image-*</filename> images are affected.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-imagefeatures'>
            <title>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and
                <filename>EXTRA_IMAGE_FEATURES</filename></title>

            <para>
                Another method for customizing your image is to enable or
                disable high-level image features by using the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
                variables.
                Although the functions for both variables are nearly equivalent,
                best practices dictate using <filename>IMAGE_FEATURES</filename>
                from within a recipe and using
                <filename>EXTRA_IMAGE_FEATURES</filename> from within
                your <filename>local.conf</filename> file, which is found in the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
            </para>

            <para>
                To understand how these features work, the best reference is
                <filename>meta/classes/core-image.bbclass</filename>.
                This class lists out the available
                <filename>IMAGE_FEATURES</filename> of which most map to
                package groups while some, such as
                <filename>debug-tweaks</filename> and
                <filename>read-only-rootfs</filename>, resolve as general
                configuration settings.
            </para>

            <para>
                In summary, the file looks at the contents of the
                <filename>IMAGE_FEATURES</filename> variable and then maps
                or configures the feature accordingly.
                Based on this information, the build system automatically
                adds the appropriate packages or configurations to the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>
                variable.
                Effectively, you are enabling extra features by extending the
                class or creating a custom class for use with specialized image
                <filename>.bb</filename> files.
            </para>

            <para>
                Use the <filename>EXTRA_IMAGE_FEATURES</filename> variable
                from within your local configuration file.
                Using a separate area from which to enable features with
                this variable helps you avoid overwriting the features in the
                image recipe that are enabled with
                <filename>IMAGE_FEATURES</filename>.
                The value of <filename>EXTRA_IMAGE_FEATURES</filename> is added
                to <filename>IMAGE_FEATURES</filename> within
                <filename>meta/conf/bitbake.conf</filename>.
            </para>

            <para>
                To illustrate how you can use these variables to modify your
                image, consider an example that selects the SSH server.
                The Yocto Project ships with two SSH servers you can use
                with your images: Dropbear and OpenSSH.
                Dropbear is a minimal SSH server appropriate for
                resource-constrained environments, while OpenSSH is a
                well-known standard SSH server implementation.
                By default, the <filename>core-image-sato</filename> image
                is configured to use Dropbear.
                The <filename>core-image-full-cmdline</filename> and
                <filename>core-image-lsb</filename> images both
                include OpenSSH.
                The <filename>core-image-minimal</filename> image does not
                contain an SSH server.
            </para>

            <para>
                You can customize your image and change these defaults.
                Edit the <filename>IMAGE_FEATURES</filename> variable
                in your recipe or use the
                <filename>EXTRA_IMAGE_FEATURES</filename> in your
                <filename>local.conf</filename> file so that it configures the
                image you are working with to include
                <filename>ssh-server-dropbear</filename> or
                <filename>ssh-server-openssh</filename>.
            </para>

            <note>
                See the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
                section in the Yocto Project Reference Manual for a complete
                list of image features that ship with the Yocto Project.
            </note>
        </section>

        <section id='usingpoky-extend-customimage-custombb'>
            <title>Customizing Images Using Custom .bb Files</title>

            <para>
                You can also customize an image by creating a custom recipe
                that defines additional software as part of the image.
                The following example shows the form for the two lines you need:
                <literallayout class='monospaced'>
     IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

     inherit core-image
                </literallayout>
            </para>

            <para>
                Defining the software using a custom recipe gives you total
                control over the contents of the image.
                It is important to use the correct names of packages in the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable.
                You must use the OpenEmbedded notation and not the Debian notation for the names
                (e.g. <filename>glibc-dev</filename> instead of <filename>libc6-dev</filename>).
            </para>

            <para>
                The other method for creating a custom image is to base it on an existing image.
                For example, if you want to create an image based on <filename>core-image-sato</filename>
                but add the additional package <filename>strace</filename> to the image,
                copy the <filename>meta/recipes-sato/images/core-image-sato.bb</filename> to a
                new <filename>.bb</filename> and add the following line to the end of the copy:
                <literallayout class='monospaced'>
     IMAGE_INSTALL += "strace"
                </literallayout>
            </para>
        </section>

        <section id='usingpoky-extend-customimage-customtasks'>
            <title>Customizing Images Using Custom Package Groups</title>

            <para>
                For complex custom images, the best approach for customizing
                an image is to create a custom package group recipe that is
                used to build the image or images.
                A good example of a package group recipe is
                <filename>meta/recipes-core/packagegroups/packagegroup-base.bb</filename>.
            </para>

            <para>
                If you examine that recipe, you see that the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename>
                variable lists the package group packages to produce.
                The <filename>inherit packagegroup</filename> statement
                sets appropriate default values and automatically adds
                <filename>-dev</filename>, <filename>-dbg</filename>, and
                <filename>-ptest</filename> complementary packages for each
                package specified in the <filename>PACKAGES</filename>
                statement.
                <note>
                    The <filename>inherit packagegroup</filename> line should be
                    located near the top of the recipe, certainly before
                    the <filename>PACKAGES</filename> statement.
                </note>
            </para>

            <para>
                For each package you specify in <filename>PACKAGES</filename>,
                you can use
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'>RDEPENDS</ulink></filename>
                and
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'>RRECOMMENDS</ulink></filename>
                entries to provide a list of packages the parent task package
                should contain.
                You can see examples of these further down in the
                <filename>packagegroup-base.bb</filename> recipe.
            </para>

            <para>
                Here is a short, fabricated example showing the same basic
                pieces for a hypothetical packagegroup defined in
                <filename>packagegroup-custom.bb</filename>, where the
                variable <filename>PN</filename> is the standard way to
                abbreviate the reference to the full packagegroup name
                <filename>packagegroup-custom</filename>:
                <literallayout class='monospaced'>
     DESCRIPTION = "My Custom Package Groups"

     inherit packagegroup

     PACKAGES = "\
         ${PN}-apps \
         ${PN}-tools \
         "

     RDEPENDS_${PN}-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_${PN}-tools = "\
         oprofile \
         oprofileui-server \
         lttng-tools"

     RRECOMMENDS_${PN}-tools = "\
         kernel-module-oprofile"
                </literallayout>
            </para>

            <para>
                In the previous example, two package group packages are created with their dependencies and their
                recommended package dependencies listed: <filename>packagegroup-custom-apps</filename>, and
                <filename>packagegroup-custom-tools</filename>.
                To build an image using these package group packages, you need to add
                <filename>packagegroup-custom-apps</filename> and/or
                <filename>packagegroup-custom-tools</filename> to
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>.
                For other forms of image dependencies see the other areas of this section.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-image-name'>
            <title>Customizing an Image Hostname</title>

            <para>
                By default, the configured hostname (i.e.
                <filename>/etc/hostname</filename>) in an image is the
                same as the machine name.
                For example, if
                <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                equals "qemux86", the configured hostname written to
                <filename>/etc/hostname</filename> is "qemux86".
            </para>

            <para>
                You can customize this name by altering the value of the
                "hostname" variable in the
                <filename>base-files</filename> recipe using either
                an append file or a configuration file.
                Use the following in an append file:
                <literallayout class='monospaced'>
     hostname="myhostname"
                </literallayout>
                Use the following in a configuration file:
                <literallayout class='monospaced'>
     hostname_pn-base-files = "myhostname"
                </literallayout>
            </para>

            <para>
                Changing the default value of the variable "hostname" can be
                useful in certain situations.
                For example, suppose you need to do extensive testing on an
                image and you would like to easily identify the image
                under test from existing images with typical default
                hostnames.
                In this situation, you could change the default hostname to
                "testme", which results in all the images using the name
                "testme".
                Once testing is complete and you do not need to rebuild the
                image for test any longer, you can easily reset the default
                hostname.
            </para>

            <para>
                Another point of interest is that if you unset the variable,
                the image will have no default hostname in the filesystem.
                Here is an example that unsets the variable in a
                configuration file:
                <literallayout class='monospaced'>
     hostname_pn-base-files = ""
                </literallayout>
                Having no default hostname in the filesystem is suitable for
                environments that use dynamic hostnames such as virtual
                machines.
            </para>
        </section>
    </section>

    <section id='new-recipe-writing-a-new-recipe'>
        <title>Writing a New Recipe</title>

        <para>
            Recipes (<filename>.bb</filename> files) are fundamental components
            in the Yocto Project environment.
            Each software component built by the OpenEmbedded build system
            requires a recipe to define the component.
            This section describes how to create, write, and test a new
            recipe.
            <note>
                For information on variables that are useful for recipes and
                for information about recipe naming issues, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-varlocality-recipe-required'>Required</ulink>"
                section of the Yocto Project Reference Manual.
            </note>
        </para>

        <section id='new-recipe-overview'>
            <title>Overview</title>

            <para>
                The following figure shows the basic process for creating a
                new recipe.
                The remainder of the section provides details for the steps.
                <imagedata fileref="figures/recipe-workflow.png" width="6in" depth="7in" align="center" scalefit="1" />
            </para>
        </section>

        <section id='new-recipe-locate-or-automatically-create-a-base-recipe'>
            <title>Locate or Automatically Create a Base Recipe</title>

            <para>
                You can always write a recipe from scratch.
                However, three choices exist that can help you quickly get a
                start on a new recipe:
                <itemizedlist>
                    <listitem><para>
                        <emphasis><filename>devtool add</filename>:</emphasis>
                        A command that assists in creating a recipe and
                        an environment conducive to development.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>recipetool create</filename>:</emphasis>
                        A command provided by the Yocto Project that automates
                        creation of a base recipe based on the source
                        files.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Existing Recipes:</emphasis>
                        Location and modification of an existing recipe that is
                        similar in function to the recipe you need.
                        </para></listitem>
                </itemizedlist>
                <note>
                    For information on recipe syntax, see the
                    "<link linkend='recipe-syntax'>Recipe Syntax</link>"
                    section.
                </note>
            </para>

            <section id='new-recipe-creating-the-base-recipe-using-devtool'>
                <title>Creating the Base Recipe Using <filename>devtool add</filename></title>

                <para>
                    The <filename>devtool add</filename> command uses the same
                    logic for auto-creating the recipe as
                    <filename>recipetool create</filename>, which is listed
                    below.
                    Additionally, however, <filename>devtool add</filename>
                    sets up an environment that makes it easy for you to
                    patch the source and to make changes to the recipe as
                    is often necessary when adding a recipe to build a new
                    piece of software to be included in a build.
                </para>

                <para>
                    You can find a complete description of the
                    <filename>devtool add</filename> command in the
                    "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-a-closer-look-at-devtool-add'>A Closer Look at <filename>devtool</filename> add</ulink>"
                    section in the Yocto Project Application Development
                    and the Extensible Software Development Kit (eSDK) manual.
                </para>
            </section>

            <section id='new-recipe-creating-the-base-recipe-using-recipetool'>
                <title>Creating the Base Recipe Using <filename>recipetool create</filename></title>

                <para>
                    <filename>recipetool create</filename> automates creation
                    of a base recipe given a set of source code files.
                    As long as you can extract or point to the source files,
                    the tool will construct a recipe and automatically
                    configure all pre-build information into the recipe.
                    For example, suppose you have an application that builds
                    using Autotools.
                    Creating the base recipe using
                    <filename>recipetool</filename> results in a recipe
                    that has the pre-build dependencies, license requirements,
                    and checksums configured.
                </para>

                <para>
                    To run the tool, you just need to be in your
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                    and have sourced the build environment setup script
                    (i.e.
                    <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>oe-init-build-env</filename></ulink>).
                    To get help on the tool, use the following command:
                    <literallayout class='monospaced'>
     $ recipetool -h
     NOTE: Starting bitbake server...
     usage: recipetool [-d] [-q] [--color COLOR] [-h] &lt;subcommand&gt; ...

     OpenEmbedded recipe tool

     options:
       -d, --debug     Enable debug output
       -q, --quiet     Print only errors
       --color COLOR   Colorize output (where COLOR is auto, always, never)
       -h, --help      show this help message and exit

     subcommands:
       create          Create a new recipe
       newappend       Create a bbappend for the specified target in the specified
                       layer
       setvar          Set a variable within a recipe
       appendfile      Create/update a bbappend to replace a target file
       appendsrcfiles  Create/update a bbappend to add or replace source files
       appendsrcfile   Create/update a bbappend to add or replace a source file
     Use recipetool &lt;subcommand&gt; --help to get help on a specific command
                    </literallayout>
                </para>

                <para>
                    Running
                    <filename>recipetool create -o</filename>&nbsp;<replaceable>OUTFILE</replaceable>
                    creates the base recipe and locates it properly in the
                    layer that contains your source files.
                    Following are some syntax examples:
                </para>

                <para>
                    Use this syntax to generate a recipe based on
                    <replaceable>source</replaceable>.
                    Once generated, the recipe resides in the existing source
                    code layer:
                    <literallayout class='monospaced'>
     recipetool create -o <replaceable>OUTFILE</replaceable>&nbsp;<replaceable>source</replaceable>
                    </literallayout>
                    Use this syntax to generate a recipe using code that you
                    extract from <replaceable>source</replaceable>.
                    The extracted code is placed in its own layer defined
                    by <replaceable>EXTERNALSRC</replaceable>.
                    <literallayout class='monospaced'>
     recipetool create -o <replaceable>OUTFILE</replaceable> -x <replaceable>EXTERNALSRC</replaceable> <replaceable>source</replaceable>
                    </literallayout>
                    Use this syntax to generate a recipe based on
                    <replaceable>source</replaceable>.
                    The options direct <filename>recipetool</filename> to
                    generate debugging information.
                    Once generated, the recipe resides in the existing source
                    code layer:
                    <literallayout class='monospaced'>
     recipetool create -d -o <replaceable>OUTFILE</replaceable> <replaceable>source</replaceable>
                    </literallayout>
                </para>
            </section>

            <section id='new-recipe-locating-and-using-a-similar-recipe'>
                <title>Locating and Using a Similar Recipe</title>

                <para>
                    Before writing a recipe from scratch, it is often useful to
                    discover whether someone else has already written one that
                    meets (or comes close to meeting) your needs.
                    The Yocto Project and OpenEmbedded communities maintain many
                    recipes that might be candidates for what you are doing.
                    You can find a good central index of these recipes in the
                    <ulink url='http://layers.openembedded.org'>OpenEmbedded Layer Index</ulink>.
                </para>

                <para>
                    Working from an existing recipe or a skeleton recipe is the
                    best way to get started.
                    Here are some points on both methods:
                    <itemizedlist>
                        <listitem><para><emphasis>Locate and modify a recipe that
                            is close to what you want to do:</emphasis>
                            This method works when you are familiar with the
                            current recipe space.
                            The method does not work so well for those new to
                            the Yocto Project or writing recipes.</para>
                            <para>Some risks associated with this method are
                            using a recipe that has areas totally unrelated to
                            what you are trying to accomplish with your recipe,
                            not recognizing areas of the recipe that you might
                            have to add from scratch, and so forth.
                            All these risks stem from unfamiliarity with the
                            existing recipe space.</para></listitem>
                        <listitem><para><emphasis>Use and modify the following
                            skeleton recipe:</emphasis>
                            If for some reason you do not want to use
                            <filename>recipetool</filename> and you cannot
                            find an existing recipe that is close to meeting
                            your needs, you can use the following structure to
                            provide the fundamental areas of a new recipe.
                            <literallayout class='monospaced'>
     DESCRIPTION = ""
     HOMEPAGE = ""
     LICENSE = ""
     SECTION = ""
     DEPENDS = ""
     LIC_FILES_CHKSUM = ""

     SRC_URI = ""
                            </literallayout>
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='new-recipe-storing-and-naming-the-recipe'>
            <title>Storing and Naming the Recipe</title>

            <para>
                Once you have your base recipe, you should put it in your
                own layer and name it appropriately.
                Locating it correctly ensures that the OpenEmbedded build
                system can find it when you use BitBake to process the
                recipe.
            </para>

            <itemizedlist>
                <listitem><para><emphasis>Storing Your Recipe:</emphasis>
                    The OpenEmbedded build system locates your recipe
                    through the layer's <filename>conf/layer.conf</filename>
                    file and the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'><filename>BBFILES</filename></ulink>
                    variable.
                    This variable sets up a path from which the build system can
                    locate recipes.
                    Here is the typical use:
                    <literallayout class='monospaced'>
     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"
                    </literallayout>
                    Consequently, you need to be sure you locate your new recipe
                    inside your layer such that it can be found.</para>
                    <para>You can find more information on how layers are
                    structured in the
                    "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>"
                    section.</para></listitem>
                <listitem><para><emphasis>Naming Your Recipe:</emphasis>
                    When you name your recipe, you need to follow this naming
                    convention:
                    <literallayout class='monospaced'>
     <replaceable>basename</replaceable>_<replaceable>version</replaceable>.bb
                    </literallayout>
                    Use lower-cased characters and do not include the reserved
                    suffixes <filename>-native</filename>,
                    <filename>-cross</filename>, <filename>-initial</filename>,
                    or <filename>-dev</filename> casually (i.e. do not use them
                    as part of your recipe name unless the string applies).
                    Here are some examples:
                    <literallayout class='monospaced'>
     cups_1.7.0.bb
     gawk_4.0.2.bb
     irssi_0.8.16-rc1.bb
                    </literallayout></para></listitem>
            </itemizedlist>
        </section>

        <section id='new-recipe-running-a-build-on-the-recipe'>
            <title>Running a Build on the Recipe</title>

            <para>
                Creating a new recipe is usually an iterative process that
                requires using BitBake to process the recipe multiple times in
                order to progressively discover and add information to the
                recipe file.
            </para>

            <para>
                Assuming you have sourced the build environment setup script (i.e.
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>)
                and you are in the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>,
                use BitBake to process your recipe.
                All you need to provide is the
                <filename><replaceable>basename</replaceable></filename> of the recipe as described
                in the previous section:
                <literallayout class='monospaced'>
     $ bitbake <replaceable>basename</replaceable>
                </literallayout>

            </para>

            <para>
                During the build, the OpenEmbedded build system creates a
                temporary work directory for each recipe
                (<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename>)
                where it keeps extracted source files, log files, intermediate
                compilation and packaging files, and so forth.
            </para>

            <para>
                The path to the per-recipe temporary work directory depends
                on the context in which it is being built.
                The quickest way to find this path is to have BitBake return it
                by running the following:
                <literallayout class='monospaced'>
     $ bitbake -e <replaceable>basename</replaceable> | grep ^WORKDIR=
                </literallayout>
                As an example, assume a Source Directory top-level folder named
                <filename>poky</filename>, a default Build Directory at
                <filename>poky/build</filename>, and a
                <filename>qemux86-poky-linux</filename> machine target system.
                Furthermore, suppose your recipe is named
                <filename>foo_1.3.0.bb</filename>.
                In this case, the work directory the build system uses to
                build the package would be as follows:
                <literallayout class='monospaced'>
     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
                </literallayout>
                Inside this directory you can find sub-directories such as
                <filename>image</filename>, <filename>packages-split</filename>,
                and <filename>temp</filename>.
                After the build, you can examine these to determine how well
                the build went.
                <note>
                    You can find log files for each task in the recipe's
                    <filename>temp</filename> directory (e.g.
                    <filename>poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0/temp</filename>).
                    Log files are named <filename>log.<replaceable>taskname</replaceable></filename>
                    (e.g. <filename>log.do_configure</filename>,
                    <filename>log.do_fetch</filename>, and
                    <filename>log.do_compile</filename>).
                </note>
            </para>

            <para>
                You can find more information about the build process in
                "<ulink url='&YOCTO_DOCS_OM_URL;#overview-development-environment'>The Yocto Project Development Environment</ulink>"
                chapter of the Yocto Project Overview and Concepts Manual.
            </para>
        </section>

        <section id='new-recipe-fetching-code'>
            <title>Fetching Code</title>

            <para>
                The first thing your recipe must do is specify how to fetch
                the source files.
                Fetching is controlled mainly through the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                variable.
                Your recipe must have a <filename>SRC_URI</filename> variable
                that points to where the source is located.
                For a graphical representation of source locations, see the
                "<ulink url='&YOCTO_DOCS_OM_URL;#sources-dev-environment'>Sources</ulink>"
                section in the Yocto Project Overview and Concepts Manual.
            </para>

            <para>
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>
                task uses the prefix of each entry in the
                <filename>SRC_URI</filename> variable value to determine which
                <ulink url='&YOCTO_DOCS_BB_URL;#bb-fetchers'>fetcher</ulink>
                to use to get your source files.
                It is the <filename>SRC_URI</filename> variable that triggers
                the fetcher.
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
                task uses the variable after source is fetched to apply
                patches.
                The OpenEmbedded build system uses
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESOVERRIDES'><filename>FILESOVERRIDES</filename></ulink>
                for scanning directory locations for local files in
                <filename>SRC_URI</filename>.
            </para>

            <para>
                The <filename>SRC_URI</filename> variable in your recipe must
                define each unique location for your source files.
                It is good practice to not hard-code version numbers in a URL used
                in <filename>SRC_URI</filename>.
                Rather than hard-code these values, use
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink><filename>}</filename>,
                which causes the fetch process to use the version specified in
                the recipe filename.
                Specifying the version in this manner means that upgrading the
                recipe to a future version is as simple as renaming the recipe
                to match the new version.
            </para>

            <para>
                Here is a simple example from the
                <filename>meta/recipes-devtools/strace/strace_5.5.bb</filename>
                recipe where the source comes from a single tarball.
                Notice the use of the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                variable:
                <literallayout class='monospaced'>
     SRC_URI = "https://strace.io/files/${PV}/strace-${PV}.tar.xz \
                </literallayout>
            </para>

            <para>
                Files mentioned in <filename>SRC_URI</filename> whose names end
                in a typical archive extension (e.g. <filename>.tar</filename>,
                <filename>.tar.gz</filename>, <filename>.tar.bz2</filename>,
                <filename>.zip</filename>, and so forth), are automatically
                extracted during the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>
                task.
                For another example that specifies these types of files, see
                the
                "<link linkend='new-recipe-autotooled-package'>Autotooled Package</link>"
                section.
            </para>

            <para>
                Another way of specifying source is from an SCM.
                For Git repositories, you must specify
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
                and you should specify
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                to include the revision with
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>.
                Here is an example from the recipe
                <filename>meta/recipes-kernel/blktrace/blktrace_git.bb</filename>:
                <literallayout class='monospaced'>
     SRCREV = "d6918c8832793b4205ed3bfede78c2f915c23385"

     PR = "r6"
     PV = "1.0.5+git${SRCPV}"

     SRC_URI = "git://git.kernel.dk/blktrace.git \
                file://ldflags.patch"
                </literallayout>
            </para>

            <para>
                If your <filename>SRC_URI</filename> statement includes
                URLs pointing to individual files fetched from a remote server
                other than a version control system, BitBake attempts to
                verify the files against checksums defined in your recipe to
                ensure they have not been tampered with or otherwise modified
                since the recipe was written.
                Two checksums are used:
                <filename>SRC_URI[md5sum]</filename> and
                <filename>SRC_URI[sha256sum]</filename>.
            </para>

            <para>
                If your <filename>SRC_URI</filename> variable points to
                more than a single URL (excluding SCM URLs), you need to
                provide the <filename>md5</filename> and
                <filename>sha256</filename> checksums for each URL.
                For these cases, you provide a name for each URL as part of
                the <filename>SRC_URI</filename> and then reference that name
                in the subsequent checksum statements.
                Here is an example combining lines from the files
                <filename>git.inc</filename> and
                <filename>git_2.24.1.bb</filename>:
                <literallayout class='monospaced'>
     SRC_URI = "${KERNELORG_MIRROR}/software/scm/git/git-${PV}.tar.gz;name=tarball \
                ${KERNELORG_MIRROR}/software/scm/git/git-manpages-${PV}.tar.gz;name=manpages"

     SRC_URI[tarball.md5sum] = "166bde96adbbc11c8843d4f8f4f9811b"
     SRC_URI[tarball.sha256sum] = "ad5334956301c86841eb1e5b1bb20884a6bad89a10a6762c958220c7cf64da02"
     SRC_URI[manpages.md5sum] = "31c2272a8979022497ba3d4202df145d"
     SRC_URI[manpages.sha256sum] = "9a7ae3a093bea39770eb96ca3e5b40bff7af0b9f6123f089d7821d0e5b8e1230"
                </literallayout>
            </para>

            <para>
                Proper values for <filename>md5</filename> and
                <filename>sha256</filename> checksums might be available
                with other signatures on the download page for the upstream
                source (e.g. <filename>md5</filename>,
                <filename>sha1</filename>, <filename>sha256</filename>,
                <filename>GPG</filename>, and so forth).
                Because the OpenEmbedded build system only deals with
                <filename>sha256sum</filename> and <filename>md5sum</filename>,
                you should verify all the signatures you find by hand.
            </para>

            <para>
                If no <filename>SRC_URI</filename> checksums are specified
                when you attempt to build the recipe, or you provide an
                incorrect checksum, the build will produce an error for each
                missing or incorrect checksum.
                As part of the error message, the build system provides
                the checksum string corresponding to the fetched file.
                Once you have the correct checksums, you can copy and paste
                them into your recipe and then run the build again to continue.
                <note>
                    As mentioned, if the upstream source provides signatures
                    for verifying the downloaded source code, you should
                    verify those manually before setting the checksum values
                    in the recipe and continuing with the build.
                </note>
            </para>

            <para>
                This final example is a bit more complicated and is from the
                <filename>meta/recipes-sato/rxvt-unicode/rxvt-unicode_9.20.bb</filename>
                recipe.
                The example's <filename>SRC_URI</filename> statement identifies
                multiple files as the source files for the recipe: a tarball, a
                patch file, a desktop file, and an icon.
                <literallayout class='monospaced'>
     SRC_URI = "http://dist.schmorp.de/rxvt-unicode/Attic/rxvt-unicode-${PV}.tar.bz2 \
                file://xwc.patch \
                file://rxvt.desktop \
                file://rxvt.png"
                </literallayout>
            </para>

            <para>
                When you specify local files using the
                <filename>file://</filename> URI protocol, the build system
                fetches files from the local machine.
                The path is relative to the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                variable and searches specific directories in a certain order:
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink><filename>}</filename>,
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink><filename>}</filename>,
                and <filename>files</filename>.
                The directories are assumed to be subdirectories of the
                directory in which the recipe or append file resides.
                For another example that specifies these types of files, see the
                "<link linkend='new-recipe-single-c-file-package-hello-world'>Single .c File Package (Hello World!)</link>"
                section.
            </para>

            <para>
                The previous example also specifies a patch file.
                Patch files are files whose names usually end in
                <filename>.patch</filename> or <filename>.diff</filename> but
                can end with compressed suffixes such as
                <filename>diff.gz</filename> and
                <filename>patch.bz2</filename>, for example.
                The build system automatically applies patches as described
                in the
                "<link linkend='new-recipe-patching-code'>Patching Code</link>" section.
            </para>
        </section>

        <section id='new-recipe-unpacking-code'>
            <title>Unpacking Code</title>

            <para>
                During the build, the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>
                task unpacks the source with
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>
                pointing to where it is unpacked.
            </para>

            <para>
                If you are fetching your source files from an upstream source
                archived tarball and the tarball's internal structure matches
                the common convention of a top-level subdirectory named
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink><filename>}-${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink><filename>}</filename>,
                then you do not need to set <filename>S</filename>.
                However, if <filename>SRC_URI</filename> specifies to fetch
                source from an archive that does not use this convention,
                or from an SCM like Git or Subversion, your recipe needs to
                define <filename>S</filename>.
            </para>

            <para>
                If processing your recipe using BitBake successfully unpacks
                the source files, you need to be sure that the directory
                pointed to by <filename>${S}</filename> matches the structure
                of the source.
            </para>
        </section>

        <section id='new-recipe-patching-code'>
            <title>Patching Code</title>

            <para>
                Sometimes it is necessary to patch code after it has been
                fetched.
                Any files mentioned in <filename>SRC_URI</filename> whose
                names end in <filename>.patch</filename> or
                <filename>.diff</filename> or compressed versions of these
                suffixes (e.g. <filename>diff.gz</filename> are treated as
                patches.
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
                task automatically applies these patches.
            </para>

            <para>
                The build system should be able to apply patches with the "-p1"
                option (i.e. one directory level in the path will be stripped
                off).
                If your patch needs to have more directory levels stripped off,
                specify the number of levels using the "striplevel" option in
                the <filename>SRC_URI</filename> entry for the patch.
                Alternatively, if your patch needs to be applied in a specific
                subdirectory that is not specified in the patch file, use the
                "patchdir" option in the entry.
            </para>

            <para>
                As with all local files referenced in
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                using <filename>file://</filename>, you should place
                patch files in a directory next to the recipe either
                named the same as the base name of the recipe
                (<ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink>
                and
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink>)
                or "files".
            </para>
        </section>

        <section id='new-recipe-licensing'>
            <title>Licensing</title>

            <para>
                Your recipe needs to have both the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                and
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
                variables:
                <itemizedlist>
                    <listitem><para><emphasis><filename>LICENSE</filename>:</emphasis>
                        This variable specifies the license for the software.
                        If you do not know the license under which the software
                        you are building is distributed, you should go to the
                        source code and look for that information.
                        Typical files containing this information include
                        <filename>COPYING</filename>,
                        <filename>LICENSE</filename>, and
                        <filename>README</filename> files.
                        You could also find the information near the top of
                        a source file.
                        For example, given a piece of software licensed under
                        the GNU General Public License version 2, you would
                        set <filename>LICENSE</filename> as follows:
                        <literallayout class='monospaced'>
     LICENSE = "GPLv2"
                        </literallayout></para>
                        <para>The licenses you specify within
                        <filename>LICENSE</filename> can have any name as long
                        as you do not use spaces, since spaces are used as
                        separators between license names.
                        For standard licenses, use the names of the files in
                        <filename>meta/files/common-licenses/</filename>
                        or the <filename>SPDXLICENSEMAP</filename> flag names
                        defined in <filename>meta/conf/licenses.conf</filename>.
                        </para></listitem>
                    <listitem><para><emphasis><filename>LIC_FILES_CHKSUM</filename>:</emphasis>
                        The OpenEmbedded build system uses this variable to
                        make sure the license text has not changed.
                        If it has, the build produces an error and it affords
                        you the chance to figure it out and correct the problem.
                        </para>
                        <para>You need to specify all applicable licensing
                        files for the software.
                        At the end of the configuration step, the build process
                        will compare the checksums of the files to be sure
                        the text has not changed.
                        Any differences result in an error with the message
                        containing the current checksum.
                        For more explanation and examples of how to set the
                        <filename>LIC_FILES_CHKSUM</filename> variable, see the
                        "<link link='usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</link>"
                        section.</para>

                        <para>To determine the correct checksum string, you
                        can list the appropriate files in the
                        <filename>LIC_FILES_CHKSUM</filename> variable with
                        incorrect md5 strings, attempt to build the software,
                        and then note the resulting error messages that will
                        report the correct md5 strings.
                        See the
                        "<link linkend='new-recipe-fetching-code'>Fetching Code</link>"
                        section for additional information.
                    </para>

                    <para>
                        Here is an example that assumes the software has a
                        <filename>COPYING</filename> file:
                        <literallayout class='monospaced'>
     LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"
                        </literallayout>
                        When you try to build the software, the build system
                        will produce an error and give you the correct string
                        that you can substitute into the recipe file for a
                        subsequent build.
                        </para></listitem>
                </itemizedlist>
            </para>

<!--

            <para>
                For trying this out I created a new recipe named
                <filename>htop_1.0.2.bb</filename> and put it in
                <filename>poky/meta/recipes-extended/htop</filename>.
                There are two license type statements in my very simple
                recipe:
                <literallayout class='monospaced'>
     LICENSE = ""

     LIC_FILES_CHKSUM = ""

     SRC_URI[md5sum] = ""
     SRC_URI[sha256sum] = ""
                </literallayout>
                Evidently, you need to run a <filename>bitbake -c cleanall htop</filename>.
                Next, you delete or comment out the two <filename>SRC_URI</filename>
                lines at the end and then attempt to build the software with
                <filename>bitbake htop</filename>.
                Doing so causes BitBake to report some errors and and give
                you the actual strings you need for the last two
                <filename>SRC_URI</filename> lines.
                Prior to this, you have to dig around in the home page of the
                source for <filename>htop</filename> and determine that the
                software is released under GPLv2.
                You can provide that in the <filename>LICENSE</filename>
                statement.
                Now you edit your recipe to have those two strings for
                the <filename>SRC_URI</filename> statements:
                <literallayout class='monospaced'>
     LICENSE = "GPLv2"

     LIC_FILES_CHKSUM = ""

     SRC_URI = "${SOURCEFORGE_MIRROR}/htop/htop-${PV}.tar.gz"
     SRC_URI[md5sum] = "0d01cca8df3349c74569cefebbd9919e"
     SRC_URI[sha256sum] = "ee60657b044ece0df096c053060df7abf3cce3a568ab34d260049e6a37ccd8a1"
                </literallayout>
                At this point, you can build the software again using the
                <filename>bitbake htop</filename> command.
                There is just a set of errors now associated with the
                empty <filename>LIC_FILES_CHKSUM</filename> variable now.
            </para>
-->

        </section>

        <section id='new-dependencies'>
            <title>Dependencies</title>

            <para>
                Most software packages have a short list of other packages
                that they require, which are called dependencies.
                These dependencies fall into two main categories: build-time
                dependencies, which are required when the software is built;
                and runtime dependencies, which are required to be installed
                on the target in order for the software to run.
            </para>

            <para>
                Within a recipe, you specify build-time dependencies using the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                variable.
                Although nuances exist, items specified in
                <filename>DEPENDS</filename> should be names of other recipes.
                It is important that you specify all build-time dependencies
                explicitly.
                If you do not, due to the parallel nature of BitBake's
                execution, you can end up with a race condition where the
                dependency is present for one task of a recipe (e.g.
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>)
                and then gone when the next task runs (e.g.
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>).
            </para>

            <para>
                Another consideration is that configure scripts might
                automatically check for optional dependencies and enable
                corresponding functionality if those dependencies are found.
                This behavior means that to ensure deterministic results and
                thus avoid more race conditions, you need to either explicitly
                specify these dependencies as well, or tell the configure
                script explicitly to disable the functionality.
                If you wish to make a recipe that is more generally useful
                (e.g. publish the recipe in a layer for others to use),
                instead of hard-disabling the functionality, you can use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG'><filename>PACKAGECONFIG</filename></ulink>
                variable to allow functionality and the corresponding
                dependencies to be enabled and disabled easily by other
                users of the recipe.
            </para>

            <para>
                Similar to build-time dependencies, you specify runtime
                dependencies through a variable -
                <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
                which is package-specific.
                All variables that are package-specific need to have the name
                of the package added to the end as an override.
                Since the main package for a recipe has the same name as the
                recipe, and the recipe's name can be found through the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
                variable, then you specify the dependencies for the main
                package by setting <filename>RDEPENDS_${PN}</filename>.
                If the package were named <filename>${PN}-tools</filename>,
                then you would set <filename>RDEPENDS_${PN}-tools</filename>,
                and so forth.
            </para>

            <para>
                Some runtime dependencies will be set automatically at
                packaging time.
                These dependencies include any shared library dependencies
                (i.e. if a package "example" contains "libexample" and
                another package "mypackage" contains a binary that links to
                "libexample" then the OpenEmbedded build system will
                automatically add a runtime dependency to "mypackage" on
                "example").
                See the
                "<ulink url='&YOCTO_DOCS_OM_URL;#automatically-added-runtime-dependencies'>Automatically Added Runtime Dependencies</ulink>"
                section in the Yocto Project Overview and Concepts Manual for
                further details.
            </para>
        </section>

        <section id='new-recipe-configuring-the-recipe'>
            <title>Configuring the Recipe</title>

            <para>
                Most software provides some means of setting build-time
                configuration options before compilation.
                Typically, setting these options is accomplished by running a
                configure script with options, or by modifying a build
                configuration file.
                <note>
                    As of Yocto Project Release 1.7, some of the core recipes
                    that package binary configuration scripts now disable the
                    scripts due to the scripts previously requiring error-prone
                    path substitution.
                    The OpenEmbedded build system uses
                    <filename>pkg-config</filename> now, which is much more
                    robust.
                    You can find a list of the <filename>*-config</filename>
                    scripts that are disabled list in the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#migration-1.7-binary-configuration-scripts-disabled'>Binary Configuration Scripts Disabled</ulink>"
                    section in the Yocto Project Reference Manual.
                </note>
            </para>

            <para>
                A major part of build-time configuration is about checking for
                build-time dependencies and possibly enabling optional
                functionality as a result.
                You need to specify any build-time dependencies for the
                software you are building in your recipe's
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                value, in terms of other recipes that satisfy those
                dependencies.
                You can often find build-time or runtime
                dependencies described in the software's documentation.
            </para>

            <para>
                The following list provides configuration items of note based
                on how your software is built:
                <itemizedlist>
                    <listitem><para><emphasis>Autotools:</emphasis>
                        If your source files have a
                        <filename>configure.ac</filename> file, then your
                        software is built using Autotools.
                        If this is the case, you just need to worry about
                        modifying the configuration.</para>

                        <para>When using Autotools, your recipe needs to inherit
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                        class and your recipe does not have to contain a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task.
                        However, you might still want to make some adjustments.
                        For example, you can set
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></ulink>
                        or
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></ulink>
                        to pass any needed configure options that are specific
                        to the recipe.
                        </para></listitem>
                    <listitem><para><emphasis>CMake:</emphasis>
                        If your source files have a
                        <filename>CMakeLists.txt</filename> file, then your
                        software is built using CMake.
                        If this is the case, you just need to worry about
                        modifying the configuration.</para>

                        <para>When you use CMake, your recipe needs to inherit
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-cmake'><filename>cmake</filename></ulink>
                        class and your recipe does not have to contain a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task.
                        You can make some adjustments by setting
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></ulink>
                        to pass any needed configure options that are specific
                        to the recipe.
                        <note>
                            If you need to install one or more custom CMake
                            toolchain files that are supplied by the
                            application you are building, install the files to
                            <filename>${D}${datadir}/cmake/</filename> Modules
                            during
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>.
                        </note>
                        </para></listitem>
                    <listitem><para><emphasis>Other:</emphasis>
                        If your source files do not have a
                        <filename>configure.ac</filename> or
                        <filename>CMakeLists.txt</filename> file, then your
                        software is built using some method other than Autotools
                        or CMake.
                        If this is the case, you normally need to provide a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task in your recipe
                        unless, of course, there is nothing to configure.
                        </para>
                        <para>Even if your software is not being built by
                        Autotools or CMake, you still might not need to deal
                        with any configuration issues.
                        You need to determine if configuration is even a required step.
                        You might need to modify a Makefile or some configuration file
                        used for the build to specify necessary build options.
                        Or, perhaps you might need to run a provided, custom
                        configure script with the appropriate options.</para>
                        <para>For the case involving a custom configure
                        script, you would run
                        <filename>./configure --help</filename> and look for
                        the options you need to set.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                Once configuration succeeds, it is always good practice to
                look at the <filename>log.do_configure</filename> file to
                ensure that the appropriate options have been enabled and no
                additional build-time dependencies need to be added to
                <filename>DEPENDS</filename>.
                For example, if the configure script reports that it found
                something not mentioned in <filename>DEPENDS</filename>, or
                that it did not find something that it needed for some
                desired optional functionality, then you would need to add
                those to <filename>DEPENDS</filename>.
                Looking at the log might also reveal items being checked for,
                enabled, or both that you do not want, or items not being found
                that are in <filename>DEPENDS</filename>, in which case
                you would need to look at passing extra options to the
                configure script as needed.
                For reference information on configure options specific to the
                software you are building, you can consult the output of the
                <filename>./configure --help</filename> command within
                <filename>${S}</filename> or consult the software's upstream
                documentation.
            </para>
        </section>

        <section id='new-recipe-using-headers-to-interface-with-devices'>
            <title>Using Headers to Interface with Devices</title>

            <para>
                If your recipe builds an application that needs to
                communicate with some device or needs an API into a custom
                kernel, you will need to provide appropriate header files.
                Under no circumstances should you ever modify the existing
                <filename>meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc</filename>
                file.
                These headers are used to build <filename>libc</filename> and
                must not be compromised with custom or machine-specific
                header information.
                If you customize <filename>libc</filename> through modified
                headers all other applications that use
                <filename>libc</filename> thus become affected.
                <note><title>Warning</title>
                    Never copy and customize the <filename>libc</filename>
                    header file (i.e.
                    <filename>meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc</filename>).
                </note>
                The correct way to interface to a device or custom kernel is
                to use a separate package that provides the additional headers
                for the driver or other unique interfaces.
                When doing so, your application also becomes responsible for
                creating a dependency on that specific provider.
            </para>

            <para>
                Consider the following:
                <itemizedlist>
                    <listitem><para>
                        Never modify
                        <filename>linux-libc-headers.inc</filename>.
                        Consider that file to be part of the
                        <filename>libc</filename> system, and not something
                        you use to access the kernel directly.
                        You should access <filename>libc</filename> through
                        specific <filename>libc</filename> calls.
                        </para></listitem>
                    <listitem><para>
                        Applications that must talk directly to devices
                        should either provide necessary headers themselves,
                        or establish a dependency on a special headers package
                        that is specific to that driver.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                For example, suppose you want to modify an existing header
                that adds I/O control or network support.
                If the modifications are used by a small number programs,
                providing a unique version of a header is easy and has little
                impact.
                When doing so, bear in mind the guidelines in the previous
                list.
                <note>
                    If for some reason your changes need to modify the behavior
                    of the <filename>libc</filename>, and subsequently all
                    other applications on the system, use a
                    <filename>.bbappend</filename> to modify the
                    <filename>linux-kernel-headers.inc</filename> file.
                    However, take care to not make the changes
                    machine specific.
                </note>
            </para>

            <para>
                Consider a case where your kernel is older and you need
                an older <filename>libc</filename> ABI.
                The headers installed by your recipe should still be a
                standard mainline kernel, not your own custom one.
            </para>

            <para>
                When you use custom kernel headers you need to get them from
                <ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_KERNEL_DIR'><filename>STAGING_KERNEL_DIR</filename></ulink>,
                which is the directory with kernel headers that are
                required to build out-of-tree modules.
                Your recipe will also need the following:
                <literallayout class='monospaced'>
     do_configure[depends] += "virtual/kernel:do_shared_workdir"
                </literallayout>
            </para>
        </section>

        <section id='new-recipe-compilation'>
            <title>Compilation</title>

            <para>
                During a build, the <filename>do_compile</filename> task
                happens after source is fetched, unpacked, and configured.
                If the recipe passes through <filename>do_compile</filename>
                successfully, nothing needs to be done.
            </para>

            <para>
                However, if the compile step fails, you need to diagnose the
                failure.
                Here are some common issues that cause failures.
                <note>
                    For cases where improper paths are detected for
                    configuration files or for when libraries/headers cannot
                    be found, be sure you are using the more robust
                    <filename>pkg-config</filename>.
                    See the note in section
                    "<link linkend='new-recipe-configuring-the-recipe'>Configuring the Recipe</link>"
                    for additional information.
                </note>
                <itemizedlist>
                    <listitem><para><emphasis>Parallel build failures:</emphasis>
                        These failures manifest themselves as intermittent
                        errors, or errors reporting that a file or directory
                        that should be created by some other part of the build
                        process could not be found.
                        This type of failure can occur even if, upon inspection,
                        the file or directory does exist after the build has
                        failed, because that part of the build process happened
                        in the wrong order.</para>
                        <para>To fix the problem, you need to either satisfy
                        the missing dependency in the Makefile or whatever
                        script produced the Makefile, or (as a workaround)
                        set
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink>
                        to an empty string:
                        <literallayout class='monospaced'>
     PARALLEL_MAKE = ""
                        </literallayout></para>
                        <para>
                            For information on parallel Makefile issues, see the
                            "<link linkend='debugging-parallel-make-races'>Debugging Parallel Make Races</link>"
                            section.
                            </para></listitem>
                    <listitem><para><emphasis>Improper host path usage:</emphasis>
                        This failure applies to recipes building for the target
                        or <filename>nativesdk</filename> only.
                        The failure occurs when the compilation process uses
                        improper headers, libraries, or other files from the
                        host system when cross-compiling for the target.
                        </para>
                        <para>To fix the problem, examine the
                        <filename>log.do_compile</filename> file to identify
                        the host paths being used (e.g.
                        <filename>/usr/include</filename>,
                        <filename>/usr/lib</filename>, and so forth) and then
                        either add configure options, apply a patch, or do both.
                        </para></listitem>
                    <listitem><para><emphasis>Failure to find required
                        libraries/headers:</emphasis>
                        If a build-time dependency is missing because it has
                        not been declared in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                        or because the dependency exists but the path used by
                        the build process to find the file is incorrect and the
                        configure step did not detect it, the compilation
                        process could fail.
                        For either of these failures, the compilation process
                        notes that files could not be found.
                        In these cases, you need to go back and add additional
                        options to the configure script as well as possibly
                        add additional build-time dependencies to
                        <filename>DEPENDS</filename>.</para>
                        <para>Occasionally, it is necessary to apply a patch
                        to the source to ensure the correct paths are used.
                        If you need to specify paths to find files staged
                        into the sysroot from other recipes, use the variables
                        that the OpenEmbedded build system provides
                        (e.g.
                        <filename>STAGING_BINDIR</filename>,
                        <filename>STAGING_INCDIR</filename>,
                        <filename>STAGING_DATADIR</filename>, and so forth).
<!--
                        (e.g.
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_BINDIR'><filename>STAGING_BINDIR</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_INCDIR'><filename>STAGING_INCDIR</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_DATADIR'><filename>STAGING_DATADIR</filename></ulink>,
                        and so forth).
-->
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-installing'>
            <title>Installing</title>

            <para>
                During <filename>do_install</filename>, the task copies the
                built files along with their hierarchy to locations that
                would mirror their locations on the target device.
                The installation process copies files from the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>,
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-B'><filename>B</filename></ulink><filename>}</filename>,
                and
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename>
                directories to the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>
                directory to create the structure as it should appear on the
                target system.
            </para>

            <para>
                How your software is built affects what you must do to be
                sure your software is installed correctly.
                The following list describes what you must do for installation
                depending on the type of build system used by the software
                being built:
                <itemizedlist>
                    <listitem><para><emphasis>Autotools and CMake:</emphasis>
                        If the software your recipe is building uses Autotools
                        or CMake, the OpenEmbedded build
                        system understands how to install the software.
                        Consequently, you do not have to have a
                        <filename>do_install</filename> task as part of your
                        recipe.
                        You just need to make sure the install portion of the
                        build completes with no issues.
                        However, if you wish to install additional files not
                        already being installed by
                        <filename>make install</filename>, you should do this
                        using a <filename>do_install_append</filename> function
                        using the install command as described in
                        the "Manual" bulleted item later in this list.
                        </para></listitem>
                    <listitem><para><emphasis>Other (using
                        <filename>make install</filename>):</emphasis>
                        You need to define a
                        <filename>do_install</filename> function in your
                        recipe.
                        The function should call
                        <filename>oe_runmake install</filename> and will likely
                        need to pass in the destination directory as well.
                        How you pass that path is dependent on how the
                        <filename>Makefile</filename> being run is written
                        (e.g. <filename>DESTDIR=${D}</filename>,
                        <filename>PREFIX=${D}</filename>,
                        <filename>INSTALLROOT=${D}</filename>, and so forth).
                        </para>
                        <para>For an example recipe using
                        <filename>make install</filename>, see the
                        "<link linkend='new-recipe-makefile-based-package'>Makefile-Based Package</link>"
                        section.</para></listitem>
                    <listitem><para><emphasis>Manual:</emphasis>
                        You need to define a
                        <filename>do_install</filename> function in your
                        recipe.
                        The function must first use
                        <filename>install -d</filename> to create the
                        directories under
                        <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>.
                        Once the directories exist, your function can use
                        <filename>install</filename> to manually install the
                        built software into the directories.</para>
                        <para>You can find more information on
                        <filename>install</filename> at
                        <ulink url='http://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html'></ulink>.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                For the scenarios that do not use Autotools or
                CMake, you need to track the installation
                and diagnose and fix any issues until everything installs
                correctly.
                You need to look in the default location of
                <filename>${D}</filename>, which is
                <filename>${WORKDIR}/image</filename>, to be sure your
                files have been installed correctly.
            </para>

            <note><title>Notes</title>
                <itemizedlist>
                    <listitem><para>
                        During the installation process, you might need to
                        modify some of the installed files to suit the target
                        layout.
                        For example, you might need to replace hard-coded paths
                        in an initscript with values of variables provided by
                        the build system, such as replacing
                        <filename>/usr/bin/</filename> with
                        <filename>${bindir}</filename>.
                        If you do perform such modifications during
                        <filename>do_install</filename>, be sure to modify the
                        destination file after copying rather than before
                        copying.
                        Modifying after copying ensures that the build system
                        can re-execute <filename>do_install</filename> if
                        needed.
                        </para></listitem>
                    <listitem><para>
                        <filename>oe_runmake install</filename>, which can be
                        run directly or can be run indirectly by the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-cmake'><filename>cmake</filename></ulink>
                        classes, runs <filename>make install</filename> in
                        parallel.
                        Sometimes, a Makefile can have missing dependencies
                        between targets that can result in race conditions.
                        If you experience intermittent failures during
                        <filename>do_install</filename>, you might be able to
                        work around them by disabling parallel Makefile
                        installs by adding the following to the recipe:
                        <literallayout class='monospaced'>
     PARALLEL_MAKEINST = ""
                        </literallayout>
                        See
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename></ulink>
                        for additional information.
                        </para></listitem>
                    <listitem><para>
                        If you need to install one or more custom CMake
                        toolchain files that are supplied by the
                        application you are building, install the files to
                        <filename>${D}${datadir}/cmake/</filename> Modules
                        during
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>.
                        </para></listitem>
                </itemizedlist>
            </note>
        </section>

        <section id='new-recipe-enabling-system-services'>
            <title>Enabling System Services</title>

            <para>
                If you want to install a service, which is a process that
                usually starts on boot and runs in the background, then
                you must include some additional definitions in your recipe.
            </para>

            <para>
                If you are adding services and the service initialization
                script or the service file itself is not installed, you must
                provide for that installation in your recipe using a
                <filename>do_install_append</filename> function.
                If your recipe already has a <filename>do_install</filename>
                function, update the function near its end rather than
                adding an additional <filename>do_install_append</filename>
                function.
            </para>

            <para>
                When you create the installation for your services, you need
                to accomplish what is normally done by
                <filename>make install</filename>.
                In other words, make sure your installation arranges the output
                similar to how it is arranged on the target system.
            </para>

            <para>
                The OpenEmbedded build system provides support for starting
                services two different ways:
                <itemizedlist>
                    <listitem><para><emphasis>SysVinit:</emphasis>
                        SysVinit is a system and service manager that
                        manages the init system used to control the very basic
                        functions of your system.
                        The init program is the first program
                        started by the Linux kernel when the system boots.
                        Init then controls the startup, running and shutdown
                        of all other programs.</para>
                        <para>To enable a service using SysVinit, your recipe
                        needs to inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-update-rc.d'><filename>update-rc.d</filename></ulink>
                        class.
                        The class helps facilitate safely installing the
                        package on the target.</para>
                        <para>You will need to set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_PACKAGES'><filename>INITSCRIPT_PACKAGES</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_NAME'><filename>INITSCRIPT_NAME</filename></ulink>,
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_PARAMS'><filename>INITSCRIPT_PARAMS</filename></ulink>
                        variables within your recipe.</para></listitem>
                    <listitem><para><emphasis>systemd:</emphasis>
                        System Management Daemon (systemd) was designed to
                        replace SysVinit and to provide
                        enhanced management of services.
                        For more information on systemd, see the systemd
                        homepage at
                        <ulink url='http://freedesktop.org/wiki/Software/systemd/'></ulink>.
                        </para>
                        <para>To enable a service using systemd, your recipe
                        needs to inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-systemd'><filename>systemd</filename></ulink>
                        class.
                        See the <filename>systemd.bbclass</filename> file
                        located in your
                        <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
                        section for more information.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-packaging'>
            <title>Packaging</title>

            <para>
                Successful packaging is a combination of automated processes
                performed by the OpenEmbedded build system and some
                specific steps you need to take.
                The following list describes the process:
                <itemizedlist>
                    <listitem><para><emphasis>Splitting Files</emphasis>:
                        The <filename>do_package</filename> task splits the
                        files produced by the recipe into logical components.
                        Even software that produces a single binary might
                        still have debug symbols, documentation, and other
                        logical components that should be split out.
                        The <filename>do_package</filename> task ensures
                        that files are split up and packaged correctly.
                        </para></listitem>
                    <listitem><para><emphasis>Running QA Checks</emphasis>:
                        The
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-insane'><filename>insane</filename></ulink>
                        class adds a step to
                        the package generation process so that output quality
                        assurance checks are generated by the OpenEmbedded
                        build system.
                        This step performs a range of checks to be sure the
                        build's output is free of common problems that show
                        up during runtime.
                        For information on these checks, see the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-insane'><filename>insane</filename></ulink>
                        class and the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#ref-qa-checks'>QA Error and Warning Messages</ulink>"
                        chapter in the Yocto Project Reference Manual.
                        </para></listitem>
                    <listitem><para><emphasis>Hand-Checking Your Packages</emphasis>:
                        After you build your software, you need to be sure
                        your packages are correct.
                        Examine the
                        <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/packages-split</filename>
                        directory and make sure files are where you expect
                        them to be.
                        If you discover problems, you can set
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>,
                        <filename>do_install(_append)</filename>, and so forth as
                        needed.
                        </para></listitem>
                    <listitem><para><emphasis>Splitting an Application into Multiple Packages</emphasis>:
                        If you need to split an application into several
                        packages, see the
                        "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application into Multiple Packages</link>"
                        section for an example.
                        </para></listitem>
                    <listitem><para><emphasis>Installing a Post-Installation Script</emphasis>:
                        For an example showing how to install a
                        post-installation script, see the
                        "<link linkend='new-recipe-post-installation-scripts'>Post-Installation Scripts</link>"
                        section.
                        </para></listitem>
                    <listitem><para><emphasis>Marking Package Architecture</emphasis>:
                        Depending on what your recipe is building and how it
                        is configured, it might be important to mark the
                        packages produced as being specific to a particular
                        machine, or to mark them as not being specific to
                        a particular machine or architecture at all.</para>
                        <para>By default, packages apply to any machine with the
                        same architecture as the target machine.
                        When a recipe produces packages that are
                        machine-specific (e.g. the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        value is passed into the configure script or a patch
                        is applied only for a particular machine), you should
                        mark them as such by adding the following to the
                        recipe:
                        <literallayout class='monospaced'>
     PACKAGE_ARCH = "${MACHINE_ARCH}"
                        </literallayout></para>
                        <para>On the other hand, if the recipe produces packages
                        that do not contain anything specific to the target
                        machine or architecture at all (e.g. recipes
                        that simply package script files or configuration
                        files), you should use the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-allarch'><filename>allarch</filename></ulink>
                        class to do this for you by adding this to your
                        recipe:
                        <literallayout class='monospaced'>
     inherit allarch
                        </literallayout>
                        Ensuring that the package architecture is correct is
                        not critical while you are doing the first few builds
                        of your recipe.
                        However, it is important in order
                        to ensure that your recipe rebuilds (or does not
                        rebuild) appropriately in response to changes in
                        configuration, and to ensure that you get the
                        appropriate packages installed on the target machine,
                        particularly if you run separate builds for more
                        than one target machine.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-sharing-files-between-recipes'>
            <title>Sharing Files Between Recipes</title>

            <para>
                Recipes often need to use files provided by other recipes on
                the build host.
                For example, an application linking to a common library needs
                access to the library itself and its associated headers.
                The way this access is accomplished is by populating a sysroot
                with files.
                Each recipe has two sysroots in its work directory, one for
                target files
                (<filename>recipe-sysroot</filename>) and one for files that
                are native to the build host
                (<filename>recipe-sysroot-native</filename>).
                <note>
                    You could find the term "staging" used within the Yocto
                    project regarding files populating sysroots (e.g. the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_DIR'><filename>STAGING_DIR</filename></ulink>
                    variable).
                </note>
            </para>

            <para>
                Recipes should never populate the sysroot directly (i.e. write
                files into sysroot).
                Instead, files should be installed into standard locations
                during the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
                task within the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>
                directory.
                The reason for this limitation is that almost all files that
                populate the sysroot are cataloged in manifests in order to
                ensure the files can be removed later when a recipe is either
                modified or removed.
                Thus, the sysroot is able to remain free from stale files.
            </para>

            <para>
                A subset of the files installed by the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
                task are used by the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></ulink>
                task as defined by the the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SYSROOT_DIRS'><filename>SYSROOT_DIRS</filename></ulink>
                variable to automatically populate the sysroot.
                It is possible to modify the list of directories that populate
                the sysroot.
                The following example shows how you could add the
                <filename>/opt</filename> directory to the list of
                directories within a recipe:
                <literallayout class='monospaced'>
     SYSROOT_DIRS += "/opt"
                </literallayout>
            </para>

            <para>
                For a more complete description of the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></ulink>
                task and its associated functions, see the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-staging'><filename>staging</filename></ulink>
                class.
            </para>
        </section>

        <section id='metadata-virtual-providers'>
            <title>Using Virtual Providers</title>

            <para>
                Prior to a build, if you know that several different recipes
                provide the same functionality, you can use a virtual provider
                (i.e. <filename>virtual/*</filename>) as a placeholder for the
                actual provider.
                The actual provider is determined at build-time.
            </para>

            <para>
                A common scenario where a virtual provider is used would be
                for the kernel recipe.
                Suppose you have three kernel recipes whose
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>
                values map to <filename>kernel-big</filename>,
                <filename>kernel-mid</filename>, and
                <filename>kernel-small</filename>.
                Furthermore, each of these recipes in some way uses a
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PROVIDES'><filename>PROVIDES</filename></ulink>
                statement that essentially identifies itself as being able
                to provide <filename>virtual/kernel</filename>.
                Here is one way through the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-kernel'><filename>kernel</filename></ulink>
                class:
                <literallayout class='monospaced'>
     PROVIDES += "${@ "virtual/kernel" if (d.getVar("KERNEL_PACKAGE_NAME") == "kernel") else "" }"
                </literallayout>
                Any recipe that inherits the <filename>kernel</filename> class
                is going to utilize a <filename>PROVIDES</filename> statement
                that identifies that recipe as being able to provide the
                <filename>virtual/kernel</filename> item.
            </para>

            <para>
                Now comes the time to actually build an image and you need a
                kernel recipe, but which one?
                You can configure your build to call out the kernel recipe
                you want by using the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'><filename>PREFERRED_PROVIDER</filename></ulink>
                variable.
                As an example, consider the
                <ulink url='https://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/meta/conf/machine/include/x86-base.inc'><filename>x86-base.inc</filename></ulink>
                include file, which is a machine
                (i.e. <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>)
                configuration file.
                This include file is the reason all x86-based machines use the
                <filename>linux-yocto</filename> kernel.
                Here are the relevant lines from the include file:
                <literallayout class='monospaced'>
     PREFERRED_PROVIDER_virtual/kernel ??= "linux-yocto"
     PREFERRED_VERSION_linux-yocto ??= "4.15%"
                </literallayout>
            </para>

            <para>
                When you use a virtual provider, you do not have to
                "hard code" a recipe name as a build dependency.
                You can use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                variable to state the build is dependent on
                <filename>virtual/kernel</filename> for example:
                <literallayout class='monospaced'>
     DEPENDS = "virtual/kernel"
                </literallayout>
                During the build, the OpenEmbedded build system picks
                the correct recipe needed for the
                <filename>virtual/kernel</filename> dependency based on the
                <filename>PREFERRED_PROVIDER</filename> variable.
                If you want to use the small kernel mentioned at the beginning
                of this section, configure your build as follows:
                <literallayout class='monospaced'>
     PREFERRED_PROVIDER_virtual/kernel ??= "kernel-small"
                </literallayout>
                <note>
                    Any recipe that
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PROVIDES'><filename>PROVIDES</filename></ulink>
                    a <filename>virtual/*</filename> item that is ultimately
                    not selected through
                    <filename>PREFERRED_PROVIDER</filename> does not get built.
                    Preventing these recipes from building is usually the
                    desired behavior since this mechanism's purpose is to
                    select between mutually exclusive alternative providers.
                </note>
            </para>

            <para>
                The following lists specific examples of virtual providers:
                <itemizedlist>
                    <listitem><para>
                        <filename>virtual/kernel</filename>:
                        Provides the name of the kernel recipe to use when
                        building a kernel image.
                        </para></listitem>
                    <listitem><para>
                        <filename>virtual/bootloader</filename>:
                        Provides the name of the bootloader to use when
                        building an image.
                        </para></listitem>
                    <listitem><para>
                        <filename>virtual/libgbm</filename>:
                        Provides <filename>gbm.pc</filename>.
                        </para></listitem>
                    <listitem><para>
                        <filename>virtual/egl</filename>:
                        Provides <filename>egl.pc</filename> and possibly
                        <filename>wayland-egl.pc</filename>.
                        </para></listitem>
                    <listitem><para>
                        <filename>virtual/libgl</filename>:
                        Provides <filename>gl.pc</filename> (i.e. libGL).
                        </para></listitem>
                    <listitem><para>
                        <filename>virtual/libgles1</filename>:
                        Provides <filename>glesv1_cm.pc</filename>
                        (i.e. libGLESv1_CM).
                        </para></listitem>
                    <listitem><para>
                        <filename>virtual/libgles2</filename>:
                        Provides <filename>glesv2.pc</filename>
                        (i.e. libGLESv2).
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='properly-versioning-pre-release-recipes'>
            <title>Properly Versioning Pre-Release Recipes</title>

            <para>
                Sometimes the name of a recipe can lead to versioning
                problems when the recipe is upgraded to a final release.
                For example, consider the
                <filename>irssi_0.8.16-rc1.bb</filename> recipe file in
                the list of example recipes in the
                "<link linkend='new-recipe-storing-and-naming-the-recipe'>Storing and Naming the Recipe</link>"
                section.
                This recipe is at a release candidate stage (i.e.
                "rc1").
                When the recipe is released, the recipe filename becomes
                <filename>irssi_0.8.16.bb</filename>.
                The version change from <filename>0.8.16-rc1</filename>
                to <filename>0.8.16</filename> is seen as a decrease by the
                build system and package managers, so the resulting packages
                will not correctly trigger an upgrade.
            </para>

            <para>
                In order to ensure the versions compare properly, the
                recommended convention is to set
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                within the recipe to
                "<replaceable>previous_version</replaceable>+<replaceable>current_version</replaceable>".
                You can use an additional variable so that you can use the
                current version elsewhere.
                Here is an example:
                <literallayout class='monospaced'>
     REALPV = "0.8.16-rc1"
     PV = "0.8.15+${REALPV}"
                </literallayout>
            </para>
        </section>

        <section id='new-recipe-post-installation-scripts'>
            <title>Post-Installation Scripts</title>

            <para>
                Post-installation scripts run immediately after installing
                a package on the target or during image creation when a
                package is included in an image.
                To add a post-installation script to a package, add a
                <filename>pkg_postinst_</filename><replaceable>PACKAGENAME</replaceable><filename>()</filename> function to
                the recipe file (<filename>.bb</filename>) and replace
                <replaceable>PACKAGENAME</replaceable> with the name of the package
                you want to attach to the <filename>postinst</filename>
                script.
                To apply the post-installation script to the main package
                for the recipe, which is usually what is required, specify
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
                in place of <replaceable>PACKAGENAME</replaceable>.
            </para>

            <para>
                A post-installation function has the following structure:
                <literallayout class='monospaced'>
     pkg_postinst_<replaceable>PACKAGENAME</replaceable>() {
     # Commands to carry out
     }
                </literallayout>
            </para>

            <para>
                The script defined in the post-installation function is
                called when the root filesystem is created.
                If the script succeeds, the package is marked as installed.
                <note>
                    Any RPM post-installation script that runs on the target
                    should return a 0 exit code.
                    RPM does not allow non-zero exit codes for these scripts,
                    and the RPM package manager will cause the package to fail
                    installation on the target.
                </note>
            </para>

            <para>
                Sometimes it is necessary for the execution of a
                post-installation script to be delayed until the first boot.
                For example, the script might need to be executed on the
                device itself.
                To delay script execution until boot time, you must explicitly
                mark post installs to defer to the target.
                You can use <filename>pkg_postinst_ontarget()</filename> or
                call
                <filename>postinst_intercept delay_to_first_boot</filename>
                from <filename>pkg_postinst()</filename>.
                Any failure of a <filename>pkg_postinst()</filename> script
                (including exit 1) triggers an error during the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-rootfs'><filename>do_rootfs</filename></ulink>
                task.
            </para>

            <para>
                If you have recipes that use
                <filename>pkg_postinst</filename> function
                and they require the use of non-standard native
                tools that have dependencies during rootfs construction, you
                need to use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_WRITE_DEPS'><filename>PACKAGE_WRITE_DEPS</filename></ulink>
                variable in your recipe to list these tools.
                If you do not use this variable, the tools might be missing and
                execution of the post-installation script is deferred until
                first boot.
                Deferring the script to first boot is undesirable and for
                read-only rootfs impossible.
            </para>

            <note>
                Equivalent support for pre-install, pre-uninstall, and
                post-uninstall scripts exist by way of
                <filename>pkg_preinst</filename>,
                <filename>pkg_prerm</filename>, and
                <filename>pkg_postrm</filename>, respectively.
                These scrips work in exactly the same way as does
                <filename>pkg_postinst</filename> with the exception
                that they run at different times.
                Also, because of when they run, they are not applicable to
                being run at image creation time like
                <filename>pkg_postinst</filename>.
            </note>
        </section>

        <section id='new-recipe-testing'>
            <title>Testing</title>

            <para>
                The final step for completing your recipe is to be sure that
                the software you built runs correctly.
                To accomplish runtime testing, add the build's output
                packages to your image and test them on the target.
            </para>

            <para>
                For information on how to customize your image by adding
                specific packages, see the
                "<link linkend='usingpoky-extend-customimage'>Customizing Images</link>"
                section.
            </para>
        </section>

        <section id='new-recipe-testing-examples'>
            <title>Examples</title>

            <para>
                To help summarize how to write a recipe, this section provides
                some examples given various scenarios:
                <itemizedlist>
                    <listitem><para>Recipes that use local files</para></listitem>
                    <listitem><para>Using an Autotooled package</para></listitem>
                    <listitem><para>Using a Makefile-based package</para></listitem>
                    <listitem><para>Splitting an application into multiple packages</para></listitem>
                    <listitem><para>Adding binaries to an image</para></listitem>
                </itemizedlist>
            </para>

            <section id='new-recipe-single-c-file-package-hello-world'>
                <title>Single .c File Package (Hello World!)</title>

                <para>
                    Building an application from a single file that is stored
                    locally (e.g. under <filename>files</filename>) requires
                    a recipe that has the file listed in the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
                    variable.
                    Additionally, you need to manually write the
                    <filename>do_compile</filename> and
                    <filename>do_install</filename> tasks.
                    The <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
                    variable defines the directory containing the source code,
                    which is set to
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
                    in this case - the directory BitBake uses for the build.
                    <literallayout class='monospaced'>
     SUMMARY = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                    </literallayout>
                </para>

                <para>
                    By default, the <filename>helloworld</filename>,
                    <filename>helloworld-dbg</filename>, and
                    <filename>helloworld-dev</filename> packages are built.
                    For information on how to customize the packaging process,
                    see the
                    "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application into Multiple Packages</link>"
                    section.
                </para>
            </section>

            <section id='new-recipe-autotooled-package'>
                <title>Autotooled Package</title>
                <para>
                    Applications that use Autotools such as <filename>autoconf</filename> and
                    <filename>automake</filename> require a recipe that has a source archive listed in
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> and
                    also inherit the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                    class, which contains the definitions of all the steps
                    needed to build an Autotool-based application.
                    The result of the build is automatically packaged.
                    And, if the application uses NLS for localization, packages with local information are
                    generated (one package per language).
                    Following is one example: (<filename>hello_2.3.bb</filename>)
                    <literallayout class='monospaced'>
     SUMMARY = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                     </literallayout>
                </para>

                <para>
                    The variable
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</ulink></filename>
                    is used to track source license changes as described in the
                    "<link linkend='usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</link>"
                    section in the Yocto Project Overview and Concepts Manual.
                    You can quickly create Autotool-based recipes in a manner
                    similar to the previous example.
                </para>
            </section>

            <section id='new-recipe-makefile-based-package'>
                <title>Makefile-Based Package</title>

                <para>
                    Applications that use GNU <filename>make</filename> also require a recipe that has
                    the source archive listed in
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
                    You do not need to add a <filename>do_compile</filename> step since by default BitBake
                    starts the <filename>make</filename> command to compile the application.
                    If you need additional <filename>make</filename> options, you should store them in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'><filename>EXTRA_OEMAKE</filename></ulink>
                    or
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></ulink>
                    variables.
                    BitBake passes these options into the GNU <filename>make</filename> invocation.
                    Note that a <filename>do_install</filename> task is still required.
                    Otherwise, BitBake runs an empty <filename>do_install</filename> task by default.
                </para>

               <para>
                    Some applications might require extra parameters to be passed to the compiler.
                    For example, the application might need an additional header path.
                    You can accomplish this by adding to the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink></filename> variable.
                    The following example shows this:
                    <literallayout class='monospaced'>
     CFLAGS_prepend = "-I ${S}/include "
                    </literallayout>
                </para>

                <para>
                In the following example, <filename>mtd-utils</filename> is a makefile-based package:
                    <literallayout class='monospaced'>
     SUMMARY = "Tools for managing memory technology devices"
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                         file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     # Use the latest version at 26 Oct, 2013
     SRCREV = "9f107132a6a073cce37434ca9cda6917dd8d866b"
     SRC_URI = "git://git.infradead.org/mtd-utils.git \
                     file://add-exclusion-to-mkfs-jffs2-git-2.patch \
     "

     PV = "1.5.1+git${SRCPV}"

     S = "${WORKDIR}/git"

     EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' 'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"

     do_install () {
             oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} INCLUDEDIR=${includedir}
     }

     PACKAGES =+ "mtd-utils-jffs2 mtd-utils-ubifs mtd-utils-misc"

     FILES_mtd-utils-jffs2 = "${sbindir}/mkfs.jffs2 ${sbindir}/jffs2dump ${sbindir}/jffs2reader ${sbindir}/sumtool"
     FILES_mtd-utils-ubifs = "${sbindir}/mkfs.ubifs ${sbindir}/ubi*"
     FILES_mtd-utils-misc = "${sbindir}/nftl* ${sbindir}/ftl* ${sbindir}/rfd* ${sbindir}/doc* ${sbindir}/serve_image ${sbindir}/recv_image"

     PARALLEL_MAKE = ""

     BBCLASSEXTEND = "native"
                    </literallayout>
                </para>
            </section>

            <section id='splitting-an-application-into-multiple-packages'>
                <title>Splitting an Application into Multiple Packages</title>

                <para>
                    You can use the variables
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> and
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink></filename>
                    to split an application into multiple packages.
                </para>

                <para>
                    Following is an example that uses the <filename>libxpm</filename> recipe.
                    By default, this recipe generates a single package that contains the library along
                    with a few binaries.
                    You can modify the recipe to split the binaries into separate packages:
                    <literallayout class='monospaced'>
     require xorg-lib-common.inc

     SUMMARY = "Xpm: X Pixmap extension library"
     LICENSE = "BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=51f4270b012ecd4ab1a164f5f4ed6cf7"
     DEPENDS += "libxext libsm libxt"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                    </literallayout>
                </para>

                <para>
                    In the previous example, we want to ship the <filename>sxpm</filename>
                    and <filename>cxpm</filename> binaries in separate packages.
                    Since <filename>bindir</filename> would be packaged into the main
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename>
                    package by default, we prepend the <filename>PACKAGES</filename>
                    variable so additional package names are added to the start of list.
                    This results in the extra <filename>FILES_*</filename>
                    variables then containing information that define which files and
                    directories go into which packages.
                    Files included by earlier packages are skipped by latter packages.
                    Thus, the main <filename>PN</filename> package
                    does not include the above listed files.
                </para>
            </section>

            <section id='packaging-externally-produced-binaries'>
                <title>Packaging Externally Produced Binaries</title>

                <para>
                    Sometimes, you need to add pre-compiled binaries to an
                    image.
                    For example, suppose that binaries for proprietary code
                    exist, which are created by a particular division of a
                    company.
                    Your part of the company needs to use those binaries as
                    part of an image that you are building using the
                    OpenEmbedded build system.
                    Since you only have the binaries and not the source code,
                    you cannot use a typical recipe that expects to fetch the
                    source specified in
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                    and then compile it.
                </para>

                <para>
                    One method is to package the binaries and then install them
                    as part of the image.
                    Generally, it is not a good idea to package binaries
                    since, among other things, it can hinder the ability to
                    reproduce builds and could lead to compatibility problems
                    with ABI in the future.
                    However, sometimes you have no choice.
                </para>

                <para>
                    The easiest solution is to create a recipe that uses
                    the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-bin-package'><filename>bin_package</filename></ulink>
                    class and to be sure that you are using default locations
                    for build artifacts.
                    In most cases, the <filename>bin_package</filename> class
                    handles "skipping" the configure and compile steps as well
                    as sets things up to grab packages from the appropriate
                    area.
                    In particular, this class sets <filename>noexec</filename>
                    on both the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                    and
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
                    tasks, sets
                    <filename>FILES_${PN}</filename> to "/" so that it picks
                    up all files, and sets up a
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
                    task, which effectively copies all files from
                    <filename>${S}</filename> to <filename>${D}</filename>.
                    The <filename>bin_package</filename> class works well when
                    the files extracted into <filename>${S}</filename> are
                    already laid out in the way they should be laid out
                    on the target.
                    For more information on these variables, see the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>,
                    and
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink>
                    variables in the Yocto Project Reference Manual's variable
                    glossary.
                    <note><title>Notes</title>
                        <itemizedlist>
                            <listitem><para>
                                Using
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                                is a good idea even for components distributed
                                in binary form, and is often necessary for
                                shared libraries.
                                For a shared library, listing the library
                                dependencies in
                                <filename>DEPENDS</filename> makes sure that
                                the libraries are available in the staging
                                sysroot when other recipes link against the
                                library, which might be necessary for
                                successful linking.
                                </para></listitem>
                            <listitem><para>
                                Using <filename>DEPENDS</filename> also
                                allows runtime dependencies between packages
                                to be added automatically.
                                See the
                                "<ulink url='&YOCTO_DOCS_OM_URL;#automatically-added-runtime-dependencies'>Automatically Added Runtime Dependencies</ulink>"
                                section in the Yocto Project Overview and
                                Concepts Manual for more information.
                                </para></listitem>
                        </itemizedlist>
                    </note>
                </para>

                <para>
                    If you cannot use the <filename>bin_package</filename>
                    class, you need to be sure you are doing the following:
                    <itemizedlist>
                        <listitem><para>
                            Create a recipe where the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                            and
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
                            tasks do nothing:
                            It is usually sufficient to just not define these
                            tasks in the recipe, because the default
                            implementations do nothing unless a Makefile is
                            found in
                            <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>.
                            </para>

                            <para>If
                            <filename>${S}</filename> might contain a Makefile,
                            or if you inherit some class that replaces
                            <filename>do_configure</filename> and
                            <filename>do_compile</filename> with custom
                            versions, then you can use the
                            <filename>[</filename><ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'><filename>noexec</filename></ulink><filename>]</filename>
                            flag to turn the tasks into no-ops, as follows:
                            <literallayout class='monospaced'>
     do_configure[noexec] = "1"
     do_compile[noexec] = "1"
                            </literallayout>
                            Unlike
                            <ulink url='&YOCTO_DOCS_BB_URL;#deleting-a-task'><filename>deleting the tasks</filename></ulink>,
                            using the flag preserves the dependency chain from
                            the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>,                     <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>,
                            and
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
                            tasks to the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
                            task.
                            </para></listitem>
                        <listitem><para>Make sure your
                            <filename>do_install</filename> task installs the
                            binaries appropriately.
                            </para></listitem>
                        <listitem><para>Ensure that you set up
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>
                            (usually
                            <filename>FILES_${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>)
                            to point to the files you have installed, which of
                            course depends on where you have installed them
                            and whether those files are in different locations
                            than the defaults.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id="following-recipe-style-guidelines">
            <title>Following Recipe Style Guidelines</title>

            <para>
                When writing recipes, it is good to conform to existing
                style guidelines.
                The
                <ulink url='http://www.openembedded.org/wiki/Styleguide'>OpenEmbedded Styleguide</ulink>
                wiki page provides rough guidelines for preferred recipe style.
            </para>

            <para>
                It is common for existing recipes to deviate a bit from this
                style.
                However, aiming for at least a consistent style is a good idea.
                Some practices, such as omitting spaces around
                <filename>=</filename> operators in assignments or ordering
                recipe components in an erratic way, are widely seen as poor
                style.
            </para>
        </section>

        <section id='recipe-syntax'>
            <title>Recipe Syntax</title>

            <para>
                Understanding recipe file syntax is important for writing
                recipes.
                The following list overviews the basic items that make up a
                BitBake recipe file.
                For more complete BitBake syntax descriptions, see the
                "<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>"
                chapter of the BitBake User Manual.
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Variable Assignments and Manipulations:</emphasis>
                        Variable assignments allow a value to be assigned to a
                        variable.
                        The assignment can be static text or might include
                        the contents of other variables.
                        In addition to the assignment, appending and prepending
                        operations are also supported.</para>

                        <para>The following example shows some of the ways
                        you can use variables in recipes:
                        <literallayout class='monospaced'>
     S = "${WORKDIR}/postfix-${PV}"
     CFLAGS += "-DNO_ASM"
     SRC_URI_append = " file://fixup.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Functions:</emphasis>
                        Functions provide a series of actions to be performed.
                        You usually use functions to override the default
                        implementation of a task function or to complement
                        a default function (i.e. append or prepend to an
                        existing function).
                        Standard functions use <filename>sh</filename> shell
                        syntax, although access to OpenEmbedded variables and
                        internal methods are also available.</para>

                        <para>The following is an example function from the
                        <filename>sed</filename> recipe:
                        <literallayout class='monospaced'>
     do_install () {
         autotools_do_install
         install -d ${D}${base_bindir}
         mv ${D}${bindir}/sed ${D}${base_bindir}/sed
         rmdir ${D}${bindir}/
     }
                        </literallayout>
                        It is also possible to implement new functions that
                        are called between existing tasks as long as the
                        new functions are not replacing or complementing the
                        default functions.
                        You can implement functions in Python
                        instead of shell.
                        Both of these options are not seen in the majority of
                        recipes.
                        </para></listitem>
                    <listitem><para><emphasis>Keywords:</emphasis>
                        BitBake recipes use only a few keywords.
                        You use keywords to include common
                        functions (<filename>inherit</filename>), load parts
                        of a recipe from other files
                        (<filename>include</filename> and
                        <filename>require</filename>) and export variables
                        to the environment (<filename>export</filename>).
                        </para>

                        <para>The following example shows the use of some of
                        these keywords:
                        <literallayout class='monospaced'>
     export POSTCONF = "${STAGING_BINDIR}/postconf"
     inherit autoconf
     require otherfile.inc
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Comments (#):</emphasis>
                        Any lines that begin with the hash character
                        (<filename>#</filename>) are treated as comment lines
                        and are ignored:
                        <literallayout class='monospaced'>
     # This is a comment
                        </literallayout>
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                This next list summarizes the most important and most commonly
                used parts of the recipe syntax.
                For more information on these parts of the syntax, you can
                reference the
                <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>
                chapter in the BitBake User Manual.
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Line Continuation (\):</emphasis>
                        Use the backward slash (<filename>\</filename>)
                        character to split a statement over multiple lines.
                        Place the slash character at the end of the line that
                        is to be continued on the next line:
                        <literallayout class='monospaced'>
     VAR = "A really long \
            line"
                        </literallayout>
                        <note>
                            You cannot have any characters including spaces
                            or tabs after the slash character.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Using Variables (${<replaceable>VARNAME</replaceable>}):</emphasis>
                        Use the <filename>${<replaceable>VARNAME</replaceable>}</filename>
                        syntax to access the contents of a variable:
                        <literallayout class='monospaced'>
     SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz"
                        </literallayout>
                        <note>
                            It is important to understand that the value of a
                            variable expressed in this form does not get
                            substituted automatically.
                            The expansion of these expressions happens
                            on-demand later (e.g. usually when a function that
                            makes reference to the variable executes).
                            This behavior ensures that the values are most
                            appropriate for the context in which they are
                            finally used.
                            On the rare occasion that you do need the variable
                            expression to be expanded immediately, you can use
                            the <filename>:=</filename> operator instead of
                            <filename>=</filename> when you make the
                            assignment, but this is not generally needed.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Quote All Assignments ("<replaceable>value</replaceable>"):</emphasis>
                        Use double quotes around values in all variable
                        assignments (e.g.
                        <filename>"<replaceable>value</replaceable>"</filename>).
                        Following is an example:
                        <literallayout class='monospaced'>
     VAR1 = "${OTHERVAR}"
     VAR2 = "The version is ${PV}"
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Conditional Assignment (?=):</emphasis>
                        Conditional assignment is used to assign a
                        value to a variable, but only when the variable is
                        currently unset.
                        Use the question mark followed by the equal sign
                        (<filename>?=</filename>) to make a "soft" assignment
                        used for conditional assignment.
                        Typically, "soft" assignments are used in the
                        <filename>local.conf</filename> file for variables
                        that are allowed to come through from the external
                        environment.
                        </para>

                        <para>Here is an example where
                        <filename>VAR1</filename> is set to "New value" if
                        it is currently empty.
                        However, if <filename>VAR1</filename> has already been
                        set, it remains unchanged:
                        <literallayout class='monospaced'>
     VAR1 ?= "New value"
                        </literallayout>
                        In this next example, <filename>VAR1</filename>
                        is left with the value "Original value":
                        <literallayout class='monospaced'>
     VAR1 = "Original value"
     VAR1 ?= "New value"
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Appending (+=):</emphasis>
                        Use the plus character followed by the equals sign
                        (<filename>+=</filename>) to append values to existing
                        variables.
                        <note>
                            This operator adds a space between the existing
                            content of the variable and the new content.
                        </note></para>

                        <para>Here is an example:
                        <literallayout class='monospaced'>
     SRC_URI += "file://fix-makefile.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Prepending (=+):</emphasis>
                        Use the equals sign followed by the plus character
                        (<filename>=+</filename>) to prepend values to existing
                        variables.
                        <note>
                            This operator adds a space between the new content
                            and the existing content of the variable.
                        </note></para>

                        <para>Here is an example:
                        <literallayout class='monospaced'>
     VAR =+ "Starts"
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Appending (_append):</emphasis>
                        Use the <filename>_append</filename> operator to
                        append values to existing variables.
                        This operator does not add any additional space.
                        Also, the operator is applied after all the
                        <filename>+=</filename>, and
                        <filename>=+</filename> operators have been applied and
                        after all <filename>=</filename> assignments have
                        occurred.
                        </para>

                        <para>The following example shows the space being
                        explicitly added to the start to ensure the appended
                        value is not merged with the existing value:
                        <literallayout class='monospaced'>
     SRC_URI_append = " file://fix-makefile.patch"
                        </literallayout>
                        You can also use the <filename>_append</filename>
                        operator with overrides, which results in the actions
                        only being performed for the specified target or
                        machine:
                        <literallayout class='monospaced'>
     SRC_URI_append_sh4 = " file://fix-makefile.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Prepending (_prepend):</emphasis>
                        Use the <filename>_prepend</filename> operator to
                        prepend values to existing variables.
                        This operator does not add any additional space.
                        Also, the operator is applied after all the
                        <filename>+=</filename>, and
                        <filename>=+</filename> operators have been applied and
                        after all <filename>=</filename> assignments have
                        occurred.
                        </para>

                        <para>The following example shows the space being
                        explicitly added to the end to ensure the prepended
                        value is not merged with the existing value:
                        <literallayout class='monospaced'>
     CFLAGS_prepend = "-I${S}/myincludes "
                        </literallayout>
                        You can also use the <filename>_prepend</filename>
                        operator with overrides, which results in the actions
                        only being performed for the specified target or
                        machine:
                        <literallayout class='monospaced'>
     CFLAGS_prepend_sh4 = "-I${S}/myincludes "
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Overrides:</emphasis>
                        You can use overrides to set a value conditionally,
                        typically based on how the recipe is being built.
                        For example, to set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
                        variable's value to "standard/base" for any target
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
                        except for qemuarm where it should be set to
                        "standard/arm-versatile-926ejs", you would do the
                        following:
                        <literallayout class='monospaced'>
     KBRANCH = "standard/base"
     KBRANCH_qemuarm  = "standard/arm-versatile-926ejs"
                        </literallayout>
                        Overrides are also used to separate alternate values
                        of a variable in other situations.
                        For example, when setting variables such as
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
                        that are specific to individual packages produced by
                        a recipe, you should always use an override that
                        specifies the name of the package.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Indentation:</emphasis>
                        Use spaces for indentation rather than than tabs.
                        For shell functions, both currently work.
                        However, it is a policy decision of the Yocto Project
                        to use tabs in shell functions.
                        Realize that some layers have a policy to use spaces
                        for all indentation.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Using Python for Complex Operations:</emphasis>
                        For more advanced processing, it is possible to use
                        Python code during variable assignments (e.g.
                        search and replacement on a variable).</para>

                        <para>You indicate Python code using the
                        <filename>${@<replaceable>python_code</replaceable>}</filename>
                        syntax for the variable assignment:
                        <literallayout class='monospaced'>
     SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Shell Function Syntax:</emphasis>
                        Write shell functions as if you were writing a shell
                        script when you describe a list of actions to take.
                        You should ensure that your script works with a generic
                        <filename>sh</filename> and that it does not require
                        any <filename>bash</filename> or other shell-specific
                        functionality.
                        The same considerations apply to various system
                        utilities (e.g. <filename>sed</filename>,
                        <filename>grep</filename>, <filename>awk</filename>,
                        and so forth) that you might wish to use.
                        If in doubt, you should check with multiple
                        implementations - including those from BusyBox.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id="platdev-newmachine">
        <title>Adding a New Machine</title>

        <para>
            Adding a new machine to the Yocto Project is a straightforward
            process.
            This section describes how to add machines that are similar
            to those that the Yocto Project already supports.
            <note>
                Although well within the capabilities of the Yocto Project,
                adding a totally new architecture might require
                changes to <filename>gcc/glibc</filename> and to the site
                information, which is beyond the scope of this manual.
            </note>
        </para>

        <para>
            For a complete example that shows how to add a new machine,
            see the
            "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-bitbake-layers-script'>Creating a New BSP Layer Using the <filename>bitbake-layers</filename> Script</ulink>"
            section in the Yocto Project Board Support Package (BSP)
            Developer's Guide.
        </para>

        <section id="platdev-newmachine-conffile">
            <title>Adding the Machine Configuration File</title>

            <para>
                To add a new machine, you need to add a new machine
                configuration file to the layer's
                <filename>conf/machine</filename> directory.
                This configuration file provides details about the device
                you are adding.
            </para>

            <para>
                The OpenEmbedded build system uses the root name of the
                machine configuration file to reference the new machine.
                For example, given a machine configuration file named
                <filename>crownbay.conf</filename>, the build system
                recognizes the machine as "crownbay".
            </para>

            <para>
                The most important variables you must set in your machine
                configuration file or include from a lower-level configuration
                file are as follows:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_ARCH'>TARGET_ARCH</ulink></filename>
                        (e.g. "arm")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'>PREFERRED_PROVIDER</ulink>_virtual/kernel</filename>
                        </para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'>MACHINE_FEATURES</ulink></filename>
                        (e.g. "apm screen wifi")</para></listitem>
                </itemizedlist>
            </para>

            <para>
                You might also need these variables:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLES'>SERIAL_CONSOLES</ulink></filename>
                        (e.g. "115200;ttyS0 115200;ttyS1")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_IMAGETYPE'>KERNEL_IMAGETYPE</ulink></filename>
                        (e.g. "zImage")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'>IMAGE_FSTYPES</ulink></filename>
                        (e.g. "tar.gz jffs2")</para></listitem>
                </itemizedlist>
            </para>

            <para>
                You can find full details on these variables in the reference
                section.
                You can leverage existing machine <filename>.conf</filename>
                files from <filename>meta-yocto-bsp/conf/machine/</filename>.
            </para>
        </section>

        <section id="platdev-newmachine-kernel">
            <title>Adding a Kernel for the Machine</title>

            <para>
                The OpenEmbedded build system needs to be able to build a kernel
                for the machine.
                You need to either create a new kernel recipe for this machine,
                or extend an existing kernel recipe.
                You can find several kernel recipe examples in the
                Source Directory at
                <filename>meta/recipes-kernel/linux</filename>
                that you can use as references.
            </para>

            <para>
                If you are creating a new kernel recipe, normal recipe-writing
                rules apply for setting up a
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
                Thus, you need to specify any necessary patches and set
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
                to point at the source code.
                You need to create a <filename>do_configure</filename> task that
                configures the unpacked kernel with a
                <filename>defconfig</filename> file.
                You can do this by using a <filename>make defconfig</filename>
                command or, more commonly, by copying in a suitable
                <filename>defconfig</filename> file and then running
                <filename>make oldconfig</filename>.
                By making use of <filename>inherit kernel</filename> and
                potentially some of the <filename>linux-*.inc</filename> files,
                most other functionality is centralized and the defaults of the
                class normally work well.
            </para>

            <para>
                If you are extending an existing kernel recipe, it is usually
                a matter of adding a suitable <filename>defconfig</filename>
                file.
                The file needs to be added into a location similar to
                <filename>defconfig</filename> files used for other machines
                in a given kernel recipe.
                A possible way to do this is by listing the file in the
                <filename>SRC_URI</filename> and adding the machine to the
                expression in
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'>COMPATIBLE_MACHINE</ulink></filename>:
                <literallayout class='monospaced'>
     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                </literallayout>
                For more information on <filename>defconfig</filename> files,
                see the
                "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
                section in the Yocto Project Linux Kernel Development Manual.
            </para>
        </section>

        <section id="platdev-newmachine-formfactor">
            <title>Adding a Formfactor Configuration File</title>

            <para>
                A formfactor configuration file provides information about the
                target hardware for which the image is being built and information that
                the build system cannot obtain from other sources such as the kernel.
                Some examples of information contained in a formfactor configuration file include
                framebuffer orientation, whether or not the system has a keyboard,
                the positioning of the keyboard in relation to the screen, and
                the screen resolution.
            </para>

            <para>
                The build system uses reasonable defaults in most cases.
                However, if customization is
                necessary, you need to create a <filename>machconfig</filename> file
                in the <filename>meta/recipes-bsp/formfactor/files</filename>
                directory.
                This directory contains directories for specific machines such as
                <filename>qemuarm</filename> and <filename>qemux86</filename>.
                For information about the settings available and the defaults, see the
                <filename>meta/recipes-bsp/formfactor/files/config</filename> file found in the
                same area.
            </para>

            <para>
                Following is an example for "qemuarm" machine:
                <literallayout class='monospaced'>
     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                </literallayout>
            </para>
        </section>
    </section>

    <section id='gs-upgrading-recipes'>
        <title>Upgrading Recipes</title>

        <para>
            Over time, upstream developers publish new versions for software
            built by layer recipes.
            It is recommended to keep recipes up-to-date with upstream
            version releases.
        </para>

        <para>
            While several methods exist that allow you upgrade a recipe,
            you might consider checking on the upgrade status of a recipe
            first.
            You can do so using the
            <filename>devtool check-upgrade-status</filename> command.
            See the
            "<ulink url='&YOCTO_DOCS_REF_URL;#devtool-checking-on-the-upgrade-status-of-a-recipe'>Checking on the Upgrade Status of a Recipe</ulink>"
            section in the Yocto Project Reference Manual for more information.
        </para>

        <para>
            The remainder of this section describes three ways you can
            upgrade a recipe.
            You can use the Automated Upgrade Helper (AUH) to set up
            automatic version upgrades.
            Alternatively, you can use <filename>devtool upgrade</filename>
            to set up semi-automatic version upgrades.
            Finally, you can manually upgrade a recipe by editing the
            recipe itself.
        </para>

        <section id='gs-using-the-auto-upgrade-helper'>
            <title>Using the Auto Upgrade Helper (AUH)</title>

            <para>
                The AUH utility works in conjunction with the
                OpenEmbedded build system in order to automatically generate
                upgrades for recipes based on new versions being
                published upstream.
                Use AUH when you want to create a service that performs the
                upgrades automatically and optionally sends you an email with
                the results.
            </para>

            <para>
                AUH allows you to update several recipes with a single use.
                You can also optionally perform build and integration tests
                using images with the results saved to your hard drive and
                emails of results optionally sent to recipe maintainers.
                Finally, AUH creates Git commits with appropriate commit
                messages in the layer's tree for the changes made to recipes.
                <note>
                    Conditions do exist when you should not use AUH to upgrade
                    recipes and you should instead use either
                    <filename>devtool upgrade</filename> or upgrade your
                    recipes manually:
                    <itemizedlist>
                        <listitem><para>
                            When AUH cannot complete the upgrade sequence.
                            This situation usually results because custom
                            patches carried by the recipe cannot be
                            automatically rebased to the new version.
                            In this case, <filename>devtool upgrade</filename>
                            allows you to manually resolve conflicts.
                            </para></listitem>
                        <listitem><para>
                            When for any reason you want fuller control over
                            the upgrade process.
                            For example, when you want special arrangements
                            for testing.
                            </para></listitem>
                    </itemizedlist>
                </note>
            </para>

            <para>
                The following steps describe how to set up the AUH utility:
                <orderedlist>
                    <listitem><para>
                        <emphasis>Be Sure the Development Host is Set Up:</emphasis>
                        You need to be sure that your development host is
                        set up to use the Yocto Project.
                        For information on how to set up your host, see the
                        "<link linkend='dev-preparing-the-build-host'>Preparing the Build Host</link>"
                        section.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Make Sure Git is Configured:</emphasis>
                        The AUH utility requires Git to be configured because
                        AUH uses Git to save upgrades.
                        Thus, you must have Git user and email configured.
                        The following command shows your configurations:
                        <literallayout class='monospaced'>
     $ git config --list
                        </literallayout>
                        If you do not have the user and email configured, you
                        can use the following commands to do so:
                        <literallayout class='monospaced'>
     $ git config --global user.name <replaceable>some_name</replaceable>
     $ git config --global user.email <replaceable>username</replaceable>@<replaceable>domain</replaceable>.com
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Clone the AUH Repository:</emphasis>
                        To use AUH, you must clone the repository onto your
                        development host.
                        The following command uses Git to create a local
                        copy of the repository on your system:
                        <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/auto-upgrade-helper
     Cloning into 'auto-upgrade-helper'...
     remote: Counting objects: 768, done.
     remote: Compressing objects: 100% (300/300), done.
     remote: Total 768 (delta 499), reused 703 (delta 434)
     Receiving objects: 100% (768/768), 191.47 KiB | 98.00 KiB/s, done.
     Resolving deltas: 100% (499/499), done.
     Checking connectivity... done.
                        </literallayout>
                        AUH is not part of the
                        <ulink url='&YOCTO_DOCS_REF_URL;#oe-core'>OpenEmbedded-Core (OE-Core)</ulink>
                        or
                        <ulink url='&YOCTO_DOCS_REF_URL;#poky'>Poky</ulink>
                        repositories.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Create a Dedicated Build Directory:</emphasis>
                        Run the
                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>oe-init-build-env</filename></ulink>
                        script to create a fresh build directory that you
                        use exclusively for running the AUH utility:
                        <literallayout class='monospaced'>
     $ cd ~/poky
     $ source oe-init-build-env <replaceable>your_AUH_build_directory</replaceable>
                        </literallayout>
                        Re-using an existing build directory and its
                        configurations is not recommended as existing settings
                        could cause AUH to fail or behave undesirably.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Make Configurations in Your Local Configuration File:</emphasis>
                        Several settings need to exist in the
                        <filename>local.conf</filename> file in the build
                        directory you just created for AUH.
                        Make these following configurations:
                        <itemizedlist>
                            <listitem><para>
                                If you want to enable
                                <ulink url='&YOCTO_DOCS_DEV_URL;#maintaining-build-output-quality'>Build History</ulink>,
                                which is optional, you need the following
                                lines in the
                                <filename>conf/local.conf</filename> file:
                                <literallayout class='monospaced'>
     INHERIT =+ "buildhistory"
     BUILDHISTORY_COMMIT = "1"
                                </literallayout>
                                With this configuration and a successful
                                upgrade, a build history "diff" file appears in
                                the
                                <filename>upgrade-helper/work/recipe/buildhistory-diff.txt</filename>
                                file found in your build directory.
                                </para></listitem>
                            <listitem><para>
                                If you want to enable testing through the
                                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-testimage*'><filename>testimage</filename></ulink>
                                class, which is optional, you need to have the
                                following set in your
                                <filename>conf/local.conf</filename> file:
                                <literallayout class='monospaced'>
     INHERIT += "testimage"
                                </literallayout>
                                <note>
                                    If your distro does not enable by default
                                    ptest, which Poky does, you need the
                                    following in your
                                    <filename>local.conf</filename> file:
                                    <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " ptest"
                                    </literallayout>
                                </note>
                                </para></listitem>
                        </itemizedlist>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Optionally Start a vncserver:</emphasis>
                        If you are running in a server without an X11 session,
                        you need to start a vncserver:
                        <literallayout class='monospaced'>
     $ vncserver :1
     $ export DISPLAY=:1
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Create and Edit an AUH Configuration File:</emphasis>
                        You need to have the
                        <filename>upgrade-helper/upgrade-helper.conf</filename>
                        configuration file in your build directory.
                        You can find a sample configuration file in the
                        <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/auto-upgrade-helper/tree/'>AUH source repository</ulink>.
                        </para>

                        <para>Read through the sample file and make
                        configurations as needed.
                        For example, if you enabled build history in your
                        <filename>local.conf</filename> as described earlier,
                        you must enable it in
                        <filename>upgrade-helper.conf</filename>.</para>

                        <para>Also, if you are using the default
                        <filename>maintainers.inc</filename> file supplied
                        with Poky and located in
                        <filename>meta-yocto</filename> and you do not set a
                        "maintainers_whitelist" or "global_maintainer_override"
                        in the <filename>upgrade-helper.conf</filename>
                        configuration, and you specify "-e all" on the
                        AUH command-line, the utility automatically sends out
                        emails to all the default maintainers.
                        Please avoid this.
                        </para></listitem>
                </orderedlist>
            </para>

            <para>
                This next set of examples describes how to use the AUH:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Upgrading a Specific Recipe:</emphasis>
                        To upgrade a specific recipe, use the following
                        form:
                        <literallayout class='monospaced'>
     $ upgrade-helper.py <replaceable>recipe_name</replaceable>
                        </literallayout>
                        For example, this command upgrades the
                        <filename>xmodmap</filename> recipe:
                        <literallayout class='monospaced'>
     $ upgrade-helper.py xmodmap
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Upgrading a Specific Recipe to a Particular Version:</emphasis>
                        To upgrade a specific recipe to a particular version,
                        use the following form:
                        <literallayout class='monospaced'>
     $ upgrade-helper.py <replaceable>recipe_name</replaceable> -t <replaceable>version</replaceable>
                        </literallayout>
                        For example, this command upgrades the
                        <filename>xmodmap</filename> recipe to version
                        1.2.3:
                        <literallayout class='monospaced'>
     $ upgrade-helper.py xmodmap -t 1.2.3
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Upgrading all Recipes to the Latest Versions and Suppressing Email Notifications:</emphasis>
                        To upgrade all recipes to their most recent versions
                        and suppress the email notifications, use the following
                        command:
                        <literallayout class='monospaced'>
     $ upgrade-helper.py all
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Upgrading all Recipes to the Latest Versions and Send Email Notifications:</emphasis>
                        To upgrade all recipes to their most recent versions
                        and send email messages to maintainers for each
                        attempted recipe as well as a status email, use the
                        following command:
                        <literallayout class='monospaced'>
     $ upgrade-helper.py -e all
                        </literallayout>
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Once you have run the AUH utility, you can find the results
                in the AUH build directory:
                <literallayout class='monospaced'>
     ${BUILDDIR}/upgrade-helper/<replaceable>timestamp</replaceable>
                </literallayout>
                The AUH utility also creates recipe update commits from
                successful upgrade attempts in the layer tree.
            </para>

            <para>
                You can easily set up to run the AUH utility on a regular
                basis by using a cron job.
                See the
                <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/auto-upgrade-helper/tree/weeklyjob.sh'><filename>weeklyjob.sh</filename></ulink>
                file distributed with the utility for an example.
            </para>
        </section>

        <section id='gs-using-devtool-upgrade'>
            <title>Using <filename>devtool upgrade</filename></title>

            <para>
                As mentioned earlier, an alternative method for upgrading
                recipes to newer versions is to use
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-devtool-reference'><filename>devtool upgrade</filename></ulink>.
                You can read about <filename>devtool upgrade</filename> in
                general in the
                "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-devtool-use-devtool-upgrade-to-create-a-version-of-the-recipe-that-supports-a-newer-version-of-the-software'>Use <filename>devtool upgrade</filename> to Create a Version of the Recipe that Supports a Newer Version of the Software</ulink>"
                section in the Yocto Project Application Development and the
                Extensible Software Development Kit (eSDK) Manual.
            </para>

            <para>
                To see all the command-line options available with
                <filename>devtool upgrade</filename>, use the following help
                command:
                <literallayout class='monospaced'>
     $ devtool upgrade -h
                </literallayout>
            </para>

            <para>
                If you want to find out what version a recipe is currently at
                upstream without any attempt to upgrade your local version of
                the recipe, you can use the following command:
                <literallayout class='monospaced'>
     $ devtool latest-version <replaceable>recipe_name</replaceable>
                </literallayout>
            </para>

            <para>
                As mentioned in the previous section describing AUH,
                <filename>devtool upgrade</filename> works in a
                less-automated manner than AUH.
                Specifically, <filename>devtool upgrade</filename> only
                works on a single recipe that you name on the command line,
                cannot perform build and integration testing using images,
                and does not automatically generate commits for changes in
                the source tree.
                Despite all these "limitations",
                <filename>devtool upgrade</filename> updates the recipe file
                to the new upstream version and attempts to rebase custom
                patches contained by the recipe as needed.
                <note>
                    AUH uses much of <filename>devtool upgrade</filename>
                    behind the scenes making AUH somewhat of a "wrapper"
                    application for <filename>devtool upgrade</filename>.
                </note>
            </para>

            <para>
                A typical scenario involves having used Git to clone an
                upstream repository that you use during build operations.
                Because you are (or have) built the recipe in the past, the
                layer is likely added to your configuration already.
                If for some reason, the layer is not added, you could add
                it easily using the
                <ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-bitbake-layers-script'><filename>bitbake-layers</filename></ulink>
                script.
                For example, suppose you use the <filename>nano.bb</filename>
                recipe from the <filename>meta-oe</filename> layer in the
                <filename>meta-openembedded</filename> repository.
                For this example, assume that the layer has been cloned into
                following area:
                <literallayout class='monospaced'>
     /home/scottrif/meta-openembedded
                </literallayout>
                The following command from your
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                adds the layer to your build configuration (i.e.
                <filename>${BUILDDIR}/conf/bblayers.conf</filename>):
                <literallayout class='monospaced'>
     $ bitbake-layers add-layer /home/scottrif/meta-openembedded/meta-oe
     NOTE: Starting bitbake server...
     Parsing recipes: 100% |##########################################| Time: 0:00:55
     Parsing of 1431 .bb files complete (0 cached, 1431 parsed). 2040 targets, 56 skipped, 0 masked, 0 errors.
     Removing 12 recipes from the x86_64 sysroot: 100% |##############| Time: 0:00:00
     Removing 1 recipes from the x86_64_i586 sysroot: 100% |##########| Time: 0:00:00
     Removing 5 recipes from the i586 sysroot: 100% |#################| Time: 0:00:00
     Removing 5 recipes from the qemux86 sysroot: 100% |##############| Time: 0:00:00
                </literallayout>
                For this example, assume that the <filename>nano.bb</filename>
                recipe that is upstream has a 2.9.3 version number.
                However, the version in the local repository is 2.7.4.
                The following command from your build directory automatically
                upgrades the recipe for you:
                <note>
                    Using the <filename>-V</filename> option is not necessary.
                    Omitting the version number causes
                    <filename>devtool upgrade</filename> to upgrade the recipe
                    to the most recent version.
                </note>
                <literallayout class='monospaced'>
     $ devtool upgrade nano -V 2.9.3
     NOTE: Starting bitbake server...
     NOTE: Creating workspace layer in /home/scottrif/poky/build/workspace
     Parsing recipes: 100% |##########################################| Time: 0:00:46
     Parsing of 1431 .bb files complete (0 cached, 1431 parsed). 2040 targets, 56 skipped, 0 masked, 0 errors.
     NOTE: Extracting current version source...
     NOTE: Resolving any missing task queue dependencies
            .
            .
            .
     NOTE: Executing SetScene Tasks
     NOTE: Executing RunQueue Tasks
     NOTE: Tasks Summary: Attempted 74 tasks of which 72 didn't need to be rerun and all succeeded.
     Adding changed files: 100% |#####################################| Time: 0:00:00
     NOTE: Upgraded source extracted to /home/scottrif/poky/build/workspace/sources/nano
     NOTE: New recipe is /home/scottrif/poky/build/workspace/recipes/nano/nano_2.9.3.bb
                </literallayout>
                Continuing with this example, you can use
                <filename>devtool build</filename> to build the newly upgraded
                recipe:
                <literallayout class='monospaced'>
     $ devtool build nano
     NOTE: Starting bitbake server...
     Loading cache: 100% |################################################################################################| Time: 0:00:01
     Loaded 2040 entries from dependency cache.
     Parsing recipes: 100% |##############################################################################################| Time: 0:00:00
     Parsing of 1432 .bb files complete (1431 cached, 1 parsed). 2041 targets, 56 skipped, 0 masked, 0 errors.
     NOTE: Resolving any missing task queue dependencies
            .
            .
            .
     NOTE: Executing SetScene Tasks
     NOTE: Executing RunQueue Tasks
     NOTE: nano: compiling from external source tree /home/scottrif/poky/build/workspace/sources/nano
     NOTE: Tasks Summary: Attempted 520 tasks of which 304 didn't need to be rerun and all succeeded.
                </literallayout>
                Within the <filename>devtool upgrade</filename> workflow,
                opportunity exists to deploy and test your rebuilt software.
                For this example, however, running
                <filename>devtool finish</filename> cleans up the workspace
                once the source in your workspace is clean.
                This usually means using Git to stage and submit commits
                for the changes generated by the upgrade process.
            </para>

            <para>
                Once the tree is clean, you can clean things up in this
                example with the following command from the
                <filename>${BUILDDIR}/workspace/sources/nano</filename>
                directory:
                <literallayout class='monospaced'>
     $ devtool finish nano meta-oe
     NOTE: Starting bitbake server...
     Loading cache: 100% |################################################################################################| Time: 0:00:00
     Loaded 2040 entries from dependency cache.
     Parsing recipes: 100% |##############################################################################################| Time: 0:00:01
     Parsing of 1432 .bb files complete (1431 cached, 1 parsed). 2041 targets, 56 skipped, 0 masked, 0 errors.
     NOTE: Adding new patch 0001-nano.bb-Stuff-I-changed-when-upgrading-nano.bb.patch
     NOTE: Updating recipe nano_2.9.3.bb
     NOTE: Removing file /home/scottrif/meta-openembedded/meta-oe/recipes-support/nano/nano_2.7.4.bb
     NOTE: Moving recipe file to /home/scottrif/meta-openembedded/meta-oe/recipes-support/nano
     NOTE: Leaving source tree /home/scottrif/poky/build/workspace/sources/nano as-is; if you no longer need it then please delete it manually
                </literallayout>
                Using the <filename>devtool finish</filename> command cleans
                up the workspace and creates a patch file based on your
                commits.
                The tool puts all patch files back into the source directory
                in a sub-directory named <filename>nano</filename> in this
                case.
            </para>
        </section>

        <section id='dev-manually-upgrading-a-recipe'>
            <title>Manually Upgrading a Recipe</title>

            <para>
                If for some reason you choose not to upgrade recipes using the
                <link linkend='gs-using-the-auto-upgrade-helper'>Auto Upgrade Helper (AUH)</link>
                or by using
                <link linkend='gs-using-devtool-upgrade'><filename>devtool upgrade</filename></link>,
                you can manually edit the recipe files to upgrade the versions.
                <note><title>Caution</title>
                    Manually updating multiple recipes scales poorly and
                    involves many steps.
                    The recommendation to upgrade recipe versions is through
                    AUH or <filename>devtool upgrade</filename>, both of which
                    automate some steps and provide guidance for others needed
                    for the manual process.
                </note>
            </para>

            <para>
                To manually upgrade recipe versions, follow these general steps:
                <orderedlist>
                    <listitem><para>
                        <emphasis>Change the Version:</emphasis>
                        Rename the recipe such that the version (i.e. the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                        part of the recipe name) changes appropriately.
                        If the version is not part of the recipe name, change
                        the value as it is set for <filename>PV</filename>
                        within the recipe itself.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Update <filename>SRCREV</filename> if Needed:</emphasis>
                        If the source code your recipe builds is fetched from
                        Git or some other version control system, update
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
                        to point to the commit hash that matches the new
                        version.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Build the Software:</emphasis>
                        Try to build the recipe using BitBake.
                        Typical build failures include the following:
                        <itemizedlist>
                            <listitem><para>
                                License statements were updated for the new
                                version.
                                For this case, you need to review any changes
                                to the license and update the values of
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                                and
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
                                as needed.
                                <note>
                                    License changes are often inconsequential.
                                    For example, the license text's copyright
                                    year might have changed.
                                </note>
                                </para></listitem>
                            <listitem><para>
                                Custom patches carried by the older version of
                                the recipe might fail to apply to the new
                                version.
                                For these cases, you need to review the
                                failures.
                                Patches might not be necessary for the new
                                version of the software if the upgraded version
                                has fixed those issues.
                                If a patch is necessary and failing, you need
                                to rebase it into the new version.
                                </para></listitem>
                        </itemizedlist>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Optionally Attempt to Build for Several Architectures:</emphasis>
                        Once you successfully build the new software for a
                        given architecture, you could test the build for
                        other architectures by changing the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        variable and rebuilding the software.
                        This optional step is especially important if the
                        recipe is to be released publicly.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Check the Upstream Change Log or Release Notes:</emphasis>
                        Checking both these reveals if new features exist that
                        could break backwards-compatibility.
                        If so, you need to take steps to mitigate or eliminate
                        that situation.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Optionally Create a Bootable Image and Test:</emphasis>
                        If you want, you can test the new software by booting
                        it onto actual hardware.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Create a Commit with the Change in the Layer Repository:</emphasis>
                        After all builds work and any testing is successful,
                        you can create commits for any changes in the layer
                        holding your upgraded recipe.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>

    <section id='finding-the-temporary-source-code'>
        <title>Finding Temporary Source Code</title>

        <para>
            You might find it helpful during development to modify the
            temporary source code used by recipes to build packages.
            For example, suppose you are developing a patch and you need to
            experiment a bit to figure out your solution.
            After you have initially built the package, you can iteratively
            tweak the source code, which is located in the
            <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>,
            and then you can force a re-compile and quickly test your altered
            code.
            Once you settle on a solution, you can then preserve your changes
            in the form of patches.
        </para>

        <para>
            During a build, the unpacked temporary source code used by recipes
            to build packages is available in the Build Directory as
            defined by the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
            variable.
            Below is the default value for the <filename>S</filename> variable
            as defined in the
            <filename>meta/conf/bitbake.conf</filename> configuration file
            in the
            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>:
            <literallayout class='monospaced'>
     S = "${WORKDIR}/${BP}"
            </literallayout>
            You should be aware that many recipes override the
            <filename>S</filename> variable.
            For example, recipes that fetch their source from Git usually set
            <filename>S</filename> to <filename>${WORKDIR}/git</filename>.
            <note>
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink>
                represents the base recipe name, which consists of the name
                and version:
                <literallayout class='monospaced'>
     BP = "${BPN}-${PV}"
                </literallayout>
            </note>
        </para>

        <para>
            The path to the work directory for the recipe
            (<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>)
            is defined as follows:
            <literallayout class='monospaced'>
     ${TMPDIR}/work/${MULTIMACH_TARGET_SYS}/${PN}/${EXTENDPE}${PV}-${PR}
            </literallayout>
            The actual directory depends on several things:
            <itemizedlist>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>:
                    The top-level build output directory.
                    </para></listitem>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MULTIMACH_TARGET_SYS'><filename>MULTIMACH_TARGET_SYS</filename></ulink>:
                    The target system identifier.
                    </para></listitem>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>:
                    The recipe name.
                    </para></listitem>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTENDPE'><filename>EXTENDPE</filename></ulink>:
                    The epoch - (if
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>
                    is not specified, which is usually the case for most
                    recipes, then <filename>EXTENDPE</filename> is blank).
                    </para></listitem>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>:
                    The recipe version.
                    </para></listitem>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>:
                    The recipe revision.
                    </para></listitem>
            </itemizedlist>
        </para>

        <para>
            As an example, assume a Source Directory top-level folder
            named <filename>poky</filename>, a default Build Directory at
            <filename>poky/build</filename>, and a
            <filename>qemux86-poky-linux</filename> machine target
            system.
            Furthermore, suppose your recipe is named
            <filename>foo_1.3.0.bb</filename>.
            In this case, the work directory the build system uses to
            build the package would be as follows:
            <literallayout class='monospaced'>
     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
            </literallayout>
        </para>
    </section>

    <section id="using-a-quilt-workflow">
        <title>Using Quilt in Your Workflow</title>

        <para>
            <ulink url='http://savannah.nongnu.org/projects/quilt'>Quilt</ulink>
            is a powerful tool that allows you to capture source code changes
            without having a clean source tree.
            This section outlines the typical workflow you can use to modify
            source code, test changes, and then preserve the changes in the
            form of a patch all using Quilt.
            <note><title>Tip</title>
                With regard to preserving changes to source files, if you
                clean a recipe or have <filename>rm_work</filename> enabled,
                the
                <ulink url='&YOCTO_DOCS_SDK_URL;#using-devtool-in-your-sdk-workflow'><filename>devtool</filename> workflow</ulink>
                as described in the Yocto Project Application Development
                and the Extensible Software Development Kit (eSDK) manual
                is a safer development flow than the flow that uses Quilt.
            </note>
        </para>

        <para>
            Follow these general steps:
            <orderedlist>
                <listitem><para>
                    <emphasis>Find the Source Code:</emphasis>
                    Temporary source code used by the OpenEmbedded build system
                    is kept in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                    See the
                    "<link linkend='finding-the-temporary-source-code'>Finding Temporary Source Code</link>"
                    section to learn how to locate the directory that has the
                    temporary source code for a particular package.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Change Your Working Directory:</emphasis>
                    You need to be in the directory that has the temporary
                    source code.
                    That directory is defined by the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
                    variable.</para></listitem>
                <listitem><para>
                    <emphasis>Create a New Patch:</emphasis>
                    Before modifying source code, you need to create a new
                    patch.
                    To create a new patch file, use
                    <filename>quilt new</filename> as below:
                    <literallayout class='monospaced'>
     $ quilt new my_changes.patch
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Notify Quilt and Add Files:</emphasis>
                    After creating the patch, you need to notify Quilt about
                    the files you plan to edit.
                    You notify Quilt by adding the files to the patch you
                    just created:
                    <literallayout class='monospaced'>
     $ quilt add file1.c file2.c file3.c
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Edit the Files:</emphasis>
                    Make your changes in the source code to the files you added
                    to the patch.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Test Your Changes:</emphasis>
                    Once you have modified the source code, the easiest way to
                    test your changes is by calling the
                    <filename>do_compile</filename> task as shown in the
                    following example:
                    <literallayout class='monospaced'>
     $ bitbake -c compile -f <replaceable>package</replaceable>
                    </literallayout>
                    The <filename>-f</filename> or <filename>--force</filename>
                    option forces the specified task to execute.
                    If you find problems with your code, you can just keep
                    editing and re-testing iteratively until things work
                    as expected.
                    <note>
                        All the modifications you make to the temporary
                        source code disappear once you run the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-clean'><filename>do_clean</filename></ulink>
                        or
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleanall'><filename>do_cleanall</filename></ulink>
                        tasks using BitBake (i.e.
                        <filename>bitbake -c clean <replaceable>package</replaceable></filename>
                        and
                        <filename>bitbake -c cleanall <replaceable>package</replaceable></filename>).
                        Modifications will also disappear if you use the
                        <filename>rm_work</filename> feature as described
                        in the
                        "<ulink url='&YOCTO_DOCS_DEV_URL;#dev-saving-memory-during-a-build'>Conserving Disk Space During Builds</ulink>"
                        section.
                    </note>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Generate the Patch:</emphasis>
                    Once your changes work as expected, you need to use Quilt
                    to generate the final patch that contains all your
                    modifications.
                    <literallayout class='monospaced'>
     $ quilt refresh
                    </literallayout>
                    At this point, the <filename>my_changes.patch</filename>
                    file has all your edits made to the
                    <filename>file1.c</filename>, <filename>file2.c</filename>,
                    and <filename>file3.c</filename> files.</para>

                    <para>You can find the resulting patch file in the
                    <filename>patches/</filename> subdirectory of the source
                    (<filename>S</filename>) directory.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Copy the Patch File:</emphasis>
                    For simplicity, copy the patch file into a directory
                    named <filename>files</filename>, which you can create
                    in the same directory that holds the recipe
                    (<filename>.bb</filename>) file or the append
                    (<filename>.bbappend</filename>) file.
                    Placing the patch here guarantees that the OpenEmbedded
                    build system will find the patch.
                    Next, add the patch into the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
                    of the recipe.
                    Here is an example:
                    <literallayout class='monospaced'>
     SRC_URI += "file://my_changes.patch"
                    </literallayout>
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id="platdev-appdev-devshell">
        <title>Using a Development Shell</title>

        <para>
            When debugging certain commands or even when just editing packages,
            <filename>devshell</filename> can be a useful tool.
            When you invoke <filename>devshell</filename>, all tasks up to and
            including
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
            are run for the specified target.
            Then, a new terminal is opened and you are placed in
            <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>,
            the source directory.
            In the new terminal, all the OpenEmbedded build-related environment variables are
            still defined so you can use commands such as <filename>configure</filename> and
            <filename>make</filename>.
            The commands execute just as if the OpenEmbedded build system were executing them.
            Consequently, working this way can be helpful when debugging a build or preparing
            software to be used with the OpenEmbedded build system.
        </para>

        <para>
            Following is an example that uses <filename>devshell</filename> on a target named
            <filename>matchbox-desktop</filename>:
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devshell
            </literallayout>
        </para>

        <para>
            This command spawns a terminal with a shell prompt within the OpenEmbedded build environment.
            The <ulink url='&YOCTO_DOCS_REF_URL;#var-OE_TERMINAL'><filename>OE_TERMINAL</filename></ulink>
            variable controls what type of shell is opened.
        </para>

        <para>
            For spawned terminals, the following occurs:
            <itemizedlist>
                <listitem><para>The <filename>PATH</filename> variable includes the
                    cross-toolchain.</para></listitem>
                <listitem><para>The <filename>pkgconfig</filename> variables find the correct
                    <filename>.pc</filename> files.</para></listitem>
                <listitem><para>The <filename>configure</filename> command finds the
                    Yocto Project site files as well as any other necessary files.</para></listitem>
            </itemizedlist>
        </para>

        <para>
            Within this environment, you can run configure or compile
            commands as if they were being run by
            the OpenEmbedded build system itself.
            As noted earlier, the working directory also automatically changes to the
            Source Directory (<ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>).
        </para>

        <para>
            To manually run a specific task using <filename>devshell</filename>,
            run the corresponding <filename>run.*</filename> script in
            the
            <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/temp</filename>
            directory (e.g.,
            <filename>run.do_configure.</filename><replaceable>pid</replaceable>).
            If a task's script does not exist, which would be the case if the task was
            skipped by way of the sstate cache, you can create the task by first running
            it outside of the <filename>devshell</filename>:
            <literallayout class='monospaced'>
     $ bitbake -c <replaceable>task</replaceable>
            </literallayout>
            <note><title>Notes</title>
                <itemizedlist>
                    <listitem><para>Execution of a task's <filename>run.*</filename>
                        script and BitBake's execution of a task are identical.
                        In other words, running the script re-runs the task
                        just as it would be run using the
                        <filename>bitbake -c</filename> command.
                        </para></listitem>
                    <listitem><para>Any <filename>run.*</filename> file that does not
                        have a <filename>.pid</filename> extension is a
                        symbolic link (symlink) to the most recent version of that
                        file.
                        </para></listitem>
                </itemizedlist>
            </note>
        </para>

        <para>
            Remember, that the <filename>devshell</filename> is a mechanism that allows
            you to get into the BitBake task execution environment.
            And as such, all commands must be called just as BitBake would call them.
            That means you need to provide the appropriate options for
            cross-compilation and so forth as applicable.
        </para>

        <para>
            When you are finished using <filename>devshell</filename>, exit the shell
            or close the terminal window.
        </para>

        <note><title>Notes</title>
            <itemizedlist>
                <listitem><para>
                    It is worth remembering that when using <filename>devshell</filename>
                    you need to use the full compiler name such as <filename>arm-poky-linux-gnueabi-gcc</filename>
                    instead of just using <filename>gcc</filename>.
                    The same applies to other applications such as <filename>binutils</filename>,
                    <filename>libtool</filename> and so forth.
                    BitBake sets up environment variables such as <filename>CC</filename>
                    to assist applications, such as <filename>make</filename> to find the correct tools.
                    </para></listitem>
                <listitem><para>
                    It is also worth noting that <filename>devshell</filename> still works over
                    X11 forwarding and similar situations.
                    </para></listitem>
            </itemizedlist>
        </note>
    </section>

    <section id="platdev-appdev-devpyshell">
        <title>Using a Development Python Shell</title>

        <para>
            Similar to working within a development shell as described in
            the previous section, you can also spawn and work within an
            interactive Python development shell.
            When debugging certain commands or even when just editing packages,
            <filename>devpyshell</filename> can be a useful tool.
            When you invoke <filename>devpyshell</filename>, all tasks up to and
            including
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
            are run for the specified target.
            Then a new terminal is opened.
            Additionally, key Python objects and code are available in the same
            way they are to BitBake tasks, in particular, the data store 'd'.
            So, commands such as the following are useful when exploring the data
            store and running functions:
            <literallayout class='monospaced'>
     pydevshell> d.getVar("STAGING_DIR")
     '/media/build1/poky/build/tmp/sysroots'
     pydevshell> d.getVar("STAGING_DIR")
     '${TMPDIR}/sysroots'
     pydevshell> d.setVar("FOO", "bar")
     pydevshell> d.getVar("FOO")
     'bar'
     pydevshell> d.delVar("FOO")
     pydevshell> d.getVar("FOO")
     pydevshell> bb.build.exec_func("do_unpack", d)
     pydevshell>
            </literallayout>
            The commands execute just as if the OpenEmbedded build system were executing them.
            Consequently, working this way can be helpful when debugging a build or preparing
            software to be used with the OpenEmbedded build system.
        </para>

        <para>
            Following is an example that uses <filename>devpyshell</filename> on a target named
            <filename>matchbox-desktop</filename>:
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devpyshell
            </literallayout>
        </para>

        <para>
            This command spawns a terminal and places you in an interactive
            Python interpreter within the OpenEmbedded build environment.
            The <ulink url='&YOCTO_DOCS_REF_URL;#var-OE_TERMINAL'><filename>OE_TERMINAL</filename></ulink>
            variable controls what type of shell is opened.
        </para>

        <para>
            When you are finished using <filename>devpyshell</filename>, you
            can exit the shell either by using Ctrl+d or closing the terminal
            window.
        </para>
    </section>

    <section id='dev-building'>
        <title>Building</title>

        <para>
            This section describes various build procedures.
            For example, the steps needed for a simple build, a target that
            uses multiple configurations, building an image for more than
            one machine, and so forth.
        </para>

        <section id='dev-building-a-simple-image'>
            <title>Building a Simple Image</title>

            <para>
                In the development environment, you need to build an image
                whenever you change hardware support, add or change system
                libraries, or add or change services that have dependencies.
                Several methods exist that allow you to build an image within
                the Yocto Project.
                This section presents the basic steps you need to build a
                simple image using BitBake from a build host running Linux.
                <note><title>Notes</title>
                    <itemizedlist>
                        <listitem><para>
                            For information on how to build an image using
                            <ulink url='&YOCTO_DOCS_REF_URL;#toaster-term'>Toaster</ulink>,
                            see the
                            <ulink url='&YOCTO_DOCS_TOAST_URL;'>Toaster User Manual</ulink>.
                            </para></listitem>
                        <listitem><para>
                            For information on how to use
                            <filename>devtool</filename> to build images, see
                            the
                            "<ulink url='&YOCTO_DOCS_SDK_URL;#using-devtool-in-your-sdk-workflow'>Using <filename>devtool</filename> in Your SDK Workflow</ulink>"
                            section in the Yocto Project Application
                            Development and the Extensible Software Development
                            Kit (eSDK) manual.
                            </para></listitem>
                        <listitem><para>
                            For a quick example on how to build an image using
                            the OpenEmbedded build system, see the
                            <ulink url='&YOCTO_DOCS_BRIEF_URL;'>Yocto Project Quick Build</ulink>
                            document.
                            </para></listitem>
                    </itemizedlist>
                </note>
            </para>

            <para>
                The build process creates an entire Linux distribution from
                source and places it in your
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                under <filename>tmp/deploy/images</filename>.
                For detailed information on the build process using BitBake,
                see the
                "<ulink url='&YOCTO_DOCS_OM_URL;#images-dev-environment'>Images</ulink>"
                section in the Yocto Project Overview and Concepts Manual.
            </para>

            <para>
                The following figure and list overviews the build process:
                <imagedata fileref="figures/bitbake-build-flow.png" width="7in" depth="4in" align="center" scalefit="1" />
                <orderedlist>
                    <listitem><para>
                        <emphasis>Set up Your Host Development System to Support
                        Development Using the Yocto Project</emphasis>:
                        See the
                        "<link linkend='dev-manual-start'>Setting Up to Use the Yocto Project</link>"
                        section for options on how to get a build host ready to
                        use the Yocto Project.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Initialize the Build Environment:</emphasis>
                        Initialize the build environment by sourcing the build
                        environment script (i.e.
                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>):
                        <literallayout class='monospaced'>
     $ source &OE_INIT_FILE; [<replaceable>build_dir</replaceable>]
                        </literallayout></para>

                        <para>When you use the initialization script, the
                        OpenEmbedded build system uses
                        <filename>build</filename> as the default Build
                        Directory in your current work directory.
                        You can use a <replaceable>build_dir</replaceable>
                        argument with the script to specify a different build
                        directory.
                        <note><title>Tip</title>
                            A common practice is to use a different Build
                            Directory for different targets.
                            For example, <filename>~/build/x86</filename> for a
                            <filename>qemux86</filename> target, and
                            <filename>~/build/arm</filename> for a
                            <filename>qemuarm</filename> target.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Make Sure Your <filename>local.conf</filename>
                        File is Correct:</emphasis>
                        Ensure the <filename>conf/local.conf</filename>
                        configuration file, which is found in the Build
                        Directory, is set up how you want it.
                        This file defines many aspects of the build environment
                        including the target machine architecture through the
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'>MACHINE</ulink></filename> variable,
                        the packaging format used during the build
                        (<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>),
                        and a centralized tarball download directory through the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink> variable.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Build the Image:</emphasis>
                        Build the image using the <filename>bitbake</filename>
                        command:
                        <literallayout class='monospaced'>
     $ bitbake <replaceable>target</replaceable>
                        </literallayout>
                        <note>
                            For information on BitBake, see the
                            <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
                        </note>
                        The <replaceable>target</replaceable> is the name of the
                        recipe you want to build.
                        Common targets are the images in
                        <filename>meta/recipes-core/images</filename>,
                        <filename>meta/recipes-sato/images</filename>, and so
                        forth all found in the
                        <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
                        Or, the target can be the name of a recipe for a
                        specific piece of software such as BusyBox.
                        For more details about the images the OpenEmbedded build
                        system supports, see the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
                        chapter in the Yocto Project Reference Manual.</para>

                        <para>As an example, the following command builds the
                        <filename>core-image-minimal</filename> image:
                        <literallayout class='monospaced'>
     $ bitbake core-image-minimal
                        </literallayout>
                        Once an image has been built, it often needs to be
                        installed.
                        The images and kernels built by the OpenEmbedded
                        build system are placed in the Build Directory in
                        <filename class="directory">tmp/deploy/images</filename>.
                        For information on how to run pre-built images such as
                        <filename>qemux86</filename> and <filename>qemuarm</filename>,
                        see the
                        <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink>
                        manual.
                        For information about how to install these images,
                        see the documentation for your particular board or
                        machine.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='dev-building-images-for-multiple-targets-using-multiple-configurations'>
            <title>Building Images for Multiple Targets Using Multiple Configurations</title>

            <para>
                You can use a single <filename>bitbake</filename> command
                to build multiple images or packages for different targets
                where each image or package requires a different configuration
                (multiple configuration builds).
                The builds, in this scenario, are sometimes referred to as
                "multiconfigs", and this section uses that term throughout.
            </para>

            <para>
                This section describes how to set up for multiple
                configuration builds and how to account for cross-build
                dependencies between the multiconfigs.
            </para>

            <section id='dev-setting-up-and-running-a-multiple-configuration-build'>
                <title>Setting Up and Running a Multiple Configuration Build</title>

                <para>
                    To accomplish a multiple configuration build, you must
                    define each target's configuration separately using
                    a parallel configuration file in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>,
                    and you must follow a required file hierarchy.
                    Additionally, you must enable the multiple configuration
                    builds in your <filename>local.conf</filename> file.
                </para>

                <para>
                    Follow these steps to set up and execute multiple
                    configuration builds:
                    <itemizedlist>
                        <listitem><para>
                            <emphasis>Create Separate Configuration Files</emphasis>:
                            You need to create a single configuration file for
                            each build target (each multiconfig).
                            Minimally, each configuration file must define the
                            machine and the temporary directory BitBake uses
                            for the build.
                            Suggested practice dictates that you do not
                            overlap the temporary directories
                            used during the builds.
                            However, it is possible that you can share the
                            temporary directory
                            (<ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>).
                            For example, consider a scenario with two
                            different multiconfigs for the same
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>: "qemux86" built for
                            two distributions such as "poky" and "poky-lsb".
                            In this case, you might want to use the same
                            <filename>TMPDIR</filename>.</para>

                            <para>Here is an example showing the minimal
                            statements needed in a configuration file for
                            a "qemux86" target whose temporary build directory
                            is <filename>tmpmultix86</filename>:
                            <literallayout class='monospaced'>
     MACHINE="qemux86"
     TMPDIR="${TOPDIR}/tmpmultix86"
                            </literallayout></para>

                            <para>The location for these multiconfig
                            configuration files is specific.
                            They must reside in the current build directory in
                            a sub-directory of <filename>conf</filename> named
                            <filename>multiconfig</filename>.
                            Following is an example that defines two
                            configuration files for the "x86" and "arm"
                            multiconfigs:
                            <imagedata fileref="figures/multiconfig_files.png" align="center" width="4in" depth="3in" />
                            </para>

                            <para>The reason for this required file hierarchy
                            is because the <filename>BBPATH</filename> variable
                            is not constructed until the layers are parsed.
                            Consequently, using the configuration file as a
                            pre-configuration file is not possible unless it is
                            located in the current working directory.
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Add the BitBake Multi-configuration Variable to the Local Configuration File</emphasis>:
                            Use the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-BBMULTICONFIG'><filename>BBMULTICONFIG</filename></ulink>
                            variable in your
                            <filename>conf/local.conf</filename> configuration
                            file to specify each multiconfig.
                            Continuing with the example from the previous
                            figure, the <filename>BBMULTICONFIG</filename>
                            variable needs to enable two multiconfigs: "x86"
                            and "arm" by specifying each configuration file:
                            <literallayout class='monospaced'>
     BBMULTICONFIG = "x86 arm"
                            </literallayout>
                            <note>
                                A "default" configuration already exists by
                                definition.
                                This configuration is named: "" (i.e. empty
                                string) and is defined by the variables coming
                                from your <filename>local.conf</filename> file.
                                Consequently, the previous example actually
                                adds two additional configurations to your
                                build: "arm" and "x86" along with "".
                            </note>
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Launch BitBake</emphasis>:
                            Use the following BitBake command form to launch the
                            multiple configuration build:
                            <literallayout class='monospaced'>
     $ bitbake [mc:<replaceable>multiconfigname</replaceable>:]<replaceable>target</replaceable> [[[mc:<replaceable>multiconfigname</replaceable>:]<replaceable>target</replaceable>] ... ]
                            </literallayout>
                            For the example in this section, the following
                            command applies:
                            <literallayout class='monospaced'>
     $ bitbake mc:x86:core-image-minimal mc:arm:core-image-sato mc::core-image-base
                            </literallayout>
                            The previous BitBake command builds a
                            <filename>core-image-minimal</filename> image that
                            is configured through the
                            <filename>x86.conf</filename> configuration file,
                            a <filename>core-image-sato</filename>
                            image that is configured through the
                            <filename>arm.conf</filename> configuration file
                            and a <filename>core-image-base</filename> that is
                            configured through your
                            <filename>local.conf</filename> configuration file.
                            </para></listitem>
                    </itemizedlist>
                    <note>
                        Support for multiple configuration builds in the
                        Yocto Project &DISTRO; (&DISTRO_NAME;) Release does
                        not include Shared State (sstate) optimizations.
                        Consequently, if a build uses the same object twice
                        in, for example, two different
                        <filename>TMPDIR</filename> directories, the build
                        either loads from an existing sstate cache for that
                        build at the start or builds the object fresh.
                    </note>
                </para>
            </section>

            <section id='dev-enabling-multiple-configuration-build-dependencies'>
                <title>Enabling Multiple Configuration Build Dependencies</title>

                <para>
                    Sometimes dependencies can exist between targets
                    (multiconfigs) in a multiple configuration build.
                    For example, suppose that in order to build a
                    <filename>core-image-sato</filename> image for an "x86"
                    multiconfig, the root filesystem of an "arm"
                    multiconfig must exist.
                    This dependency is essentially that the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-image'><filename>do_image</filename></ulink>
                    task in the <filename>core-image-sato</filename> recipe
                    depends on the completion of the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-rootfs'><filename>do_rootfs</filename></ulink>
                    task of the <filename>core-image-minimal</filename>
                    recipe.
                </para>

                <para>
                    To enable dependencies in a multiple configuration
                    build, you must declare the dependencies in the recipe
                    using the following statement form:
                    <literallayout class='monospaced'>
     <replaceable>task_or_package</replaceable>[mcdepends] = "mc:<replaceable>from_multiconfig</replaceable>:<replaceable>to_multiconfig</replaceable>:<replaceable>recipe_name</replaceable>:<replaceable>task_on_which_to_depend</replaceable>"
                    </literallayout>
                    To better show how to use this statement, consider the
                    example scenario from the first paragraph of this section.
                    The following statement needs to be added to the recipe
                    that builds the <filename>core-image-sato</filename>
                    image:
                    <literallayout class='monospaced'>
     do_image[mcdepends] = "mc:x86:arm:core-image-minimal:do_rootfs"
                    </literallayout>
                    In this example, the
                    <replaceable>from_multiconfig</replaceable> is "x86".
                    The <replaceable>to_multiconfig</replaceable> is "arm".
                    The task on which the <filename>do_image</filename> task
                    in the recipe depends is the <filename>do_rootfs</filename>
                    task from the <filename>core-image-minimal</filename>
                    recipe associated with the "arm" multiconfig.
               </para>

               <para>
                   Once you set up this dependency, you can build the
                   "x86" multiconfig using a BitBake command as follows:
                   <literallayout class='monospaced'>
     $ bitbake mc:x86:core-image-sato
                   </literallayout>
                   This command executes all the tasks needed to create
                   the <filename>core-image-sato</filename> image for the
                   "x86" multiconfig.
                   Because of the dependency, BitBake also executes through
                   the <filename>do_rootfs</filename> task for the "arm"
                   multiconfig build.
               </para>

               <para>
                   Having a recipe depend on the root filesystem of another
                   build might not seem that useful.
                   Consider this change to the statement in the
                   <filename>core-image-sato</filename> recipe:
                   <literallayout class='monospaced'>
     do_image[mcdepends] = "mc:x86:arm:core-image-minimal:do_image"
                   </literallayout>
                   In this case, BitBake must create the
                   <filename>core-image-minimal</filename> image for the
                   "arm" build since the "x86" build depends on it.
               </para>

               <para>
                   Because "x86" and "arm" are enabled for multiple
                   configuration builds and have separate configuration
                   files, BitBake places the artifacts for each build in the
                   respective temporary build directories (i.e.
                   <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>).
               </para>
            </section>
        </section>

        <section id='building-an-initramfs-image'>
            <title>Building an Initial RAM Filesystem (initramfs) Image</title>

            <para>
                An initial RAM filesystem (initramfs) image provides a temporary
                root filesystem used for early system initialization (e.g.
                loading of modules needed to locate and mount the "real" root
                filesystem).
                <note>
                    The initramfs image is the successor of initial RAM disk
                    (initrd).
                    It is a "copy in and out" (cpio) archive of the initial
                    filesystem that gets loaded into memory during the Linux
                    startup process.
                    Because Linux uses the contents of the archive during
                    initialization, the initramfs image needs to contain all of the
                    device drivers and tools needed to mount the final root
                    filesystem.
                </note>
            </para>

            <para>
                Follow these steps to create an initramfs image:
                <orderedlist>
                    <listitem><para>
                        <emphasis>Create the initramfs Image Recipe:</emphasis>
                        You can reference the
                        <filename>core-image-minimal-initramfs.bb</filename>
                        recipe found in the <filename>meta/recipes-core</filename>
                        directory of the
                        <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                        as an example from which to work.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Decide if You Need to Bundle the initramfs Image
                        Into the Kernel Image:</emphasis>
                        If you want the initramfs image that is built to be
                        bundled in with the kernel image, set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE_BUNDLE'><filename>INITRAMFS_IMAGE_BUNDLE</filename></ulink>
                        variable to "1" in your <filename>local.conf</filename>
                        configuration file and set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE'><filename>INITRAMFS_IMAGE</filename></ulink>
                        variable in the recipe that builds the kernel image.
                        <note><title>Tip</title>
                            It is recommended that you do bundle the initramfs
                            image with the kernel image to avoid circular
                            dependencies between the kernel recipe and the
                            initramfs recipe should the initramfs image
                            include kernel modules.
                        </note>
                        Setting the <filename>INITRAMFS_IMAGE_BUNDLE</filename>
                        flag causes the initramfs image to be unpacked
                        into the <filename>${B}/usr/</filename> directory.
                        The unpacked initramfs image is then passed to the kernel's
                        <filename>Makefile</filename> using the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-CONFIG_INITRAMFS_SOURCE'><filename>CONFIG_INITRAMFS_SOURCE</filename></ulink>
                        variable, allowing the initramfs image to be built into
                        the kernel normally.
                        <note>
                            If you choose to not bundle the initramfs image with
                            the kernel image, you are essentially using an
                            <ulink url='https://en.wikipedia.org/wiki/Initrd'>Initial RAM Disk (initrd)</ulink>.
                            Creating an initrd is handled primarily through the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-INITRD_IMAGE'><filename>INITRD_IMAGE</filename></ulink>,
                            <filename>INITRD_LIVE</filename>, and
                            <filename>INITRD_IMAGE_LIVE</filename> variables.
                            For more information, see the
                            <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta/classes/image-live.bbclass'><filename>image-live.bbclass</filename></ulink>
                            file.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Optionally Add Items to the initramfs Image
                        Through the initramfs Image Recipe:</emphasis>
                        If you add items to the initramfs image by way of its
                        recipe, you should use
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_INSTALL'><filename>PACKAGE_INSTALL</filename></ulink>
                        rather than
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>.
                        <filename>PACKAGE_INSTALL</filename> gives more direct
                        control of what is added to the image as compared to
                        the defaults you might not necessarily want that are
                        set by the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-image'><filename>image</filename></ulink>
                        or
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-core-image'><filename>core-image</filename></ulink>
                        classes.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Build the Kernel Image and the initramfs
                        Image:</emphasis>
                        Build your kernel image using BitBake.
                        Because the initramfs image recipe is a dependency of the
                        kernel image, the initramfs image is built as well and
                        bundled with the kernel image if you used the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE_BUNDLE'><filename>INITRAMFS_IMAGE_BUNDLE</filename></ulink>
                        variable described earlier.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='building-a-tiny-system'>
            <title>Building a Tiny System</title>

            <para>
                Very small distributions have some significant advantages such
                as requiring less on-die or in-package memory (cheaper), better
                performance through efficient cache usage, lower power requirements
                due to less memory, faster boot times, and reduced development
                overhead.
                Some real-world examples where a very small distribution gives
                you distinct advantages are digital cameras, medical devices,
                and small headless systems.
            </para>

            <para>
                This section presents information that shows you how you can
                trim your distribution to even smaller sizes than the
                <filename>poky-tiny</filename> distribution, which is around
                5 Mbytes, that can be built out-of-the-box using the Yocto Project.
            </para>

            <section id='tiny-system-overview'>
                <title>Overview</title>

                <para>
                    The following list presents the overall steps you need to
                    consider and perform to create distributions with smaller
                    root filesystems, achieve faster boot times, maintain your critical
                    functionality, and avoid initial RAM disks:
                    <itemizedlist>
                        <listitem><para>
                            <link linkend='goals-and-guiding-principles'>Determine your goals and guiding principles.</link>
                            </para></listitem>
                        <listitem><para>
                            <link linkend='understand-what-gives-your-image-size'>Understand what contributes to your image size.</link>
                            </para></listitem>
                        <listitem><para>
                            <link linkend='trim-the-root-filesystem'>Reduce the size of the root filesystem.</link>
                            </para></listitem>
                        <listitem><para>
                            <link linkend='trim-the-kernel'>Reduce the size of the kernel.</link>
                            </para></listitem>
                        <listitem><para>
                            <link linkend='remove-package-management-requirements'>Eliminate packaging requirements.</link>
                            </para></listitem>
                        <listitem><para>
                            <link linkend='look-for-other-ways-to-minimize-size'>Look for other ways to minimize size.</link>
                            </para></listitem>
                        <listitem><para>
                            <link linkend='iterate-on-the-process'>Iterate on the process.</link>
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='goals-and-guiding-principles'>
                <title>Goals and Guiding Principles</title>

                <para>
                    Before you can reach your destination, you need to know
                    where you are going.
                    Here is an example list that you can use as a guide when
                    creating very small distributions:
                    <itemizedlist>
                        <listitem><para>Determine how much space you need
                            (e.g. a kernel that is 1 Mbyte or less and
                            a root filesystem that is 3 Mbytes or less).
                            </para></listitem>
                        <listitem><para>Find the areas that are currently
                            taking 90% of the space and concentrate on reducing
                            those areas.
                            </para></listitem>
                        <listitem><para>Do not create any difficult "hacks"
                            to achieve your goals.</para></listitem>
                        <listitem><para>Leverage the device-specific
                            options.</para></listitem>
                        <listitem><para>Work in a separate layer so that you
                            keep changes isolated.
                            For information on how to create layers, see
                            the "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>" section.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='understand-what-gives-your-image-size'>
                <title>Understand What Contributes to Your Image Size</title>

                <para>
                    It is easiest to have something to start with when creating
                    your own distribution.
                    You can use the Yocto Project out-of-the-box to create the
                    <filename>poky-tiny</filename> distribution.
                    Ultimately, you will want to make changes in your own
                    distribution that are likely modeled after
                    <filename>poky-tiny</filename>.
                    <note>
                        To use <filename>poky-tiny</filename> in your build,
                        set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                        variable in your
                        <filename>local.conf</filename> file to "poky-tiny"
                        as described in the
                        "<link linkend='creating-your-own-distribution'>Creating Your Own Distribution</link>"
                        section.
                    </note>
                </para>

                <para>
                    Understanding some memory concepts will help you reduce the
                    system size.
                    Memory consists of static, dynamic, and temporary memory.
                    Static memory is the TEXT (code), DATA (initialized data
                    in the code), and BSS (uninitialized data) sections.
                    Dynamic memory represents memory that is allocated at runtime:
                    stacks, hash tables, and so forth.
                    Temporary memory is recovered after the boot process.
                    This memory consists of memory used for decompressing
                    the kernel and for the <filename>__init__</filename>
                    functions.
                </para>

                <para>
                    To help you see where you currently are with kernel and root
                    filesystem sizes, you can use two tools found in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink> in
                    the <filename>scripts/tiny/</filename> directory:
                    <itemizedlist>
                        <listitem><para><filename>ksize.py</filename>: Reports
                            component sizes for the kernel build objects.
                            </para></listitem>
                        <listitem><para><filename>dirsize.py</filename>: Reports
                            component sizes for the root filesystem.</para></listitem>
                    </itemizedlist>
                    This next tool and command help you organize configuration
                    fragments and view file dependencies in a human-readable form:
                    <itemizedlist>
                        <listitem><para><filename>merge_config.sh</filename>:
                            Helps you manage configuration files and fragments
                            within the kernel.
                            With this tool, you can merge individual configuration
                            fragments together.
                            The tool allows you to make overrides and warns you
                            of any missing configuration options.
                            The tool is ideal for allowing you to iterate on
                            configurations, create minimal configurations, and
                            create configuration files for different machines
                            without having to duplicate your process.</para>
                            <para>The <filename>merge_config.sh</filename> script is
                            part of the Linux Yocto kernel Git repositories
                            (i.e. <filename>linux-yocto-3.14</filename>,
                            <filename>linux-yocto-3.10</filename>,
                            <filename>linux-yocto-3.8</filename>, and so forth)
                            in the
                            <filename>scripts/kconfig</filename> directory.</para>
                            <para>For more information on configuration fragments,
                            see the
                            "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#creating-config-fragments'>Creating Configuration Fragments</ulink>"
                            section in the Yocto Project Linux Kernel Development
                            Manual.
                            </para></listitem>
                        <listitem><para><filename>bitbake -u taskexp -g <replaceable>bitbake_target</replaceable></filename>:
                            Using the BitBake command with these options brings up
                            a Dependency Explorer from which you can view file
                            dependencies.
                            Understanding these dependencies allows you to make
                            informed decisions when cutting out various pieces of the
                            kernel and root filesystem.</para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='trim-the-root-filesystem'>
                <title>Trim the Root Filesystem</title>

                <para>
                    The root filesystem is made up of packages for booting,
                    libraries, and applications.
                    To change things, you can configure how the packaging happens,
                    which changes the way you build them.
                    You can also modify the filesystem itself or select a different
                    filesystem.
                </para>

                <para>
                    First, find out what is hogging your root filesystem by running the
                    <filename>dirsize.py</filename> script from your root directory:
                    <literallayout class='monospaced'>
     $ cd <replaceable>root-directory-of-image</replaceable>
     $ dirsize.py 100000 > dirsize-100k.log
     $ cat dirsize-100k.log
                    </literallayout>
                    You can apply a filter to the script to ignore files under
                    a certain size.
                    The previous example filters out any files below 100 Kbytes.
                    The sizes reported by the tool are uncompressed, and thus
                    will be smaller by a relatively constant factor in a
                    compressed root filesystem.
                    When you examine your log file, you can focus on areas of the
                    root filesystem that take up large amounts of memory.
                </para>

                <para>
                    You need to be sure that what you eliminate does not cripple
                    the functionality you need.
                    One way to see how packages relate to each other is by using
                    the Dependency Explorer UI with the BitBake command:
                    <literallayout class='monospaced'>
     $ cd <replaceable>image-directory</replaceable>
     $ bitbake -u taskexp -g <replaceable>image</replaceable>
                    </literallayout>
                    Use the interface to select potential packages you wish to
                    eliminate and see their dependency relationships.
                </para>

                <para>
                    When deciding how to reduce the size, get rid of packages that
                    result in minimal impact on the feature set.
                    For example, you might not need a VGA display.
                    Or, you might be able to get by with <filename>devtmpfs</filename>
                    and <filename>mdev</filename> instead of
                    <filename>udev</filename>.
                </para>

                <para>
                    Use your <filename>local.conf</filename> file to make changes.
                    For example, to eliminate <filename>udev</filename> and
                    <filename>glib</filename>, set the following in the
                    local configuration file:
                    <literallayout class='monospaced'>
     VIRTUAL-RUNTIME_dev_manager = ""
                    </literallayout>
                </para>

                <para>
                    Finally, you should consider exactly the type of root
                    filesystem you need to meet your needs while also reducing
                    its size.
                    For example, consider <filename>cramfs</filename>,
                    <filename>squashfs</filename>, <filename>ubifs</filename>,
                    <filename>ext2</filename>, or an <filename>initramfs</filename>
                    using <filename>initramfs</filename>.
                    Be aware that <filename>ext3</filename> requires a 1 Mbyte
                    journal.
                    If you are okay with running read-only, you do not need this
                    journal.
                </para>

                <note>
                    After each round of elimination, you need to rebuild your
                    system and then use the tools to see the effects of your
                    reductions.
                </note>
            </section>

            <section id='trim-the-kernel'>
                <title>Trim the Kernel</title>

                <para>
                    The kernel is built by including policies for hardware-independent
                    aspects.
                    What subsystems do you enable?
                    For what architecture are you building?
                    Which drivers do you build by default?
                    <note>You can modify the kernel source if you want to help
                        with boot time.
                    </note>
                </para>

                <para>
                    Run the <filename>ksize.py</filename> script from the top-level
                    Linux build directory to get an idea of what is making up
                    the kernel:
                    <literallayout class='monospaced'>
     $ cd <replaceable>top-level-linux-build-directory</replaceable>
     $ ksize.py > ksize.log
     $ cat ksize.log
                    </literallayout>
                    When you examine the log, you will see how much space is
                    taken up with the built-in <filename>.o</filename> files for
                    drivers, networking, core kernel files, filesystem, sound,
                    and so forth.
                    The sizes reported by the tool are uncompressed, and thus
                    will be smaller by a relatively constant factor in a compressed
                    kernel image.
                    Look to reduce the areas that are large and taking up around
                    the "90% rule."
                </para>

                <para>
                    To examine, or drill down, into any particular area, use the
                    <filename>-d</filename> option with the script:
                    <literallayout class='monospaced'>
     $ ksize.py -d > ksize.log
                    </literallayout>
                    Using this option breaks out the individual file information
                    for each area of the kernel (e.g. drivers, networking, and
                    so forth).
                </para>

                <para>
                    Use your log file to see what you can eliminate from the kernel
                    based on features you can let go.
                    For example, if you are not going to need sound, you do not
                    need any drivers that support sound.
                </para>

                <para>
                    After figuring out what to eliminate, you need to reconfigure
                    the kernel to reflect those changes during the next build.
                    You could run <filename>menuconfig</filename> and make all your
                    changes at once.
                    However, that makes it difficult to see the effects of your
                    individual eliminations and also makes it difficult to replicate
                    the changes for perhaps another target device.
                    A better method is to start with no configurations using
                    <filename>allnoconfig</filename>, create configuration
                    fragments for individual changes, and then manage the
                    fragments into a single configuration file using
                    <filename>merge_config.sh</filename>.
                    The tool makes it easy for you to iterate using the
                    configuration change and build cycle.
                </para>

                <para>
                    Each time you make configuration changes, you need to rebuild
                    the kernel and check to see what impact your changes had on
                    the overall size.
                </para>
            </section>

            <section id='remove-package-management-requirements'>
                <title>Remove Package Management Requirements</title>

                <para>
                    Packaging requirements add size to the image.
                    One way to reduce the size of the image is to remove all the
                    packaging requirements from the image.
                    This reduction includes both removing the package manager
                    and its unique dependencies as well as removing the package
                    management data itself.
                </para>

                <para>
                    To eliminate all the packaging requirements for an image,
                    be sure that "package-management" is not part of your
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                    statement for the image.
                    When you remove this feature, you are removing the package
                    manager as well as its dependencies from the root filesystem.
                </para>
            </section>

            <section id='look-for-other-ways-to-minimize-size'>
                <title>Look for Other Ways to Minimize Size</title>

                <para>
                    Depending on your particular circumstances, other areas that you
                    can trim likely exist.
                    The key to finding these areas is through tools and methods
                    described here combined with experimentation and iteration.
                    Here are a couple of areas to experiment with:
                    <itemizedlist>
                        <listitem><para><filename>glibc</filename>:
                            In general, follow this process:
                            <orderedlist>
                                <listitem><para>Remove <filename>glibc</filename>
                                    features from
                                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                                    that you think you do not need.</para></listitem>
                                <listitem><para>Build your distribution.
                                    </para></listitem>
                                <listitem><para>If the build fails due to missing
                                    symbols in a package, determine if you can
                                    reconfigure the package to not need those
                                    features.
                                    For example, change the configuration to not
                                    support wide character support as is done for
                                    <filename>ncurses</filename>.
                                    Or, if support for those characters is needed,
                                    determine what <filename>glibc</filename>
                                    features provide the support and restore the
                                    configuration.
                                    </para></listitem>
                                <listitem><para>Rebuild and repeat the process.
                                    </para></listitem>
                            </orderedlist></para></listitem>
                        <listitem><para><filename>busybox</filename>:
                            For BusyBox, use a process similar as described for
                            <filename>glibc</filename>.
                            A difference is you will need to boot the resulting
                            system to see if you are able to do everything you
                            expect from the running system.
                            You need to be sure to integrate configuration fragments
                            into Busybox because BusyBox handles its own core
                            features and then allows you to add configuration
                            fragments on top.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='iterate-on-the-process'>
                <title>Iterate on the Process</title>

                <para>
                    If you have not reached your goals on system size, you need
                    to iterate on the process.
                    The process is the same.
                    Use the tools and see just what is taking up 90% of the root
                    filesystem and the kernel.
                    Decide what you can eliminate without limiting your device
                    beyond what you need.
                </para>

                <para>
                    Depending on your system, a good place to look might be
                    Busybox, which provides a stripped down
                    version of Unix tools in a single, executable file.
                    You might be able to drop virtual terminal services or perhaps
                    ipv6.
                </para>
            </section>
        </section>

        <section id='building-images-for-more-than-one-machine'>
            <title>Building Images for More than One Machine</title>

            <para>
                A common scenario developers face is creating images for several
                different machines that use the same software environment.
                In this situation, it is tempting to set the
                tunings and optimization flags for each build specifically for
                the targeted hardware (i.e. "maxing out" the tunings).
                Doing so can considerably add to build times and package feed
                maintenance collectively for the machines.
                For example, selecting tunes that are extremely specific to a
                CPU core used in a system might enable some micro optimizations
                in GCC for that particular system but would otherwise not gain
                you much of a performance difference across the other systems
                as compared to using a more general tuning across all the builds
                (e.g. setting
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEFAULTTUNE'><filename>DEFAULTTUNE</filename></ulink>
                specifically for each machine's build).
                Rather than "max out" each build's tunings, you can take steps that
                cause the OpenEmbedded build system to reuse software across the
                various machines where it makes sense.
            </para>

            <para>
                If build speed and package feed maintenance are considerations,
                you should consider the points in this section that can help you
                optimize your tunings to best consider build times and package
                feed maintenance.
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Share the Build Directory:</emphasis>
                        If at all possible, share the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
                        across builds.
                        The Yocto Project supports switching between different
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        values in the same <filename>TMPDIR</filename>.
                        This practice is well supported and regularly used by
                        developers when building for multiple machines.
                        When you use the same <filename>TMPDIR</filename> for
                        multiple machine builds, the OpenEmbedded build system can
                        reuse the existing native and often cross-recipes for
                        multiple machines.
                        Thus, build time decreases.
                        <note>
                            If
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                            settings change or fundamental configuration settings
                            such as the filesystem layout, you need to work with
                            a clean <filename>TMPDIR</filename>.
                            Sharing <filename>TMPDIR</filename> under these
                            circumstances might work but since it is not
                            guaranteed, you should use a clean
                            <filename>TMPDIR</filename>.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Enable the Appropriate Package Architecture:</emphasis>
                        By default, the OpenEmbedded build system enables three
                        levels of package architectures: "all", "tune" or "package",
                        and "machine".
                        Any given recipe usually selects one of these package
                        architectures (types) for its output.
                        Depending for what a given recipe creates packages, making
                        sure you enable the appropriate package architecture can
                        directly impact the build time.</para>

                        <para>A recipe that just generates scripts can enable
                        "all" architecture because there are no binaries to build.
                        To specifically enable "all" architecture, be sure your
                        recipe inherits the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-allarch'><filename>allarch</filename></ulink>
                        class.
                        This class is useful for "all" architectures because it
                        configures many variables so packages can be used across
                        multiple architectures.</para>

                        <para>If your recipe needs to generate packages that are
                        machine-specific or when one of the build or runtime
                        dependencies is already machine-architecture dependent,
                        which makes your recipe also machine-architecture dependent,
                        make sure your recipe enables the "machine" package
                        architecture through the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ARCH'><filename>MACHINE_ARCH</filename></ulink>
                        variable:
                        <literallayout class='monospaced'>
     PACKAGE_ARCH = "${MACHINE_ARCH}"
                        </literallayout>
                        When you do not specifically enable a package
                        architecture through the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>,
                        The OpenEmbedded build system defaults to the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-TUNE_PKGARCH'><filename>TUNE_PKGARCH</filename></ulink>
                        setting:
                        <literallayout class='monospaced'>
     PACKAGE_ARCH = "${TUNE_PKGARCH}"
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Choose a Generic Tuning File if Possible:</emphasis>
                        Some tunes are more generic and can run on multiple targets
                        (e.g. an <filename>armv5</filename> set of packages could
                        run on <filename>armv6</filename> and
                        <filename>armv7</filename> processors in most cases).
                        Similarly, <filename>i486</filename> binaries could work
                        on <filename>i586</filename> and higher processors.
                        You should realize, however, that advances on newer
                        processor versions would not be used.</para>

                        <para>If you select the same tune for several different
                        machines, the OpenEmbedded build system reuses software
                        previously built, thus speeding up the overall build time.
                        Realize that even though a new sysroot for each machine is
                        generated, the software is not recompiled and only one
                        package feed exists.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Manage Granular Level Packaging:</emphasis>
                        Sometimes cases exist where injecting another level of
                        package architecture beyond the three higher levels noted
                        earlier can be useful.
                        For example, consider how NXP (formerly Freescale) allows
                        for the easy reuse of binary packages in their layer
                        <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/meta-freescale/'><filename>meta-freescale</filename></ulink>.
                        In this example, the
                        <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/meta-freescale/tree/classes/fsl-dynamic-packagearch.bbclass'><filename>fsl-dynamic-packagearch</filename></ulink>
                        class shares GPU packages for i.MX53 boards because
                        all boards share the AMD GPU.
                        The i.MX6-based boards can do the same because all boards
                        share the Vivante GPU.
                        This class inspects the BitBake datastore to identify if
                        the package provides or depends on one of the
                        sub-architecture values.
                        If so, the class sets the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>
                        value based on the <filename>MACHINE_SUBARCH</filename>
                        value.
                        If the package does not provide or depend on one of the
                        sub-architecture values but it matches a value in the
                        machine-specific filter, it sets
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ARCH'><filename>MACHINE_ARCH</filename></ulink>.
                        This behavior reduces the number of packages built and
                        saves build time by reusing binaries.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Use Tools to Debug Issues:</emphasis>
                        Sometimes you can run into situations where software is
                        being rebuilt when you think it should not be.
                        For example, the OpenEmbedded build system might not be
                        using shared state between machines when you think it
                        should be.
                        These types of situations are usually due to references
                        to machine-specific variables such as
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLES'><filename>SERIAL_CONSOLES</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-XSERVER'><filename>XSERVER</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'><filename>MACHINE_FEATURES</filename></ulink>,
                        and so forth in code that is supposed to only be
                        tune-specific or when the recipe depends
                        (<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-RSUGGESTS'><filename>RSUGGESTS</filename></ulink>,
                        and so forth) on some other recipe that already has
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>
                        defined as "${MACHINE_ARCH}".
                        <note>
                            Patches to fix any issues identified are most welcome
                            as these issues occasionally do occur.
                        </note></para>

                        <para>For such cases, you can use some tools to help you
                        sort out the situation:
                        <itemizedlist>
                            <listitem><para>
                                <emphasis><filename>sstate-diff-machines.sh</filename>:</emphasis>
                                You can find this tool in the
                                <filename>scripts</filename> directory of the
                                Source Repositories.
                                See the comments in the script for information on
                                how to use the tool.
                                </para></listitem>
                            <listitem><para>
                                <emphasis>BitBake's "-S printdiff" Option:</emphasis>
                                Using this option causes BitBake to try to
                                establish the closest signature match it can
                                (e.g. in the shared state cache) and then run
                                <filename>bitbake-diffsigs</filename> over the
                                matches to determine the stamps and delta where
                                these two stamp trees diverge.
                                </para></listitem>
                        </itemizedlist>
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id="building-software-from-an-external-source">
            <title>Building Software from an External Source</title>

            <para>
                By default, the OpenEmbedded build system uses the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                when building source code.
                The build process involves fetching the source files, unpacking
                them, and then patching them if necessary before the build takes
                place.
            </para>

            <para>
                Situations exist where you might want to build software from source
                files that are external to and thus outside of the
                OpenEmbedded build system.
                For example, suppose you have a project that includes a new BSP with
                a heavily customized kernel.
                And, you want to minimize exposing the build system to the
                development team so that they can focus on their project and
                maintain everyone's workflow as much as possible.
                In this case, you want a kernel source directory on the development
                machine where the development occurs.
                You want the recipe's
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                variable to point to the external directory and use it as is, not
                copy it.
            </para>

            <para>
                To build from software that comes from an external source, all you
                need to do is inherit the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc</filename></ulink>
                class and then set the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC'><filename>EXTERNALSRC</filename></ulink>
                variable to point to your external source code.
                Here are the statements to put in your
                <filename>local.conf</filename> file:
                <literallayout class='monospaced'>
     INHERIT += "externalsrc"
     EXTERNALSRC_pn-<replaceable>myrecipe</replaceable> = "<replaceable>path-to-your-source-tree</replaceable>"
                </literallayout>
            </para>

            <para>
                This next example shows how to accomplish the same thing by setting
                <filename>EXTERNALSRC</filename> in the recipe itself or in the
                recipe's append file:
                <literallayout class='monospaced'>
     EXTERNALSRC = "<replaceable>path</replaceable>"
     EXTERNALSRC_BUILD = "<replaceable>path</replaceable>"
                </literallayout>
                <note>
                    In order for these settings to take effect, you must globally
                    or locally inherit the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc</filename></ulink>
                    class.
                </note>
            </para>

            <para>
                By default, <filename>externalsrc.bbclass</filename> builds
                the source code in a directory separate from the external source
                directory as specified by
                <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC'><filename>EXTERNALSRC</filename></ulink>.
                If you need to have the source built in the same directory in
                which it resides, or some other nominated directory, you can set
                <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC_BUILD'><filename>EXTERNALSRC_BUILD</filename></ulink>
                to point to that directory:
                <literallayout class='monospaced'>
     EXTERNALSRC_BUILD_pn-<replaceable>myrecipe</replaceable> = "<replaceable>path-to-your-source-tree</replaceable>"
                </literallayout>
            </para>
        </section>

        <section id="replicating-a-build-offline">
            <title>Replicating a Build Offline</title>

            <para>
                It can be useful to take a "snapshot" of upstream sources
                used in a build and then use that "snapshot" later to
                replicate the build offline.
                To do so, you need to first prepare and populate your downloads
                directory your "snapshot" of files.
                Once your downloads directory is ready, you can use it at
                any time and from any machine to replicate your build.
            </para>

            <para>
                Follow these steps to populate your Downloads directory:
                <orderedlist>
                    <listitem><para>
                        <emphasis>Create a Clean Downloads Directory:</emphasis>
                        Start with an empty downloads directory
                        (<ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>).
                        You start with an empty downloads directory by either
                        removing the files in the existing directory or by
                        setting
                        <filename>DL_DIR</filename> to point to either an
                        empty location or one that does not yet exist.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Generate Tarballs of the Source Git Repositories:</emphasis>
                        Edit your <filename>local.conf</filename> configuration
                        file as follows:
                        <literallayout class='monospaced'>
     DL_DIR = "/home/<replaceable>your-download-dir</replaceable>/"
     BB_GENERATE_MIRROR_TARBALLS = "1"
                        </literallayout>
                        During the fetch process in the next step, BitBake
                        gathers the source files and creates tarballs in
                        the directory pointed to by <filename>DL_DIR</filename>.
                        See the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></ulink>
                        variable for more information.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Populate Your Downloads Directory Without Building:</emphasis>
                        Use BitBake to fetch your sources but inhibit the
                        build:
                        <literallayout class='monospaced'>
     $ bitbake <replaceable>target</replaceable> --runonly=fetch
                        </literallayout>
                        The downloads directory (i.e.
                        <filename>${DL_DIR}</filename>) now has a "snapshot" of
                        the source files in the form of tarballs, which can
                        be used for the build.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Optionally Remove Any Git or other SCM Subdirectories From the Downloads Directory:</emphasis>
                        If you want, you can clean up your downloads directory
                        by removing any Git or other Source Control Management
                        (SCM) subdirectories such as
                        <filename>${DL_DIR}/git2/*</filename>.
                        The tarballs already contain these subdirectories.
                        </para></listitem>
                </orderedlist>
            </para>

            <para>
                Once your downloads directory has everything it needs regarding
                source files, you can create your "own-mirror" and build
                your target.
                Understand that you can use the files to build the target
                offline from any machine and at any time.
            </para>

            <para>
                Follow these steps to build your target using the files in the
                downloads directory:
                <orderedlist>
                    <listitem><para>
                        <emphasis>Using Local Files Only:</emphasis>
                        Inside your <filename>local.conf</filename> file, add
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-SOURCE_MIRROR_URL'><filename>SOURCE_MIRROR_URL</filename></ulink>
                        variable,
                        inherit the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-own-mirrors'><filename>own-mirrors</filename></ulink>
                        class, and use the
                        <ulink url='&YOCTO_DOCS_BB_URL;#var-bb-BB_NO_NETWORK'><filename>BB_NO_NETWORK</filename></ulink>
                        variable to your <filename>local.conf</filename>.
                        <literallayout class='monospaced'>
     SOURCE_MIRROR_URL ?= "file:///home/<replaceable>your-download-dir</replaceable>/"
     INHERIT += "own-mirrors"
     BB_NO_NETWORK = "1"
                        </literallayout>
                        The <filename>SOURCE_MIRROR_URL</filename> and
                        <filename>own-mirror</filename> class set up the system
                        to use the downloads directory as your "own mirror".
                        Using the <filename>BB_NO_NETWORK</filename>
                        variable makes sure that BitBake's fetching process
                        in step 3 stays local, which means files from
                        your "own-mirror" are used.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Start With a Clean Build:</emphasis>
                        You can start with a clean build by removing the
                        <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink><filename>}</filename>
                        directory or using a new
                        <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Build Your Target:</emphasis>
                        Use BitBake to build your target:
                        <literallayout class='monospaced'>
     $ bitbake <replaceable>target</replaceable>
                        </literallayout>
                        The build completes using the known local "snapshot" of
                        source files from your mirror.
                        The resulting tarballs for your "snapshot" of source
                        files are in the downloads directory.
                        <note>
                            <para>The offline build does not work if recipes
                            attempt to find the latest version of software
                            by setting
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
                            to
                            <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-AUTOREV'><filename>AUTOREV</filename></ulink><filename>}</filename>:
                            <literallayout class='monospaced'>
     SRCREV = "${AUTOREV}"
                            </literallayout>
                            When a recipe sets
                            <filename>SRCREV</filename> to
                            <filename>${AUTOREV}</filename>, the build system
                            accesses the network in an attempt to determine the
                            latest version of software from the SCM.
                            Typically, recipes that use
                            <filename>AUTOREV</filename> are custom or
                            modified recipes.
                            Recipes that reside in public repositories
                            usually do not use <filename>AUTOREV</filename>.
                            </para>

                            <para>If you do have recipes that use
                            <filename>AUTOREV</filename>, you can take steps to
                            still use the recipes in an offline build.
                            Do the following:
                                <orderedlist>
                                    <listitem><para>
                                        Use a configuration generated by
                                        enabling
                                        <link linkend='maintaining-build-output-quality'>build history</link>.
                                        </para></listitem>
                                    <listitem><para>
                                        Use the
                                        <filename>buildhistory-collect-srcrevs</filename>
                                        command to collect the stored
                                        <filename>SRCREV</filename> values from
                                        the build's history.
                                        For more information on collecting these
                                        values, see the
                                        "<link linkend='build-history-package-information'>Build History Package Information</link>"
                                        section.
                                        </para></listitem>
                                    <listitem><para>
                                        Once you have the correct source
                                        revisions, you can modify those recipes
                                        to to set <filename>SRCREV</filename>
                                        to specific versions of the software.
                                        </para></listitem>
                                </orderedlist>
                            </para>
                        </note>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>

    <section id='speeding-up-a-build'>
        <title>Speeding Up a Build</title>

        <para>
            Build time can be an issue.
            By default, the build system uses simple controls to try and maximize
            build efficiency.
            In general, the default settings for all the following variables
            result in the most efficient build times when dealing with single
            socket systems (i.e. a single CPU).
            If you have multiple CPUs, you might try increasing the default
            values to gain more speed.
            See the descriptions in the glossary for each variable for more
            information:
            <itemizedlist>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename>:</ulink>
                    The maximum number of threads BitBake simultaneously executes.
                    </para></listitem>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_NUMBER_PARSE_THREADS'><filename>BB_NUMBER_PARSE_THREADS</filename>:</ulink>
                    The number of threads BitBake uses during parsing.
                    </para></listitem>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename>:</ulink>
                    Extra options passed to the <filename>make</filename> command
                    during the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
                    task in order to specify parallel compilation on the
                    local build host.
                    </para></listitem>
                <listitem><para>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename>:</ulink>
                    Extra options passed to the <filename>make</filename> command
                    during the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
                    task in order to specify parallel installation on the
                    local build host.
                    </para></listitem>
            </itemizedlist>
            As mentioned, these variables all scale to the number of processor
            cores available on the build system.
            For single socket systems, this auto-scaling ensures that the build
            system fundamentally takes advantage of potential parallel operations
            during the build based on the build machine's capabilities.
        </para>

        <para>
            Following are additional factors that can affect build speed:
            <itemizedlist>
                <listitem><para>
                    File system type:
                    The file system type that the build is being performed on can
                    also influence performance.
                    Using <filename>ext4</filename> is recommended as compared
                    to <filename>ext2</filename> and <filename>ext3</filename>
                    due to <filename>ext4</filename> improved features
                    such as extents.
                    </para></listitem>
                <listitem><para>
                    Disabling the updating of access time using
                    <filename>noatime</filename>:
                    The <filename>noatime</filename> mount option prevents the
                    build system from updating file and directory access times.
                    </para></listitem>
                <listitem><para>
                    Setting a longer commit:
                    Using the "commit=" mount option increases the interval
                    in seconds between disk cache writes.
                    Changing this interval from the five second default to
                    something longer increases the risk of data loss but decreases
                    the need to write to the disk, thus increasing the build
                    performance.
                    </para></listitem>
                <listitem><para>
                    Choosing the packaging backend:
                    Of the available packaging backends, IPK is the fastest.
                    Additionally, selecting a singular packaging backend also
                    helps.
                    </para></listitem>
                <listitem><para>
                    Using <filename>tmpfs</filename> for
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
                    as a temporary file system:
                    While this can help speed up the build, the benefits are
                    limited due to the compiler using
                    <filename>-pipe</filename>.
                    The build system goes to some lengths to avoid
                    <filename>sync()</filename> calls into the
                    file system on the principle that if there was a significant
                    failure, the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                    contents could easily be rebuilt.
                    </para></listitem>
                <listitem><para>
                    Inheriting the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-rm-work'><filename>rm_work</filename></ulink>
                    class:
                    Inheriting this class has shown to speed up builds due to
                    significantly lower amounts of data stored in the data
                    cache as well as on disk.
                    Inheriting this class also makes cleanup of
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
                    faster, at the expense of being easily able to dive into the
                    source code.
                    File system maintainers have recommended that the fastest way
                    to clean up large numbers of files is to reformat partitions
                    rather than delete files due to the linear nature of
                    partitions.
                    This, of course, assumes you structure the disk partitions and
                    file systems in a way that this is practical.
                    </para></listitem>
            </itemizedlist>
            Aside from the previous list, you should keep some trade offs in
            mind that can help you speed up the build:
            <itemizedlist>
                <listitem><para>
                    Remove items from
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                    that you might not need.
                    </para></listitem>
                <listitem><para>
                    Exclude debug symbols and other debug information:
                    If you do not need these symbols and other debug information,
                    disabling the <filename>*-dbg</filename> package generation
                    can speed up the build.
                    You can disable this generation by setting the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-INHIBIT_PACKAGE_DEBUG_SPLIT'><filename>INHIBIT_PACKAGE_DEBUG_SPLIT</filename></ulink>
                    variable to "1".
                    </para></listitem>
                <listitem><para>
                    Disable static library generation for recipes derived from
                    <filename>autoconf</filename> or <filename>libtool</filename>:
                    Following is an example showing how to disable static
                    libraries and still provide an override to handle exceptions:
                    <literallayout class='monospaced'>
     STATICLIBCONF = "--disable-static"
     STATICLIBCONF_sqlite3-native = ""
     EXTRA_OECONF += "${STATICLIBCONF}"
                    </literallayout>
                    <note><title>Notes</title>
                        <itemizedlist>
                            <listitem><para>
                                Some recipes need static libraries in order to work
                                correctly (e.g. <filename>pseudo-native</filename>
                                needs <filename>sqlite3-native</filename>).
                                Overrides, as in the previous example, account for
                                these kinds of exceptions.
                                </para></listitem>
                            <listitem><para>
                                Some packages have packaging code that assumes the
                                presence of the static libraries.
                                If so, you might need to exclude them as well.
                                </para></listitem>
                        </itemizedlist>
                    </note>
                </para></listitem>
            </itemizedlist>
        </para>
    </section>

    <section id="platdev-working-with-libraries">
        <title>Working With Libraries</title>

        <para>
            Libraries are an integral part of your system.
            This section describes some common practices you might find
            helpful when working with libraries to build your system:
            <itemizedlist>
                <listitem><para><link linkend='including-static-library-files'>How to include static library files</link>
                    </para></listitem>
                <listitem><para><link linkend='combining-multiple-versions-library-files-into-one-image'>How to use the Multilib feature to combine multiple versions of library files into a single image</link>
                    </para></listitem>
                <listitem><para><link linkend='installing-multiple-versions-of-the-same-library'>How to install multiple versions of the same library in parallel on the same system</link>
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id='including-static-library-files'>
            <title>Including Static Library Files</title>

            <para>
                If you are building a library and the library offers static linking, you can control
                which static library files (<filename>*.a</filename> files) get included in the
                built library.
            </para>

            <para>
                The <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES_*</filename></ulink>
                variables in the
                <filename>meta/conf/bitbake.conf</filename> configuration file define how files installed
                by the <filename>do_install</filename> task are packaged.
                By default, the <filename>PACKAGES</filename> variable includes
                <filename>${PN}-staticdev</filename>, which represents all static library files.
                <note>
                    Some previously released versions of the Yocto Project
                    defined the static library files through
                    <filename>${PN}-dev</filename>.
                </note>
                Following is part of the BitBake configuration file, where
                you can see how the static library files are defined:
                <literallayout class='monospaced'>
     PACKAGE_BEFORE_PN ?= ""
     PACKAGES = "${PN}-dbg ${PN}-staticdev ${PN}-dev ${PN}-doc ${PN}-locale ${PACKAGE_BEFORE_PN} ${PN}"
     PACKAGES_DYNAMIC = "^${PN}-locale-.*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${base_prefix}/lib/udev/rules.d ${prefix}/lib/udev/rules.d \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-bin = "${bindir}/* ${sbindir}/*"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"

     FILES_SOLIBSDEV ?= "${base_libdir}/lib*${SOLIBSDEV} ${libdir}/lib*${SOLIBSDEV}"
     FILES_${PN}-dev = "${includedir} ${FILES_SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o \
                     ${libdir}/${BPN}/*.la ${base_libdir}/*.la"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"

     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a ${libdir}/${BPN}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                </literallayout>
            </para>
        </section>

        <section id="combining-multiple-versions-library-files-into-one-image">
            <title>Combining Multiple Versions of Library Files into One Image</title>

            <para>
                The build system offers the ability to build libraries with different
                target optimizations or architecture formats and combine these together
                into one system image.
                You can link different binaries in the image
                against the different libraries as needed for specific use cases.
                This feature is called "Multilib."
            </para>

            <para>
                An example would be where you have most of a system compiled in 32-bit
                mode using 32-bit libraries, but you have something large, like a database
                engine, that needs to be a 64-bit application and uses 64-bit libraries.
                Multilib allows you to get the best of both 32-bit and 64-bit libraries.
            </para>

            <para>
                While the Multilib feature is most commonly used for 32 and 64-bit differences,
                the approach the build system uses facilitates different target optimizations.
                You could compile some binaries to use one set of libraries and other binaries
                to use a different set of libraries.
                The libraries could differ in architecture, compiler options, or other
                optimizations.
            </para>

            <para>
                Several examples exist in the
                <filename>meta-skeleton</filename> layer found in the
               <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>:
                <itemizedlist>
                    <listitem><para><filename>conf/multilib-example.conf</filename>
                        configuration file</para></listitem>
                    <listitem><para><filename>conf/multilib-example2.conf</filename>
                        configuration file</para></listitem>
                    <listitem><para><filename>recipes-multilib/images/core-image-multilib-example.bb</filename>
                        recipe</para></listitem>
                </itemizedlist>
            </para>

            <section id='preparing-to-use-multilib'>
                <title>Preparing to Use Multilib</title>

                <para>
                    User-specific requirements drive the Multilib feature.
                    Consequently, there is no one "out-of-the-box" configuration that likely
                    exists to meet your needs.
                </para>

                <para>
                    In order to enable Multilib, you first need to ensure your recipe is
                    extended to support multiple libraries.
                    Many standard recipes are already extended and support multiple libraries.
                    You can check in the <filename>meta/conf/multilib.conf</filename>
                    configuration file in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink> to see how this is
                    done using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
                    variable.
                    Eventually, all recipes will be covered and this list will
                    not be needed.
                </para>

                <para>
                    For the most part, the Multilib class extension works automatically to
                    extend the package name from <filename>${PN}</filename> to
                    <filename>${MLPREFIX}${PN}</filename>, where <filename>MLPREFIX</filename>
                    is the particular multilib (e.g. "lib32-" or "lib64-").
                    Standard variables such as
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RPROVIDES'><filename>RPROVIDES</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>, and
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES_DYNAMIC'><filename>PACKAGES_DYNAMIC</filename></ulink>
                    are automatically extended by the system.
                    If you are extending any manual code in the recipe, you can use the
                    <filename>${MLPREFIX}</filename> variable to ensure those names are extended
                    correctly.
                    This automatic extension code resides in <filename>multilib.bbclass</filename>.
                </para>
            </section>

            <section id='using-multilib'>
                <title>Using Multilib</title>

                <para>
                    After you have set up the recipes, you need to define the actual
                    combination of multiple libraries you want to build.
                    You accomplish this through your <filename>local.conf</filename>
                    configuration file in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                    An example configuration would be as follows:
                    <literallayout class='monospaced'>
     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     IMAGE_INSTALL_append = " lib32-glib-2.0"
                    </literallayout>
                    This example enables an
                    additional library named <filename>lib32</filename> alongside the
                    normal target packages.
                    When combining these "lib32" alternatives, the example uses "x86" for tuning.
                    For information on this particular tuning, see
                    <filename>meta/conf/machine/include/ia32/arch-ia32.inc</filename>.
                </para>

                <para>
                    The example then includes <filename>lib32-glib-2.0</filename>
                    in all the images, which illustrates one method of including a
                    multiple library dependency.
                    You can use a normal image build to include this dependency,
                    for example:
                    <literallayout class='monospaced'>
     $ bitbake core-image-sato
                    </literallayout>
                    You can also build Multilib packages specifically with a command like this:
                    <literallayout class='monospaced'>
     $ bitbake lib32-glib-2.0
                    </literallayout>
                </para>
            </section>

            <section id='additional-implementation-details'>
                <title>Additional Implementation Details</title>

                <para>
                    Generic implementation details as well as details that are
                    specific to package management systems exist.
                    Following are implementation details that exist regardless
                    of the package management system:
                    <itemizedlist>
                        <listitem><para>The typical convention used for the
                            class extension code as used by
                            Multilib assumes that all package names specified
                            in
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                            that contain <filename>${PN}</filename> have
                            <filename>${PN}</filename> at the start of the name.
                            When that convention is not followed and
                            <filename>${PN}</filename> appears at
                            the middle or the end of a name, problems occur.
                            </para></listitem>
                        <listitem><para>The
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_VENDOR'><filename>TARGET_VENDOR</filename></ulink>
                            value under Multilib will be extended to
                            "-<replaceable>vendor</replaceable>ml<replaceable>multilib</replaceable>"
                            (e.g. "-pokymllib32" for a "lib32" Multilib with
                            Poky).
                            The reason for this slightly unwieldy contraction
                            is that any "-" characters in the vendor
                            string presently break Autoconf's
                            <filename>config.sub</filename>, and
                            other separators are problematic for different
                            reasons.
                            </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    For the RPM Package Management System, the following implementation details
                    exist:
                    <itemizedlist>
                        <listitem><para>A unique architecture is defined for the Multilib packages,
                            along with creating a unique deploy folder under
                            <filename>tmp/deploy/rpm</filename> in the
                            <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                            For example, consider <filename>lib32</filename> in a
                            <filename>qemux86-64</filename> image.
                            The possible architectures in the system are "all", "qemux86_64",
                            "lib32_qemux86_64", and "lib32_x86".</para></listitem>
                        <listitem><para>The <filename>${MLPREFIX}</filename> variable is stripped from
                            <filename>${PN}</filename> during RPM packaging.
                            The naming for a normal RPM package and a Multilib RPM package in a
                            <filename>qemux86-64</filename> system resolves to something similar to
                            <filename>bash-4.1-r2.x86_64.rpm</filename> and
                            <filename>bash-4.1.r2.lib32_x86.rpm</filename>, respectively.
                            </para></listitem>
                        <listitem><para>When installing a Multilib image, the RPM backend first
                            installs the base image and then installs the Multilib libraries.
                            </para></listitem>
                        <listitem><para>The build system relies on RPM to resolve the identical files in the
                            two (or more) Multilib packages.</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    For the IPK Package Management System, the following implementation details exist:
                    <itemizedlist>
                        <listitem><para>The <filename>${MLPREFIX}</filename> is not stripped from
                            <filename>${PN}</filename> during IPK packaging.
                            The naming for a normal RPM package and a Multilib IPK package in a
                            <filename>qemux86-64</filename> system resolves to something like
                            <filename>bash_4.1-r2.x86_64.ipk</filename> and
                            <filename>lib32-bash_4.1-rw_x86.ipk</filename>, respectively.
                            </para></listitem>
                        <listitem><para>The IPK deploy folder is not modified with
                            <filename>${MLPREFIX}</filename> because packages with and without
                            the Multilib feature can exist in the same folder due to the
                            <filename>${PN}</filename> differences.</para></listitem>
                        <listitem><para>IPK defines a sanity check for Multilib installation
                            using certain rules for file comparison, overridden, etc.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='installing-multiple-versions-of-the-same-library'>
            <title>Installing Multiple Versions of the Same Library</title>

            <para>
                Situations can exist where you need to install and use
                multiple versions of the same library on the same system
                at the same time.
                These situations almost always exist when a library API
                changes and you have multiple pieces of software that
                depend on the separate versions of the library.
                To accommodate these situations, you can install multiple
                versions of the same library in parallel on the same system.
            </para>

            <para>
                The process is straightforward as long as the libraries use
                proper versioning.
                With properly versioned libraries, all you need to do to
                individually specify the libraries is create separate,
                appropriately named recipes where the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink> part of the
                name includes a portion that differentiates each library version
                (e.g.the major part of the version number).
                Thus, instead of having a single recipe that loads one version
                of a library (e.g. <filename>clutter</filename>), you provide
                multiple recipes that result in different versions
                of the libraries you want.
                As an example, the following two recipes would allow the
                two separate versions of the <filename>clutter</filename>
                library to co-exist on the same system:
                <literallayout class='monospaced'>
     clutter-1.6_1.6.20.bb
     clutter-1.8_1.8.4.bb
                </literallayout>
                Additionally, if you have other recipes that depend on a given
                library, you need to use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                variable to create the dependency.
                Continuing with the same example, if you want to have a recipe
                depend on the 1.8 version of the <filename>clutter</filename>
                library, use the following in your recipe:
                <literallayout class='monospaced'>
     DEPENDS = "clutter-1.8"
                </literallayout>
            </para>
        </section>
    </section>

    <section id='using-x32-psabi'>
        <title>Using x32 psABI</title>

        <para>
            x32 processor-specific Application Binary Interface
            (<ulink url='https://software.intel.com/en-us/node/628948'>x32 psABI</ulink>)
            is a native 32-bit processor-specific ABI for
            <trademark class='registered'>Intel</trademark> 64 (x86-64)
            architectures.
            An ABI defines the calling conventions between functions in a
            processing environment.
            The interface determines what registers are used and what the
            sizes are for various C data types.
        </para>

        <para>
            Some processing environments prefer using 32-bit applications even
            when running on Intel 64-bit platforms.
            Consider the i386 psABI, which is a very old 32-bit ABI for Intel
            64-bit platforms.
            The i386 psABI does not provide efficient use and access of the
            Intel 64-bit processor resources, leaving the system underutilized.
            Now consider the x86_64 psABI.
            This ABI is newer and uses 64-bits for data sizes and program
            pointers.
            The extra bits increase the footprint size of the programs,
            libraries, and also increases the memory and file system size
            requirements.
            Executing under the x32 psABI enables user programs to utilize CPU
            and system resources more efficiently while keeping the memory
            footprint of the applications low.
            Extra bits are used for registers but not for addressing mechanisms.
        </para>

        <para>
            The Yocto Project supports the final specifications of x32 psABI
            as follows:
            <itemizedlist>
                <listitem><para>
                    You can create packages and images in x32 psABI format on
                    x86_64 architecture targets.
                    </para></listitem>
                <listitem><para>
                    You can successfully build recipes with the x32 toolchain.
                    </para></listitem>
                <listitem><para>
                    You can create and boot
                    <filename>core-image-minimal</filename> and
                    <filename>core-image-sato</filename> images.
                    </para></listitem>
                <listitem><para>
                    RPM Package Manager (RPM) support exists for x32 binaries.
                    </para></listitem>
                <listitem><para>
                    Support for large images exists.
                    </para></listitem>
            </itemizedlist>
        </para>

        <para>
            To use the x32 psABI, you need to edit your
            <filename>conf/local.conf</filename> configuration file as
            follows:
            <literallayout class='monospaced'>
     MACHINE = "qemux86-64"
     DEFAULTTUNE = "x86-64-x32"
     baselib = "${@d.getVar('BASE_LIB_tune-' + (d.getVar('DEFAULTTUNE') \
        or 'INVALID')) or 'lib'}"
            </literallayout>
            Once you have set up your configuration file, use BitBake to
            build an image that supports the x32 psABI.
            Here is an example:
            <literallayout class='monospaced'>
     $ bitbake core-image-sato
            </literallayout>
        </para>
    </section>

    <section id='enabling-gobject-introspection-support'>
        <title>Enabling GObject Introspection Support</title>

        <para>
            <ulink url='https://wiki.gnome.org/Projects/GObjectIntrospection'>GObject introspection</ulink>
            is the standard mechanism for accessing GObject-based software
            from runtime environments.
            GObject is a feature of the GLib library that provides an object
            framework for the GNOME desktop and related software.
            GObject Introspection adds information to GObject that allows
            objects created within it to be represented across different
            programming languages.
            If you want to construct GStreamer pipelines using Python, or
            control UPnP infrastructure using Javascript and GUPnP,
            GObject introspection is the only way to do it.
        </para>

        <para>
            This section describes the Yocto Project support for generating
            and packaging GObject introspection data.
            GObject introspection data is a description of the
            API provided by libraries built on top of GLib framework,
            and, in particular, that framework's GObject mechanism.
            GObject Introspection Repository (GIR) files go to
            <filename>-dev</filename> packages,
            <filename>typelib</filename> files go to main packages as they
            are packaged together with libraries that are introspected.
        </para>

        <para>
            The data is generated when building such a library, by linking
            the library with a small executable binary that asks the library
            to describe itself, and then executing the binary and
            processing its output.
        </para>

        <para>
            Generating this data in a cross-compilation environment
            is difficult because the library is produced for the target
            architecture, but its code needs to be executed on the build host.
            This problem is solved with the OpenEmbedded build system by
            running the code through QEMU, which allows precisely that.
            Unfortunately, QEMU does not always work perfectly as mentioned
            in the
            "<link linkend='known-issues'>Known Issues</link>" section.
        </para>

        <section id='enabling-the-generation-of-introspection-data'>
            <title>Enabling the Generation of Introspection Data</title>

            <para>
                Enabling the generation of introspection data (GIR files)
                in your library package involves the following:
                <orderedlist>
                    <listitem><para>
                        Inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-gobject-introspection'><filename>gobject-introspection</filename></ulink>
                        class.
                        </para></listitem>
                    <listitem><para>
                        Make sure introspection is not disabled anywhere in
                        the recipe or from anything the recipe includes.
                        Also, make sure that "gobject-introspection-data" is
                        not in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>
                        and that "qemu-usermode" is not in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
                        If either of these conditions exist, nothing will
                        happen.
                        </para></listitem>
                    <listitem><para>
                        Try to build the recipe.
                        If you encounter build errors that look like
                        something is unable to find
                        <filename>.so</filename> libraries, check where these
                        libraries are located in the source tree and add
                        the following to the recipe:
                        <literallayout class='monospaced'>
     GIR_EXTRA_LIBS_PATH = "${B}/<replaceable>something</replaceable>/.libs"
                        </literallayout>
                        <note>
                            See recipes in the <filename>oe-core</filename>
                            repository that use that
                            <filename>GIR_EXTRA_LIBS_PATH</filename> variable
                            as an example.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        Look for any other errors, which probably mean that
                        introspection support in a package is not entirely
                        standard, and thus breaks down in a cross-compilation
                        environment.
                        For such cases, custom-made fixes are needed.
                        A good place to ask and receive help in these cases
                        is the
                        <ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Yocto Project mailing lists</ulink>.
                        </para></listitem>
                </orderedlist>
                <note>
                    Using a library that no longer builds against the latest
                    Yocto Project release and prints introspection related
                    errors is a good candidate for the previous procedure.
                </note>
            </para>
        </section>

        <section id='disabling-the-generation-of-introspection-data'>
            <title>Disabling the Generation of Introspection Data</title>

            <para>
                You might find that you do not want to generate
                introspection data.
                Or, perhaps QEMU does not work on your build host and
                target architecture combination.
                If so, you can use either of the following methods to
                disable GIR file generations:
                <itemizedlist>
                    <listitem><para>
                        Add the following to your distro configuration:
                        <literallayout class='monospaced'>
     DISTRO_FEATURES_BACKFILL_CONSIDERED = "gobject-introspection-data"
                        </literallayout>
                        Adding this statement disables generating
                        introspection data using QEMU but will still enable
                        building introspection tools and libraries
                        (i.e. building them does not require the use of QEMU).
                        </para></listitem>
                    <listitem><para>
                        Add the following to your machine configuration:
                        <literallayout class='monospaced'>
     MACHINE_FEATURES_BACKFILL_CONSIDERED = "qemu-usermode"
                        </literallayout>
                        Adding this statement disables the use of QEMU
                        when building packages for your machine.
                        Currently, this feature is used only by introspection
                        recipes and has the same effect as the previously
                        described option.
                        <note>
                            Future releases of the Yocto Project might have
                            other features affected by this option.
                        </note>
                        </para></listitem>
                </itemizedlist>
                If you disable introspection data, you can still
                obtain it through other means such as copying the data
                from a suitable sysroot, or by generating it on the
                target hardware.
                The OpenEmbedded build system does not currently
                provide specific support for these techniques.
            </para>
        </section>

        <section id='testing-that-introspection-works-in-an-image'>
            <title>Testing that Introspection Works in an Image</title>

            <para>
                Use the following procedure to test if generating
                introspection data is working in an image:
                <orderedlist>
                    <listitem><para>
                        Make sure that "gobject-introspection-data" is not in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>
                        and that "qemu-usermode" is not in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
                        </para></listitem>
                    <listitem><para>
                        Build <filename>core-image-sato</filename>.
                        </para></listitem>
                    <listitem><para>
                        Launch a Terminal and then start Python in the
                        terminal.
                        </para></listitem>
                    <listitem><para>
                        Enter the following in the terminal:
                        <literallayout class='monospaced'>
     >>> from gi.repository import GLib
     >>> GLib.get_host_name()
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        For something a little more advanced, enter the
                        following:
                        <literallayout class='monospaced'>
     http://python-gtk-3-tutorial.readthedocs.org/en/latest/introduction.html
                        </literallayout>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='known-issues'>
            <title>Known Issues</title>

            <para>
                The following know issues exist for
                GObject Introspection Support:
                <itemizedlist>
                    <listitem><para>
                        <filename>qemu-ppc64</filename> immediately crashes.
                        Consequently, you cannot build introspection data on
                        that architecture.
                        </para></listitem>
                    <listitem><para>
                        x32 is not supported by QEMU.
                        Consequently, introspection data is disabled.
                        </para></listitem>
                    <listitem><para>
                        musl causes transient GLib binaries to crash on
                        assertion failures.
                        Consequently, generating introspection data is
                        disabled.
                        </para></listitem>
                    <listitem><para>
                        Because QEMU is not able to run the binaries correctly,
                        introspection is disabled for some specific packages
                        under specific architectures (e.g.
                        <filename>gcr</filename>,
                        <filename>libsecret</filename>, and
                        <filename>webkit</filename>).
                        </para></listitem>
                    <listitem><para>
                        QEMU usermode might not work properly when running
                        64-bit binaries under 32-bit host machines.
                        In particular, "qemumips64" is known to not work under
                        i686.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id='dev-optionally-using-an-external-toolchain'>
        <title>Optionally Using an External Toolchain</title>

        <para>
            You might want to use an external toolchain as part of your
            development.
            If this is the case, the fundamental steps you need to accomplish
            are as follows:
            <itemizedlist>
                <listitem><para>
                    Understand where the installed toolchain resides.
                    For cases where you need to build the external toolchain,
                    you would need to take separate steps to build and install
                    the toolchain.
                    </para></listitem>
                <listitem><para>
                    Make sure you add the layer that contains the toolchain to
                    your <filename>bblayers.conf</filename> file through the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
                    variable.
                    </para></listitem>
                <listitem><para>
                    Set the <filename>EXTERNAL_TOOLCHAIN</filename>
                    variable in your <filename>local.conf</filename> file
                    to the location in which you installed the toolchain.
                    </para></listitem>
            </itemizedlist>
            A good example of an external toolchain used with the Yocto Project
            is <trademark class='registered'>Mentor Graphics</trademark>
            Sourcery G++ Toolchain.
            You can see information on how to use that particular layer in the
            <filename>README</filename> file at
            <ulink url='http://github.com/MentorEmbedded/meta-sourcery/'></ulink>.
            You can find further information by reading about the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-TCMODE'><filename>TCMODE</filename></ulink>
            variable in the Yocto Project Reference Manual's variable glossary.
        </para>
    </section>

    <section id='creating-partitioned-images-using-wic'>
        <title>Creating Partitioned Images Using Wic</title>

        <para>
            Creating an image for a particular hardware target using the
            OpenEmbedded build system does not necessarily mean you can boot
            that image as is on your device.
            Physical devices accept and boot images in various ways depending
            on the specifics of the device.
            Usually, information about the hardware can tell you what image
            format the device requires.
            Should your device require multiple partitions on an SD card, flash,
            or an HDD, you can use the OpenEmbedded Image Creator,
	        Wic, to create the properly partitioned image.
        </para>

        <para>
            The <filename>wic</filename> command generates partitioned
            images from existing OpenEmbedded build artifacts.
            Image generation is driven by partitioning commands
            contained in an Openembedded kickstart file
            (<filename>.wks</filename>) specified either directly on
            the command line or as one of a selection of canned
            kickstart files as shown with the
            <filename>wic list images</filename> command in the
            "<link linkend='using-a-provided-kickstart-file'>Using an Existing Kickstart File</link>"
            section.
            When you apply the command to a given set of build
            artifacts, the result is an image or set of images that
            can be directly written onto media and used on a particular
            system.
            <note>
                For a kickstart file reference, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-kickstart'>OpenEmbedded Kickstart (<filename>.wks</filename>) Reference</ulink>"
                Chapter in the Yocto Project Reference Manual.
            </note>
        </para>

        <para>
            The <filename>wic</filename> command and the infrastructure
            it is based on is by definition incomplete.
            The purpose of the command is to allow the generation of
            customized images, and as such, was designed to be
            completely extensible through a plugin interface.
            See the
            "<link linkend='wic-using-the-wic-plugin-interface'>Using the Wic PlugIn Interface</link>"
            section for information on these plugins.
        </para>

        <para>
            This section provides some background information on Wic,
            describes what you need to have in
            place to run the tool, provides instruction on how to use
            the Wic utility, provides information on using the Wic plugins
            interface, and provides several examples that show how to use
            Wic.
        </para>

        <section id='wic-background'>
            <title>Background</title>

            <para>
                This section provides some background on the Wic utility.
                While none of this information is required to use
                Wic, you might find it interesting.
                <itemizedlist>
                    <listitem><para>
                        The name "Wic" is derived from OpenEmbedded
                        Image Creator (oeic).
                        The "oe" diphthong in "oeic" was promoted to the
                        letter "w", because "oeic" is both difficult to
                        remember and to pronounce.
                        </para></listitem>
                    <listitem><para>
                        Wic is loosely based on the
                        Meego Image Creator (<filename>mic</filename>)
                        framework.
                        The Wic implementation has been
                        heavily modified to make direct use of OpenEmbedded
                        build artifacts instead of package installation and
                        configuration, which are already incorporated within
                        the OpenEmbedded artifacts.
                        </para></listitem>
                    <listitem><para>
                        Wic is a completely independent
                        standalone utility that initially provides
                        easier-to-use and more flexible replacements for an
                        existing functionality in OE-Core's
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-image-live'><filename>image-live</filename></ulink>
                        class.
                        The difference between Wic and those examples is
                        that with Wic the functionality of those scripts is
                        implemented by a general-purpose partitioning language,
                        which is based on Redhat kickstart syntax.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='wic-requirements'>
            <title>Requirements</title>

            <para>
                In order to use the Wic utility with the OpenEmbedded Build
                system, your system needs to meet the following
                requirements:
                <itemizedlist>
                    <listitem><para>
                        The Linux distribution on your development host must
                        support the Yocto Project.
                        See the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#detailed-supported-distros'>Supported Linux Distributions</ulink>"
                        section in the Yocto Project Reference Manual for
                        the list of distributions that support the
                        Yocto Project.
                        </para></listitem>
                    <listitem><para>
                        The standard system utilities, such as
                        <filename>cp</filename>, must be installed on your
                        development host system.
                        </para></listitem>
                    <listitem><para>
                        You must have sourced the build environment
                        setup script (i.e.
                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>)
                        found in the
                        <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                        </para></listitem>
                    <listitem><para>
                        You need to have the build artifacts already
                        available, which typically means that you must
                        have already created an image using the
                        Openembedded build system (e.g.
                        <filename>core-image-minimal</filename>).
                        While it might seem redundant to generate an image
                        in order to create an image using
                        Wic, the current version of
                        Wic requires the artifacts
                        in the form generated by the OpenEmbedded build
                        system.
                        </para></listitem>
                    <listitem><para>
                        You must build several native tools, which are
                        built to run on the build system:
                        <literallayout class='monospaced'>
     $ bitbake parted-native dosfstools-native mtools-native
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Include "wic" as part of the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></ulink>
                        variable.
                        </para></listitem>
                    <listitem><para>
                        Include the name of the
                        <ulink url='&YOCTO_DOCS_REF_URL;#openembedded-kickstart-wks-reference'>wic kickstart file</ulink>
                        as part of the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-WKS_FILE'><filename>WKS_FILE</filename></ulink>
                        variable
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='wic-getting-help'>
            <title>Getting Help</title>

            <para>
                You can get general help for the <filename>wic</filename>
                command by entering the <filename>wic</filename> command
                by itself or by entering the command with a help argument
                as follows:
                <literallayout class='monospaced'>
     $ wic -h
     $ wic --help
     $ wic help
                </literallayout>
            </para>

            <para>
                Currently, Wic supports seven commands:
                <filename>cp</filename>, <filename>create</filename>,
                <filename>help</filename>, <filename>list</filename>,
                <filename>ls</filename>, <filename>rm</filename>, and
                <filename>write</filename>.
                You can get help for all these commands except "help" by
                using the following form:
                <literallayout class='monospaced'>
     $ wic help <replaceable>command</replaceable>
                </literallayout>
                For example, the following command returns help for the
                <filename>write</filename> command:
                <literallayout class='monospaced'>
     $ wic help write
                </literallayout>
            </para>

            <para>
                Wic supports help for three topics:
                <filename>overview</filename>,
                <filename>plugins</filename>, and
                <filename>kickstart</filename>.
                You can get help for any topic using the following form:
                <literallayout class='monospaced'>
     $ wic help <replaceable>topic</replaceable>
                </literallayout>
                For example, the following returns overview help for Wic:
                <literallayout class='monospaced'>
     $ wic help overview
                </literallayout>
            </para>

            <para>
                One additional level of help exists for Wic.
                You can get help on individual images through the
                <filename>list</filename> command.
                You can use the <filename>list</filename> command to return the
                available Wic images as follows:
                <literallayout class='monospaced'>
     $ wic list images
       genericx86                    		Create an EFI disk image for genericx86*
       beaglebone-yocto              		Create SD card image for Beaglebone
       edgerouter                    		Create SD card image for Edgerouter
       qemux86-directdisk            		Create a qemu machine 'pcbios' direct disk image
       directdisk-gpt                		Create a 'pcbios' direct disk image
       mkefidisk                     		Create an EFI disk image
       directdisk                    		Create a 'pcbios' direct disk image
       systemd-bootdisk              		Create an EFI disk image with systemd-boot
       mkhybridiso                   		Create a hybrid ISO image
       sdimage-bootpart              		Create SD card image with a boot partition
       directdisk-multi-rootfs       		Create multi rootfs image using rootfs plugin
       directdisk-bootloader-config  		Create a 'pcbios' direct disk image with custom bootloader config
                </literallayout>
                Once you know the list of available Wic images, you can use
                <filename>help</filename> with the command to get help on a
                particular image.
                For example, the following command returns help on the
                "beaglebone-yocto" image:
                <literallayout class='monospaced'>
     $ wic list beaglebone-yocto help


     Creates a partitioned SD card image for Beaglebone.
     Boot files are located in the first vfat partition.
                </literallayout>
            </para>
        </section>

        <section id='operational-modes'>
            <title>Operational Modes</title>

            <para>
                You can use Wic in two different
                modes, depending on how much control you need for
                specifying the Openembedded build artifacts that are
                used for creating the image: Raw and Cooked:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Raw Mode:</emphasis>
                        You explicitly specify build artifacts through
                        Wic command-line arguments.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Cooked Mode:</emphasis>
                        The current
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        setting and image name are used to automatically
                        locate and provide the build artifacts.
                        You just supply a kickstart file and the name
                        of the image from which to use artifacts.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Regardless of the mode you use, you need to have the build
                artifacts ready and available.
            </para>

            <section id='raw-mode'>
                <title>Raw Mode</title>

                <para>
                    Running Wic in raw mode allows you to specify all the
                    partitions through the <filename>wic</filename>
                    command line.
                    The primary use for raw mode is if you have built
                    your kernel outside of the Yocto Project
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                    In other words, you can point to arbitrary kernel,
                    root filesystem locations, and so forth.
                    Contrast this behavior with cooked mode where Wic
                    looks in the Build Directory (e.g.
                    <filename>tmp/deploy/images/</filename><replaceable>machine</replaceable>).
                </para>

                <para>
                    The general form of the
                    <filename>wic</filename> command in raw mode is:
                    <literallayout class='monospaced'>
     $ wic create <replaceable>wks_file</replaceable> <replaceable>options</replaceable> ...

       Where:

          <replaceable>wks_file</replaceable>:
             An OpenEmbedded kickstart file.  You can provide
             your own custom file or use a file from a set of
             existing files as described by further options.

          optional arguments:
            -h, --help            show this help message and exit
            -o <replaceable>OUTDIR</replaceable>, --outdir <replaceable>OUTDIR</replaceable>
                                  name of directory to create image in
            -e <replaceable>IMAGE_NAME</replaceable>, --image-name <replaceable>IMAGE_NAME</replaceable>
                                  name of the image to use the artifacts from e.g. core-
                                  image-sato
            -r <replaceable>ROOTFS_DIR</replaceable>, --rootfs-dir <replaceable>ROOTFS_DIR</replaceable>
                                  path to the /rootfs dir to use as the .wks rootfs
                                  source
            -b <replaceable>BOOTIMG_DIR</replaceable>, --bootimg-dir <replaceable>BOOTIMG_DIR</replaceable>
                                  path to the dir containing the boot artifacts (e.g.
                                  /EFI or /syslinux dirs) to use as the .wks bootimg
                                  source
            -k <replaceable>KERNEL_DIR</replaceable>, --kernel-dir <replaceable>KERNEL_DIR</replaceable>
                                  path to the dir containing the kernel to use in the
                                  .wks bootimg
            -n <replaceable>NATIVE_SYSROOT</replaceable>, --native-sysroot <replaceable>NATIVE_SYSROOT</replaceable>
                                  path to the native sysroot containing the tools to use
                                  to build the image
            -s, --skip-build-check
                                  skip the build check
            -f, --build-rootfs    build rootfs
            -c {gzip,bzip2,xz}, --compress-with {gzip,bzip2,xz}
                                  compress image with specified compressor
            -m, --bmap            generate .bmap
            --no-fstab-update     Do not change fstab file.
            -v <replaceable>VARS_DIR</replaceable>, --vars <replaceable>VARS_DIR</replaceable>
                                  directory with &lt;image&gt;.env files that store bitbake
                                  variables
            -D, --debug           output debug information
                    </literallayout>
                    <note>
                        You do not need root privileges to run
                        Wic.
                        In fact, you should not run as root when using the
                        utility.
                    </note>
                </para>
            </section>

            <section id='cooked-mode'>
                <title>Cooked Mode</title>

                <para>
                    Running Wic in cooked mode leverages off artifacts in
                    the Build Directory.
                    In other words, you do not have to specify kernel or
                    root filesystem locations as part of the command.
                    All you need to provide is a kickstart file and the
                    name of the image from which to use artifacts by using
                    the "-e" option.
                    Wic looks in the Build Directory (e.g.
                    <filename>tmp/deploy/images/</filename><replaceable>machine</replaceable>)
                    for artifacts.
                </para>

                <para>
                    The general form of the <filename>wic</filename>
                    command using Cooked Mode is as follows:
                    <literallayout class='monospaced'>
     $ wic create <replaceable>wks_file</replaceable> -e <replaceable>IMAGE_NAME</replaceable>

       Where:

          <replaceable>wks_file</replaceable>:
             An OpenEmbedded kickstart file.  You can provide
             your own custom file or use a file from a set of
             existing files provided with the Yocto Project
             release.

          required argument:
             -e <replaceable>IMAGE_NAME</replaceable>, --image-name <replaceable>IMAGE_NAME</replaceable>
                                  name of the image to use the artifacts from e.g. core-
                                  image-sato
                    </literallayout>
                </para>
            </section>
        </section>

        <section id='using-a-provided-kickstart-file'>
            <title>Using an Existing Kickstart File</title>

            <para>
                If you do not want to create your own kickstart file, you
                can use an existing file provided by the Wic installation.
                As shipped, kickstart files can be found in the
                Yocto Project
                <ulink url='&YOCTO_DOCS_OM_URL;#source-repositories'>Source Repositories</ulink>
                in the following two locations:
                <literallayout class='monospaced'>
     poky/meta-yocto-bsp/wic
     poky/scripts/lib/wic/canned-wks
                </literallayout>
                Use the following command to list the available kickstart
                files:
                <literallayout class='monospaced'>
     $ wic list images
       genericx86                    		Create an EFI disk image for genericx86*
       beaglebone-yocto              		Create SD card image for Beaglebone
       edgerouter                    		Create SD card image for Edgerouter
       qemux86-directdisk            		Create a qemu machine 'pcbios' direct disk image
       directdisk-gpt                		Create a 'pcbios' direct disk image
       mkefidisk                     		Create an EFI disk image
       directdisk                    		Create a 'pcbios' direct disk image
       systemd-bootdisk              		Create an EFI disk image with systemd-boot
       mkhybridiso                   		Create a hybrid ISO image
       sdimage-bootpart              		Create SD card image with a boot partition
       directdisk-multi-rootfs       		Create multi rootfs image using rootfs plugin
       directdisk-bootloader-config  		Create a 'pcbios' direct disk image with custom bootloader config
                </literallayout>
                When you use an existing file, you do not have to use the
                <filename>.wks</filename> extension.
                Here is an example in Raw Mode that uses the
                <filename>directdisk</filename> file:
                <literallayout class='monospaced'>
     $ wic create directdisk -r <replaceable>rootfs_dir</replaceable> -b <replaceable>bootimg_dir</replaceable> \
           -k <replaceable>kernel_dir</replaceable> -n <replaceable>native_sysroot</replaceable>
                </literallayout>
            </para>

            <para>
                Here are the actual partition language commands
                used in the <filename>genericx86.wks</filename> file to
                generate an image:
                <literallayout class='monospaced'>
     # short-description: Create an EFI disk image for genericx86*
     # long-description: Creates a partitioned EFI disk image for genericx86* machines
     part /boot --source bootimg-efi --sourceparams="loader=grub-efi" --ondisk sda --label msdos --active --align 1024
     part / --source rootfs --ondisk sda --fstype=ext4 --label platform --align 1024 --use-uuid
     part swap --ondisk sda --size 44 --label swap1 --fstype=swap

     bootloader --ptable gpt --timeout=5 --append="rootfstype=ext4 console=ttyS0,115200 console=tty0"
                </literallayout>
            </para>
        </section>

        <section id='wic-using-the-wic-plugin-interface'>
            <title>Using the Wic Plugin Interface</title>

            <para>
                You can extend and specialize Wic functionality by using
                Wic plugins.
                This section explains the Wic plugin interface.
                <note>
                    Wic plugins consist of "source" and "imager" plugins.
                    Imager plugins are beyond the scope of this section.
                </note>
            </para>

            <para>
                Source plugins provide a mechanism to customize partition
                content during the Wic image generation process.
                You can use source plugins to map values that you specify
                using <filename>--source</filename> commands in kickstart
                files (i.e. <filename>*.wks</filename>) to a plugin
                implementation used to populate a given partition.
                <note>
                    If you use plugins that have build-time dependencies
                    (e.g. native tools, bootloaders, and so forth)
                    when building a Wic image, you need to specify those
                    dependencies using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-WKS_FILE_DEPENDS'><filename>WKS_FILE_DEPENDS</filename></ulink>
                    variable.
                </note>
            </para>

            <para>
                Source plugins are subclasses defined in plugin files.
                As shipped, the Yocto Project provides several plugin
                files.
                You can see the source plugin files that ship with the
                Yocto Project
                <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/scripts/lib/wic/plugins/source'>here</ulink>.
                Each of these plugin files contains source plugins that
                are designed to populate a specific Wic image partition.
            </para>

            <para>
                Source plugins are subclasses of the
                <filename>SourcePlugin</filename> class, which is
                defined in the
                <filename>poky/scripts/lib/wic/pluginbase.py</filename>
                file.
                For example, the <filename>BootimgEFIPlugin</filename>
                source plugin found in the
                <filename>bootimg-efi.py</filename> file is a subclass of
                the <filename>SourcePlugin</filename> class, which is found
                in the <filename>pluginbase.py</filename> file.
            </para>

            <para>
                You can also implement source plugins in a layer outside
                of the Source Repositories (external layer).
                To do so, be sure that your plugin files are located in
                a directory whose path is
                <filename>scripts/lib/wic/plugins/source/</filename>
                within your external layer.
                When the plugin files are located there, the source
                plugins they contain are made available to Wic.
            </para>

            <para>
                When the Wic implementation needs to invoke a
                partition-specific implementation, it looks for the plugin
                with the same name as the <filename>--source</filename>
                parameter used in the kickstart file given to that
                partition.
                For example, if the partition is set up using the following
                command in a kickstart file:
                <literallayout class='monospaced'>
     part /boot --source bootimg-pcbios --ondisk sda --label boot --active --align 1024
                </literallayout>
                The methods defined as class members of the matching
                source plugin (i.e. <filename>bootimg-pcbios</filename>)
                in the <filename>bootimg-pcbios.py</filename> plugin file
                are used.
            </para>

            <para>
                To be more concrete, here is the corresponding plugin
                definition from the <filename>bootimg-pcbios.py</filename>
                file for the previous command along with an example
                method called by the Wic implementation when it needs to
                prepare a partition using an implementation-specific
                function:
                <literallayout class='monospaced'>
                  .
                  .
                  .
     class BootimgPcbiosPlugin(SourcePlugin):
         """
         Create MBR boot partition and install syslinux on it.
         """

         name = 'bootimg-pcbios'
                  .
                  .
                  .
         @classmethod
         def do_prepare_partition(cls, part, source_params, creator, cr_workdir,
                                  oe_builddir, bootimg_dir, kernel_dir,
                                  rootfs_dir, native_sysroot):
             """
             Called to do the actual content population for a partition i.e. it
             'prepares' the partition to be incorporated into the image.
             In this case, prepare content for legacy bios boot partition.
             """
                  .
                  .
                  .
                </literallayout>
                If a subclass (plugin) itself does not implement a
                particular function, Wic locates and uses the default
                version in the superclass.
                It is for this reason that all source plugins are derived
                from the <filename>SourcePlugin</filename> class.
            </para>

            <para>
                The <filename>SourcePlugin</filename> class defined in
                the <filename>pluginbase.py</filename> file defines
                a set of methods that source plugins can implement or
                override.
                Any plugins (subclass of
                <filename>SourcePlugin</filename>) that do not implement
                a particular method inherit the implementation of the
                method from the <filename>SourcePlugin</filename> class.
                For more information, see the
                <filename>SourcePlugin</filename> class in the
                <filename>pluginbase.py</filename> file for details:
            </para>

            <para>
                The following list describes the methods implemented in the
                <filename>SourcePlugin</filename> class:
                <itemizedlist>
                    <listitem><para>
                        <emphasis><filename>do_prepare_partition()</filename>:</emphasis>
                        Called to populate a partition with actual content.
                        In other words, the method prepares the final
                        partition image that is incorporated into the
                        disk image.
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>do_configure_partition()</filename>:</emphasis>
                        Called before
                        <filename>do_prepare_partition()</filename> to
                        create custom configuration files for a partition
                        (e.g. syslinux or grub configuration files).
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>do_install_disk()</filename>:</emphasis>
                        Called after all partitions have been prepared and
                        assembled into a disk image.
                        This method provides a hook to allow finalization
                        of a disk image (e.g. writing an MBR).
                        </para></listitem>
                    <listitem><para>
                        <emphasis><filename>do_stage_partition()</filename>:</emphasis>
                        Special content-staging hook called before
                        <filename>do_prepare_partition()</filename>.
                        This method is normally empty.</para>

                        <para>Typically, a partition just uses the passed-in
                        parameters (e.g. the unmodified value of
                        <filename>bootimg_dir</filename>).
                        However, in some cases, things might need to be
                        more tailored.
                        As an example, certain files might additionally
                        need to be taken from
                        <filename>bootimg_dir + /boot</filename>.
                        This hook allows those files to be staged in a
                        customized fashion.
                        <note>
                            <filename>get_bitbake_var()</filename>
                            allows you to access non-standard variables
                            that you might want to use for this
                            behavior.
                        </note>
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                You can extend the source plugin mechanism.
                To add more hooks, create more source plugin methods
                within <filename>SourcePlugin</filename> and the
                corresponding derived subclasses.
                The code that calls the plugin methods uses the
                <filename>plugin.get_source_plugin_methods()</filename>
                function to find the method or methods needed by the call.
                Retrieval of those methods is accomplished by filling up
                a dict with keys that contain the method names of interest.
                On success, these will be filled in with the actual
                methods.
                See the Wic implementation for examples and details.
            </para>
        </section>

        <section id='wic-usage-examples'>
            <title>Examples</title>

            <para>
                This section provides several examples that show how to use
                the Wic utility.
                All the examples assume the list of requirements in the
                "<link linkend='wic-requirements'>Requirements</link>"
                section have been met.
                The examples assume the previously generated image is
                <filename>core-image-minimal</filename>.
            </para>

            <section id='generate-an-image-using-a-provided-kickstart-file'>
                <title>Generate an Image using an Existing Kickstart File</title>

                <para>
                    This example runs in Cooked Mode and uses the
                    <filename>mkefidisk</filename> kickstart file:
                    <literallayout class='monospaced'>
     $ wic create mkefidisk -e core-image-minimal
     INFO: Building wic-tools...
               .
               .
               .
     INFO: The new image(s) can be found here:
       ./mkefidisk-201804191017-sda.direct

     The following build artifacts were used to create the image(s):
       ROOTFS_DIR:                   /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
       BOOTIMG_DIR:                  /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
       KERNEL_DIR:                   /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86
       NATIVE_SYSROOT:               /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

     INFO: The image(s) were created using OE kickstart file:
       /home/stephano/build/master/openembedded-core/scripts/lib/wic/canned-wks/mkefidisk.wks
                    </literallayout>
                    The previous example shows the easiest way to create
                    an image by running in cooked mode and supplying
                    a kickstart file and the "-e" option to point to the
                    existing build artifacts.
                    Your <filename>local.conf</filename> file needs to have
                    the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                    variable set to the machine you are using, which is
                    "qemux86" in this example.
                </para>

                <para>
                    Once the image builds, the output provides image
                    location, artifact use, and kickstart file information.
                    <note>
                        You should always verify the details provided in the
                        output to make sure that the image was indeed
                        created exactly as expected.
                    </note>
                </para>

                <para>
                    Continuing with the example, you can now write the
                    image from the Build Directory onto a USB stick, or
                    whatever media for which you built your image, and boot
                    from the media.
                    You can write the image by using
                    <filename>bmaptool</filename> or
                    <filename>dd</filename>:
                    <literallayout class='monospaced'>
     $ oe-run-native bmaptool copy mkefidisk-201804191017-sda.direct /dev/sd<replaceable>X</replaceable>
                    </literallayout>
                    or
                    <literallayout class='monospaced'>
     $ sudo dd if=mkefidisk-201804191017-sda.direct of=/dev/sd<replaceable>X</replaceable>
                    </literallayout>
                    <note>
                        For more information on how to use the
                        <filename>bmaptool</filename> to flash a device
                        with an image, see the
                        "<link linkend='flashing-images-using-bmaptool'>Flashing Images Using <filename>bmaptool</filename></link>"
                        section.
                    </note>
                </para>
            </section>

            <section id='using-a-modified-kickstart-file'>
                <title>Using a Modified Kickstart File</title>

                <para>
                    Because partitioned image creation is driven by the
                    kickstart file, it is easy to affect image creation by
                    changing the parameters in the file.
                    This next example demonstrates that through modification
                    of the <filename>directdisk-gpt</filename> kickstart
                    file.
                </para>

                <para>
                    As mentioned earlier, you can use the command
                    <filename>wic list images</filename> to show the list
                    of existing kickstart files.
                    The directory in which the
                    <filename>directdisk-gpt.wks</filename> file resides is
                    <filename>scripts/lib/image/canned-wks/</filename>,
                    which is located in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                    (e.g. <filename>poky</filename>).
                    Because available files reside in this directory,
                    you can create and add your own custom files to the
                    directory.
                    Subsequent use of the
                    <filename>wic list images</filename> command would then
                    include your kickstart files.
                </para>

                <para>
                    In this example, the existing
                    <filename>directdisk-gpt</filename> file already does
                    most of what is needed.
                    However, for the hardware in this example, the image
                    will need to boot from <filename>sdb</filename> instead
                    of <filename>sda</filename>, which is what the
                    <filename>directdisk-gpt</filename> kickstart file
                    uses.
                </para>

                <para>
                    The example begins by making a copy of the
                    <filename>directdisk-gpt.wks</filename> file in the
                    <filename>scripts/lib/image/canned-wks</filename>
                    directory and then by changing the lines that specify
                    the target disk from which to boot.
                    <literallayout class='monospaced'>
     $ cp /home/stephano/poky/scripts/lib/wic/canned-wks/directdisk-gpt.wks \
          /home/stephano/poky/scripts/lib/wic/canned-wks/directdisksdb-gpt.wks
                    </literallayout>
                    Next, the example modifies the
                    <filename>directdisksdb-gpt.wks</filename> file and
                    changes all instances of
                    "<filename>--ondisk sda</filename>" to
                    "<filename>--ondisk sdb</filename>".
                    The example changes the following two lines and leaves
                    the remaining lines untouched:
                    <literallayout class='monospaced'>
     part /boot --source bootimg-pcbios --ondisk sdb --label boot --active --align 1024
     part / --source rootfs --ondisk sdb --fstype=ext4 --label platform --align 1024 --use-uuid
                    </literallayout>
                    Once the lines are changed, the example generates the
                    <filename>directdisksdb-gpt</filename> image.
                    The command points the process at the
                    <filename>core-image-minimal</filename> artifacts for
                    the Next Unit of Computing (nuc)
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                    the <filename>local.conf</filename>.
                    <literallayout class='monospaced'>
     $ wic create directdisksdb-gpt -e core-image-minimal
     INFO: Building wic-tools...
                .
                .
                .
     Initialising tasks: 100% |#######################################| Time: 0:00:01
     NOTE: Executing SetScene Tasks
     NOTE: Executing RunQueue Tasks
     NOTE: Tasks Summary: Attempted 1161 tasks of which 1157 didn't need to be rerun and all succeeded.
     INFO: Creating image(s)...

     INFO: The new image(s) can be found here:
       ./directdisksdb-gpt-201710090938-sdb.direct

     The following build artifacts were used to create the image(s):
       ROOTFS_DIR:                   /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
       BOOTIMG_DIR:                  /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
       KERNEL_DIR:                   /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86
       NATIVE_SYSROOT:               /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

     INFO: The image(s) were created using OE kickstart file:
       /home/stephano/poky/scripts/lib/wic/canned-wks/directdisksdb-gpt.wks
                    </literallayout>
                    Continuing with the example, you can now directly
                    <filename>dd</filename> the image to a USB stick, or
                    whatever media for which you built your image,
                    and boot the resulting media:
                    <literallayout class='monospaced'>
     $ sudo dd if=directdisksdb-gpt-201710090938-sdb.direct of=/dev/sdb
     140966+0 records in
     140966+0 records out
     72174592 bytes (72 MB, 69 MiB) copied, 78.0282 s, 925 kB/s
     $ sudo eject /dev/sdb
                    </literallayout>
                </para>
            </section>

            <section id='using-a-modified-kickstart-file-and-running-in-raw-mode'>
                <title>Using a Modified Kickstart File and Running in Raw Mode</title>

                <para>
                    This next example manually specifies each build artifact
                    (runs in Raw Mode) and uses a modified kickstart file.
                    The example also uses the <filename>-o</filename> option
                    to cause Wic to create the output
                    somewhere other than the default output directory,
                    which is the current directory:
                    <literallayout class='monospaced'>
     $ wic create /home/stephano/my_yocto/test.wks -o /home/stephano/testwic \
          --rootfs-dir /home/stephano/build/master/build/tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/rootfs \
          --bootimg-dir /home/stephano/build/master/build/tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share \
          --kernel-dir /home/stephano/build/master/build/tmp/deploy/images/qemux86 \
          --native-sysroot /home/stephano/build/master/build/tmp/work/i586-poky-linux/wic-tools/1.0-r0/recipe-sysroot-native

     INFO: Creating image(s)...

     INFO: The new image(s) can be found here:
       /home/stephano/testwic/test-201710091445-sdb.direct

     The following build artifacts were used to create the image(s):
       ROOTFS_DIR:                   /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
       BOOTIMG_DIR:                  /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
       KERNEL_DIR:                   /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86
       NATIVE_SYSROOT:               /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

     INFO: The image(s) were created using OE kickstart file:
       /home/stephano/my_yocto/test.wks
                    </literallayout>
                    For this example,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                    did not have to be specified in the
                    <filename>local.conf</filename> file since the
                    artifact is manually specified.
                </para>
            </section>

            <section id='using-wic-to-manipulate-an-image'>
                <title>Using Wic to Manipulate an Image</title>

                <para>
                    Wic image manipulation allows you to shorten turnaround
                    time during image development.
                    For example, you can use Wic to delete the kernel partition
                    of a Wic image and then insert a newly built kernel.
                    This saves you time from having to rebuild the entire image
                    each time you modify the kernel.
                    <note>
                        In order to use Wic to manipulate a Wic image as in
                        this example, your development machine must have the
                        <filename>mtools</filename> package installed.
                    </note>
                </para>

                <para>
                    The following example examines the contents of the Wic
                    image, deletes the existing kernel, and then inserts a
                    new kernel:
                    <orderedlist>
                        <listitem><para>
                            <emphasis>List the Partitions:</emphasis>
                            Use the <filename>wic ls</filename> command to list
                            all the partitions in the Wic image:
                            <literallayout class='monospaced'>
     $ wic ls tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic
     Num     Start        End          Size      Fstype
      1       1048576     25041919     23993344  fat16
      2      25165824     72157183     46991360  ext4
                            </literallayout>
                            The previous output shows two partitions in the
                            <filename>core-image-minimal-qemux86.wic</filename>
                            image.
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Examine a Particular Partition:</emphasis>
                            Use the <filename>wic ls</filename> command again
                            but in a different form to examine a particular
                            partition.
                            <note>
                                You can get command usage on any Wic command
                                using the following form:
                                <literallayout class='monospaced'>
     $ wic help <replaceable>command</replaceable>
                                </literallayout>
                                For example, the following command shows you
                                the various ways to use the
                                <filename>wic ls</filename> command:
                                <literallayout class='monospaced'>
     $ wic help ls
                                </literallayout>
                            </note>
                            The following command shows what is in Partition
                            one:
                            <literallayout class='monospaced'>
     $ wic ls tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1
     Volume in drive : is boot
      Volume Serial Number is E894-1809
     Directory for ::/

     libcom32 c32    186500 2017-10-09  16:06
     libutil  c32     24148 2017-10-09  16:06
     syslinux cfg       220 2017-10-09  16:06
     vesamenu c32     27104 2017-10-09  16:06
     vmlinuz        6904608 2017-10-09  16:06
             5 files           7 142 580 bytes
                              16 582 656 bytes free
                            </literallayout>
                            The previous output shows five files, with the
                            <filename>vmlinuz</filename> being the kernel.
                            <note>
                                If you see the following error, you need to
                                update or create a
                                <filename>~/.mtoolsrc</filename> file and
                                be sure to have the line “mtools_skip_check=1“
                                in the file.
                                Then, run the Wic command again:
                                <literallayout class='monospaced'>
     ERROR: _exec_cmd: /usr/bin/mdir -i /tmp/wic-parttfokuwra ::/ returned '1' instead of 0
      output: Total number of sectors (47824) not a multiple of sectors per track (32)!
      Add mtools_skip_check=1 to your .mtoolsrc file to skip this test
                                </literallayout>
                             </note>
                             </para></listitem>
                         <listitem><para>
                             <emphasis>Remove the Old Kernel:</emphasis>
                             Use the <filename>wic rm</filename> command to
                             remove the <filename>vmlinuz</filename> file
                             (kernel):
                             <literallayout class='monospaced'>
     $ wic rm tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1/vmlinuz
                             </literallayout>
                             </para></listitem>
                         <listitem><para>
                             <emphasis>Add In the New Kernel:</emphasis>
                             Use the <filename>wic cp</filename> command to
                             add the updated kernel to the Wic image.
                             Depending on how you built your kernel, it could
                             be in different places.
                             If you used <filename>devtool</filename> and
                             an SDK to build your kernel, it resides in the
                             <filename>tmp/work</filename> directory of the
                             extensible SDK.
                             If you used <filename>make</filename> to build the
                             kernel, the kernel will be in the
                             <filename>workspace/sources</filename> area.
                             </para>

                             <para>The following example assumes
                             <filename>devtool</filename> was used to build
                             the kernel:
                             <literallayout class='monospaced'>
     cp ~/poky_sdk/tmp/work/qemux86-poky-linux/linux-yocto/4.12.12+git999-r0/linux-yocto-4.12.12+git999/arch/x86/boot/bzImage \
        ~/poky/build/tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1/vmlinuz
                             </literallayout>
                             Once the new kernel is added back into the image,
                             you can use the <filename>dd</filename>
                             command or
                             <link linkend='flashing-images-using-bmaptool'><filename>bmaptool</filename></link>
                             to flash your wic image onto an SD card
                             or USB stick and test your target.
                             <note>
                                 Using <filename>bmaptool</filename> is
                                 generally 10 to 20 times faster than using
                                 <filename>dd</filename>.
                             </note>
                             </para></listitem>
                     </orderedlist>
                 </para>
             </section>
        </section>
    </section>

    <section id='flashing-images-using-bmaptool'>
        <title>Flashing Images Using <filename>bmaptool</filename></title>

        <para>
            A fast and easy way to flash an image to a bootable device
            is to use Bmaptool, which is integrated into the OpenEmbedded
            build system.
            Bmaptool is a generic tool that creates a file's block map (bmap)
            and then uses that map to copy the file.
            As compared to traditional tools such as dd or cp, Bmaptool
            can copy (or flash) large files like raw system image files
            much faster.
            <note><title>Notes</title>
                <itemizedlist>
                    <listitem><para>
                        If you are using Ubuntu or Debian distributions, you
                        can install the <filename>bmap-tools</filename> package
                        using the following command and then use the tool
                        without specifying <filename>PATH</filename> even from
                        the root account:
                        <literallayout class='monospaced'>
     $ sudo apt-get install bmap-tools
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        If you are unable to install the
                        <filename>bmap-tools</filename> package, you will
                        need to build Bmaptool before using it.
                        Use the following command:
                        <literallayout class='monospaced'>
     $ bitbake bmap-tools-native
                        </literallayout>
                        </para></listitem>
                </itemizedlist>
            </note>
        </para>

        <para>
            Following, is an example that shows how to flash a Wic image.
            Realize that while this example uses a Wic image, you can use
            Bmaptool to flash any type of image.
            Use these steps to flash an image using Bmaptool:
            <orderedlist>
                <listitem><para>
                    <emphasis>Update your <filename>local.conf</filename> File:</emphasis>
                    You need to have the following set in your
                    <filename>local.conf</filename> file before building
                    your image:
                    <literallayout class='monospaced'>
     IMAGE_FSTYPES += "wic wic.bmap"
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Get Your Image:</emphasis>
                    Either have your image ready (pre-built with the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></ulink>
                    setting previously mentioned) or take the step to build
                    the image:
                    <literallayout class='monospaced'>
     $ bitbake <replaceable>image</replaceable>
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Flash the Device:</emphasis>
                    Flash the device with the image by using Bmaptool
                    depending on your particular setup.
                    The following commands assume the image resides in the
                    Build Directory's <filename>deploy/images/</filename>
                    area:
                    <itemizedlist>
                        <listitem><para>
                            If you have write access to the media, use this
                            command form:
                            <literallayout class='monospaced'>
     $ oe-run-native bmap-tools-native bmaptool copy <replaceable>build-directory</replaceable>/tmp/deploy/images/<replaceable>machine</replaceable>/<replaceable>image</replaceable>.wic /dev/sd<replaceable>X</replaceable>
                            </literallayout>
                            </para></listitem>
                        <listitem><para>
                            If you do not have write access to the media, set
                            your permissions first and then use the same
                            command form:
                            <literallayout class='monospaced'>
     $ sudo chmod 666 /dev/sd<replaceable>X</replaceable>
     $ oe-run-native bmap-tools-native bmaptool copy <replaceable>build-directory</replaceable>/tmp/deploy/images/<replaceable>machine</replaceable>/<replaceable>image</replaceable>.wic /dev/sd<replaceable>X</replaceable>
                            </literallayout>
                            </para></listitem>
                    </itemizedlist>
                    </para></listitem>
            </orderedlist>
        </para>

        <para>
            For help on the <filename>bmaptool</filename> command, use the
            following command:
            <literallayout class='monospaced'>
     $ bmaptool --help
            </literallayout>
        </para>
    </section>

    <section id='making-images-more-secure'>
        <title>Making Images More Secure</title>

        <para>
            Security is of increasing concern for embedded devices.
            Consider the issues and problems discussed in just this
            sampling of work found across the Internet:
            <itemizedlist>
                <listitem><para><emphasis>
                    "<ulink url='https://www.schneier.com/blog/archives/2014/01/security_risks_9.html'>Security Risks of Embedded Systems</ulink>"</emphasis>
                    by Bruce Schneier
                    </para></listitem>
                <listitem><para><emphasis>
                    "<ulink url='http://census2012.sourceforge.net/paper.html'>Internet Census 2012</ulink>"</emphasis>
                    by Carna Botnet</para></listitem>
                <listitem><para><emphasis>
                    "<ulink url='http://elinux.org/images/6/6f/Security-issues.pdf'>Security Issues for Embedded Devices</ulink>"</emphasis>
                    by Jake Edge
                    </para></listitem>
            </itemizedlist>
        </para>

        <para>
            When securing your image is of concern, there are steps, tools,
            and variables that you can consider to help you reach the
            security goals you need for your particular device.
            Not all situations are identical when it comes to making an
            image secure.
            Consequently, this section provides some guidance and suggestions
            for consideration when you want to make your image more secure.
            <note>
                Because the security requirements and risks are
                different for every type of device, this section cannot
                provide a complete reference on securing your custom OS.
                It is strongly recommended that you also consult other sources
                of information on embedded Linux system hardening and on
                security.
            </note>
        </para>

        <section id='general-considerations'>
            <title>General Considerations</title>

            <para>
                General considerations exist that help you create more
                secure images.
                You should consider the following suggestions to help
                make your device more secure:
                <itemizedlist>
                    <listitem><para>
                        Scan additional code you are adding to the system
                        (e.g. application code) by using static analysis
                        tools.
                        Look for buffer overflows and other potential
                        security problems.
                    </para></listitem>
                    <listitem><para>
                        Pay particular attention to the security for
                        any web-based administration interface.
                        </para>
                        <para>Web interfaces typically need to perform
                        administrative functions and tend to need to run with
                        elevated privileges.
                        Thus, the consequences resulting from the interface's
                        security becoming compromised can be serious.
                        Look for common web vulnerabilities such as
                        cross-site-scripting (XSS), unvalidated inputs,
                        and so forth.</para>
                        <para>As with system passwords, the default credentials
                        for accessing a web-based interface should not be the
                        same across all devices.
                        This is particularly true if the interface is enabled
                        by default as it can be assumed that many end-users
                        will not change the credentials.
                    </para></listitem>
                    <listitem><para>
                        Ensure you can update the software on the device to
                        mitigate vulnerabilities discovered in the future.
                        This consideration especially applies when your
                        device is network-enabled.
                    </para></listitem>
                    <listitem><para>
                        Ensure you remove or disable debugging functionality
                        before producing the final image.
                        For information on how to do this, see the
                        "<link linkend='considerations-specific-to-the-openembedded-build-system'>Considerations Specific to the OpenEmbedded Build System</link>"
                        section.
                        </para></listitem>
                    <listitem><para>
                        Ensure you have no network services listening that
                        are not needed.
                    </para></listitem>
                    <listitem><para>
                        Remove any software from the image that is not needed.
                    </para></listitem>
                    <listitem><para>
                        Enable hardware support for secure boot functionality
                        when your device supports this functionality.
                    </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='security-flags'>
            <title>Security Flags</title>

            <para>
                The Yocto Project has security flags that you can enable that
                help make your build output more secure.
                The security flags are in the
                <filename>meta/conf/distro/include/security_flags.inc</filename>
                file in your
                <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                (e.g. <filename>poky</filename>).
                <note>
                    Depending on the recipe, certain security flags are enabled
                    and disabled by default.
                </note>
            </para>

            <para>
<!--
                The GCC/LD flags in <filename>security_flags.inc</filename>
                enable more secure code generation.
                By including the <filename>security_flags.inc</filename>
                file, you enable flags to the compiler and linker that cause
                them to generate more secure code.
                <note>
                    The GCC/LD flags are enabled by default in the
                    <filename>poky-lsb</filename> distribution.
                </note>
-->
                Use the following line in your
                <filename>local.conf</filename> file or in your custom
                distribution configuration file to enable the security
                compiler and linker flags for your build:
                <literallayout class='monospaced'>
     require conf/distro/include/security_flags.inc
                </literallayout>
            </para>
        </section>

        <section id='considerations-specific-to-the-openembedded-build-system'>
            <title>Considerations Specific to the OpenEmbedded Build System</title>

            <para>
                You can take some steps that are specific to the
                OpenEmbedded build system to make your images more secure:
                <itemizedlist>
                    <listitem><para>
                        Ensure "debug-tweaks" is not one of your selected
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>.
                        When creating a new project, the default is to provide you
                        with an initial <filename>local.conf</filename> file that
                        enables this feature using the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink> variable with the line:
                <literallayout class='monospaced'>
     EXTRA_IMAGE_FEATURES = "debug-tweaks"
                </literallayout>
                        To disable that feature, simply comment out that line in your
                        <filename>local.conf</filename> file, or
                        make sure <filename>IMAGE_FEATURES</filename> does not contain
                        "debug-tweaks" before producing your final image.
                        Among other things, leaving this in place sets the
                        root password as blank, which makes logging in for
                        debugging or inspection easy during
                        development but also means anyone can easily log in
                        during production.
                        </para></listitem>
                    <listitem><para>
                        It is possible to set a root password for the image
                        and also to set passwords for any extra users you might
                        add (e.g. administrative or service type users).
                        When you set up passwords for multiple images or
                        users, you should not duplicate passwords.
                        </para>
                        <para>
                        To set up passwords, use the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers</filename></ulink>
                        class, which is the preferred method.
                        For an example on how to set up both root and user
                        passwords, see the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers.bbclass</filename></ulink>"
                        section.
                        <note>
                            When adding extra user accounts or setting a
                            root password, be cautious about setting the
                            same password on every device.
                            If you do this, and the password you have set
                            is exposed, then every device is now potentially
                            compromised.
                            If you need this access but want to ensure
                            security, consider setting a different,
                            random password for each device.
                            Typically, you do this as a separate step after
                            you deploy the image onto the device.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        Consider enabling a Mandatory Access Control (MAC)
                        framework such as SMACK or SELinux and tuning it
                        appropriately for your device's usage.
                        You can find more information in the
                        <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/meta-selinux/'><filename>meta-selinux</filename></ulink>
                        layer.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
            </para>
        </section>

        <section id='tools-for-hardening-your-image'>
            <title>Tools for Hardening Your Image</title>

            <para>
                The Yocto Project provides tools for making your image
                more secure.
                You can find these tools in the
                <filename>meta-security</filename> layer of the
                <ulink url='&YOCTO_GIT_URL;'>Yocto Project Source Repositories</ulink>.
            </para>
        </section>
    </section>

    <section id='creating-your-own-distribution'>
        <title>Creating Your Own Distribution</title>

        <para>
            When you build an image using the Yocto Project and
            do not alter any distribution
            <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink>,
            you are creating a Poky distribution.
            If you wish to gain more control over package alternative
            selections, compile-time options, and other low-level
            configurations, you can create your own distribution.
        </para>

        <para>
            To create your own distribution, the basic steps consist of
            creating your own distribution layer, creating your own
            distribution configuration file, and then adding any needed
            code and Metadata to the layer.
            The following steps provide some more detail:
            <itemizedlist>
                <listitem><para><emphasis>Create a layer for your new distro:</emphasis>
                    Create your distribution layer so that you can keep your
                    Metadata and code for the distribution separate.
                    It is strongly recommended that you create and use your own
                    layer for configuration and code.
                    Using your own layer as compared to just placing
                    configurations in a <filename>local.conf</filename>
                    configuration file makes it easier to reproduce the same
                    build configuration when using multiple build machines.
                    See the
                    "<link linkend='creating-a-general-layer-using-the-bitbake-layers-script'>Creating a General Layer Using the <filename>bitbake-layers</filename> Script</link>"
                    section for information on how to quickly set up a layer.
                    </para></listitem>
                <listitem><para><emphasis>Create the distribution configuration file:</emphasis>
                    The distribution configuration file needs to be created in
                    the <filename>conf/distro</filename> directory of your
                    layer.
                    You need to name it using your distribution name
                    (e.g. <filename>mydistro.conf</filename>).
                    <note>
                        The
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                        variable in your
                        <filename>local.conf</filename> file determines the
                        name of your distribution.
                    </note></para>
                    <para>You can split out parts of your configuration file
                    into include files and then "require" them from within
                    your distribution configuration file.
                    Be sure to place the include files in the
                    <filename>conf/distro/include</filename> directory of
                    your layer.
                    A common example usage of include files would be to
                    separate out the selection of desired version and revisions
                    for individual recipes.
</para>
                    <para>Your configuration file needs to set the following
                    required variables:
                    <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_NAME'><filename>DISTRO_NAME</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_VERSION'><filename>DISTRO_VERSION</filename></ulink>
                    </literallayout>
                    These following variables are optional and you typically
                    set them from the distribution configuration file:
                    <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RDEPENDS'><filename>DISTRO_EXTRA_RDEPENDS</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RRECOMMENDS'><filename>DISTRO_EXTRA_RRECOMMENDS</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-TCLIBC'><filename>TCLIBC</filename></ulink>
                    </literallayout>
                    <tip>
                        If you want to base your distribution configuration file
                        on the very basic configuration from OE-Core, you
                        can use
                        <filename>conf/distro/defaultsetup.conf</filename> as
                        a reference and just include variables that differ
                        as compared to <filename>defaultsetup.conf</filename>.
                        Alternatively, you can create a distribution
                        configuration file from scratch using the
                        <filename>defaultsetup.conf</filename> file
                        or configuration files from other distributions
                        such as Poky or Angstrom as references.
                    </tip></para></listitem>
                <listitem><para><emphasis>Provide miscellaneous variables:</emphasis>
                    Be sure to define any other variables for which you want to
                    create a default or enforce as part of the distribution
                    configuration.
                    You can include nearly any variable from the
                    <filename>local.conf</filename> file.
                    The variables you use are not limited to the list in the
                    previous bulleted item.</para></listitem>
                <listitem><para><emphasis>Point to Your distribution configuration file:</emphasis>
                    In your <filename>local.conf</filename> file in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>,
                    set your
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                    variable to point to your distribution's configuration file.
                    For example, if your distribution's configuration file is
                    named <filename>mydistro.conf</filename>, then you point
                    to it as follows:
                    <literallayout class='monospaced'>
     DISTRO = "mydistro"
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Add more to the layer if necessary:</emphasis>
                    Use your layer to hold other information needed for the
                    distribution:
                    <itemizedlist>
                        <listitem><para>Add recipes for installing
                            distro-specific configuration files that are not
                            already installed by another recipe.
                            If you have distro-specific configuration files
                            that are included by an existing recipe, you should
                            add an append file (<filename>.bbappend</filename>)
                            for those.
                            For general information and recommendations
                            on how to add recipes to your layer, see the
                            "<link linkend='creating-your-own-layer'>Creating Your Own Layer</link>"
                            and
                            "<link linkend='best-practices-to-follow-when-creating-layers'>Following Best Practices When Creating Layers</link>"
                            sections.</para></listitem>
                        <listitem><para>Add any image recipes that are specific
                            to your distribution.</para></listitem>
                        <listitem><para>Add a <filename>psplash</filename>
                            append file for a branded splash screen.
                            For information on append files, see the
                            "<link linkend='using-bbappend-files'>Using .bbappend Files in Your Layer</link>"
                            section.</para></listitem>
                        <listitem><para>Add any other append files to make
                            custom changes that are specific to individual
                            recipes.</para></listitem>
                    </itemizedlist></para></listitem>
            </itemizedlist>
        </para>
    </section>

    <section id='creating-a-custom-template-configuration-directory'>
        <title>Creating a Custom Template Configuration Directory</title>

        <para>
            If you are producing your own customized version
            of the build system for use by other users, you might
            want to customize the message shown by the setup script or
            you might want to change the template configuration files (i.e.
            <filename>local.conf</filename> and
            <filename>bblayers.conf</filename>) that are created in
            a new build directory.
        </para>

        <para>
            The OpenEmbedded build system uses the environment variable
            <filename>TEMPLATECONF</filename> to locate the directory
            from which it gathers configuration information that ultimately
            ends up in the
            <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
            <filename>conf</filename> directory.
            By default, <filename>TEMPLATECONF</filename> is set as
            follows in the <filename>poky</filename> repository:
            <literallayout class='monospaced'>
     TEMPLATECONF=${TEMPLATECONF:-meta-poky/conf}
            </literallayout>
            This is the directory used by the build system to find templates
            from which to build some key configuration files.
            If you look at this directory, you will see the
            <filename>bblayers.conf.sample</filename>,
            <filename>local.conf.sample</filename>, and
            <filename>conf-notes.txt</filename> files.
            The build system uses these files to form the respective
            <filename>bblayers.conf</filename> file,
            <filename>local.conf</filename> file, and display the list of
            BitBake targets when running the setup script.
        </para>

        <para>
            To override these default configuration files with
            configurations you want used within every new
            Build Directory, simply set the
            <filename>TEMPLATECONF</filename> variable to your directory.
            The <filename>TEMPLATECONF</filename> variable is set in the
            <filename>.templateconf</filename> file, which is in the
            top-level
            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
            folder (e.g. <filename>poky</filename>).
            Edit the <filename>.templateconf</filename> so that it can locate
            your directory.
        </para>

        <para>
            Best practices dictate that you should keep your
            template configuration directory in your custom distribution layer.
            For example, suppose you have a layer named
            <filename>meta-mylayer</filename> located in your home directory
            and you want your template configuration directory named
            <filename>myconf</filename>.
            Changing the <filename>.templateconf</filename> as follows
            causes the OpenEmbedded build system to look in your directory
            and base its configuration files on the
            <filename>*.sample</filename> configuration files it finds.
            The final configuration files (i.e.
            <filename>local.conf</filename> and
            <filename>bblayers.conf</filename> ultimately still end up in
            your Build Directory, but they are based on your
            <filename>*.sample</filename> files.
            <literallayout class='monospaced'>
     TEMPLATECONF=${TEMPLATECONF:-meta-mylayer/myconf}
            </literallayout>
        </para>

        <para>
            Aside from the <filename>*.sample</filename> configuration files,
            the <filename>conf-notes.txt</filename> also resides in the
            default <filename>meta-poky/conf</filename> directory.
            The script that sets up the build environment
            (i.e.
            <ulink url="&YOCTO_DOCS_REF_URL;#structure-core-script"><filename>&OE_INIT_FILE;</filename></ulink>)
            uses this file to display BitBake targets as part of the script
            output.
            Customizing this <filename>conf-notes.txt</filename> file is a
            good way to make sure your list of custom targets appears
            as part of the script's output.
        </para>

        <para>
            Here is the default list of targets displayed as a result of
            running either of the setup scripts:
            <literallayout class='monospaced'>
     You can now run 'bitbake &lt;target&gt;'

     Common targets are:
         core-image-minimal
         core-image-sato
         meta-toolchain
         meta-ide-support
            </literallayout>
        </para>

        <para>
            Changing the listed common targets is as easy as editing your
            version of <filename>conf-notes.txt</filename> in your
            custom template configuration directory and making sure you
            have <filename>TEMPLATECONF</filename> set to your directory.
        </para>
    </section>

    <section id='dev-saving-memory-during-a-build'>
        <title>Conserving Disk Space During Builds</title>

        <para>
            To help conserve disk space during builds, you can add the
            following statement to your project's
            <filename>local.conf</filename> configuration file found in the
            <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
            <literallayout class='monospaced'>
     INHERIT += "rm_work"
            </literallayout>
            Adding this statement deletes the work directory used for building
            a recipe once the recipe is built.
            For more information on "rm_work", see the
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-rm-work'><filename>rm_work</filename></ulink>
            class in the Yocto Project Reference Manual.
        </para>
    </section>

    <section id='working-with-packages'>
        <title>Working with Packages</title>

        <para>
            This section describes a few tasks that involve packages:
            <itemizedlist>
                <listitem><para>
                    <link linkend='excluding-packages-from-an-image'>Excluding packages from an image</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='incrementing-a-binary-package-version'>Incrementing a binary package version</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='handling-optional-module-packaging'>Handling optional module packaging</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='using-runtime-package-management'>Using runtime package management</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='generating-and-using-signed-packages'>Generating and using signed packages</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='testing-packages-with-ptest'>Setting up and running package test (ptest)</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='creating-node-package-manager-npm-packages'>Creating node package manager (NPM) packages</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='adding-custom-metadata-to-packages'>Adding custom metadata to packages</link>
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id='excluding-packages-from-an-image'>
            <title>Excluding Packages from an Image</title>

            <para>
                You might find it necessary to prevent specific packages
                from being installed into an image.
                If so, you can use several variables to direct the build
                system to essentially ignore installing recommended packages
                or to not install a package at all.
            </para>

            <para>
                The following list introduces variables you can use to
                prevent packages from being installed into your image.
                Each of these variables only works with IPK and RPM
                package types.
                Support for Debian packages does not exist.
                Also, you can use these variables from your
                <filename>local.conf</filename> file or attach them to a
                specific image recipe by using a recipe name override.
                For more detail on the variables, see the descriptions in the
                Yocto Project Reference Manual's glossary chapter.
                <itemizedlist>
                    <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-BAD_RECOMMENDATIONS'><filename>BAD_RECOMMENDATIONS</filename></ulink>:
                        Use this variable to specify "recommended-only"
                        packages that you do not want installed.
                        </para></listitem>
                    <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-NO_RECOMMENDATIONS'><filename>NO_RECOMMENDATIONS</filename></ulink>:
                        Use this variable to prevent all "recommended-only"
                        packages from being installed.
                        </para></listitem>
                    <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_EXCLUDE'><filename>PACKAGE_EXCLUDE</filename></ulink>:
                        Use this variable to prevent specific packages from
                        being installed regardless of whether they are
                        "recommended-only" or not.
                        You need to realize that the build process could
                        fail with an error when you
                        prevent the installation of a package whose presence
                        is required by an installed package.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='incrementing-a-binary-package-version'>
            <title>Incrementing a Package Version</title>

            <para>
                This section provides some background on how binary package
                versioning is accomplished and presents some of the services,
                variables, and terminology involved.
            </para>

            <para>
                In order to understand binary package versioning, you need
                to consider the following:
                <itemizedlist>
                    <listitem><para>
                        Binary Package:  The binary package that is eventually
                        built and installed into an image.
                        </para></listitem>
                    <listitem><para>
                        Binary Package Version:  The binary package version
                        is composed of two components - a version and a
                        revision.
                        <note>
                            Technically, a third component, the "epoch" (i.e.
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>)
                            is involved but this discussion for the most part
                            ignores <filename>PE</filename>.
                        </note>
                        The version and revision are taken from the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                        variables, respectively.
                        </para></listitem>
                    <listitem><para>
                        <filename>PV</filename>:  The recipe version.
                        <filename>PV</filename> represents the version of the
                        software being packaged.
                        Do not confuse <filename>PV</filename> with the
                        binary package version.
                        </para></listitem>
                    <listitem><para>
                        <filename>PR</filename>:  The recipe revision.
                        </para></listitem>
                    <listitem><para>
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>:
                        The OpenEmbedded build system uses this string
                        to help define the value of <filename>PV</filename>
                        when the source code revision needs to be included
                        in it.
                        </para></listitem>
                    <listitem><para>
                        <ulink url='https://wiki.yoctoproject.org/wiki/PR_Service'>PR Service</ulink>:
                        A network-based service that helps automate keeping
                        package feeds compatible with existing package
                        manager applications such as RPM, APT, and OPKG.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Whenever the binary package content changes, the binary package
                version must change.
                Changing the binary package version is accomplished by changing
                or "bumping" the <filename>PR</filename> and/or
                <filename>PV</filename> values.
                Increasing these values occurs one of two ways:
                <itemizedlist>
                    <listitem><para>Automatically using a Package Revision
                        Service (PR Service).
                        </para></listitem>
                    <listitem><para>Manually incrementing the
                        <filename>PR</filename> and/or
                        <filename>PV</filename> variables.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Given a primary challenge of any build system and its users
                is how to maintain a package feed that is compatible with
                existing package manager applications such as RPM, APT, and
                OPKG, using an automated system is much preferred over a
                manual system.
                In either system, the main requirement is that binary package
                version numbering increases in a linear fashion and that a
                number of version components exist that support that linear
                progression.
                For information on how to ensure package revisioning remains
                linear, see the
                "<link linkend='automatically-incrementing-a-binary-package-revision-number'>Automatically Incrementing a Binary Package Revision Number</link>"
                section.
            </para>

            <para>
                The following three sections provide related information on the
                PR Service, the manual method for "bumping"
                <filename>PR</filename> and/or <filename>PV</filename>, and
                on how to ensure binary package revisioning remains linear.
            </para>

            <section id='working-with-a-pr-service'>
                <title>Working With a PR Service</title>

                <para>
                    As mentioned, attempting to maintain revision numbers in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink>
                    is error prone, inaccurate, and causes problems for people
                    submitting recipes.
                    Conversely, the PR Service automatically generates
                    increasing numbers, particularly the revision field,
                    which removes the human element.
                    <note>
                        For additional information on using a PR Service, you
                        can see the
                        <ulink url='&YOCTO_WIKI_URL;/wiki/PR_Service'>PR Service</ulink>
                        wiki page.
                    </note>
                </para>

                <para>
                    The Yocto Project uses variables in order of
                    decreasing priority to facilitate revision numbering (i.e.
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>, and
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                    for epoch, version, and revision, respectively).
                    The values are highly dependent on the policies and
                    procedures of a given distribution and package feed.
                </para>

                <para>
                    Because the OpenEmbedded build system uses
                    "<ulink url='&YOCTO_DOCS_OM_URL;#overview-checksums'>signatures</ulink>",
                    which are unique to a given build, the build system
                    knows when to rebuild packages.
                    All the inputs into a given task are represented by a
                    signature, which can trigger a rebuild when different.
                    Thus, the build system itself does not rely on the
                    <filename>PR</filename>, <filename>PV</filename>, and
                    <filename>PE</filename> numbers to trigger a rebuild.
                    The signatures, however, can be used to generate
                    these values.
                </para>

                <para>
                    The PR Service works with both
                    <filename>OEBasic</filename> and
                    <filename>OEBasicHash</filename> generators.
                    The value of <filename>PR</filename> bumps when the
                    checksum changes and the different generator mechanisms
                    change signatures under different circumstances.
                </para>

                <para>
                    As implemented, the build system includes values from
                    the PR Service into the <filename>PR</filename> field as
                    an addition using the form "<filename>.x</filename>" so
                    <filename>r0</filename> becomes <filename>r0.1</filename>,
                    <filename>r0.2</filename> and so forth.
                    This scheme allows existing <filename>PR</filename> values
                    to be used for whatever reasons, which include manual
                    <filename>PR</filename> bumps, should it be necessary.
                </para>

                <para>
                    By default, the PR Service is not enabled or running.
                    Thus, the packages generated are just "self consistent".
                    The build system adds and removes packages and
                    there are no guarantees about upgrade paths but images
                    will be consistent and correct with the latest changes.
                </para>

                <para>
                    The simplest form for a PR Service is for it to exist
                    for a single host development system that builds the
                    package feed (building system).
                    For this scenario, you can enable a local PR Service by
                    setting
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PRSERV_HOST'><filename>PRSERV_HOST</filename></ulink>
                    in your <filename>local.conf</filename> file in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
                    <literallayout class='monospaced'>
     PRSERV_HOST = "localhost:0"
                    </literallayout>
                    Once the service is started, packages will automatically
                    get increasing <filename>PR</filename> values and
                    BitBake takes care of starting and stopping the server.
                </para>

                <para>
                    If you have a more complex setup where multiple host
                    development systems work against a common, shared package
                    feed, you have a single PR Service running and it is
                    connected to each building system.
                    For this scenario, you need to start the PR Service using
                    the <filename>bitbake-prserv</filename> command:
                    <literallayout class='monospaced'>
     bitbake-prserv --host <replaceable>ip</replaceable> --port <replaceable>port</replaceable> --start
                    </literallayout>
                    In addition to hand-starting the service, you need to
                    update the <filename>local.conf</filename> file of each
                    building system as described earlier so each system
                    points to the server and port.
                </para>

                <para>
                    It is also recommended you use build history, which adds
                    some sanity checks to binary package versions, in
                    conjunction with the server that is running the PR Service.
                    To enable build history, add the following to each building
                    system's <filename>local.conf</filename> file:
                    <literallayout class='monospaced'>
     # It is recommended to activate "buildhistory" for testing the PR service
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "1"
                    </literallayout>
                    For information on build history, see the
                    "<link linkend='maintaining-build-output-quality'>Maintaining Build Output Quality</link>"
                    section.
                </para>

                <note>
                    <para>
                        The OpenEmbedded build system does not maintain
                        <filename>PR</filename> information as part of the
                        shared state (sstate) packages.
                        If you maintain an sstate feed, its expected that either
                        all your building systems that contribute to the sstate
                         feed use a shared PR Service, or you do not run a PR
                        Service on any of your building systems.
                        Having some systems use a PR Service while others do
                        not leads to obvious problems.
                    </para>

                    <para>
                        For more information on shared state, see the
                        "<ulink url='&YOCTO_DOCS_OM_URL;#shared-state-cache'>Shared State Cache</ulink>"
                        section in the Yocto Project Overview and Concepts
                        Manual.
                    </para>
                </note>
            </section>

            <section id='manually-bumping-pr'>
                <title>Manually Bumping PR</title>

                <para>
                    The alternative to setting up a PR Service is to manually
                    "bump" the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                    variable.
                </para>

                <para>
                    If a committed change results in changing the package
                    output, then the value of the PR variable needs to be
                    increased (or "bumped") as part of that commit.
                    For new recipes you should add the <filename>PR</filename>
                    variable and set its initial value equal to "r0", which is
                    the default.
                    Even though the default value is "r0", the practice of
                    adding it to a new recipe makes it harder to forget to bump
                    the variable when you make changes to the recipe in future.
                </para>

                <para>
                    If you are sharing a common <filename>.inc</filename> file
                    with multiple recipes, you can also use the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-INC_PR'>INC_PR</ulink></filename>
                    variable to ensure that the recipes sharing the
                    <filename>.inc</filename> file are rebuilt when the
                    <filename>.inc</filename> file itself is changed.
                    The <filename>.inc</filename> file must set
                    <filename>INC_PR</filename> (initially to "r0"), and all
                    recipes referring to it should set <filename>PR</filename>
                    to "${INC_PR}.0" initially, incrementing the last number
                    when the recipe is changed.
                    If the <filename>.inc</filename> file is changed then its
                    <filename>INC_PR</filename> should be incremented.
                </para>

                <para>
                    When upgrading the version of a binary package, assuming the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'>PV</ulink></filename>
                    changes, the <filename>PR</filename> variable should be
                    reset to "r0" (or "${INC_PR}.0" if you are using
                    <filename>INC_PR</filename>).
                </para>

                <para>
                    Usually, version increases occur only to binary packages.
                    However, if for some reason <filename>PV</filename> changes
                    but does not increase, you can increase the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PE'>PE</ulink></filename>
                    variable (Package Epoch).
                    The <filename>PE</filename> variable defaults to "0".
                </para>

                <para>
                    Binary package version numbering strives to follow the
                    <ulink url='http://www.debian.org/doc/debian-policy/ch-controlfields.html'>
                    Debian Version Field Policy Guidelines</ulink>.
                    These guidelines define how versions are compared and what
                    "increasing" a version means.
                </para>
            </section>

            <section id='automatically-incrementing-a-binary-package-revision-number'>
                <title>Automatically Incrementing a Package Version Number</title>

                <para>
                    When fetching a repository, BitBake uses the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
                    variable to determine the specific source code revision
                    from which to build.
                    You set the <filename>SRCREV</filename> variable to
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-AUTOREV'><filename>AUTOREV</filename></ulink>
                    to cause the OpenEmbedded build system to automatically use the
                    latest revision of the software:
                    <literallayout class='monospaced'>
     SRCREV = "${AUTOREV}"
                    </literallayout>
                </para>

                <para>
                    Furthermore, you need to reference <filename>SRCPV</filename>
                    in <filename>PV</filename> in order to automatically update
                    the version whenever the revision of the source code
                    changes.
                    Here is an example:
                    <literallayout class='monospaced'>
     PV = "1.0+git${SRCPV}"
                    </literallayout>
                    The OpenEmbedded build system substitutes
                    <filename>SRCPV</filename> with the following:
                    <literallayout class='monospaced'>
     AUTOINC+<replaceable>source_code_revision</replaceable>
                    </literallayout>
                    The build system replaces the <filename>AUTOINC</filename> with
                    a number.
                    The number used depends on the state of the PR Service:
                    <itemizedlist>
                        <listitem><para>
                            If PR Service is enabled, the build system increments
                            the number, which is similar to the behavior of
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>.
                            This behavior results in linearly increasing package
                            versions, which is desirable.
                            Here is an example:
                            <literallayout class='monospaced'>
     hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
     hello-world-git_0.0+git1+dd2f5c3565-r0.0_armv7a-neon.ipk
                            </literallayout>
                            </para></listitem>
                        <listitem><para>
                            If PR Service is not enabled, the build system
                            replaces the <filename>AUTOINC</filename>
                            placeholder with zero (i.e. "0").
                            This results in changing the package version since
                            the source revision is included.
                            However, package versions are not increased linearly.
                            Here is an example:
                            <literallayout class='monospaced'>
     hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
     hello-world-git_0.0+git0+dd2f5c3565-r0.0_armv7a-neon.ipk
                            </literallayout>
                            </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    In summary, the OpenEmbedded build system does not track the
                    history of binary package versions for this purpose.
                    <filename>AUTOINC</filename>, in this case, is comparable to
                    <filename>PR</filename>.
                    If PR server is not enabled, <filename>AUTOINC</filename>
                    in the package version is simply replaced by "0".
                    If PR server is enabled, the build system keeps track of the
                    package versions and bumps the number when the package
                    revision changes.
                </para>
            </section>
        </section>

        <section id='handling-optional-module-packaging'>
            <title>Handling Optional Module Packaging</title>

            <para>
                Many pieces of software split functionality into optional
                modules (or plugins) and the plugins that are built
                might depend on configuration options.
                To avoid having to duplicate the logic that determines what
                modules are available in your recipe or to avoid having
                to package each module by hand, the OpenEmbedded build system
                provides functionality to handle module packaging dynamically.
            </para>

            <para>
                To handle optional module packaging, you need to do two things:
                <itemizedlist>
                    <listitem><para>Ensure the module packaging is actually
                        done.</para></listitem>
                    <listitem><para>Ensure that any dependencies on optional
                        modules from other recipes are satisfied by your recipe.
                        </para></listitem>
                </itemizedlist>
            </para>

            <section id='making-sure-the-packaging-is-done'>
                <title>Making Sure the Packaging is Done</title>

                <para>
                    To ensure the module packaging actually gets done, you use
                    the <filename>do_split_packages</filename> function within
                    the <filename>populate_packages</filename> Python function
                    in your recipe.
                    The <filename>do_split_packages</filename> function
                    searches for a pattern of files or directories under a
                    specified path and creates a package for each one it finds
                    by appending to the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                    variable and setting the appropriate values for
                    <filename>FILES_packagename</filename>,
                    <filename>RDEPENDS_packagename</filename>,
                    <filename>DESCRIPTION_packagename</filename>, and so forth.
                    Here is an example from the <filename>lighttpd</filename>
                    recipe:
                    <literallayout class='monospaced'>
     python populate_packages_prepend () {
         lighttpd_libdir = d.expand('${libdir}')
         do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$',
                          'lighttpd-module-%s', 'Lighttpd module for %s',
                           extra_depends='')
     }
                    </literallayout>
                    The previous example specifies a number of things in the
                    call to <filename>do_split_packages</filename>.
                    <itemizedlist>
                        <listitem><para>A directory within the files installed
                            by your recipe through <filename>do_install</filename>
                            in which to search.</para></listitem>
                        <listitem><para>A regular expression used to match module
                            files in that directory.
                            In the example, note the parentheses () that mark
                            the part of the expression from which the module
                            name should be derived.</para></listitem>
                        <listitem><para>A pattern to use for the package names.
                            </para></listitem>
                        <listitem><para>A description for each package.
                            </para></listitem>
                        <listitem><para>An empty string for
                            <filename>extra_depends</filename>, which disables
                            the default dependency on the main
                            <filename>lighttpd</filename> package.
                            Thus, if a file in <filename>${libdir}</filename>
                            called <filename>mod_alias.so</filename> is found,
                            a package called <filename>lighttpd-module-alias</filename>
                            is created for it and the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DESCRIPTION'><filename>DESCRIPTION</filename></ulink>
                            is set to "Lighttpd module for alias".</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    Often, packaging modules is as simple as the previous
                    example.
                    However, more advanced options exist that you can use
                    within <filename>do_split_packages</filename> to modify its
                    behavior.
                    And, if you need to, you can add more logic by specifying
                    a hook function that is called for each package.
                    It is also perfectly acceptable to call
                    <filename>do_split_packages</filename> multiple times if
                    you have more than one set of modules to package.
                </para>

                <para>
                    For more examples that show how to use
                    <filename>do_split_packages</filename>, see the
                    <filename>connman.inc</filename> file in the
                    <filename>meta/recipes-connectivity/connman/</filename>
                    directory of the <filename>poky</filename>
                    <ulink url='&YOCTO_DOCS_OM_URL;#yocto-project-repositories'>source repository</ulink>.
                    You can also find examples in
                    <filename>meta/classes/kernel.bbclass</filename>.
                 </para>

                 <para>
                     Following is a reference that shows
                     <filename>do_split_packages</filename> mandatory and
                     optional arguments:
                     <literallayout class='monospaced'>
     Mandatory arguments

     root
        The path in which to search
     file_regex
        Regular expression to match searched files.
        Use parentheses () to mark the part of this
        expression that should be used to derive the
        module name (to be substituted where %s is
        used in other function arguments as noted below)
     output_pattern
        Pattern to use for the package names. Must
        include %s.
     description
        Description to set for each package. Must
        include %s.

     Optional arguments

     postinst
        Postinstall script to use for all packages
        (as a string)
     recursive
        True to perform a recursive search - default
        False
     hook
        A hook function to be called for every match.
        The function will be called with the following
        arguments (in the order listed):

        f
           Full path to the file/directory match
        pkg
           The package name
        file_regex
           As above
        output_pattern
           As above
        modulename
           The module name derived using file_regex

     extra_depends
        Extra runtime dependencies (RDEPENDS) to be
        set for all packages. The default value of None
        causes a dependency on the main package
        (${PN}) - if you do not want this, pass empty
        string '' for this parameter.
     aux_files_pattern
        Extra item(s) to be added to FILES for each
        package. Can be a single string item or a list
        of strings for multiple items. Must include %s.
     postrm
        postrm script to use for all packages (as a
        string)
     allow_dirs
        True to allow directories to be matched -
        default False
     prepend
        If True, prepend created packages to PACKAGES
        instead of the default False which appends them
     match_path
        match file_regex on the whole relative path to
        the root rather than just the file name
     aux_files_pattern_verbatim
        Extra item(s) to be added to FILES for each
        package, using the actual derived module name
        rather than converting it to something legal
        for a package name. Can be a single string item
        or a list of strings for multiple items. Must
        include %s.
     allow_links
        True to allow symlinks to be matched - default
        False
     summary
        Summary to set for each package. Must include %s;
        defaults to description if not set.
                     </literallayout>
                 </para>
            </section>

            <section id='satisfying-dependencies'>
                <title>Satisfying Dependencies</title>

                <para>
                    The second part for handling optional module packaging
                    is to ensure that any dependencies on optional modules
                    from other recipes are satisfied by your recipe.
                    You can be sure these dependencies are satisfied by
                    using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES_DYNAMIC'><filename>PACKAGES_DYNAMIC</filename></ulink> variable.
                    Here is an example that continues with the
                    <filename>lighttpd</filename> recipe shown earlier:
                    <literallayout class='monospaced'>
     PACKAGES_DYNAMIC = "lighttpd-module-.*"
                    </literallayout>
                    The name specified in the regular expression can of
                    course be anything.
                    In this example, it is <filename>lighttpd-module-</filename>
                    and is specified as the prefix to ensure that any
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
                    and <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>
                    on a package name starting with the prefix are satisfied
                    during build time.
                    If you are using <filename>do_split_packages</filename>
                    as described in the previous section, the value you put in
                    <filename>PACKAGES_DYNAMIC</filename> should correspond to
                    the name pattern specified in the call to
                    <filename>do_split_packages</filename>.
                </para>
            </section>
        </section>

        <section id='using-runtime-package-management'>
            <title>Using Runtime Package Management</title>

            <para>
                During a build, BitBake always transforms a recipe into one or
                more packages.
                For example, BitBake takes the <filename>bash</filename> recipe
                and produces a number of packages (e.g.
                <filename>bash</filename>, <filename>bash-bashbug</filename>,
                <filename>bash-completion</filename>,
                <filename>bash-completion-dbg</filename>,
                <filename>bash-completion-dev</filename>,
                <filename>bash-completion-extra</filename>,
                <filename>bash-dbg</filename>, and so forth).
                Not all generated packages are included in an image.
            </para>

            <para>
                In several situations, you might need to update, add, remove,
                or query the packages on a target device at runtime
                (i.e. without having to generate a new image).
                Examples of such situations include:
                <itemizedlist>
                    <listitem><para>
                        You want to provide in-the-field updates to deployed
                        devices (e.g. security updates).
                        </para></listitem>
                    <listitem><para>
                        You want to have a fast turn-around development cycle
                        for one or more applications that run on your device.
                        </para></listitem>
                    <listitem><para>
                        You want to temporarily install the "debug" packages
                        of various applications on your device so that
                        debugging can be greatly improved by allowing
                        access to symbols and source debugging.
                        </para></listitem>
                    <listitem><para>
                        You want to deploy a more minimal package selection of
                        your device but allow in-the-field updates to add a
                        larger selection for customization.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                In all these situations, you have something similar to a more
                traditional Linux distribution in that in-field devices
                are able to receive pre-compiled packages from a server for
                installation or update.
                Being able to install these packages on a running,
                in-field device is what is termed "runtime package
                management".
            </para>

            <para>
                In order to use runtime package management, you
                need a host or server machine that serves up the pre-compiled
                packages plus the required metadata.
                You also need package manipulation tools on the target.
                The build machine is a likely candidate to act as the server.
                However, that machine does not necessarily have to be the
                package server.
                The build machine could push its artifacts to another machine
                that acts as the server (e.g. Internet-facing).
                In fact, doing so is advantageous for a production
                environment as getting the packages away from the
                development system's build directory prevents accidental
                overwrites.
            </para>

            <para>
                A simple build that targets just one device produces
                more than one package database.
                In other words, the packages produced by a build are separated
                out into a couple of different package groupings based on
                criteria such as the target's CPU architecture, the target
                board, or the C library used on the target.
                For example, a build targeting the <filename>qemux86</filename>
                device produces the following three package databases:
                <filename>noarch</filename>, <filename>i586</filename>, and
                <filename>qemux86</filename>.
                If you wanted your <filename>qemux86</filename> device to be
                aware of all the packages that were available to it,
                you would need to point it to each of these databases
                individually.
                In a similar way, a traditional Linux distribution usually is
                configured to be aware of a number of software repositories
                from which it retrieves packages.
            </para>

            <para>
                Using runtime package management is completely optional and
                not required for a successful build or deployment in any
                way.
                But if you want to make use of runtime package management,
                you need to do a couple things above and beyond the basics.
                The remainder of this section describes what you need to do.
            </para>

            <section id='runtime-package-management-build'>
                <title>Build Considerations</title>

                <para>
                    This section describes build considerations of which you
                    need to be aware in order to provide support for runtime
                    package management.
                </para>

                <para>
                    When BitBake generates packages, it needs to know
                    what format or formats to use.
                    In your configuration, you use the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>
                    variable to specify the format:
                    <orderedlist>
                        <listitem><para>
                            Open the <filename>local.conf</filename> file
                            inside your
                            <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                            (e.g. <filename>~/poky/build/conf/local.conf</filename>).
                            </para></listitem>
                        <listitem><para>
                            Select the desired package format as follows:
                            <literallayout class='monospaced'>
     PACKAGE_CLASSES ?= “package_<replaceable>packageformat</replaceable>”
                            </literallayout>
                            where <replaceable>packageformat</replaceable>
                            can be "ipk", "rpm", "deb", or "tar" which are the
                            supported package formats.
                            <note>
                                Because the Yocto Project supports four
                                different package formats, you can set the
                                variable with more than one argument.
                                However, the OpenEmbedded build system only
                                uses the first argument when creating an image
                                or Software Development Kit (SDK).
                            </note>
                            </para></listitem>
                    </orderedlist>
                </para>

                <para>
                    If you would like your image to start off with a basic
                    package database containing the packages in your current
                    build as well as to have the relevant tools available on the
                    target for runtime package management, you can include
                    "package-management" in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                    variable.
                    Including "package-management" in this configuration
                    variable ensures that when the image is assembled for your
                    target, the image includes the currently-known package
                    databases as well as the target-specific tools required
                    for runtime package management to be performed on the
                    target.
                    However, this is not strictly necessary.
                    You could start your image off without any databases
                    but only include the required on-target package
                    tool(s).
                    As an example, you could include "opkg" in your
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>
                    variable if you are using the IPK package format.
                    You can then initialize your target's package database(s)
                    later once your image is up and running.
                </para>

                <para>
                    Whenever you perform any sort of build step that can
                    potentially generate a package or modify   existing
                    package, it is always a good idea to re-generate the
                    package index after the build by using the following
                    command:
                    <literallayout class='monospaced'>
    $ bitbake package-index
                    </literallayout>
                    It might be tempting to build the package and the
                    package index at the same time with a command such as
                    the following:
                    <literallayout class='monospaced'>
    $ bitbake <replaceable>some-package</replaceable> package-index
                    </literallayout>
                    Do not do this as BitBake does not schedule the package
                    index for after the completion of the package you are
                    building.
                    Consequently, you cannot be sure of the package index
                    including information for the package you just built.
                    Thus, be sure to run the package update step separately
                    after building any packages.
                </para>

                <para>
                    You can use the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_ARCHS'><filename>PACKAGE_FEED_ARCHS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_BASE_PATHS'><filename>PACKAGE_FEED_BASE_PATHS</filename></ulink>,
                    and
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_URIS'><filename>PACKAGE_FEED_URIS</filename></ulink>
                    variables to pre-configure target images to use a package
                    feed.
                    If you do not define these variables, then manual steps
                    as described in the subsequent sections are necessary to
                    configure the target.
                    You should set these variables before building the image
                    in order to produce a correctly configured image.
                </para>

                <para>
                    When your build is complete, your packages reside in the
                    <filename>${TMPDIR}/deploy/<replaceable>packageformat</replaceable></filename>
                    directory.
                    For example, if
                    <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink><filename>}</filename>
                    is <filename>tmp</filename> and your selected package type
                    is RPM, then your RPM packages are available in
                    <filename>tmp/deploy/rpm</filename>.
                </para>
            </section>

            <section id='runtime-package-management-server'>
                <title>Host or Server Machine Setup</title>

                <para>
                    Although other protocols are possible, a server using HTTP
                    typically serves packages.
                    If you want to use HTTP, then set up and configure a
                    web server such as Apache 2, lighttpd, or
                    SimpleHTTPServer on the machine serving the packages.
                </para>

                <para>
                    To keep things simple, this section describes how to set
                    up a SimpleHTTPServer web server to share package feeds
                    from the developer's machine.
                    Although this server might not be the best for a production
                    environment, the setup is simple and straight forward.
                    Should you want to use a different server more suited for
                    production (e.g. Apache 2, Lighttpd, or Nginx), take the
                    appropriate steps to do so.
                </para>

                <para>
                    From within the build directory where you have built an
                    image based on your packaging choice (i.e. the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>
                    setting), simply start the server.
                    The following example assumes a build directory of
                    <filename>~/poky/build/tmp/deploy/rpm</filename> and a
                    <filename>PACKAGE_CLASSES</filename> setting of
                    "package_rpm":
                    <literallayout class='monospaced'>
     $ cd ~/poky/build/tmp/deploy/rpm
     $ python -m SimpleHTTPServer
                    </literallayout>
                </para>
            </section>

            <section id='runtime-package-management-target'>
                <title>Target Setup</title>

                <para>
                    Setting up the target differs depending on the
                    package management system.
                    This section provides information for RPM, IPK, and DEB.
                </para>

                <section id='runtime-package-management-target-rpm'>
                    <title>Using RPM</title>

                    <para>
                        The
                        <ulink url='https://en.wikipedia.org/wiki/DNF_(software)'>Dandified Packaging Tool</ulink>
                        (DNF) performs runtime package management of RPM
                        packages.
                        In order to use DNF for runtime package management,
                        you must perform an initial setup on the target
                        machine for cases where the
                        <filename>PACKAGE_FEED_*</filename> variables were not
                        set as part of the image that is running on the
                        target.
                        This means if you built your image and did not not use
                        these variables as part of the build and your image is
                        now running on the target, you need to perform the
                        steps in this section if you want to use runtime
                        package management.
                        <note>
                            For information on the
                            <filename>PACKAGE_FEED_*</filename> variables, see
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_ARCHS'><filename>PACKAGE_FEED_ARCHS</filename></ulink>,
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_BASE_PATHS'><filename>PACKAGE_FEED_BASE_PATHS</filename></ulink>,
                            and
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_URIS'><filename>PACKAGE_FEED_URIS</filename></ulink>
                            in the Yocto Project Reference Manual variables
                            glossary.
                        </note>
                    </para>

                    <para>
                        On the target, you must inform DNF that package
                        databases are available.
                        You do this by creating a file named
                        <filename>/etc/yum.repos.d/oe-packages.repo</filename>
                        and defining the <filename>oe-packages</filename>.
                    </para>

                    <para>
                        As an example, assume the target is able to use the
                        following package databases:
                        <filename>all</filename>, <filename>i586</filename>,
                        and <filename>qemux86</filename> from a server named
                        <filename>my.server</filename>.
                        The specifics for setting up the web server are up to
                        you.
                        The critical requirement is that the URIs in the
                        target repository configuration point to the
                        correct remote location for the feeds.
                        <note><title>Tip</title>
                            For development purposes, you can point the web
                            server to the build system's
                            <filename>deploy</filename> directory.
                            However, for production use, it is better to copy
                            the package directories to a location outside of
                            the build area and use that location.
                            Doing so avoids situations where the build system
                            overwrites or changes the
                            <filename>deploy</filename> directory.
                        </note>
                    </para>

                    <para>
                        When telling DNF where to look for the package
                        databases, you must declare individual locations
                        per architecture or a single location used for all
                        architectures.
                        You cannot do both:
                        <itemizedlist>
                            <listitem><para>
                                <emphasis>Create an Explicit List of Architectures:</emphasis>
                                Define individual base URLs to identify where
                                each package database is located:
                                <literallayout class='monospaced'>
     [oe-packages]
     baseurl=http://my.server/rpm/i586 http://my.server/rpm/qemux86 http://my.server/rpm/all
                                </literallayout>
                                This example informs DNF about individual
                                package databases for all three architectures.
                                </para></listitem>
                            <listitem><para>
                                <emphasis>Create a Single (Full) Package Index:</emphasis>
                                Define a single base URL that identifies where
                                a full package database is located:
                                <literallayout class='monospaced'>
     [oe-packages]
     baseurl=http://my.server/rpm
                                </literallayout>
                                This example informs DNF about a single package
                                database that contains all the package index
                                information for all supported architectures.
                                </para></listitem>
                        </itemizedlist>
                    </para>

                    <para>
                        Once you have informed DNF where to find the package
                        databases, you need to fetch them:
                        <literallayout class='monospaced'>
     # dnf makecache
                        </literallayout>
                        DNF is now able to find, install, and upgrade packages
                        from the specified repository or repositories.
                        <note>
                            See the
                            <ulink url='http://dnf.readthedocs.io/en/latest/'>DNF documentation</ulink>
                            for additional information.
                        </note>
                    </para>
                </section>

                <section id='runtime-package-management-target-ipk'>
                    <title>Using IPK</title>

                    <para>
                        The <filename>opkg</filename> application performs
                        runtime package management of IPK packages.
                        You must perform an initial setup for
                        <filename>opkg</filename> on the target machine
                        if the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_ARCHS'><filename>PACKAGE_FEED_ARCHS</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_BASE_PATHS'><filename>PACKAGE_FEED_BASE_PATHS</filename></ulink>, and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_URIS'><filename>PACKAGE_FEED_URIS</filename></ulink>
                        variables have not been set or the target image was
                        built before the variables were set.
                    </para>

                    <para>
                        The <filename>opkg</filename> application uses
                        configuration files to find available package
                        databases.
                        Thus, you need to create a configuration file inside
                        the <filename>/etc/opkg/</filename> direction, which
                        informs <filename>opkg</filename> of any repository
                        you want to use.
                    </para>

                    <para>
                        As an example, suppose you are serving packages from a
                        <filename>ipk/</filename> directory containing the
                        <filename>i586</filename>,
                        <filename>all</filename>, and
                        <filename>qemux86</filename> databases through an
                        HTTP server named <filename>my.server</filename>.
                        On the target, create a configuration file
                        (e.g. <filename>my_repo.conf</filename>) inside the
                        <filename>/etc/opkg/</filename> directory containing
                        the following:
                        <literallayout class='monospaced'>
     src/gz all http://my.server/ipk/all
     src/gz i586 http://my.server/ipk/i586
     src/gz qemux86 http://my.server/ipk/qemux86
                        </literallayout>
                        Next, instruct <filename>opkg</filename> to fetch
                        the repository information:
                        <literallayout class='monospaced'>
     # opkg update
                        </literallayout>
                        The <filename>opkg</filename> application is now able
                        to find, install, and upgrade packages from the
                        specified repository.
                    </para>
                </section>

                <section id='runtime-package-management-target-deb'>
                    <title>Using DEB</title>

                    <para>
                        The <filename>apt</filename> application performs
                        runtime package management of DEB packages.
                        This application uses a source list file to find
                        available package databases.
                        You must perform an initial setup for
                        <filename>apt</filename> on the target machine
                        if the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_ARCHS'><filename>PACKAGE_FEED_ARCHS</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_BASE_PATHS'><filename>PACKAGE_FEED_BASE_PATHS</filename></ulink>, and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_URIS'><filename>PACKAGE_FEED_URIS</filename></ulink>
                        variables have not been set or the target image was
                        built before the variables were set.
                    </para>

                    <para>
                        To inform <filename>apt</filename> of the repository
                        you want to use, you might create a list file (e.g.
                        <filename>my_repo.list</filename>) inside the
                        <filename>/etc/apt/sources.list.d/</filename>
                        directory.
                        As an example, suppose you are serving packages from a
                        <filename>deb/</filename> directory containing the
                        <filename>i586</filename>,
                        <filename>all</filename>, and
                        <filename>qemux86</filename> databases through an
                        HTTP server named <filename>my.server</filename>.
                        The list file should contain:
                        <literallayout class='monospaced'>
     deb http://my.server/deb/all ./
     deb http://my.server/deb/i586 ./
     deb http://my.server/deb/qemux86 ./
                        </literallayout>
                        Next, instruct the <filename>apt</filename>
                        application to fetch the repository information:
                        <literallayout class='monospaced'>
     # apt-get update
                        </literallayout>
                        After this step, <filename>apt</filename> is able
                        to find, install, and upgrade packages from the
                        specified repository.
                    </para>
                </section>
            </section>
        </section>

        <section id='generating-and-using-signed-packages'>
            <title>Generating and Using Signed Packages</title>
            <para>
                In order to add security to RPM packages used during a build,
                you can take steps to securely sign them.
                Once a signature is verified, the OpenEmbedded build system
                can use the package in the build.
                If security fails for a signed package, the build system
                aborts the build.
            </para>

            <para>
                This section describes how to sign RPM packages during a build
                and how to use signed package feeds (repositories) when
                doing a build.
            </para>

            <section id='signing-rpm-packages'>
                <title>Signing RPM Packages</title>

                <para>
                    To enable signing RPM packages, you must set up the
                    following configurations in either your
                    <filename>local.config</filename> or
                    <filename>distro.config</filename> file:
                    <literallayout class='monospaced'>
     # Inherit sign_rpm.bbclass to enable signing functionality
     INHERIT += " sign_rpm"
     # Define the GPG key that will be used for signing.
     RPM_GPG_NAME = "<replaceable>key_name</replaceable>"
     # Provide passphrase for the key
     RPM_GPG_PASSPHRASE = "<replaceable>passphrase</replaceable>"
                    </literallayout>
                    <note>
                        Be sure to supply appropriate values for both
                        <replaceable>key_name</replaceable> and
                        <replaceable>passphrase</replaceable>
                    </note>
                    Aside from the
                    <filename>RPM_GPG_NAME</filename> and
                    <filename>RPM_GPG_PASSPHRASE</filename> variables in the
                    previous example, two optional variables related to signing
                    exist:
                    <itemizedlist>
                        <listitem><para>
                            <emphasis><filename>GPG_BIN</filename>:</emphasis>
                            Specifies a <filename>gpg</filename> binary/wrapper
                            that is executed when the package is signed.
                            </para></listitem>
                        <listitem><para>
                            <emphasis><filename>GPG_PATH</filename>:</emphasis>
                            Specifies the <filename>gpg</filename> home
                            directory used when the package is signed.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='processing-package-feeds'>
                <title>Processing Package Feeds</title>

                <para>
                    In addition to being able to sign RPM packages, you can
                    also enable signed package feeds for IPK and RPM packages.
                </para>

                <para>
                    The steps you need to take to enable signed package feed
                    use are similar to the steps used to sign RPM packages.
                    You must define the following in your
                    <filename>local.config</filename> or
                    <filename>distro.config</filename> file:
                    <literallayout class='monospaced'>
     INHERIT += "sign_package_feed"
     PACKAGE_FEED_GPG_NAME = "<replaceable>key_name</replaceable>"
     PACKAGE_FEED_GPG_PASSPHRASE_FILE = "<replaceable>path_to_file_containing_passphrase</replaceable>"
                    </literallayout>
                    For signed package feeds, the passphrase must exist in a
                    separate file, which is pointed to by the
                    <filename>PACKAGE_FEED_GPG_PASSPHRASE_FILE</filename>
                    variable.
                    Regarding security, keeping a plain text passphrase out of
                    the configuration is more secure.
                </para>

                <para>
                    Aside from the
                    <filename>PACKAGE_FEED_GPG_NAME</filename> and
                    <filename>PACKAGE_FEED_GPG_PASSPHRASE_FILE</filename>
                    variables, three optional variables related to signed
                    package feeds exist:
                    <itemizedlist>
                        <listitem><para>
                            <emphasis><filename>GPG_BIN</filename>:</emphasis>
                            Specifies a <filename>gpg</filename> binary/wrapper
                            that is executed when the package is signed.
                            </para></listitem>
                        <listitem><para>
                            <emphasis><filename>GPG_PATH</filename>:</emphasis>
                            Specifies the <filename>gpg</filename> home
                            directory used when the package is signed.
                            </para></listitem>
                        <listitem><para>
                            <emphasis><filename>PACKAGE_FEED_GPG_SIGNATURE_TYPE</filename>:</emphasis>
                            Specifies the type of <filename>gpg</filename>
                            signature.
                            This variable applies only to RPM and IPK package
                            feeds.
                            Allowable values for the
                            <filename>PACKAGE_FEED_GPG_SIGNATURE_TYPE</filename>
                            are "ASC", which is the default and specifies ascii
                            armored, and "BIN", which specifies binary.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='testing-packages-with-ptest'>
            <title>Testing Packages With ptest</title>

            <para>
                A Package Test (ptest) runs tests against packages built
                by the OpenEmbedded build system on the target machine.
                A ptest contains at least two items: the actual test, and
                a shell script (<filename>run-ptest</filename>) that starts
                the test.
                The shell script that starts the test must not contain
                the actual test - the script only starts the test.
                On the other hand, the test can be anything from a simple
                shell script that runs a binary and checks the output to
                an elaborate system of test binaries and data files.
            </para>

            <para>
                The test generates output in the format used by
                Automake:
                <literallayout class='monospaced'>
     <replaceable>result</replaceable>: <replaceable>testname</replaceable>
                </literallayout>
                where the result can be <filename>PASS</filename>,
                <filename>FAIL</filename>, or <filename>SKIP</filename>,
                and the testname can be any identifying string.
            </para>

            <para>
                For a list of Yocto Project recipes that are already
                enabled with ptest, see the
                <ulink url='https://wiki.yoctoproject.org/wiki/Ptest'>Ptest</ulink>
                wiki page.
                <note>
                    A recipe is "ptest-enabled" if it inherits the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-ptest'><filename>ptest</filename></ulink>
                    class.
                </note>
            </para>

            <section id='adding-ptest-to-your-build'>
                <title>Adding ptest to Your Build</title>

                <para>
                    To add package testing to your build, add the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                    and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
                    variables to your <filename>local.conf</filename> file,
                    which is found in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
                    <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " ptest"
     EXTRA_IMAGE_FEATURES += "ptest-pkgs"
                    </literallayout>
                    Once your build is complete, the ptest files are installed
                    into the
                    <filename>/usr/lib/<replaceable>package</replaceable>/ptest</filename>
                    directory within the image, where
                    <filename><replaceable>package</replaceable></filename>
                    is the name of the package.
                </para>
            </section>

            <section id='running-ptest'>
                <title>Running ptest</title>

                <para>
                    The <filename>ptest-runner</filename> package installs a
                    shell script that loops through all installed ptest test
                    suites and runs them in sequence.
                    Consequently, you might want to add this package to
                    your image.
                </para>
            </section>

            <section id='getting-your-package-ready'>
                <title>Getting Your Package Ready</title>

                <para>
                    In order to enable a recipe to run installed ptests
                    on target hardware,
                    you need to prepare the recipes that build the packages
                    you want to test.
                    Here is what you have to do for each recipe:
                    <itemizedlist>
                        <listitem><para><emphasis>Be sure the recipe
                            inherits the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-ptest'><filename>ptest</filename></ulink>
                            class:</emphasis>
                            Include the following line in each recipe:
                            <literallayout class='monospaced'>
     inherit ptest
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Create <filename>run-ptest</filename>:</emphasis>
                            This script starts your test.
                            Locate the script where you will refer to it
                            using
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
                            Here is an example that starts a test for
                            <filename>dbus</filename>:
                            <literallayout class='monospaced'>
     #!/bin/sh
     cd test
     make -k runtest-TESTS
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Ensure dependencies are
                            met:</emphasis>
                            If the test adds build or runtime dependencies
                            that normally do not exist for the package
                            (such as requiring "make" to run the test suite),
                            use the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                            and
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
                            variables in your recipe in order for the package
                            to meet the dependencies.
                            Here is an example where the package has a runtime
                            dependency on "make":
                            <literallayout class='monospaced'>
     RDEPENDS_${PN}-ptest += "make"
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Add a function to build the
                            test suite:</emphasis>
                            Not many packages support cross-compilation of
                            their test suites.
                            Consequently, you usually need to add a
                            cross-compilation function to the package.
                            </para>

                            <para>Many packages based on Automake compile and
                            run the test suite by using a single command
                            such as <filename>make check</filename>.
                            However, the host <filename>make check</filename>
                            builds and runs on the same computer, while
                            cross-compiling requires that the package is built
                            on the host but executed for the target
                            architecture (though often, as in the case for
                            ptest, the execution occurs on the host).
                            The built version of Automake that ships with the
                            Yocto Project includes a patch that separates
                            building and execution.
                            Consequently, packages that use the unaltered,
                            patched version of <filename>make check</filename>
                            automatically cross-compiles.</para>
                            <para>Regardless, you still must add a
                            <filename>do_compile_ptest</filename> function to
                            build the test suite.
                            Add a function similar to the following to your
                            recipe:
                            <literallayout class='monospaced'>
     do_compile_ptest() {
        oe_runmake buildtest-TESTS
     }
                            </literallayout>
                            </para></listitem>
                       <listitem><para><emphasis>Ensure special configurations
                            are set:</emphasis>
                            If the package requires special configurations
                            prior to compiling the test code, you must
                            insert a <filename>do_configure_ptest</filename>
                            function into the recipe.
                            </para></listitem>
                       <listitem><para><emphasis>Install the test
                            suite:</emphasis>
                            The <filename>ptest</filename> class
                            automatically copies the file
                            <filename>run-ptest</filename> to the target and
                            then runs make <filename>install-ptest</filename>
                            to run the tests.
                            If this is not enough, you need to create a
                            <filename>do_install_ptest</filename> function and
                            make sure it gets called after the
                            "make install-ptest" completes.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='creating-node-package-manager-npm-packages'>
            <title>Creating Node Package Manager (NPM) Packages</title>

            <para>
                <ulink url='https://en.wikipedia.org/wiki/Npm_(software)'>NPM</ulink>
                is a package manager for the JavaScript programming
                language.
                The Yocto Project supports the NPM
                <ulink url='&YOCTO_DOCS_BB_URL;#bb-fetchers'>fetcher</ulink>.
                You can use this fetcher in combination with
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-devtool-reference'><filename>devtool</filename></ulink>
                to create recipes that produce NPM packages.
            </para>

            <para>
                Two workflows exist that allow you to create NPM packages
                using <filename>devtool</filename>: the NPM registry modules
                method and the NPM project code method.
                <note>
                    While it is possible to create NPM recipes manually,
                    using <filename>devtool</filename> is far simpler.
                </note>
                Additionally, some requirements and caveats exist.
            </para>

            <section id='npm-package-creation-requirements'>
                <title>Requirements and Caveats</title>

                <para>
                    You need to be aware of the following before using
                    <filename>devtool</filename> to create NPM packages:
                    <itemizedlist>
                        <listitem><para>
                            Of the two methods that you can use
                            <filename>devtool</filename> to create NPM
                            packages, the registry approach is slightly
                            simpler.
                            However, you might consider the project
                            approach because you do not have to publish
                            your module in the NPM registry
                            (<ulink url='https://docs.npmjs.com/misc/registry'><filename>npm-registry</filename></ulink>),
                            which is NPM's public registry.
                            </para></listitem>
                        <listitem><para>
                            Be familiar with
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-devtool-reference'><filename>devtool</filename></ulink>.
                            </para></listitem>
                        <listitem><para>
                            The NPM host tools need the native
                            <filename>nodejs-npm</filename> package, which
                            is part of the OpenEmbedded environment.
                            You need to get the package by cloning the
                            <ulink url='https://github.com/openembedded/meta-openembedded'></ulink>
                            repository out of GitHub.
                            Be sure to add the path to your local copy to
                            your <filename>bblayers.conf</filename> file.
                            </para></listitem>
                        <listitem><para>
                            <filename>devtool</filename> cannot detect
                            native libraries in module dependencies.
                            Consequently, you must manually add packages
                            to your recipe.
                            </para></listitem>
                        <listitem><para>
                            While deploying NPM packages,
                            <filename>devtool</filename> cannot determine
                            which dependent packages are missing on the
                            target (e.g. the node runtime
                            <filename>nodejs</filename>).
                            Consequently, you need to find out what
                            files are missing and be sure they are on the
                            target.
                            </para></listitem>
                        <listitem><para>
                            Although you might not need NPM to run your
                            node package, it is useful to have NPM on your
                            target.
                            The NPM package name is
                            <filename>nodejs-npm</filename>.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='npm-using-the-registry-modules-method'>
                <title>Using the Registry Modules Method</title>

                <para>
                    This section presents an example that uses the
                    <filename>cute-files</filename> module, which is a
                    file browser web application.
                    <note>
                        You must know the <filename>cute-files</filename>
                        module version.
                    </note>
                </para>

                <para>
                    The first thing you need to do is use
                    <filename>devtool</filename> and the NPM fetcher to
                    create the recipe:
                    <literallayout class='monospaced'>
     $ devtool add "npm://registry.npmjs.org;package=cute-files;version=1.0.2"
                    </literallayout>
                    The <filename>devtool add</filename> command runs
                    <filename>recipetool create</filename> and uses the
                    same fetch URI to download each dependency and capture
                    license details where possible.
                    The result is a generated recipe.
                </para>

                <para>
                    The recipe file is fairly simple and contains every
                    license that <filename>recipetool</filename> finds
                    and includes the licenses in the recipe's
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
                    variables.
                    You need to examine the variables and look for those
                    with "unknown" in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                    field.
                    You need to track down the license information for
                    "unknown" modules and manually add the information to the
                    recipe.
                </para>

                <para>
                    <filename>recipetool</filename> creates a "shrinkwrap" file
                    for your recipe.
                    Shrinkwrap files capture the version of all dependent
                    modules.
                    Many packages do not provide shrinkwrap files.
                    <filename>recipetool</filename> create a shrinkwrap
                    file as it runs.
                    <note>
                        A package is created for each sub-module.
                        This policy is the only practical way to have the
                        licenses for all of the dependencies represented
                        in the license manifest of the image.
                    </note>
                </para>

                <para>
                    The <filename>devtool edit-recipe</filename> command
                    lets you take a look at the recipe:
                    <literallayout class='monospaced'>
     $ devtool edit-recipe cute-files
     SUMMARY = "Turn any folder on your computer into a cute file browser, available on the local network."
     LICENSE = "MIT &amp; ISC &amp; Unknown"
     LIC_FILES_CHKSUM = "file://LICENSE;md5=71d98c0a1db42956787b1909c74a86ca \
                         file://node_modules/toidentifier/LICENSE;md5=1a261071a044d02eb6f2bb47f51a3502 \
                         file://node_modules/debug/LICENSE;md5=ddd815a475e7338b0be7a14d8ee35a99 \
                         ...

     SRC_URI = " \
         npm://registry.npmjs.org/;package=cute-files;version=${PV} \
         npmsw://${THISDIR}/${BPN}/npm-shrinkwrap.json \
     "

     S = "${WORKDIR}/npm"

     inherit npm

     LICENSE_${PN} = "MIT"
     LICENSE_${PN}-accepts = "MIT"
     LICENSE_${PN}-array-flatten = "MIT"
     ...
     LICENSE_${PN}-vary = "MIT"
                    </literallayout>
                    Three key points exist in the previous example:
                    <itemizedlist>
                        <listitem><para>
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                            uses the NPM scheme so that the NPM fetcher
                            is used.
                            </para></listitem>
                        <listitem><para>
                            <filename>recipetool</filename> collects all
                            the license information.
                            If a sub-module's license is unavailable,
                            the sub-module's name appears in the comments.
                            </para></listitem>
                        <listitem><para>
                            The <filename>inherit npm</filename> statement
                            causes the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-npm'><filename>npm</filename></ulink>
                            class to package up all the modules.
                            </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    You can run the following command to build the
                    <filename>cute-files</filename> package:
                    <literallayout class='monospaced'>
     $ devtool build cute-files
                    </literallayout>
                    Remember that <filename>nodejs</filename> must be
                    installed on the target before your package.
                </para>

                <para>
                    Assuming 192.168.7.2 for the target's IP address, use
                    the following command to deploy your package:
                    <literallayout class='monospaced'>
     $ devtool deploy-target -s cute-files root@192.168.7.2
                    </literallayout>
                    Once the package is installed on the target, you can
                    test the application:
                    <note>
                        Because of a know issue, you cannot simply run
                        <filename>cute-files</filename> as you would if you
                        had run <filename>npm install</filename>.
                    </note>
                    <literallayout class='monospaced'>
     $ cd /usr/lib/node_modules/cute-files
     $ node cute-files.js
                    </literallayout>
                    On a browser, go to
                    <filename>http://192.168.7.2:3000</filename> and you
                    see the following:
                    <imagedata fileref="figures/cute-files-npm-example.png" align="center" width="6in" depth="4in" />
                </para>

                <para>
                    You can find the recipe in
                    <filename>workspace/recipes/cute-files</filename>.
                    You can use the recipe in any layer you choose.
                </para>
            </section>

            <section id='npm-using-the-npm-projects-method'>
                <title>Using the NPM Projects Code Method</title>

                <para>
                    Although it is useful to package modules already in the
                    NPM registry, adding <filename>node.js</filename> projects
                    under development is a more common developer use case.
                </para>

                <para>
                    This section covers the NPM projects code method, which is
                    very similar to the "registry" approach described in the
                    previous section.
                    In the NPM projects method, you provide
                    <filename>devtool</filename> with an URL that points to the
                    source files.
                </para>

                <para>
                    Replicating the same example, (i.e.
                    <filename>cute-files</filename>) use the following command:
                    <literallayout class='monospaced'>
     $ devtool add https://github.com/martinaglv/cute-files.git
                    </literallayout>
                    The recipe this command generates is very similar to the
                    recipe created in the previous section.
                    However, the <filename>SRC_URI</filename> looks like the
                    following:
                    <literallayout class='monospaced'>
     SRC_URI = " \
         git://github.com/martinaglv/cute-files.git;protocol=https \
         npmsw://${THISDIR}/${BPN}/npm-shrinkwrap.json \
         "
                    </literallayout>
                    In this example, the main module is taken from the Git
                    repository and dependents are taken from the NPM registry.
                    Other than those differences, the recipe is basically the
                    same between the two methods.
                    You can build and deploy the package exactly as described
                    in the previous section that uses the registry modules
                    method.
                </para>
            </section>
        </section>

        <section id='adding-custom-metadata-to-packages'>
            <title>Adding custom metadata to packages</title>

            <para>
                The variable <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ADD_METADATA'><filename>PACKAGE_ADD_METADATA</filename></ulink>
                can be used to add additional metadata to packages. This is
                reflected in the package control/spec file. To take the ipk
                format for example, the CONTROL file stored inside would
                contain the additional metadata as additional lines.
            </para>

            <para>
                The variable can be used in multiple ways, including using
                suffixes to set it for a specific package type and/or package.
                Note that the order of precedence is the same as this list:
                <itemizedlist>
                    <listitem><para>
                        <filename>PACKAGE_ADD_METADATA_&lt;PKGTYPE&gt;_&lt;PN&gt;</filename>
                    </para></listitem>
                    <listitem><para>
                        <filename>PACKAGE_ADD_METADATA_&lt;PKGTYPE&gt;</filename>
                    </para></listitem>
                    <listitem><para>
                        <filename>PACKAGE_ADD_METADATA_&lt;PN&gt;</filename>
                    </para></listitem>
                    <listitem><para>
                        <filename>PACKAGE_ADD_METADATA</filename>
                    </para></listitem>
                </itemizedlist>
                &lt;PKGTYPE&gt; is a parameter and expected to be a
                distinct name of specific package type:
                <itemizedlist>
                    <listitem><para>IPK for .ipk packages</para></listitem>
                    <listitem><para>DEB for .deb packages</para></listitem>
                    <listitem><para>RPM for .rpm packages</para></listitem>
                </itemizedlist>
                &lt;PN&gt; is a parameter and expected to be a package name.
            </para>

            <para>
                The variable can contain multiple [one-line] metadata fields
                separated by the literal sequence '\n'. The separator can be
                redefined using the variable flag <filename>separator</filename>.
            </para>

            <para>
                The following is an example that adds two custom fields for
                ipk packages:
                <literallayout class='monospaced'>
    PACKAGE_ADD_METADATA_IPK = "Vendor: CustomIpk\nGroup: Applications/Spreadsheets"
                </literallayout>
            </para>
        </section>

    </section>

    <section id='efficiently-fetching-source-files-during-a-build'>
        <title>Efficiently Fetching Source Files During a Build</title>

        <para>
            The OpenEmbedded build system works with source files located
            through the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
            variable.
            When you build something using BitBake, a big part of the operation
            is locating and downloading all the source tarballs.
            For images, downloading all the source for various packages can
            take a significant amount of time.
        </para>

        <para>
            This section shows you how you can use mirrors to speed up
            fetching source files and how you can pre-fetch files all of which
            leads to more efficient use of resources and time.
        </para>

        <section id='setting-up-effective-mirrors'>
            <title>Setting up Effective Mirrors</title>

            <para>
                A good deal that goes into a Yocto Project
                build is simply downloading all of the source tarballs.
                Maybe you have been working with another build system
                (OpenEmbedded or Angstrom) for which you have built up a
                sizable directory of source tarballs.
                Or, perhaps someone else has such a directory for which you
                have read access.
                If so, you can save time by adding statements to your
                configuration file so that the build process checks local
                directories first for existing tarballs before checking the
                Internet.
            </para>

            <para>
                Here is an efficient way to set it up in your
                <filename>local.conf</filename> file:
                <literallayout class='monospaced'>
     SOURCE_MIRROR_URL ?= "file:///home/you/your-download-dir/"
     INHERIT += "own-mirrors"
     BB_GENERATE_MIRROR_TARBALLS = "1"
     # BB_NO_NETWORK = "1"
                </literallayout>
            </para>

            <para>
                In the previous example, the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></ulink>
                variable causes the OpenEmbedded build system to generate
                tarballs of the Git repositories and store them in the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>
                directory.
                Due to performance reasons, generating and storing these
                tarballs is not the build system's default behavior.
            </para>

            <para>
                You can also use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PREMIRRORS'><filename>PREMIRRORS</filename></ulink>
                variable.
                For an example, see the variable's glossary entry in the
                Yocto Project Reference Manual.
            </para>
        </section>

        <section id='getting-source-files-and-suppressing-the-build'>
            <title>Getting Source Files and Suppressing the Build</title>

            <para>
                Another technique you can use to ready yourself for a
                successive string of build operations, is to pre-fetch
                all the source files without actually starting a build.
                This technique lets you work through any download issues
                and ultimately gathers all the source files into your
                download directory
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-build-downloads'><filename>build/downloads</filename></ulink>,
                which is located with
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>.
            </para>

            <para>
                Use the following BitBake command form to fetch all the
                necessary sources without starting the build:
                <literallayout class='monospaced'>
     $ bitbake <replaceable>target</replaceable> --runall=fetch
                </literallayout>
                This variation of the BitBake command guarantees that you
                have all the sources for that BitBake target should you
                disconnect from the Internet and want to do the build
                later offline.
            </para>
        </section>
    </section>

    <section id="selecting-an-initialization-manager">
        <title>Selecting an Initialization Manager</title>

        <para>
            By default, the Yocto Project uses SysVinit as the initialization
            manager.
            However, support also exists for systemd,
            which is a full replacement for init with
            parallel starting of services, reduced shell overhead and other
            features that are used by many distributions.
        </para>

        <para>
            Within the system, SysVinit treats system components as services.
            These services are maintained as shell scripts stored in the
            <filename>/etc/init.d/</filename> directory.
            Services organize into different run levels.
            This organization is maintained by putting links to the services
            in the <filename>/etc/rcN.d/</filename> directories, where
            <replaceable>N/</replaceable> is one of the following options:
            "S", "0", "1", "2", "3", "4", "5", or "6".
            <note>
                Each runlevel has a dependency on the previous runlevel.
                This dependency allows the services to work properly.
            </note>
        </para>

        <para>
            In comparison, systemd treats components as units.
            Using units is a broader concept as compared to using a service.
            A unit includes several different types of entities.
            Service is one of the types of entities.
            The runlevel concept in SysVinit corresponds to the concept of a
            target in systemd, where target is also a type of supported unit.
        </para>

        <para>
            In a SysVinit-based system, services load sequentially (i.e. one
            by one) during and parallelization is not supported.
            With systemd, services start in parallel.
            Needless to say, the method can have an impact on system startup
            performance.
        </para>

        <para>
            If you want to use SysVinit, you do
            not have to do anything.
            But, if you want to use systemd, you must
            take some steps as described in the following sections.
        </para>

        <section id='using-systemd-exclusively'>
            <title>Using systemd Exclusively</title>

            <para>
                Set these variables in your distribution configuration
                file as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                </literallayout>
                You can also prevent the SysVinit
                distribution feature from
                being automatically enabled as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"
                </literallayout>
                Doing so removes any redundant SysVinit scripts.
            </para>

            <para>
                To remove  initscripts from your image altogether,
                set this variable also:
                <literallayout class='monospaced'>
     VIRTUAL-RUNTIME_initscripts = ""
                </literallayout>
            </para>

            <para>
                For information on the backfill variable, see
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
            </para>
        </section>

        <section id='using-systemd-for-the-main-image-and-using-sysvinit-for-the-rescue-image'>
            <title>Using systemd for the Main Image and Using SysVinit for the Rescue Image</title>

            <para>
                Set these variables in your distribution configuration
                file as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                </literallayout>
                Doing so causes your main image to use the
                <filename>packagegroup-core-boot.bb</filename> recipe and
                systemd.
                The rescue/minimal image cannot use this package group.
                However, it can install SysVinit
                and the appropriate packages will have support for both
                systemd and SysVinit.
            </para>
        </section>
    </section>

    <section id="selecting-dev-manager">
        <title>Selecting a Device Manager</title>

        <para>
            The Yocto Project provides multiple ways to manage the device
            manager (<filename>/dev</filename>):
            <itemizedlist>
                <listitem><para><emphasis>Persistent and Pre-Populated<filename>/dev</filename>:</emphasis>
                    For this case, the <filename>/dev</filename> directory
                    is persistent and the required device nodes are created
                    during the build.
                    </para></listitem>
                <listitem><para><emphasis>Use <filename>devtmpfs</filename> with a Device Manager:</emphasis>
                    For this case, the <filename>/dev</filename> directory
                    is provided by the kernel as an in-memory file system and
                    is automatically populated by the kernel at runtime.
                    Additional configuration of device nodes is done in user
                    space by a device manager like
                    <filename>udev</filename> or
                    <filename>busybox-mdev</filename>.
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id="static-dev-management">
            <title>Using Persistent and Pre-Populated<filename>/dev</filename></title>

            <para>
                To use the static method for device population, you need to
                set the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-USE_DEVFS'><filename>USE_DEVFS</filename></ulink>
                variable to "0" as follows:
                <literallayout class='monospaced'>
     USE_DEVFS = "0"
                </literallayout>
            </para>

            <para>
                The content of the resulting <filename>/dev</filename>
                directory is defined in a Device Table file.
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_DEVICE_TABLES'><filename>IMAGE_DEVICE_TABLES</filename></ulink>
                variable defines the Device Table to use and should be set
                in the machine or distro configuration file.
                Alternatively, you can set this variable in your
                <filename>local.conf</filename> configuration file.
            </para>

            <para>
                If you do not define the
                <filename>IMAGE_DEVICE_TABLES</filename> variable, the default
                <filename>device_table-minimal.txt</filename> is used:
                <literallayout class='monospaced'>
     IMAGE_DEVICE_TABLES = "device_table-mymachine.txt"
                </literallayout>
            </para>

            <para>
                The population is handled by the <filename>makedevs</filename>
                utility during image creation:
            </para>
        </section>

        <section id="devtmpfs-dev-management">
            <title>Using <filename>devtmpfs</filename> and a Device Manager</title>

            <para>
                To use the dynamic method for device population, you need to
                use (or be sure to set) the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-USE_DEVFS'><filename>USE_DEVFS</filename></ulink>
                variable to "1", which is the default:
                <literallayout class='monospaced'>
     USE_DEVFS = "1"
                </literallayout>
                With this setting, the resulting <filename>/dev</filename>
                directory is populated by the kernel using
                <filename>devtmpfs</filename>.
                Make sure the corresponding kernel configuration variable
                <filename>CONFIG_DEVTMPFS</filename> is set when building
                you build a Linux kernel.
            </para>

            <para>
                All devices created by <filename>devtmpfs</filename> will be
                owned by <filename>root</filename> and have permissions
                <filename>0600</filename>.
            </para>

            <para>
                To have more control over the device nodes, you can use a
                device manager like <filename>udev</filename> or
                <filename>busybox-mdev</filename>.
                You choose the device manager by defining the
                <filename>VIRTUAL-RUNTIME_dev_manager</filename> variable
                in your machine or distro configuration file.
                Alternatively, you can set this variable in your
                <filename>local.conf</filename> configuration file:
                <literallayout class='monospaced'>
     VIRTUAL-RUNTIME_dev_manager = "udev"

     # Some alternative values
     # VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
     # VIRTUAL-RUNTIME_dev_manager = "systemd"
                </literallayout>
            </para>
        </section>
    </section>

    <section id="platdev-appdev-srcrev">
        <title>Using an External SCM</title>

        <para>
            If you're working on a recipe that pulls from an external Source
            Code Manager (SCM), it is possible to have the OpenEmbedded build
            system notice new recipe changes added to the SCM and then build
            the resulting packages that depend on the new recipes by using
            the latest versions.
            This only works for SCMs from which it is possible to get a
            sensible revision number for changes.
            Currently, you can do this with Apache Subversion (SVN), Git, and
            Bazaar (BZR) repositories.
        </para>

        <para>
            To enable this behavior, the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
            of the recipe needs to reference
            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>.
            Here is an example:
            <literallayout class='monospaced'>
     PV = "1.2.3+git${SRCPV}"
            </literallayout>
            Then, you can add the following to your
            <filename>local.conf</filename>:
            <literallayout class='monospaced'>
     SRCREV_pn-<replaceable>PN</replaceable> = "${AUTOREV}"
            </literallayout>
            <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>
            is the name of the recipe for which you want to enable automatic source
            revision updating.
        </para>

        <para>
            If you do not want to update your local configuration file, you can
            add the following directly to the recipe to finish enabling
            the feature:
            <literallayout class='monospaced'>
     SRCREV = "${AUTOREV}"
            </literallayout>
        </para>

        <para>
            The Yocto Project provides a distribution named
            <filename>poky-bleeding</filename>, whose configuration
            file contains the line:
            <literallayout class='monospaced'>
     require conf/distro/include/poky-floating-revisions.inc
            </literallayout>
            This line pulls in the listed include file that contains
            numerous lines of exactly that form:
            <literallayout class='monospaced'>
     #SRCREV_pn-opkg-native ?= "${AUTOREV}"
     #SRCREV_pn-opkg-sdk ?= "${AUTOREV}"
     #SRCREV_pn-opkg ?= "${AUTOREV}"
     #SRCREV_pn-opkg-utils-native ?= "${AUTOREV}"
     #SRCREV_pn-opkg-utils ?= "${AUTOREV}"
     SRCREV_pn-gconf-dbus ?= "${AUTOREV}"
     SRCREV_pn-matchbox-common ?= "${AUTOREV}"
     SRCREV_pn-matchbox-config-gtk ?= "${AUTOREV}"
     SRCREV_pn-matchbox-desktop ?= "${AUTOREV}"
     SRCREV_pn-matchbox-keyboard ?= "${AUTOREV}"
     SRCREV_pn-matchbox-panel-2 ?= "${AUTOREV}"
     SRCREV_pn-matchbox-themes-extra ?= "${AUTOREV}"
     SRCREV_pn-matchbox-terminal ?= "${AUTOREV}"
     SRCREV_pn-matchbox-wm ?= "${AUTOREV}"
     SRCREV_pn-settings-daemon ?= "${AUTOREV}"
     SRCREV_pn-screenshot ?= "${AUTOREV}"
          .
          .
          .
            </literallayout>
            These lines allow you to experiment with building a
            distribution that tracks the latest development source
            for numerous packages.
            <note><title>Caution</title>
                The <filename>poky-bleeding</filename> distribution
                is not tested on a regular basis.
                Keep this in mind if you use it.
            </note>
        </para>
    </section>

    <section id='creating-a-read-only-root-filesystem'>
        <title>Creating a Read-Only Root Filesystem</title>

        <para>
            Suppose, for security reasons, you need to disable
            your target device's root filesystem's write permissions
            (i.e. you need a read-only root filesystem).
            Or, perhaps you are running the device's operating system
            from a read-only storage device.
            For either case, you can customize your image for
            that behavior.
        </para>

        <note>
            Supporting a read-only root filesystem requires that the system and
            applications do not try to write to the root filesystem.
            You must configure all parts of the target system to write
            elsewhere, or to gracefully fail in the event of attempting to
            write to the root filesystem.
        </note>

        <section id='creating-the-root-filesystem'>
            <title>Creating the Root Filesystem</title>

            <para>
                To create the read-only root filesystem, simply add the
                "read-only-rootfs" feature to your image, normally in one of two ways.
                The first way is to add the "read-only-rootfs" image feature
                in the image's recipe file via the
                <filename>IMAGE_FEATURES</filename> variable:
                <literallayout class='monospaced'>
     IMAGE_FEATURES += "read-only-rootfs"
                </literallayout>
                As an alternative, you can add the same feature from within your
                build directory's <filename>local.conf</filename> file with the
                associated <filename>EXTRA_IMAGE_FEATURES</filename> variable, as in:
                <literallayout class='monospaced'>
     EXTRA_IMAGE_FEATURES = "read-only-rootfs"
                </literallayout>
            </para>

            <para>
                For more information on how to use these variables, see the
                "<link linkend='usingpoky-extend-customimage-imagefeatures'>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and <filename>EXTRA_IMAGE_FEATURES</filename></link>"
                section.
                For information on the variables, see
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>.
            </para>
        </section>

        <section id='post-installation-scripts'>
            <title>Post-Installation Scripts</title>

            <para>
                It is very important that you make sure all
                post-Installation (<filename>pkg_postinst</filename>) scripts
                for packages that are installed into the image can be run
                at the time when the root filesystem is created during the
                build on the host system.
                These scripts cannot attempt to run during first-boot on the
                target device.
                With the "read-only-rootfs" feature enabled,
                the build system checks during root filesystem creation to make
                sure all post-installation scripts succeed.
                If any of these scripts still need to be run after the root
                filesystem is created, the build immediately fails.
                These build-time checks ensure that the build fails
                rather than the target device fails later during its
                initial boot operation.
            </para>

            <para>
                Most of the common post-installation scripts generated by the
                build system for the out-of-the-box Yocto Project are engineered
                so that they can run during root filesystem creation
                (e.g. post-installation scripts for caching fonts).
                However, if you create and add custom scripts, you need
                to be sure they can be run during this file system creation.
            </para>

            <para>
                Here are some common problems that prevent
                post-installation scripts from running during root filesystem
                creation:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Not using $D in front of absolute
                        paths:</emphasis>
                        The build system defines
                        <filename>$</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink>
                        when the root filesystem is created.
                        Furthermore, <filename>$D</filename> is blank when the
                        script is run on the target device.
                        This implies two purposes for <filename>$D</filename>:
                        ensuring paths are valid in both the host and target
                        environments, and checking to determine which
                        environment is being used as a method for taking
                        appropriate actions.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Attempting to run processes that are
                        specific to or dependent on the target
                        architecture:</emphasis>
                        You can work around these attempts by using native
                        tools, which run on the host system,
                        to accomplish the same tasks, or
                        by alternatively running the processes under QEMU,
                        which has the <filename>qemu_run_binary</filename>
                        function.
                        For more information, see the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-qemu'><filename>qemu</filename></ulink>
                        class.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='areas-with-write-access'>
            <title>Areas With Write Access</title>

            <para>
                With the "read-only-rootfs" feature enabled,
                any attempt by the target to write to the root filesystem at
                runtime fails.
                Consequently, you must make sure that you configure processes
                and applications that attempt these types of writes do so
                to directories with write access (e.g.
                <filename>/tmp</filename> or <filename>/var/run</filename>).
            </para>
        </section>
    </section>


    <section id='maintaining-build-output-quality'>
        <title>Maintaining Build Output Quality</title>

        <para>
            Many factors can influence the quality of a build.
            For example, if you upgrade a recipe to use a new version of an
            upstream software package or you experiment with some new
            configuration options, subtle changes can occur that you might
            not detect until later.
            Consider the case where your recipe is using a newer version of
            an upstream package.
            In this case, a new version of a piece of software might
            introduce an optional dependency on another library, which is
            auto-detected.
            If that library has already been built when the software is
            building, the software will link to the built library and that
            library will be pulled into your image along with the new
            software even if you did not want the library.
        </para>

        <para>
            The
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-buildhistory'><filename>buildhistory</filename></ulink>
            class exists to help you maintain the quality of your build
            output.
            You can use the class to highlight unexpected and possibly
            unwanted changes in the build output.
            When you enable build history, it records information about the
            contents of each package and image and then commits that
            information to a local Git repository where you can examine
            the information.
        </para>

        <para>
            The remainder of this section describes the following:
            <itemizedlist>
               <listitem><para>
                   How you can enable and disable build history
                   </para></listitem>
               <listitem><para>
                   How to understand what the build history contains
                   </para></listitem>
               <listitem><para>
                   How to limit the information used for build history
                   </para></listitem>
               <listitem><para>
                   How to examine the build history from both a
                   command-line and web interface
                   </para></listitem>
           </itemizedlist>
        </para>

        <section id='enabling-and-disabling-build-history'>
            <title>Enabling and Disabling Build History</title>

            <para>
                Build history is disabled by default.
                To enable it, add the following <filename>INHERIT</filename>
                statement and set the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BUILDHISTORY_COMMIT'><filename>BUILDHISTORY_COMMIT</filename></ulink>
                variable to "1" at the end of your
                <filename>conf/local.conf</filename> file found in the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
                <literallayout class='monospaced'>
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "1"
                </literallayout>
                Enabling build history as previously described causes the
                OpenEmbedded build system to collect build output information
                and commit it as a single commit to a local
                <ulink url='&YOCTO_DOCS_OM_URL;#git'>Git</ulink>
                repository.
                <note>
                    Enabling build history increases your build times slightly,
                    particularly for images, and increases the amount of disk
                    space used during the build.
                </note>
            </para>

            <para>
                You can disable build history by removing the previous
                statements from your <filename>conf/local.conf</filename>
                file.
            </para>
        </section>

        <section id='understanding-what-the-build-history-contains'>
            <title>Understanding What the Build History Contains</title>

            <para>
                Build history information is kept in
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TOPDIR'><filename>TOPDIR</filename></ulink><filename>}/buildhistory</filename>
                in the Build Directory as defined by the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BUILDHISTORY_DIR'><filename>BUILDHISTORY_DIR</filename></ulink>
                variable.
                The following is an example abbreviated listing:
                <imagedata fileref="figures/buildhistory.png" align="center" width="6in" depth="4in" />
            </para>

            <para>
                At the top level, a <filename>metadata-revs</filename>
                file exists that lists the revisions of the repositories for
                the enabled layers when the build was produced.
                The rest of the data splits into separate
                <filename>packages</filename>, <filename>images</filename>
                and <filename>sdk</filename> directories, the contents of
                which are described as follows.
            </para>

            <section id='build-history-package-information'>
                <title>Build History Package Information</title>

                <para>
                    The history for each package contains a text file that has
                    name-value pairs with information about the package.
                    For example,
                    <filename>buildhistory/packages/i586-poky-linux/busybox/busybox/latest</filename>
                    contains the following:
                    <literallayout class='monospaced'>
     PV = 1.22.1
     PR = r32
     RPROVIDES =
     RDEPENDS = glibc (>= 2.20) update-alternatives-opkg
     RRECOMMENDS = busybox-syslog busybox-udhcpc update-rc.d
     PKGSIZE = 540168
     FILES = /usr/bin/* /usr/sbin/* /usr/lib/busybox/* /usr/lib/lib*.so.* \
        /etc /com /var /bin/* /sbin/* /lib/*.so.* /lib/udev/rules.d \
        /usr/lib/udev/rules.d /usr/share/busybox /usr/lib/busybox/* \
        /usr/share/pixmaps /usr/share/applications /usr/share/idl \
        /usr/share/omf /usr/share/sounds /usr/lib/bonobo/servers
     FILELIST = /bin/busybox /bin/busybox.nosuid /bin/busybox.suid /bin/sh \
        /etc/busybox.links.nosuid /etc/busybox.links.suid
                    </literallayout>
                    Most of these name-value pairs correspond to variables
                    used to produce the package.
                    The exceptions are <filename>FILELIST</filename>, which
                    is the actual list of files in the package, and
                    <filename>PKGSIZE</filename>, which is the total size of
                    files in the package in bytes.
                </para>

                <para>
                    A file also exists that corresponds to the recipe from
                    which the package came (e.g.
                    <filename>buildhistory/packages/i586-poky-linux/busybox/latest</filename>):
                    <literallayout class='monospaced'>
     PV = 1.22.1
     PR = r32
     DEPENDS = initscripts kern-tools-native update-rc.d-native \
        virtual/i586-poky-linux-compilerlibs virtual/i586-poky-linux-gcc \
        virtual/libc virtual/update-alternatives
     PACKAGES = busybox-ptest busybox-httpd busybox-udhcpd busybox-udhcpc \
        busybox-syslog busybox-mdev busybox-hwclock busybox-dbg \
        busybox-staticdev busybox-dev busybox-doc busybox-locale busybox
                    </literallayout>
                </para>

                <para>
                    Finally, for those recipes fetched from a version control
                    system (e.g., Git), a file exists that lists source
                    revisions that are specified in the recipe and lists
                    the actual revisions used during the build.
                    Listed and actual revisions might differ when
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
                    is set to
                    ${<ulink url='&YOCTO_DOCS_REF_URL;#var-AUTOREV'><filename>AUTOREV</filename></ulink>}.
                    Here is an example assuming
                    <filename>buildhistory/packages/qemux86-poky-linux/linux-yocto/latest_srcrev</filename>):
                    <literallayout class='monospaced'>
     # SRCREV_machine = "38cd560d5022ed2dbd1ab0dca9642e47c98a0aa1"
     SRCREV_machine = "38cd560d5022ed2dbd1ab0dca9642e47c98a0aa1"
     # SRCREV_meta = "a227f20eff056e511d504b2e490f3774ab260d6f"
     SRCREV_meta = "a227f20eff056e511d504b2e490f3774ab260d6f"
                    </literallayout>
                    You can use the
                    <filename>buildhistory-collect-srcrevs</filename>
                    command with the <filename>-a</filename> option to
                    collect the stored <filename>SRCREV</filename> values
                    from build history and report them in a format suitable for
                    use in global configuration (e.g.,
                    <filename>local.conf</filename> or a distro include file)
                    to override floating <filename>AUTOREV</filename> values
                    to a fixed set of revisions.
                    Here is some example output from this command:
                    <literallayout class='monospaced'>
     $ buildhistory-collect-srcrevs -a
     # i586-poky-linux
     SRCREV_pn-glibc = "b8079dd0d360648e4e8de48656c5c38972621072"
     SRCREV_pn-glibc-initial = "b8079dd0d360648e4e8de48656c5c38972621072"
     SRCREV_pn-opkg-utils = "53274f087565fd45d8452c5367997ba6a682a37a"
     SRCREV_pn-kmod = "fd56638aed3fe147015bfa10ed4a5f7491303cb4"
     # x86_64-linux
     SRCREV_pn-gtk-doc-stub-native = "1dea266593edb766d6d898c79451ef193eb17cfa"
     SRCREV_pn-dtc-native = "65cc4d2748a2c2e6f27f1cf39e07a5dbabd80ebf"
     SRCREV_pn-update-rc.d-native = "eca680ddf28d024954895f59a241a622dd575c11"
     SRCREV_glibc_pn-cross-localedef-native = "b8079dd0d360648e4e8de48656c5c38972621072"
     SRCREV_localedef_pn-cross-localedef-native = "c833367348d39dad7ba018990bfdaffaec8e9ed3"
     SRCREV_pn-prelink-native = "faa069deec99bf61418d0bab831c83d7c1b797ca"
     SRCREV_pn-opkg-utils-native = "53274f087565fd45d8452c5367997ba6a682a37a"
     SRCREV_pn-kern-tools-native = "23345b8846fe4bd167efdf1bd8a1224b2ba9a5ff"
     SRCREV_pn-kmod-native = "fd56638aed3fe147015bfa10ed4a5f7491303cb4"
     # qemux86-poky-linux
     SRCREV_machine_pn-linux-yocto = "38cd560d5022ed2dbd1ab0dca9642e47c98a0aa1"
     SRCREV_meta_pn-linux-yocto = "a227f20eff056e511d504b2e490f3774ab260d6f"
     # all-poky-linux
     SRCREV_pn-update-rc.d = "eca680ddf28d024954895f59a241a622dd575c11"
                    </literallayout>
                    <note>
                        Here are some notes on using the
                        <filename>buildhistory-collect-srcrevs</filename>
                        command:
                        <itemizedlist>
                            <listitem><para>
                                By default, only values where the
                                <filename>SRCREV</filename> was not hardcoded
                                (usually when <filename>AUTOREV</filename>
                                is used) are reported.
                                Use the <filename>-a</filename> option to
                                see all <filename>SRCREV</filename> values.
                                </para></listitem>
                            <listitem><para>
                                The output statements might not have any effect
                                if overrides are applied elsewhere in the
                                build system configuration.
                                Use the <filename>-f</filename> option to add
                                the <filename>forcevariable</filename> override
                                to each output line if you need to work around
                                this restriction.
                                </para></listitem>
                            <listitem><para>
                                The script does apply special handling when
                                building for multiple machines.
                                However, the script does place a comment before
                                each set of values that specifies which
                                triplet to which they belong as previously
                                shown (e.g.,
                                <filename>i586-poky-linux</filename>).
                                </para></listitem>
                        </itemizedlist>
                    </note>
                </para>
            </section>

            <section id='build-history-image-information'>
                <title>Build History Image Information</title>

                <para>
                    The files produced for each image are as follows:
                    <itemizedlist>
                        <listitem><para>
                            <filename>image-files:</filename>
                            A directory containing selected files from the root
                            filesystem.
                            The files are defined by
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-BUILDHISTORY_IMAGE_FILES'><filename>BUILDHISTORY_IMAGE_FILES</filename></ulink>.
                            </para></listitem>
                        <listitem><para>
                            <filename>build-id.txt:</filename>
                            Human-readable information about the build
                            configuration and metadata source revisions.
                            This file contains the full build header as printed
                            by BitBake.
                            </para></listitem>
                        <listitem><para>
                            <filename>*.dot:</filename>
                            Dependency graphs for the image that are
                            compatible with <filename>graphviz</filename>.
                            </para></listitem>
                        <listitem><para>
                            <filename>files-in-image.txt:</filename>
 	                        A list of files in the image with permissions,
                            owner, group, size, and symlink information.
                            </para></listitem>
                        <listitem><para>
                            <filename>image-info.txt:</filename>
                            A text file containing name-value pairs with
                            information about the image.
                            See the following listing example for more
                            information.
                            </para></listitem>
                        <listitem><para>
                            <filename>installed-package-names.txt:</filename>
                            A list of installed packages by name only.
                            </para></listitem>
                        <listitem><para>
                            <filename>installed-package-sizes.txt:</filename>
                            A list of installed packages ordered by size.
                            </para></listitem>
                        <listitem><para>
                            <filename>installed-packages.txt:</filename>
                            A list of installed packages with full package
                            filenames.
                            </para></listitem>
                    </itemizedlist>
                    <note>
                        Installed package information is able to be gathered
                        and produced even if package management is disabled
                        for the final image.
                    </note>
                </para>

                <para>
                    Here is an example of <filename>image-info.txt</filename>:
                    <literallayout class='monospaced'>
     DISTRO = poky
     DISTRO_VERSION = 1.7
     USER_CLASSES = buildstats image-mklibs image-prelink
     IMAGE_CLASSES = image_types
     IMAGE_FEATURES = debug-tweaks
     IMAGE_LINGUAS =
     IMAGE_INSTALL = packagegroup-core-boot run-postinsts
     BAD_RECOMMENDATIONS =
     NO_RECOMMENDATIONS =
     PACKAGE_EXCLUDE =
     ROOTFS_POSTPROCESS_COMMAND = write_package_manifest; license_create_manifest; \
        write_image_manifest ; buildhistory_list_installed_image ; \
        buildhistory_get_image_installed ; ssh_allow_empty_password;  \
        postinst_enable_logging; rootfs_update_timestamp ; ssh_disable_dns_lookup ;
     IMAGE_POSTPROCESS_COMMAND =   buildhistory_get_imageinfo ;
     IMAGESIZE = 6900
                    </literallayout>
                    Other than <filename>IMAGESIZE</filename>, which is the
                    total size of the files in the image in Kbytes, the
                    name-value pairs are variables that may have influenced the
                    content of the image.
                    This information is often useful when you are trying to
                    determine why a change in the package or file
                    listings has occurred.
                </para>
            </section>

            <section id='using-build-history-to-gather-image-information-only'>
                <title>Using Build History to Gather Image Information Only</title>

                <para>
                    As you can see, build history produces image information,
                    including dependency graphs, so you can see why something
                    was pulled into the image.
                    If you are just interested in this information and not
                    interested in collecting specific package or SDK
                    information, you can enable writing only image information
                    without any history by adding the following to your
                    <filename>conf/local.conf</filename> file found in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
                    <literallayout class='monospaced'>
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "0"
     BUILDHISTORY_FEATURES = "image"
                    </literallayout>
                    Here, you set the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BUILDHISTORY_FEATURES'><filename>BUILDHISTORY_FEATURES</filename></ulink>
                    variable to use the image feature only.
                </para>
            </section>

            <section id='build-history-sdk-information'>
                <title>Build History SDK Information</title>

                <para>
                    Build history collects similar information on the contents
                    of SDKs
                    (e.g. <filename>bitbake -c populate_sdk imagename</filename>)
                    as compared to information it collects for images.
                    Furthermore, this information differs depending on whether
                    an extensible or standard SDK is being produced.
                </para>

                <para>
                    The following list shows the files produced for SDKs:
                    <itemizedlist>
                        <listitem><para>
                            <filename>files-in-sdk.txt:</filename>
                            A list of files in the SDK with permissions,
                            owner, group, size, and symlink information.
                            This list includes both the host and target parts
                            of the SDK.
                            </para></listitem>
                        <listitem><para>
                            <filename>sdk-info.txt:</filename>
                            A text file containing name-value pairs with
                            information about the SDK.
                            See the following listing example for more
                            information.
                            </para></listitem>
                        <listitem><para>
                            <filename>sstate-task-sizes.txt:</filename>
                            A text file containing name-value pairs with
                            information about task group sizes
                            (e.g. <filename>do_populate_sysroot</filename>
                            tasks have a total size).
                            The <filename>sstate-task-sizes.txt</filename> file
                            exists only when an extensible SDK is created.
                            </para></listitem>
                        <listitem><para>
                            <filename>sstate-package-sizes.txt:</filename>
                            A text file containing name-value pairs with
                            information for the shared-state packages and
                            sizes in the SDK.
                            The <filename>sstate-package-sizes.txt</filename>
                            file exists only when an extensible SDK is created.
                            </para></listitem>
                        <listitem><para>
                            <filename>sdk-files:</filename>
                            A folder that contains copies of the files
                            mentioned in
                            <filename>BUILDHISTORY_SDK_FILES</filename> if the
                            files are present in the output.
                            Additionally, the default value of
                            <filename>BUILDHISTORY_SDK_FILES</filename> is
                            specific to the extensible SDK although you can
                            set it differently if you would like to pull in
                            specific files from the standard SDK.</para>

                            <para>The default files are
                            <filename>conf/local.conf</filename>,
                            <filename>conf/bblayers.conf</filename>,
                            <filename>conf/auto.conf</filename>,
                            <filename>conf/locked-sigs.inc</filename>, and
                            <filename>conf/devtool.conf</filename>.
                            Thus, for an extensible SDK, these files get
                            copied into the <filename>sdk-files</filename>
                            directory.
                            </para></listitem>
                        <listitem><para>
                            The following information appears under
                            each of the <filename>host</filename>
                            and <filename>target</filename> directories
                            for the portions of the SDK that run on the host
                            and on the target, respectively:
                            <note>
                                The following files for the most part are empty
                                when producing an extensible SDK because this
                                type of SDK is not constructed from packages
                                as is the standard SDK.
                            </note>
                            <itemizedlist>
                                <listitem><para>
                                    <filename>depends.dot:</filename>
                                    Dependency graph for the SDK that is
                                    compatible with
                                    <filename>graphviz</filename>.
                                    </para></listitem>
                                <listitem><para>
                                    <filename>installed-package-names.txt:</filename>
                                    A list of installed packages by name only.
                                    </para></listitem>
                                <listitem><para>
                                    <filename>installed-package-sizes.txt:</filename>
                                    A list of installed packages ordered by size.
                                    </para></listitem>
                                <listitem><para>
                                    <filename>installed-packages.txt:</filename>
                                    A list of installed packages with full
                                    package filenames.
                                    </para></listitem>
                                </itemizedlist>
                            </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    Here is an example of <filename>sdk-info.txt</filename>:
                    <literallayout class='monospaced'>
     DISTRO = poky
     DISTRO_VERSION = 1.3+snapshot-20130327
     SDK_NAME = poky-glibc-i686-arm
     SDK_VERSION = 1.3+snapshot
     SDKMACHINE =
     SDKIMAGE_FEATURES = dev-pkgs dbg-pkgs
     BAD_RECOMMENDATIONS =
     SDKSIZE = 352712
                    </literallayout>
                    Other than <filename>SDKSIZE</filename>, which is the
                    total size of the files in the SDK in Kbytes, the
                    name-value pairs are variables that might have influenced
                    the content of the SDK.
                    This information is often useful when you are trying to
                    determine why a change in the package or file listings
                    has occurred.
                </para>
            </section>

            <section id='examining-build-history-information'>
                <title>Examining Build History Information</title>

                <para>
                    You can examine build history output from the command
                    line or from a web interface.
                </para>

                <para>
                    To see any changes that have occurred (assuming you have
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BUILDHISTORY_COMMIT'><filename>BUILDHISTORY_COMMIT</filename></ulink><filename>&nbsp;= "1"</filename>),
                    you can simply use any Git command that allows you to
                    view the history of a repository.
                    Here is one method:
                    <literallayout class='monospaced'>
      $ git log -p
                    </literallayout>
                    You need to realize, however, that this method does show
                    changes that are not significant (e.g. a package's size
                    changing by a few bytes).
                </para>

                <para>
                    A command-line tool called
                    <filename>buildhistory-diff</filename> does exist, though,
                    that queries the Git repository and prints just the
                    differences that might be significant in human-readable
                    form.
                    Here is an example:
                    <literallayout class='monospaced'>
     $ ~/poky/poky/scripts/buildhistory-diff . HEAD^
     Changes to images/qemux86_64/glibc/core-image-minimal (files-in-image.txt):
        /etc/anotherpkg.conf was added
        /sbin/anotherpkg was added
        * (installed-package-names.txt):
        *   anotherpkg was added
     Changes to images/qemux86_64/glibc/core-image-minimal (installed-package-names.txt):
        anotherpkg was added
     packages/qemux86_64-poky-linux/v86d: PACKAGES: added "v86d-extras"
        * PR changed from "r0" to "r1"
        * PV changed from "0.1.10" to "0.1.12"
     packages/qemux86_64-poky-linux/v86d/v86d: PKGSIZE changed from 110579 to 144381 (+30%)
        * PR changed from "r0" to "r1"
        * PV changed from "0.1.10" to "0.1.12"
                    </literallayout>
                    <note>
                        The <filename>buildhistory-diff</filename> tool
                        requires the <filename>GitPython</filename> package.
                        Be sure to install it using Pip3 as follows:
                        <literallayout class='monospaced'>
   $ pip3 install GitPython --user
                        </literallayout>
                        Alternatively, you can install
                        <filename>python3-git</filename> using the appropriate
                        distribution package manager (e.g.
                        <filename>apt-get</filename>, <filename>dnf</filename>,
                        or <filename>zipper</filename>).
                    </note>
                </para>

                <para>
                    To see changes to the build history using a web interface,
                    follow the instruction in the <filename>README</filename>
                    file here.
                    <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/buildhistory-web/'></ulink>.
                </para>

                <para>
                    Here is a sample screenshot of the interface:
                    <imagedata fileref="figures/buildhistory-web.png" align="center" scalefit="1" width="130%" contentdepth="130%" />
                </para>
            </section>
        </section>
    </section>

    <section id="performing-automated-runtime-testing">
        <title>Performing Automated Runtime Testing</title>

        <para>
            The OpenEmbedded build system makes available a series of automated
            tests for images to verify runtime functionality.
            You can run these tests on either QEMU or actual target hardware.
            Tests are written in Python making use of the
            <filename>unittest</filename> module, and the majority of them
            run commands on the target system over SSH.
            This section describes how you set up the environment to use these
            tests, run available tests, and write and add your own tests.
        </para>

        <para>
            For information on the test and QA infrastructure available
            within the Yocto Project, see the
            "<ulink url='&YOCTO_DOCS_REF_URL;#testing-and-quality-assurance'>Testing and Quality Assurance</ulink>"
            section in the Yocto Project Reference Manual.
        </para>

        <section id='enabling-tests'>
            <title>Enabling Tests</title>

            <para>
                Depending on whether you are planning to run tests using
                QEMU or on the hardware, you have to take
                different steps to enable the tests.
                See the following subsections for information on how to
                enable both types of tests.
            </para>

            <section id='qemu-image-enabling-tests'>
                <title>Enabling Runtime Tests on QEMU</title>

                <para>
                    In order to run tests, you need to do the following:
                    <itemizedlist>
                        <listitem><para><emphasis>Set up to avoid interaction
                            with <filename>sudo</filename> for networking:</emphasis>
                            To accomplish this, you must do one of the
                            following:
                            <itemizedlist>
                                <listitem><para>Add
                                    <filename>NOPASSWD</filename> for your user
                                    in <filename>/etc/sudoers</filename> either for
                                    all commands or just for
                                    <filename>runqemu-ifup</filename>.
                                    You must provide the full path as that can
                                    change if you are using multiple clones of the
                                    source repository.
                                    <note>
                                        On some distributions, you also need to
                                        comment out "Defaults requiretty" in
                                        <filename>/etc/sudoers</filename>.
                                    </note></para></listitem>
                                <listitem><para>Manually configure a tap interface
                                    for your system.</para></listitem>
                                <listitem><para>Run as root the script in
                                    <filename>scripts/runqemu-gen-tapdevs</filename>,
                                    which should generate a list of tap devices.
                                    This is the option typically chosen for
                                    Autobuilder-type environments.
                                    <note><title>Notes</title>
                                        <itemizedlist>
                                            <listitem><para>
                                                Be sure to use an absolute path
                                                when calling this script
                                                with sudo.
                                                </para></listitem>
                                            <listitem><para>
                                                The package recipe
                                                <filename>qemu-helper-native</filename>
                                                is required to run this script.
                                                Build the package using the
                                                following command:
                                                <literallayout class='monospaced'>
     $ bitbake qemu-helper-native
                                                </literallayout>
                                                </para></listitem>
                                        </itemizedlist>
                                    </note>
                                    </para></listitem>
                            </itemizedlist></para></listitem>
                        <listitem><para><emphasis>Set the
                            <filename>DISPLAY</filename> variable:</emphasis>
                            You need to set this variable so that you have an X
                            server available (e.g. start
                            <filename>vncserver</filename> for a headless machine).
                            </para></listitem>
                        <listitem><para><emphasis>Be sure your host's firewall
                            accepts incoming connections from
                            192.168.7.0/24:</emphasis>
                            Some of the tests (in particular DNF tests) start
                            an HTTP server on a random high number port,
                            which is used to serve files to the target.
                            The DNF module serves
                            <filename>${WORKDIR}/oe-rootfs-repo</filename>
                            so it can run DNF channel commands.
                            That means your host's firewall
                            must accept incoming connections from 192.168.7.0/24,
                            which is the default IP range used for tap devices
                            by <filename>runqemu</filename>.</para></listitem>
                        <listitem><para><emphasis>Be sure your host has the
                            correct packages installed:</emphasis>
                            Depending your host's distribution, you need
                            to have the following packages installed:
                            <itemizedlist>
                                <listitem><para>Ubuntu and Debian:
                                    <filename>sysstat</filename> and
                                    <filename>iproute2</filename>
                                    </para></listitem>
                                <listitem><para>OpenSUSE:
                                    <filename>sysstat</filename> and
                                    <filename>iproute2</filename>
                                    </para></listitem>
                                <listitem><para>Fedora:
                                    <filename>sysstat</filename> and
                                    <filename>iproute</filename>
                                    </para></listitem>
                                <listitem><para>CentOS:
                                    <filename>sysstat</filename> and
                                    <filename>iproute</filename>
                                    </para></listitem>
                            </itemizedlist>
                        </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    Once you start running the tests, the following happens:
                    <orderedlist>
                        <listitem><para>A copy of the root filesystem is written
                            to <filename>${WORKDIR}/testimage</filename>.
                            </para></listitem>
                        <listitem><para>The image is booted under QEMU using the
                            standard <filename>runqemu</filename> script.
                            </para></listitem>
                        <listitem><para>A default timeout of 500 seconds occurs
                            to allow for the boot process to reach the login prompt.
                            You can change the timeout period by setting
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_QEMUBOOT_TIMEOUT'><filename>TEST_QEMUBOOT_TIMEOUT</filename></ulink>
                            in the <filename>local.conf</filename> file.
                            </para></listitem>
                        <listitem><para>Once the boot process is reached and the
                            login prompt appears, the tests run.
                            The full boot log is written to
                            <filename>${WORKDIR}/testimage/qemu_boot_log</filename>.
                            </para></listitem>
                        <listitem><para>Each test module loads in the order found
                            in <filename>TEST_SUITES</filename>.
                            You can find the full output of the commands run over
                            SSH in
                            <filename>${WORKDIR}/testimgage/ssh_target_log</filename>.
                            </para></listitem>
                        <listitem><para>If no failures occur, the task running the
                            tests ends successfully.
                            You can find the output from the
                            <filename>unittest</filename> in the task log at
                            <filename>${WORKDIR}/temp/log.do_testimage</filename>.
                            </para></listitem>
                    </orderedlist>
                </para>
            </section>

            <section id='hardware-image-enabling-tests'>
                <title>Enabling Runtime Tests on Hardware</title>

                <para>
                    The OpenEmbedded build system can run tests on real
                    hardware, and for certain devices it can also deploy
                    the image to be tested onto the device beforehand.
                </para>

                <para>
                    For automated deployment, a "master image" is installed
                    onto the hardware once as part of setup.
                    Then, each time tests are to be run, the following
                    occurs:
                    <orderedlist>
                        <listitem><para>The master image is booted into and
                            used to write the image to be tested to
                            a second partition.
                            </para></listitem>
                        <listitem><para>The device is then rebooted using an
                            external script that you need to provide.
                            </para></listitem>
                        <listitem><para>The device boots into the image to be
                            tested.
                            </para></listitem>
                    </orderedlist>
                </para>

                <para>
                    When running tests (independent of whether the image
                    has been deployed automatically or not), the device is
                    expected to be connected to a network on a
                    pre-determined IP address.
                    You can either use static IP addresses written into
                    the image, or set the image to use DHCP and have your
                    DHCP server on the test network assign a known IP address
                    based on the MAC address of the device.
                </para>

                <para>
                    In order to run tests on hardware, you need to set
                    <filename>TEST_TARGET</filename> to an appropriate value.
                    For QEMU, you do not have to change anything, the default
                    value is "qemu".
                    For running tests on hardware, the following options exist:
                    <itemizedlist>
                        <listitem><para><emphasis>"simpleremote":</emphasis>
                            Choose "simpleremote" if you are going to
                            run tests on a target system that is already
                            running the image to be tested and is available
                            on the network.
                            You can use "simpleremote" in conjunction
                            with either real hardware or an image running
                            within a separately started QEMU or any
                            other virtual machine manager.
                            </para></listitem>
                        <listitem><para><emphasis>"SystemdbootTarget":</emphasis>
                            Choose "SystemdbootTarget" if your hardware is
                            an EFI-based machine with
                            <filename>systemd-boot</filename> as bootloader and
                            <filename>core-image-testmaster</filename>
                            (or something similar) is installed.
                            Also, your hardware under test must be in a
                            DHCP-enabled network that gives it the same IP
                            address for each reboot.</para>
                            <para>If you choose "SystemdbootTarget", there are
                            additional requirements and considerations.
                            See the
                            "<link linkend='selecting-systemdboottarget'>Selecting SystemdbootTarget</link>"
                            section, which follows, for more information.
                            </para></listitem>
                        <listitem><para><emphasis>"BeagleBoneTarget":</emphasis>
                            Choose "BeagleBoneTarget" if you are deploying
                            images and running tests on the BeagleBone
                            "Black" or original "White" hardware.
                            For information on how to use these tests, see the
                            comments at the top of the BeagleBoneTarget
                            <filename>meta-yocto-bsp/lib/oeqa/controllers/beaglebonetarget.py</filename>
                            file.
                            </para></listitem>
                        <listitem><para><emphasis>"EdgeRouterTarget":</emphasis>
                            Choose "EdgeRouterTarget" is you are deploying
                            images and running tests on the Ubiquiti Networks
                            EdgeRouter Lite.
                            For information on how to use these tests, see the
                            comments at the top of the EdgeRouterTarget
                            <filename>meta-yocto-bsp/lib/oeqa/controllers/edgeroutertarget.py</filename>
                            file.
                            </para></listitem>
                        <listitem><para><emphasis>"GrubTarget":</emphasis>
                            Choose the "supports deploying images and running
                            tests on any generic PC that boots using GRUB.
                            For information on how to use these tests, see the
                            comments at the top of the GrubTarget
                            <filename>meta-yocto-bsp/lib/oeqa/controllers/grubtarget.py</filename>
                            file.
                            </para></listitem>
                        <listitem><para><emphasis>"<replaceable>your-target</replaceable>":</emphasis>
                            Create your own custom target if you want to run
                            tests when you are deploying images and running
                            tests on a custom machine within your BSP layer.
                            To do this, you need to add a Python unit that
                            defines the target class under
                            <filename>lib/oeqa/controllers/</filename> within
                            your layer.
                            You must also provide an empty
                            <filename>__init__.py</filename>.
                            For examples, see files in
                            <filename>meta-yocto-bsp/lib/oeqa/controllers/</filename>.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='selecting-systemdboottarget'>
                <title>Selecting SystemdbootTarget</title>

                <para>
                    If you did not set <filename>TEST_TARGET</filename> to
                    "SystemdbootTarget", then you do not need any information
                    in this section.
                    You can skip down to the
                    "<link linkend='qemu-image-running-tests'>Running Tests</link>"
                    section.
                </para>

                <para>
                    If you did set <filename>TEST_TARGET</filename> to
                    "SystemdbootTarget", you also need to perform a one-time
                    setup of your master image by doing the following:
                    <orderedlist>
                        <listitem><para><emphasis>Set <filename>EFI_PROVIDER</filename>:</emphasis>
                            Be sure that <filename>EFI_PROVIDER</filename>
                            is as follows:
                            <literallayout class='monospaced'>
     EFI_PROVIDER = "systemd-boot"
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Build the master image:</emphasis>
                            Build the <filename>core-image-testmaster</filename>
                            image.
                            The <filename>core-image-testmaster</filename>
                            recipe is provided as an example for a
                            "master" image and you can customize the image
                            recipe as you would any other recipe.
                            </para>
                            <para>Here are the image recipe requirements:
                            <itemizedlist>
                                <listitem><para>Inherits
                                    <filename>core-image</filename>
                                    so that kernel modules are installed.
                                    </para></listitem>
                                <listitem><para>Installs normal linux utilities
                                    not busybox ones (e.g.
                                    <filename>bash</filename>,
                                    <filename>coreutils</filename>,
                                    <filename>tar</filename>,
                                    <filename>gzip</filename>, and
                                    <filename>kmod</filename>).
                                    </para></listitem>
                                <listitem><para>Uses a custom
                                    Initial RAM Disk (initramfs) image with a
                                    custom installer.
                                    A normal image that you can install usually
                                    creates a single rootfs partition.
                                    This image uses another installer that
                                    creates a specific partition layout.
                                    Not all Board Support Packages (BSPs)
                                    can use an installer.
                                    For such cases, you need to manually create
                                    the following partition layout on the
                                    target:
                                    <itemizedlist>
                                        <listitem><para>First partition mounted
                                            under <filename>/boot</filename>,
                                            labeled "boot".
                                            </para></listitem>
                                        <listitem><para>The main rootfs
                                            partition where this image gets
                                            installed, which is mounted under
                                            <filename>/</filename>.
                                            </para></listitem>
                                        <listitem><para>Another partition
                                            labeled "testrootfs" where test
                                            images get deployed.
                                            </para></listitem>
                                    </itemizedlist>
                                    </para></listitem>
                            </itemizedlist>
                            </para></listitem>
                        <listitem><para><emphasis>Install image:</emphasis>
                            Install the image that you just built on the target
                            system.
                            </para></listitem>
                    </orderedlist>
                </para>

                <para>
                    The final thing you need to do when setting
                    <filename>TEST_TARGET</filename> to "SystemdbootTarget" is
                    to set up the test image:
                    <orderedlist>
                        <listitem><para><emphasis>Set up your <filename>local.conf</filename> file:</emphasis>
                            Make sure you have the following statements in
                            your <filename>local.conf</filename> file:
                            <literallayout class='monospaced'>
     IMAGE_FSTYPES += "tar.gz"
     INHERIT += "testimage"
     TEST_TARGET = "SystemdbootTarget"
     TEST_TARGET_IP = "192.168.2.3"
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Build your test image:</emphasis>
                            Use BitBake to build the image:
                            <literallayout class='monospaced'>
     $ bitbake core-image-sato
                            </literallayout>
                            </para></listitem>
                    </orderedlist>
                </para>
            </section>

            <section id='power-control'>
                <title>Power Control</title>

                <para>
                    For most hardware targets other than "simpleremote",
                    you can control power:
                    <itemizedlist>
                        <listitem><para>
                            You can use
                            <filename>TEST_POWERCONTROL_CMD</filename>
                            together with
                            <filename>TEST_POWERCONTROL_EXTRA_ARGS</filename>
                            as a command that runs on the host and does power
                            cycling.
                            The test code passes one argument to that command:
                            off, on or cycle (off then on).
                            Here is an example that could appear in your
                            <filename>local.conf</filename> file:
                            <literallayout class='monospaced'>
     TEST_POWERCONTROL_CMD = "powercontrol.exp test 10.11.12.1 nuc1"
                            </literallayout>
                            In this example, the expect script does the
                            following:
                            <literallayout class='monospaced'>
     ssh test@10.11.12.1 "pyctl nuc1 <replaceable>arg</replaceable>"
                            </literallayout>
                            It then runs a Python script that controls power
                            for a label called <filename>nuc1</filename>.
                            <note>
                                You need to customize
                                <filename>TEST_POWERCONTROL_CMD</filename>
                                and
                                <filename>TEST_POWERCONTROL_EXTRA_ARGS</filename>
                                for your own setup.
                                The one requirement is that it accepts
                                "on", "off", and "cycle" as the last argument.
                            </note>
                            </para></listitem>
                        <listitem><para>
                            When no command is defined, it connects to the
                            device over SSH and uses the classic reboot command
                            to reboot the device.
                            Classic reboot is fine as long as the machine
                            actually reboots (i.e. the SSH test has not
                            failed).
                            It is useful for scenarios where you have a simple
                            setup, typically with a single board, and where
                            some manual interaction is okay from time to time.
                            </para></listitem>
                    </itemizedlist>
                    If you have no hardware to automatically perform power
                    control but still wish to experiment with automated
                    hardware testing, you can use the dialog-power-control
                    script that shows a dialog prompting you to perform the
                    required power action.
                    This script requires either KDialog or Zenity to be
                    installed.
                    To use this script, set the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_POWERCONTROL_CMD'><filename>TEST_POWERCONTROL_CMD</filename></ulink>
                    variable as follows:
                    <literallayout class='monospaced'>
     TEST_POWERCONTROL_CMD = "${COREBASE}/scripts/contrib/dialog-power-control"
                    </literallayout>
                </para>
            </section>

            <section id='serial-console-connection'>
                <title>Serial Console Connection</title>

                <para>
                    For test target classes requiring a serial console
                    to interact with the bootloader (e.g. BeagleBoneTarget,
                    EdgeRouterTarget, and GrubTarget), you need to
                    specify a command to use to connect to the serial console
                    of the target machine by using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SERIALCONTROL_CMD'><filename>TEST_SERIALCONTROL_CMD</filename></ulink>
                    variable and optionally the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SERIALCONTROL_EXTRA_ARGS'><filename>TEST_SERIALCONTROL_EXTRA_ARGS</filename></ulink>
                    variable.
                </para>

                <para>
                    These cases could be a serial terminal program if the
                    machine is connected to a local serial port, or a
                    <filename>telnet</filename> or
                    <filename>ssh</filename> command connecting to a remote
                    console server.
                    Regardless of the case, the command simply needs to
                    connect to the serial console and forward that connection
                    to standard input and output as any normal terminal
                    program does.
                    For example, to use the picocom terminal program on
                    serial device <filename>/dev/ttyUSB0</filename>
                    at 115200bps, you would set the variable as follows:
                    <literallayout class='monospaced'>
     TEST_SERIALCONTROL_CMD = "picocom /dev/ttyUSB0 -b 115200"
                    </literallayout>
                    For local devices where the serial port device disappears
                    when the device reboots, an additional "serdevtry" wrapper
                    script is provided.
                    To use this wrapper, simply prefix the terminal command
                    with
                    <filename>${COREBASE}/scripts/contrib/serdevtry</filename>:
                    <literallayout class='monospaced'>
     TEST_SERIALCONTROL_CMD = "${COREBASE}/scripts/contrib/serdevtry picocom -b
115200 /dev/ttyUSB0"
                    </literallayout>
                </para>
            </section>
        </section>

        <section id="qemu-image-running-tests">
            <title>Running Tests</title>

            <para>
                You can start the tests automatically or manually:
                <itemizedlist>
                    <listitem><para><emphasis>Automatically running tests:</emphasis>
                        To run the tests automatically after the
                        OpenEmbedded build system successfully creates an image,
                        first set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-TESTIMAGE_AUTO'><filename>TESTIMAGE_AUTO</filename></ulink>
                        variable to "1" in your <filename>local.conf</filename>
                        file in the
                        <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
                        <literallayout class='monospaced'>
     TESTIMAGE_AUTO = "1"
                        </literallayout>
                        Next, build your image.
                        If the image successfully builds, the tests run:
                        <literallayout class='monospaced'>
     bitbake core-image-sato
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Manually running tests:</emphasis>
                        To manually run the tests, first globally inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-testimage*'><filename>testimage</filename></ulink>
                        class by editing your <filename>local.conf</filename>
                        file:
                        <literallayout class='monospaced'>
    INHERIT += "testimage"
                        </literallayout>
                        Next, use BitBake to run the tests:
                        <literallayout class='monospaced'>
     bitbake -c testimage <replaceable>image</replaceable>
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>

            <para>
                All test files reside in
                <filename>meta/lib/oeqa/runtime</filename> in the
                <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
                A test name maps directly to a Python module.
                Each test module may contain a number of individual tests.
                Tests are usually grouped together by the area
                tested (e.g tests for systemd reside in
                <filename>meta/lib/oeqa/runtime/systemd.py</filename>).
            </para>

            <para>
                You can add tests to any layer provided you place them in the
                proper area and you extend
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>
                in the <filename>local.conf</filename> file as normal.
                Be sure that tests reside in
                <filename><replaceable>layer</replaceable>/lib/oeqa/runtime</filename>.
                <note>
                    Be sure that module names do not collide with module names
                    used in the default set of test modules in
                    <filename>meta/lib/oeqa/runtime</filename>.
                </note>
            </para>

            <para>
                You can change the set of tests run by appending or overriding
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SUITES'><filename>TEST_SUITES</filename></ulink>
                variable in <filename>local.conf</filename>.
                Each name in <filename>TEST_SUITES</filename> represents a
                required test for the image.
                Test modules named within <filename>TEST_SUITES</filename>
                cannot be skipped even if a test is not suitable for an image
                (e.g. running the RPM tests on an image without
                <filename>rpm</filename>).
                Appending "auto" to <filename>TEST_SUITES</filename> causes the
                build system to try to run all tests that are suitable for the
                image (i.e. each test module may elect to skip itself).
            </para>

            <para>
                The order you list tests in <filename>TEST_SUITES</filename>
                is important and influences test dependencies.
                Consequently, tests that depend on other tests should be added
                after the test on which they depend.
                For example, since the <filename>ssh</filename> test
                depends on the
                <filename>ping</filename> test, "ssh" needs to come after
                "ping" in the list.
                The test class provides no re-ordering or dependency handling.
                <note>
                    Each module can have multiple classes with multiple test
                    methods.
                    And, Python <filename>unittest</filename> rules apply.
                </note>
            </para>

            <para>
                Here are some things to keep in mind when running tests:
                <itemizedlist>
                    <listitem><para>The default tests for the image are defined
                        as:
                        <literallayout class='monospaced'>
     DEFAULT_TEST_SUITES_pn-<replaceable>image</replaceable> = "ping ssh df connman syslog xorg scp vnc date rpm dnf dmesg"
                        </literallayout></para></listitem>
                    <listitem><para>Add your own test to the list of the
                        by using the following:
                        <literallayout class='monospaced'>
     TEST_SUITES_append = " mytest"
                        </literallayout></para></listitem>
                    <listitem><para>Run a specific list of tests as follows:
                        <literallayout class='monospaced'>
     TEST_SUITES = "test1 test2 test3"
                        </literallayout>
                        Remember, order is important.
                        Be sure to place a test that is dependent on another test
                        later in the order.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id="exporting-tests">
            <title>Exporting Tests</title>

            <para>
                You can export tests so that they can run independently of
                the build system.
                Exporting tests is required if you want to be able to hand
                the test execution off to a scheduler.
                You can only export tests that are defined in
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SUITES'><filename>TEST_SUITES</filename></ulink>.
            </para>

            <para>
                If your image is already built, make sure the following are set
                in your <filename>local.conf</filename> file:
                <literallayout class='monospaced'>
     INHERIT +="testexport"
     TEST_TARGET_IP = "<replaceable>IP-address-for-the-test-target</replaceable>"
     TEST_SERVER_IP = "<replaceable>IP-address-for-the-test-server</replaceable>"
                </literallayout>
                You can then export the tests with the following BitBake
                command form:
                <literallayout class='monospaced'>
     $ bitbake <replaceable>image</replaceable> -c testexport
                </literallayout>
                Exporting the tests places them in the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                in
                <filename>tmp/testexport/</filename><replaceable>image</replaceable>,
                which is controlled by the
                <filename>TEST_EXPORT_DIR</filename> variable.
            </para>

            <para>
                You can now run the tests outside of the build environment:
                <literallayout class='monospaced'>
     $ cd tmp/testexport/<replaceable>image</replaceable>
     $ ./runexported.py testdata.json
                </literallayout>
            </para>

            <para>
                Here is a complete example that shows IP addresses and uses
                the <filename>core-image-sato</filename> image:
                <literallayout class='monospaced'>
     INHERIT +="testexport"
     TEST_TARGET_IP = "192.168.7.2"
     TEST_SERVER_IP = "192.168.7.1"
                </literallayout>
                Use BitBake to export the tests:
                <literallayout class='monospaced'>
     $ bitbake core-image-sato -c testexport
                </literallayout>
                Run the tests outside of the build environment using the
                following:
                <literallayout class='monospaced'>
     $ cd tmp/testexport/core-image-sato
     $ ./runexported.py testdata.json
                </literallayout>
            </para>
        </section>

        <section id="qemu-image-writing-new-tests">
            <title>Writing New Tests</title>

            <para>
                As mentioned previously, all new test files need to be in the
                proper place for the build system to find them.
                New tests for additional functionality outside of the core
                should be added to the layer that adds the functionality, in
                <filename><replaceable>layer</replaceable>/lib/oeqa/runtime</filename>
                (as long as
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>
                is extended in the layer's
                <filename>layer.conf</filename> file as normal).
                Just remember the following:
                <itemizedlist>
                    <listitem><para>Filenames need to map directly to test
                        (module) names.
                        </para></listitem>
                    <listitem><para>Do not use module names that
                        collide with existing core tests.
                        </para></listitem>
                    <listitem><para>Minimally, an empty
                        <filename>__init__.py</filename> file must exist
                        in the runtime directory.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                To create a new test, start by copying an existing module
                (e.g. <filename>syslog.py</filename> or
                <filename>gcc.py</filename> are good ones to use).
                Test modules can use code from
                <filename>meta/lib/oeqa/utils</filename>, which are helper
                classes.
            </para>

            <note>
                Structure shell commands such that you rely on them and they
                return a single code for success.
                Be aware that sometimes you will need to parse the output.
                See the <filename>df.py</filename> and
                <filename>date.py</filename> modules for examples.
            </note>

            <para>
                You will notice that all test classes inherit
                <filename>oeRuntimeTest</filename>, which is found in
                <filename>meta/lib/oetest.py</filename>.
                This base class offers some helper attributes, which are
                described in the following sections:
            </para>

            <section id='qemu-image-writing-tests-class-methods'>
                <title>Class Methods</title>

                <para>
                    Class methods are as follows:
                    <itemizedlist>
                        <listitem><para><emphasis><filename>hasPackage(pkg)</filename>:</emphasis>
                            Returns "True" if <filename>pkg</filename> is in the
                            installed package list of the image, which is based
                            on the manifest file that is generated during the
                            <filename>do_rootfs</filename> task.
                            </para></listitem>
                        <listitem><para><emphasis><filename>hasFeature(feature)</filename>:</emphasis>
                            Returns "True" if the feature is in
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                            or
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='qemu-image-writing-tests-class-attributes'>
                <title>Class Attributes</title>

                <para>
                    Class attributes are as follows:
                    <itemizedlist>
                        <listitem><para><emphasis><filename>pscmd</filename>:</emphasis>
                            Equals "ps -ef" if <filename>procps</filename> is
                            installed in the image.
                            Otherwise, <filename>pscmd</filename> equals
                            "ps" (busybox).
                            </para></listitem>
                        <listitem><para><emphasis><filename>tc</filename>:</emphasis>
                            The called test context, which gives access to the
                            following attributes:
                            <itemizedlist>
                                <listitem><para><emphasis><filename>d</filename>:</emphasis>
                                    The BitBake datastore, which allows you to
                                    use stuff such as
                                    <filename>oeRuntimeTest.tc.d.getVar("VIRTUAL-RUNTIME_init_manager")</filename>.
                                    </para></listitem>
                                <listitem><para><emphasis><filename>testslist</filename> and <filename>testsrequired</filename>:</emphasis>
                                    Used internally.
                                    The tests do not need these.
                                    </para></listitem>
                                <listitem><para><emphasis><filename>filesdir</filename>:</emphasis>
                                    The absolute path to
                                    <filename>meta/lib/oeqa/runtime/files</filename>,
                                    which contains helper files for tests meant
                                    for copying on the target such as small
                                    files written in C for compilation.
                                    </para></listitem>
                                <listitem><para><emphasis><filename>target</filename>:</emphasis>
                                    The target controller object used to deploy
                                    and start an image on a particular target
                                    (e.g. Qemu, SimpleRemote, and
                                    SystemdbootTarget).
                                    Tests usually use the following:
                                    <itemizedlist>
                                        <listitem><para><emphasis><filename>ip</filename>:</emphasis>
                                            The target's IP address.
                                            </para></listitem>
                                        <listitem><para><emphasis><filename>server_ip</filename>:</emphasis>
                                            The host's IP address, which is
                                            usually used by the DNF test
                                            suite.
                                            </para></listitem>
                                        <listitem><para><emphasis><filename>run(cmd, timeout=None)</filename>:</emphasis>
                                            The single, most used method.
                                            This command is a wrapper for:
                                            <filename>ssh root@host "cmd"</filename>.
                                            The command returns a tuple:
                                            (status, output), which are what
                                            their names imply - the return code
                                            of "cmd" and whatever output
                                            it produces.
                                            The optional timeout argument
                                            represents the number of seconds the
                                            test should wait for "cmd" to
                                            return.
                                            If the argument is "None", the
                                            test uses the default instance's
                                            timeout period, which is 300
                                            seconds.
                                            If the argument is "0", the test
                                            runs until the command returns.
                                            </para></listitem>
                                        <listitem><para><emphasis><filename>copy_to(localpath, remotepath)</filename>:</emphasis>
                                            <filename>scp localpath root@ip:remotepath</filename>.
                                            </para></listitem>
                                        <listitem><para><emphasis><filename>copy_from(remotepath, localpath)</filename>:</emphasis>
                                            <filename>scp root@host:remotepath localpath</filename>.
                                            </para></listitem>
                                    </itemizedlist></para></listitem>
                            </itemizedlist></para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='qemu-image-writing-tests-instance-attributes'>
                <title>Instance Attributes</title>

                <para>
                    A single instance attribute exists, which is
                    <filename>target</filename>.
                    The <filename>target</filename> instance attribute is
                    identical to the class attribute of the same name, which
                    is described in the previous section.
                    This attribute exists as both an instance and class
                    attribute so tests can use
                    <filename>self.target.run(cmd)</filename> in instance
                    methods instead of
                    <filename>oeRuntimeTest.tc.target.run(cmd)</filename>.
                </para>
            </section>
        </section>

        <section id='installing-packages-in-the-dut-without-the-package-manager'>
            <title>Installing Packages in the DUT Without the Package Manager</title>

            <para>
                When a test requires a package built by BitBake, it is possible
                to install that package.
                Installing the package does not require a package manager be
                installed in the device under test (DUT).
                It does, however, require an SSH connection and the target must
                be using the <filename>sshcontrol</filename> class.
                <note>
                    This method uses <filename>scp</filename> to copy files
                    from the host to the target, which causes permissions and
                    special attributes to be lost.
                </note>
            </para>

            <para>
                A JSON file is used to define the packages needed by a test.
                This file must be in the same path as the file used to define
                the tests.
                Furthermore, the filename must map directly to the test
                module name with a <filename>.json</filename> extension.
            </para>

            <para>
                The JSON file must include an object with the test name as
                keys of an object or an array.
                This object (or array of objects) uses the following data:
                <itemizedlist>
                    <listitem><para>"pkg" - A mandatory string that is the
                        name of the package to be installed.
                        </para></listitem>
                    <listitem><para>"rm" - An optional boolean, which defaults
                        to "false", that specifies to remove the package after
                        the test.
                        </para></listitem>
                    <listitem><para>"extract" - An optional boolean, which
                        defaults to "false", that specifies if the package must
                        be extracted from the package format.
                        When set to "true", the package is not automatically
                        installed into the DUT.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Following is an example JSON file that handles test "foo"
                installing package "bar" and test "foobar" installing
                packages "foo" and "bar".
                Once the test is complete, the packages are removed from the
                DUT.
                <literallayout class='monospaced'>
     {
         "foo": {
             "pkg": "bar"
         },
         "foobar": [
             {
                 "pkg": "foo",
                 "rm": true
             },
             {
                 "pkg": "bar",
                 "rm": true
             }
         ]
     }
                </literallayout>
            </para>
        </section>
    </section>

    <section id='usingpoky-debugging-tools-and-techniques'>
        <title>Debugging Tools and Techniques</title>

        <para>
            The exact method for debugging build failures depends on the nature
            of the problem and on the system's area from which the bug
            originates.
            Standard debugging practices such as comparison against the last
            known working version with examination of the changes and the
            re-application of steps to identify the one causing the problem are
            valid for the Yocto Project just as they are for any other system.
            Even though it is impossible to detail every possible potential
            failure, this section provides some general tips to aid in
            debugging given a variety of situations.
            <note><title>Tip</title>
                A useful feature for debugging is the error reporting tool.
                Configuring the Yocto Project to use this tool causes the
                OpenEmbedded build system to produce error reporting commands as
                part of the console output.
                You can enter the commands after the build completes to log
                error information into a common database, that can help you
                figure out what might be going wrong.
                For information on how to enable and use this feature, see the
                "<link linkend='using-the-error-reporting-tool'>Using the Error Reporting Tool</link>"
                section.
            </note>
        </para>

        <para>
            The following list shows the debugging topics in the remainder of
            this section:
            <itemizedlist>
                <listitem><para>
                    "<link linkend='dev-debugging-viewing-logs-from-failed-tasks'>Viewing Logs from Failed Tasks</link>"
                    describes how to find and view logs from tasks that
                    failed during the build process.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='dev-debugging-viewing-variable-values'>Viewing Variable Values</link>"
                    describes how to use the BitBake <filename>-e</filename>
                    option to examine variable values after a recipe has been
                    parsed.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='viewing-package-information-with-oe-pkgdata-util'>Viewing Package Information with <filename>oe-pkgdata-util</filename></link>"
                    describes how to use the
                    <filename>oe-pkgdata-util</filename> utility to query
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PKGDATA_DIR'><filename>PKGDATA_DIR</filename></ulink>
                    and display package-related information for built
                    packages.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='dev-viewing-dependencies-between-recipes-and-tasks'>Viewing Dependencies Between Recipes and Tasks</link>"
                    describes how to use the BitBake <filename>-g</filename>
                    option to display recipe dependency information used
                    during the build.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='dev-viewing-task-variable-dependencies'>Viewing Task Variable Dependencies</link>"
                    describes how to use the
                    <filename>bitbake-dumpsig</filename> command in
                    conjunction with key subdirectories in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                    to determine variable dependencies.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='dev-debugging-taskrunning'>Running Specific Tasks</link>"
                    describes how to use several BitBake options (e.g.
                    <filename>-c</filename>, <filename>-C</filename>, and
                    <filename>-f</filename>) to run specific tasks in the
                    build chain.
                    It can be useful to run tasks "out-of-order" when trying
                    isolate build issues.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='dev-debugging-bitbake'>General BitBake Problems</link>"
                    describes how to use BitBake's <filename>-D</filename>
                    debug output option to reveal more about what BitBake is
                    doing during the build.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='dev-debugging-buildfile'>Building with No Dependencies</link>"
                    describes how to use the BitBake <filename>-b</filename>
                    option to build a recipe while ignoring dependencies.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='recipe-logging-mechanisms'>Recipe Logging Mechanisms</link>"
                    describes how to use the many recipe logging functions
                    to produce debugging output and report errors and warnings.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='debugging-parallel-make-races'>Debugging Parallel Make Races</link>"
                    describes how to debug situations where the build consists
                    of several parts that are run simultaneously and when the
                    output or result of one part is not ready for use with a
                    different part of the build that depends on that output.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='platdev-gdb-remotedebug'>Debugging With the GNU Project Debugger (GDB) Remotely</link>"
                    describes how to use GDB to allow you to examine running
                    programs, which can help you fix problems.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='debugging-with-the-gnu-project-debugger-gdb-on-the-target'>Debugging with the GNU Project Debugger (GDB) on the Target</link>"
                    describes how to use GDB directly on target hardware for
                    debugging.
                    </para></listitem>
                <listitem><para>
                    "<link linkend='dev-other-debugging-others'>Other Debugging Tips</link>"
                    describes miscellaneous debugging tips that can be useful.
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id='dev-debugging-viewing-logs-from-failed-tasks'>
            <title>Viewing Logs from Failed Tasks</title>

            <para>
                You can find the log for a task in the file
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/temp/log.do_</filename><replaceable>taskname</replaceable>.
                For example, the log for the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
                task of the QEMU minimal image for the x86 machine
                (<filename>qemux86</filename>) might be in
                <filename>tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/temp/log.do_compile</filename>.
                To see the commands
                <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink>
                ran to generate a log, look at the corresponding
                <filename>run.do_</filename><replaceable>taskname</replaceable>
                file in the same directory.
            </para>

            <para>
                <filename>log.do_</filename><replaceable>taskname</replaceable>
                and
                <filename>run.do_</filename><replaceable>taskname</replaceable>
                are actually symbolic links to
                <filename>log.do_</filename><replaceable>taskname</replaceable><filename>.</filename><replaceable>pid</replaceable>
                and
                <filename>log.run_</filename><replaceable>taskname</replaceable><filename>.</filename><replaceable>pid</replaceable>,
                where <replaceable>pid</replaceable> is the PID the task had
                when it ran.
                The symlinks always point to the files corresponding to the most
                recent run.
            </para>
        </section>

        <section id='dev-debugging-viewing-variable-values'>
            <title>Viewing Variable Values</title>

            <para>
                Sometimes you need to know the value of a variable as a
                result of BitBake's parsing step.
                This could be because some unexpected behavior occurred
                in your project.
                Perhaps an attempt to
                <ulink url='&YOCTO_DOCS_BB_URL;#modifying-existing-variables'>modify a variable</ulink>
                did not work out as expected.
            </para>

            <para>
                BitBake's <filename>-e</filename> option is used to display
                variable values after parsing.
                The following command displays the variable values after the
                configuration files (i.e. <filename>local.conf</filename>,
                <filename>bblayers.conf</filename>,
                <filename>bitbake.conf</filename> and so forth) have been
                parsed:
                <literallayout class='monospaced'>
     $ bitbake -e
                </literallayout>
                The following command displays variable values after a specific
                recipe has been parsed.
                The variables include those from the configuration as well:
                <literallayout class='monospaced'>
     $ bitbake -e recipename
                </literallayout>
                <note><para>
                    Each recipe has its own private set of variables
                    (datastore).
                    Internally, after parsing the configuration, a copy of the
                    resulting datastore is made prior to parsing each recipe.
                    This copying implies that variables set in one recipe will
                    not be visible to other recipes.</para>

                    <para>Likewise, each task within a recipe gets a private
                    datastore based on the recipe datastore, which means that
                    variables set within one task will not be visible to
                    other tasks.</para>
                </note>
            </para>

            <para>
                In the output of <filename>bitbake -e</filename>, each
                variable is preceded by a description of how the variable
                got its value, including temporary values that were later
                overriden.
                This description also includes variable flags (varflags) set on
                the variable.
                The output can be very helpful during debugging.
            </para>

            <para>
                Variables that are exported to the environment are preceded by
                <filename>export</filename> in the output of
                <filename>bitbake -e</filename>.
                See the following example:
                <literallayout class='monospaced'>
     export CC="i586-poky-linux-gcc -m32 -march=i586 --sysroot=/home/ulf/poky/build/tmp/sysroots/qemux86"
                </literallayout>
            </para>

            <para>
                In addition to variable values, the output of the
                <filename>bitbake -e</filename> and
                <filename>bitbake -e</filename>&nbsp;<replaceable>recipe</replaceable>
                commands includes the following information:
                <itemizedlist>
                    <listitem><para>
                        The output starts with a tree listing all configuration
                        files and classes included globally, recursively listing
                        the files they include or inherit in turn.
                        Much of the behavior of the OpenEmbedded build system
                        (including the behavior of the
                        <ulink url='&YOCTO_DOCS_REF_URL;#normal-recipe-build-tasks'>normal recipe build tasks</ulink>)
                        is implemented in the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-base'><filename>base</filename></ulink>
                        class and the classes it inherits, rather than being
                        built into BitBake itself.
                        </para></listitem>
                    <listitem><para>
                        After the variable values, all functions appear in the
                        output.
                        For shell functions, variables referenced within the
                        function body are expanded.
                        If a function has been modified using overrides or
                        using override-style operators like
                        <filename>_append</filename> and
                        <filename>_prepend</filename>, then the final assembled
                        function body appears in the output.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='viewing-package-information-with-oe-pkgdata-util'>
            <title>Viewing Package Information with <filename>oe-pkgdata-util</filename></title>

            <para>
                You can use the <filename>oe-pkgdata-util</filename>
                command-line utility to query
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PKGDATA_DIR'><filename>PKGDATA_DIR</filename></ulink>
                and display various package-related information.
                When you use the utility, you must use it to view information
                on packages that have already been built.
            </para>

            <para>
                Following are a few of the available
                <filename>oe-pkgdata-util</filename> subcommands.
                <note>
                    You can use the standard * and ? globbing wildcards as part
                    of package names and paths.
                </note>
                <itemizedlist>
                    <listitem><para>
                        <filename>oe-pkgdata-util list-pkgs [</filename><replaceable>pattern</replaceable><filename>]</filename>:
                        Lists all packages that have been built, optionally
                        limiting the match to packages that match
                        <replaceable>pattern</replaceable>.
                        </para></listitem>
                    <listitem><para>
                        <filename>oe-pkgdata-util list-pkg-files&nbsp;</filename><replaceable>package</replaceable><filename>&nbsp;...</filename>:
                        Lists the files and directories contained in the given
                        packages.
                        <note>
                            <para>
                            A different way to view the contents of a package is
                            to look at the
                            <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/packages-split</filename>
                            directory of the recipe that generates the
                            package.
                            This directory is created by the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>
                            task and has one subdirectory for each package the
                            recipe generates, which contains the files stored in
                            that package.</para>
                            <para>
                            If you want to inspect the
                            <filename>${WORKDIR}/packages-split</filename>
                            directory, make sure that
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-rm-work'><filename>rm_work</filename></ulink>
                            is not enabled when you build the recipe.
                            </para>
                            </note>
                        </para></listitem>
                    <listitem><para>
                        <filename>oe-pkgdata-util find-path&nbsp;</filename><replaceable>path</replaceable><filename>&nbsp;...</filename>:
                        Lists the names of the packages that contain the given
                        paths.
                        For example, the following tells us that
                        <filename>/usr/share/man/man1/make.1</filename>
                        is contained in the <filename>make-doc</filename>
                        package:
                        <literallayout class='monospaced'>
     $ oe-pkgdata-util find-path /usr/share/man/man1/make.1
     make-doc: /usr/share/man/man1/make.1
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <filename>oe-pkgdata-util lookup-recipe&nbsp;</filename><replaceable>package</replaceable><filename>&nbsp;...</filename>:
                        Lists the name of the recipes that
                        produce the given packages.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                For more information on the <filename>oe-pkgdata-util</filename>
                command, use the help facility:
                <literallayout class='monospaced'>
     $ oe-pkgdata-util &dash;&dash;help
     $ oe-pkgdata-util <replaceable>subcommand</replaceable> --help
                </literallayout>
            </para>
        </section>

        <section id='dev-viewing-dependencies-between-recipes-and-tasks'>
            <title>Viewing Dependencies Between Recipes and Tasks</title>

            <para>
                Sometimes it can be hard to see why BitBake wants to build other
                recipes before the one you have specified.
                Dependency information can help you understand why a recipe is
                built.
            </para>

            <para>
                To generate dependency information for a recipe, run the
                following command:
                <literallayout class='monospaced'>
     $ bitbake -g <replaceable>recipename</replaceable>
                </literallayout>
                This command writes the following files in the current
                directory:
                <itemizedlist>
                    <listitem><para>
                        <filename>pn-buildlist</filename>: A list of
                        recipes/targets involved in building
                        <replaceable>recipename</replaceable>.
                        "Involved" here means that at least one task from the
                         recipe needs to run when building
                        <replaceable>recipename</replaceable> from scratch.
                        Targets that are in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-ASSUME_PROVIDED'><filename>ASSUME_PROVIDED</filename></ulink>
                        are not listed.
                        </para></listitem>
                    <listitem><para>
                        <filename>task-depends.dot</filename>: A graph showing
                        dependencies between tasks.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                The graphs are in
                <ulink url='https://en.wikipedia.org/wiki/DOT_%28graph_description_language%29'>DOT</ulink>
                format and can be converted to images (e.g. using the
                <filename>dot</filename> tool from
                <ulink url='http://www.graphviz.org/'>Graphviz</ulink>).
                <note><title>Notes</title>
                    <itemizedlist>
                        <listitem><para>
                            DOT files use a plain text format.
                            The graphs generated using the
                            <filename>bitbake -g</filename> command are often so
                            large as to be difficult to read without special
                            pruning (e.g. with Bitbake's
                            <filename>-I</filename> option) and processing.
                            Despite the form and size of the graphs, the
                            corresponding <filename>.dot</filename> files can
                            still be possible to read and provide useful
                            information.
                            </para>

                            <para>As an example, the
                            <filename>task-depends.dot</filename> file contains
                            lines such as the following:
                            <literallayout class='monospaced'>
     "libxslt.do_configure" -> "libxml2.do_populate_sysroot"
                            </literallayout>
                            The above example line reveals that the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                            task in <filename>libxslt</filename> depends on the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></ulink>
                            task in <filename>libxml2</filename>, which is a
                            normal
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                            dependency between the two recipes.
                            </para></listitem>
                        <listitem><para>
                            For an example of how <filename>.dot</filename>
                            files can be processed, see the
                            <filename>scripts/contrib/graph-tool</filename>
                            Python script, which finds and displays paths
                            between graph nodes.
                            </para></listitem>
                    </itemizedlist>
                </note>
            </para>

            <para>
                You can use a different method to view dependency information
                by using the following command:
                <literallayout class='monospaced'>
     $ bitbake -g -u taskexp <replaceable>recipename</replaceable>
                </literallayout>
                This command displays a GUI window from which you can view
                build-time and runtime dependencies for the recipes involved in
                building <replaceable>recipename</replaceable>.
            </para>
        </section>

        <section id='dev-viewing-task-variable-dependencies'>
            <title>Viewing Task Variable Dependencies</title>

            <para>
                As mentioned in the
                "<ulink url='&YOCTO_DOCS_BB_URL;#checksums'>Checksums (Signatures)</ulink>"
                section of the BitBake User Manual, BitBake tries to
                automatically determine what variables a task depends on so
                that it can rerun the task if any values of the variables
                change.
                This determination is usually reliable.
                However, if you do things like construct variable names at
                runtime, then you might have to manually declare dependencies
                on those variables using <filename>vardeps</filename> as
                described in the
                "<ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'>Variable Flags</ulink>"
                section of the BitBake User Manual.
            </para>

            <para>
                If you are unsure whether a variable dependency is being
                picked up automatically for a given task, you can list the
                variable dependencies BitBake has determined by doing the
                following:
                <orderedlist>
                    <listitem><para>
                        Build the recipe containing the task:
                        <literallayout class='monospaced'>
     $ bitbake <replaceable>recipename</replaceable>
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Inside the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-STAMPS_DIR'><filename>STAMPS_DIR</filename></ulink>
                        directory, find the signature data
                        (<filename>sigdata</filename>) file that corresponds
                        to the task.
                        The <filename>sigdata</filename> files contain a pickled
                        Python database of all the metadata that went into
                        creating the input checksum for the task.
                        As an example, for the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>
                        task of the <filename>db</filename> recipe, the
                        <filename>sigdata</filename> file might be found in the
                        following location:
                        <literallayout class='monospaced'>
     ${BUILDDIR}/tmp/stamps/i586-poky-linux/db/6.0.30-r1.do_fetch.sigdata.7c048c18222b16ff0bcee2000ef648b1
                        </literallayout>
                        For tasks that are accelerated through the shared state
                        (<ulink url='&YOCTO_DOCS_OM_URL;#shared-state-cache'>sstate</ulink>)
                        cache, an additional <filename>siginfo</filename> file
                        is written into
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>
                        along with the cached task output.
                        The <filename>siginfo</filename> files contain exactly
                        the same information as <filename>sigdata</filename>
                        files.
                        </para></listitem>
                    <listitem><para>
                        Run <filename>bitbake-dumpsig</filename> on the
                        <filename>sigdata</filename> or
                        <filename>siginfo</filename> file.
                        Here is an example:
                        <literallayout class='monospaced'>
     $ bitbake-dumpsig ${BUILDDIR}/tmp/stamps/i586-poky-linux/db/6.0.30-r1.do_fetch.sigdata.7c048c18222b16ff0bcee2000ef648b1
                        </literallayout>
                        In the output of the above command, you will find a
                        line like the following, which lists all the (inferred)
                        variable dependencies for the task.
                        This list also includes indirect dependencies from
                        variables depending on other variables, recursively.
                        <literallayout class='monospaced'>
     Task dependencies: ['PV', 'SRCREV', 'SRC_URI', 'SRC_URI[md5sum]', 'SRC_URI[sha256sum]', 'base_do_fetch']
                        </literallayout>
                        <note>
                            Functions (e.g. <filename>base_do_fetch</filename>)
                            also count as variable dependencies.
                            These functions in turn depend on the variables they
                            reference.
                        </note>
                        The output of <filename>bitbake-dumpsig</filename> also
                        includes the value each variable had, a list of
                        dependencies for each variable, and
                        <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_HASHBASE_WHITELIST'><filename>BB_HASHBASE_WHITELIST</filename></ulink>
                        information.
                        </para></listitem>
                </orderedlist>
            </para>

            <para>
                There is also a <filename>bitbake-diffsigs</filename> command
                for comparing two <filename>siginfo</filename> or
                <filename>sigdata</filename> files.
                This command can be helpful when trying to figure out what
                changed between two versions of a task.
                If you call <filename>bitbake-diffsigs</filename> with just one
                file, the command behaves like
                <filename>bitbake-dumpsig</filename>.
            </para>

            <para>
                You can also use BitBake to dump out the signature construction
                information without executing tasks by using either of the
                following BitBake command-line options:
                <literallayout class='monospaced'>
     &dash;&dash;dump-signatures=<replaceable>SIGNATURE_HANDLER</replaceable>
     -S <replaceable>SIGNATURE_HANDLER</replaceable>
                </literallayout>
                <note>
                    Two common values for
                    <replaceable>SIGNATURE_HANDLER</replaceable> are "none" and
                    "printdiff", which dump only the signature or compare the
                    dumped signature with the cached one, respectively.
                </note>
                Using BitBake with either of these options causes BitBake to
                dump out <filename>sigdata</filename> files in the
                <filename>stamps</filename> directory for every task it would
                have executed instead of building the specified target package.
            </para>
        </section>

        <section id='dev-viewing-metadata-used-to-create-the-input-signature-of-a-shared-state-task'>
            <title>Viewing Metadata Used to Create the Input Signature of a Shared State Task</title>

            <para>
                Seeing what metadata went into creating the input signature
                of a shared state (sstate) task can be a useful debugging
                aid.
                This information is available in signature information
                (<filename>siginfo</filename>) files in
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>.
                For information on how to view and interpret information in
                <filename>siginfo</filename> files, see the
                "<link linkend='dev-viewing-task-variable-dependencies'>Viewing Task Variable Dependencies</link>"
                section.
            </para>

            <para>
                For conceptual information on shared state, see the
                "<ulink url='&YOCTO_DOCS_OM_URL;#shared-state'>Shared State</ulink>"
                section in the Yocto Project Overview and Concepts Manual.
            </para>
        </section>

        <section id='dev-invalidating-shared-state-to-force-a-task-to-run'>
            <title>Invalidating Shared State to Force a Task to Run</title>

            <para>
                The OpenEmbedded build system uses
                <ulink url='&YOCTO_DOCS_OM_URL;#overview-checksums'>checksums</ulink>
                and
                <ulink url='&YOCTO_DOCS_OM_URL;#shared-state'>shared state</ulink>
                cache to avoid unnecessarily rebuilding tasks.
                Collectively, this scheme is known as "shared state code."
            </para>

            <para>
                As with all schemes, this one has some drawbacks.
                It is possible that you could make implicit changes to your
                code that the checksum calculations do not take into
                account.
                These implicit changes affect a task's output but do not
                trigger the shared state code into rebuilding a recipe.
                Consider an example during which a tool changes its output.
                Assume that the output of <filename>rpmdeps</filename>
                changes.
                The result of the change should be that all the
                <filename>package</filename> and
                <filename>package_write_rpm</filename> shared state cache
                items become invalid.
                However, because the change to the output is
                external to the code and therefore implicit,
                the associated shared state cache items do not become
                invalidated.
                In this case, the build process uses the cached items
                rather than running the task again.
                Obviously, these types of implicit changes can cause
                problems.
            </para>

            <para>
                To avoid these problems during the build, you need to
                understand the effects of any changes you make.
                Realize that changes you make directly to a function
                are automatically factored into the checksum calculation.
                Thus, these explicit changes invalidate the associated
                area of shared state cache.
                However, you need to be aware of any implicit changes that
                are not obvious changes to the code and could affect
                the output of a given task.
            </para>

            <para>
                When you identify an implicit change, you can easily
                take steps to invalidate the cache and force the tasks
                to run.
                The steps you can take are as simple as changing a
                function's comments in the source code.
                For example, to invalidate package shared state files,
                change the comment statements of
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>
                or the comments of one of the functions it calls.
                Even though the change is purely cosmetic, it causes the
                checksum to be recalculated and forces the build system to
                run the task again.
                <note>
                    For an example of a commit that makes a cosmetic
                    change to invalidate shared state, see this
                    <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/commit/meta/classes/package.bbclass?id=737f8bbb4f27b4837047cb9b4fbfe01dfde36d54'>commit</ulink>.
                </note>
            </para>
        </section>

        <section id='dev-debugging-taskrunning'>
            <title>Running Specific Tasks</title>

            <para>
                Any given recipe consists of a set of tasks.
                The standard BitBake behavior in most cases is:
                <filename>do_fetch</filename>,
                <filename>do_unpack</filename>,
                <filename>do_patch</filename>,
                <filename>do_configure</filename>,
                <filename>do_compile</filename>,
                <filename>do_install</filename>,
                <filename>do_package</filename>,
                <filename>do_package_write_*</filename>, and
                <filename>do_build</filename>.
                The default task is <filename>do_build</filename> and any tasks
                on which it depends build first.
                Some tasks, such as <filename>do_devshell</filename>, are not
                part of the default build chain.
                If you wish to run a task that is not part of the default build
                chain, you can use the <filename>-c</filename> option in
                BitBake.
                Here is an example:
                <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devshell
                </literallayout>
            </para>

            <para>
                The <filename>-c</filename> option respects task dependencies,
                which means that all other tasks (including tasks from other
                recipes) that the specified task depends on will be run before
                the task.
                Even when you manually specify a task to run with
                <filename>-c</filename>, BitBake will only run the task if it
                considers it "out of date".
                See the
                "<ulink url='&YOCTO_DOCS_OM_URL;#stamp-files-and-the-rerunning-of-tasks'>Stamp Files and the Rerunning of Tasks</ulink>"
                section in the Yocto Project Overview and Concepts Manual for
                how BitBake determines whether a task is "out of date".
            </para>

            <para>
                If you want to force an up-to-date task to be rerun (e.g.
                because you made manual modifications to the recipe's
                <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
                that you want to try out), then you can use the
                <filename>-f</filename> option.
                <note>
                    The reason <filename>-f</filename> is never required when
                    running the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-devshell'><filename>do_devshell</filename></ulink>
                    task is because the
                    <filename>[</filename><ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'><filename>nostamp</filename></ulink><filename>]</filename>
                    variable flag is already set for the task.
                </note>
                The following example shows one way you can use the
                <filename>-f</filename> option:
                <literallayout class='monospaced'>
     $ bitbake matchbox-desktop
               .
               .
     make some changes to the source code in the work directory
               .
               .
     $ bitbake matchbox-desktop -c compile -f
     $ bitbake matchbox-desktop
                </literallayout>
            </para>

            <para>
                This sequence first builds and then recompiles
                <filename>matchbox-desktop</filename>.
                The last command reruns all tasks (basically the packaging
                tasks) after the compile.
                BitBake recognizes that the <filename>do_compile</filename>
                task was rerun and therefore understands that the other tasks
                also need to be run again.
            </para>

            <para>
                Another, shorter way to rerun a task and all
                <ulink url='&YOCTO_DOCS_REF_URL;#normal-recipe-build-tasks'>normal recipe build tasks</ulink>
                that depend on it is to use the <filename>-C</filename>
                option.
                <note>
                    This option is upper-cased and is separate from the
                    <filename>-c</filename> option, which is lower-cased.
                </note>
                Using this option invalidates the given task and then runs the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-build'><filename>do_build</filename></ulink>
                task, which is the default task if no task is given, and the
                tasks on which it depends.
                You could replace the final two commands in the previous example
                with the following single command:
                <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -C compile
                </literallayout>
                Internally, the <filename>-f</filename> and
                <filename>-C</filename> options work by tainting (modifying) the
                input checksum of the specified task.
                This tainting indirectly causes the task and its
                dependent tasks to be rerun through the normal task dependency
                mechanisms.
                <note>
                    BitBake explicitly keeps track of which tasks have been
                    tainted in this fashion, and will print warnings such as the
                    following for builds involving such tasks:
                    <literallayout class='monospaced'>
     WARNING: /home/ulf/poky/meta/recipes-sato/matchbox-desktop/matchbox-desktop_2.1.bb.do_compile is tainted from a forced run
                    </literallayout>
                    The purpose of the warning is to let you know that the work
                    directory and build output might not be in the clean state
                    they would be in for a "normal" build, depending on what
                    actions you took.
                    To get rid of such warnings, you can remove the work
                    directory and rebuild the recipe, as follows:
                    <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c clean
     $ bitbake matchbox-desktop
                    </literallayout>
                </note>
            </para>

            <para>
                You can view a list of tasks in a given package by running the
                <filename>do_listtasks</filename> task as follows:
                <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c listtasks
                </literallayout>
                The results appear as output to the console and are also in the
                file <filename>${WORKDIR}/temp/log.do_listtasks</filename>.
            </para>
        </section>

        <section id='dev-debugging-bitbake'>
            <title>General BitBake Problems</title>

            <para>
                You can see debug output from BitBake by using the
                <filename>-D</filename> option.
                The debug output gives more information about what BitBake
                is doing and the reason behind it.
                Each <filename>-D</filename> option you use increases the
                logging level.
                The most common usage is <filename>-DDD</filename>.
            </para>

            <para>
                The output from
                <filename>bitbake -DDD -v</filename> <replaceable>targetname</replaceable>
                can reveal why BitBake chose a certain version of a package or
                why BitBake picked a certain provider.
                This command could also help you in a situation where you think
                BitBake did something unexpected.
            </para>
        </section>

        <section id='dev-debugging-buildfile'>
            <title>Building with No Dependencies</title>

            <para>
                To build a specific recipe (<filename>.bb</filename> file),
                you can use the following command form:
                <literallayout class='monospaced'>
     $ bitbake -b <replaceable>somepath</replaceable>/<replaceable>somerecipe</replaceable>.bb
                </literallayout>
                This command form does not check for dependencies.
                Consequently, you should use it only when you know existing
                dependencies have been met.
                <note>
                    You can also specify fragments of the filename.
                    In this case, BitBake checks for a unique match.
                </note>
            </para>
        </section>

        <section id='recipe-logging-mechanisms'>
            <title>Recipe Logging Mechanisms</title>

            <para>
                The Yocto Project provides several logging functions for
                producing debugging output and reporting errors and warnings.
                For Python functions, the following logging functions exist.
                All of these functions log to
                <filename>${T}/log.do_</filename><replaceable>task</replaceable>,
                and can also log to standard output (stdout) with the right
                settings:
                <itemizedlist>
                    <listitem><para>
                        <filename>bb.plain(</filename><replaceable>msg</replaceable><filename>)</filename>:
                        Writes <replaceable>msg</replaceable> as is to the
                        log while also logging to stdout.
                        </para></listitem>
                    <listitem><para>
                        <filename>bb.note(</filename><replaceable>msg</replaceable><filename>)</filename>:
                        Writes "NOTE: <replaceable>msg</replaceable>" to the
                        log.
                        Also logs to stdout if BitBake is called with "-v".
                        </para></listitem>
                    <listitem><para>
                        <filename>bb.debug(</filename><replaceable>level</replaceable><filename>,&nbsp;</filename><replaceable>msg</replaceable><filename>)</filename>:
                        Writes "DEBUG: <replaceable>msg</replaceable>" to the
                        log.
                        Also logs to stdout if the log level is greater than or
                        equal to <replaceable>level</replaceable>.
                        See the
                        "<ulink url='&YOCTO_DOCS_BB_URL;#usage-and-syntax'>-D</ulink>"
                        option in the BitBake User Manual for more information.
                        </para></listitem>
                    <listitem><para>
                        <filename>bb.warn(</filename><replaceable>msg</replaceable><filename>)</filename>:
                        Writes "WARNING: <replaceable>msg</replaceable>" to the
                        log while also logging to stdout.
                        </para></listitem>
                    <listitem><para>
                        <filename>bb.error(</filename><replaceable>msg</replaceable><filename>)</filename>:
                        Writes "ERROR: <replaceable>msg</replaceable>" to the
                        log while also logging to standard out (stdout).
                        <note>
                            Calling this function does not cause the task to fail.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <filename>bb.fatal(</filename><replaceable>msg</replaceable><filename>)</filename>:
                        This logging function is similar to
                        <filename>bb.error(</filename><replaceable>msg</replaceable><filename>)</filename>
                        but also causes the calling task to fail.
                        <note>
                            <filename>bb.fatal()</filename> raises an exception,
                            which means you do not need to put a "return"
                            statement after the function.
                        </note>
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                The same logging functions are also available in shell
                functions, under the names
                <filename>bbplain</filename>, <filename>bbnote</filename>,
                <filename>bbdebug</filename>, <filename>bbwarn</filename>,
                <filename>bberror</filename>, and <filename>bbfatal</filename>.
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-logging'><filename>logging</filename></ulink>
                class implements these functions.
                See that class in the
                <filename>meta/classes</filename> folder of the
                <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                for information.
            </para>

            <section id='logging-with-python'>
                <title>Logging With Python</title>

                <para>
                    When creating recipes using Python and inserting code that
                    handles build logs, keep in mind the goal is to have
                    informative logs while keeping the console as "silent" as
                    possible.
                    Also, if you want status messages in the log, use the
                    "debug" loglevel.
                </para>

                <para>
                    Following is an example written in Python.
                    The code handles logging for a function that determines the
                    number of tasks needed to be run.
                    See the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-listtasks'><filename>do_listtasks</filename></ulink>"
                    section for additional information:
                    <literallayout class='monospaced'>
     python do_listtasks() {
         bb.debug(2, "Starting to figure out the task list")
         if noteworthy_condition:
             bb.note("There are 47 tasks to run")
         bb.debug(2, "Got to point xyz")
         if warning_trigger:
             bb.warn("Detected warning_trigger, this might be a problem later.")
         if recoverable_error:
             bb.error("Hit recoverable_error, you really need to fix this!")
         if fatal_error:
             bb.fatal("fatal_error detected, unable to print the task list")
         bb.plain("The tasks present are abc")
         bb.debug(2, "Finished figuring out the tasklist")
     }
                    </literallayout>
                </para>
            </section>

            <section id='logging-with-bash'>
                <title>Logging With Bash</title>

                <para>
                    When creating recipes using Bash and inserting code that
                    handles build logs, you have the same goals - informative
                    with minimal console output.
                    The syntax you use for recipes written in Bash is similar
                    to that of recipes written in Python described in the
                    previous section.
                </para>

                <para>
                    Following is an example written in Bash.
                    The code logs the progress of the <filename>do_my_function</filename> function.
                    <literallayout class='monospaced'>
     do_my_function() {
         bbdebug 2 "Running do_my_function"
         if [ exceptional_condition ]; then
             bbnote "Hit exceptional_condition"
         fi
         bbdebug 2  "Got to point xyz"
         if [ warning_trigger ]; then
             bbwarn "Detected warning_trigger, this might cause a problem later."
         fi
         if [ recoverable_error ]; then
             bberror "Hit recoverable_error, correcting"
         fi
         if [ fatal_error ]; then
             bbfatal "fatal_error detected"
         fi
         bbdebug 2 "Completed do_my_function"
     }
                    </literallayout>
                </para>
            </section>
        </section>

        <section id='debugging-parallel-make-races'>
            <title>Debugging Parallel Make Races</title>

            <para>
                A parallel <filename>make</filename> race occurs when the build
                consists of several parts that are run simultaneously and
                a situation occurs when the output or result of one
                part is not ready for use with a different part of the build
                that depends on that output.
                Parallel make races are annoying and can sometimes be difficult
                to reproduce and fix.
                However, some simple tips and tricks exist that can help
                you debug and fix them.
                This section presents a real-world example of an error
                encountered on the Yocto Project autobuilder and the process
                used to fix it.
                <note>
                    If you cannot properly fix a <filename>make</filename> race
                    condition, you can work around it by clearing either the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink>
                    or
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename></ulink>
                    variables.
                </note>
            </para>

            <section id='the-failure'>
                <title>The Failure</title>

                <para>
                    For this example, assume that you are building an image that
                    depends on the "neard" package.
                    And, during the build, BitBake runs into problems and
                    creates the following output.
                    <note>
                        This example log file has longer lines artificially
                        broken to make the listing easier to read.
                    </note>
                    If you examine the output or the log file, you see the
                    failure during <filename>make</filename>:
                    <literallayout class='monospaced'>
     | DEBUG: SITE files ['endian-little', 'bit-32', 'ix86-common', 'common-linux', 'common-glibc', 'i586-linux', 'common']
     | DEBUG: Executing shell function do_compile
     | NOTE: make -j 16
     | make --no-print-directory all-am
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/types.h include/near/types.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/log.h include/near/log.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/plugin.h include/near/plugin.h
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/tag.h include/near/tag.h
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/adapter.h include/near/adapter.h
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/ndef.h include/near/ndef.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/tlv.h include/near/tlv.h
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/setting.h include/near/setting.h
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/device.h include/near/device.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/nfc_copy.h include/near/nfc_copy.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/snep.h include/near/snep.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/version.h include/near/version.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/dbus.h include/near/dbus.h
     | ./src/genbuiltin nfctype1 nfctype2 nfctype3 nfctype4 p2p > src/builtin.h
     | i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/
       build/build/tmp/sysroots/qemux86 -DHAVE_CONFIG_H -I. -I./include -I./src -I./gdbus  -I/home/pokybuild/
       yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/include/glib-2.0
       -I/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/
       lib/glib-2.0/include  -I/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/
       tmp/sysroots/qemux86/usr/include/dbus-1.0 -I/home/pokybuild/yocto-autobuilder/yocto-slave/
       nightly-x86/build/build/tmp/sysroots/qemux86/usr/lib/dbus-1.0/include  -I/home/pokybuild/yocto-autobuilder/
       yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/include/libnl3
       -DNEAR_PLUGIN_BUILTIN -DPLUGINDIR=\""/usr/lib/near/plugins"\"
       -DCONFIGDIR=\""/etc/neard\"" -O2 -pipe -g -feliminate-unused-debug-types -c
       -o tools/snep-send.o tools/snep-send.c
     | In file included from tools/snep-send.c:16:0:
     | tools/../src/near.h:41:23: fatal error: near/dbus.h: No such file or directory
     |  #include &lt;near/dbus.h&gt;
     |                        ^
     | compilation terminated.
     | make[1]: *** [tools/snep-send.o] Error 1
     | make[1]: *** Waiting for unfinished jobs....
     | make: *** [all] Error 2
     | ERROR: oe_runmake failed
                    </literallayout>
                </para>
            </section>

            <section id='reproducing-the-error'>
                <title>Reproducing the Error</title>

                <para>
                    Because race conditions are intermittent, they do not
                    manifest themselves every time you do the build.
                    In fact, most times the build will complete without problems
                    even though the potential race condition exists.
                    Thus, once the error surfaces, you need a way to reproduce
                    it.
                </para>

                <para>
                    In this example, compiling the "neard" package is causing
                    the problem.
                    So the first thing to do is build "neard" locally.
                    Before you start the build, set the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink>
                    variable in your <filename>local.conf</filename> file to
                    a high number (e.g. "-j 20").
                    Using a high value for <filename>PARALLEL_MAKE</filename>
                    increases the chances of the race condition showing up:
                    <literallayout class='monospaced'>
     $ bitbake neard
                    </literallayout>
                </para>

                <para>
                    Once the local build for "neard" completes, start a
                    <filename>devshell</filename> build:
                    <literallayout class='monospaced'>
     $ bitbake neard -c devshell
                    </literallayout>
                    For information on how to use a
                    <filename>devshell</filename>, see the
                    "<link linkend='platdev-appdev-devshell'>Using a Development Shell</link>"
                    section.
                </para>

                <para>
                    In the <filename>devshell</filename>, do the following:
                    <literallayout class='monospaced'>
     $ make clean
     $ make tools/snep-send.o
                    </literallayout>
                    The <filename>devshell</filename> commands cause the failure
                    to clearly be visible.
                    In this case, a missing dependency exists for the "neard"
                    Makefile target.
                    Here is some abbreviated, sample output with the
                    missing dependency clearly visible at the end:
                    <literallayout class='monospaced'>
     i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/home/scott-lenovo/......
        .
        .
        .
     tools/snep-send.c
     In file included from tools/snep-send.c:16:0:
     tools/../src/near.h:41:23: fatal error: near/dbus.h: No such file or directory
      #include &lt;near/dbus.h&gt;
                       ^
     compilation terminated.
     make: *** [tools/snep-send.o] Error 1
     $
                    </literallayout>
                </para>
            </section>

            <section id='creating-a-patch-for-the-fix'>
                <title>Creating a Patch for the Fix</title>

                <para>
                    Because there is a missing dependency for the Makefile
                    target, you need to patch the
                    <filename>Makefile.am</filename> file, which is generated
                    from <filename>Makefile.in</filename>.
                    You can use Quilt to create the patch:
                    <literallayout class='monospaced'>
     $ quilt new parallelmake.patch
     Patch patches/parallelmake.patch is now on top
     $ quilt add Makefile.am
     File Makefile.am added to patch patches/parallelmake.patch
                    </literallayout>
                    For more information on using Quilt, see the
                    "<link linkend='using-a-quilt-workflow'>Using Quilt in Your Workflow</link>"
                    section.
                </para>

                <para>
                    At this point you need to make the edits to
                    <filename>Makefile.am</filename> to add the missing
                    dependency.
                    For our example, you have to add the following line
                    to the file:
                    <literallayout class='monospaced'>
     tools/snep-send.$(OBJEXT): include/near/dbus.h
                    </literallayout>
                </para>

                <para>
                    Once you have edited the file, use the
                    <filename>refresh</filename> command to create the patch:
                    <literallayout class='monospaced'>
     $ quilt refresh
     Refreshed patch patches/parallelmake.patch
                    </literallayout>
                    Once the patch file exists, you need to add it back to the
                    originating recipe folder.
                    Here is an example assuming a top-level
                    <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                    named <filename>poky</filename>:
                    <literallayout class='monospaced'>
     $ cp patches/parallelmake.patch poky/meta/recipes-connectivity/neard/neard
                    </literallayout>
                    The final thing you need to do to implement the fix in the
                    build is to update the "neard" recipe (i.e.
                    <filename>neard-0.14.bb</filename>) so that the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                    statement includes the patch file.
                    The recipe file is in the folder above the patch.
                    Here is what the edited <filename>SRC_URI</filename>
                    statement would look like:
                    <literallayout class='monospaced'>
     SRC_URI = "${KERNELORG_MIRROR}/linux/network/nfc/${BPN}-${PV}.tar.xz \
                file://neard.in \
                file://neard.service.in \
                file://parallelmake.patch \
               "
                    </literallayout>
                </para>

                <para>
                    With the patch complete and moved to the correct folder and
                    the <filename>SRC_URI</filename> statement updated, you can
                    exit the <filename>devshell</filename>:
                    <literallayout class='monospaced'>
     $ exit
                    </literallayout>
                </para>
            </section>

            <section id='testing-the-build'>
                <title>Testing the Build</title>

                <para>
                    With everything in place, you can get back to trying the
                    build again locally:
                    <literallayout class='monospaced'>
     $ bitbake neard
                    </literallayout>
                    This build should succeed.
                </para>

                <para>
                    Now you can open up a <filename>devshell</filename> again
                    and repeat the clean and make operations as follows:
                    <literallayout class='monospaced'>
     $ bitbake neard -c devshell
     $ make clean
     $ make tools/snep-send.o
                    </literallayout>
                    The build should work without issue.
                </para>

                <para>
                    As with all solved problems, if they originated upstream,
                    you need to submit the fix for the recipe in OE-Core and
                    upstream so that the problem is taken care of at its
                    source.
                    See the
                    "<link linkend='how-to-submit-a-change'>Submitting a Change to the Yocto Project</link>"
                    section for more information.
                </para>
            </section>
        </section>

        <section id="platdev-gdb-remotedebug">
            <title>Debugging With the GNU Project Debugger (GDB) Remotely</title>

            <para>
                GDB allows you to examine running programs, which in turn helps
                you to understand and fix problems.
                It also allows you to perform post-mortem style analysis of
                program crashes.
                GDB is available as a package within the Yocto Project and is
                installed in SDK images by default.
                See the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
                chapter in the Yocto Project Reference Manual for a description of
                these images.
                You can find information on GDB at
                <ulink url="http://sourceware.org/gdb/"/>.
                <note><title>Tip</title>
                    For best results, install debug (<filename>-dbg</filename>)
                    packages for the applications you are going to debug.
                    Doing so makes extra debug symbols available that give you
                    more meaningful output.
                </note>
            </para>

            <para>
                Sometimes, due to memory or disk space constraints, it is not
                possible to use GDB directly on the remote target to debug
                applications.
                These constraints arise because GDB needs to load the debugging
                information and the binaries of the process being debugged.
                Additionally, GDB needs to perform many computations to locate
                information such as function names, variable names and values,
                stack traces and so forth - even before starting the debugging
                process.
                These extra computations place more load on the target system
                and can alter the characteristics of the program being debugged.
            </para>

            <para>
                To help get past the previously mentioned constraints, you can
                use gdbserver, which runs on the remote target and does not
                load any debugging information from the debugged process.
                Instead, a GDB instance processes the debugging information that
                is run on a remote computer - the host GDB.
                The host GDB then sends control commands to gdbserver to make
                it stop or start the debugged program, as well as read or write
                memory regions of that debugged program.
                All the debugging information loaded and processed as well
               as all the heavy debugging is done by the host GDB.
                Offloading these processes gives the gdbserver running on the
                target a chance to remain small and fast.
            </para>

            <para>
                Because the host GDB is responsible for loading the debugging
                information and for doing the necessary processing to make
                actual debugging happen, you have to make sure the host can
                access the unstripped binaries complete with their debugging
                information and also be sure the target is compiled with no
                optimizations.
                The host GDB must also have local access to all the libraries
                used by the debugged program.
                Because gdbserver does not need any local debugging information,
                the binaries on the remote target can remain stripped.
                However, the binaries must also be compiled without optimization
                so they match the host's binaries.
            </para>

            <para>
                To remain consistent with GDB documentation and terminology,
                the binary being debugged on the remote target machine is
                referred to as the "inferior" binary.
                For documentation on GDB see the
                <ulink url="http://sourceware.org/gdb/documentation/">GDB site</ulink>.
            </para>

            <para>
                The following steps show you how to debug using the GNU project
                debugger.
                <orderedlist>
                    <listitem><para>
                        <emphasis>Configure your build system to construct the
                        companion debug filesystem:</emphasis></para>

                        <para>In your <filename>local.conf</filename> file, set
                        the following:
                        <literallayout class='monospaced'>
     IMAGE_GEN_DEBUGFS = "1"
     IMAGE_FSTYPES_DEBUGFS = "tar.bz2"
                        </literallayout>
                        These options cause the OpenEmbedded build system
                        to generate a special companion filesystem fragment,
                        which contains the matching source and debug symbols to
                        your deployable filesystem.
                        The build system does this by looking at what is in the
                        deployed filesystem, and pulling the corresponding
                        <filename>-dbg</filename> packages.</para>

                        <para>The companion debug filesystem is not a complete
                        filesystem, but only contains the debug fragments.
                        This filesystem must be combined with the full filesystem
                        for debugging.
                        Subsequent steps in this procedure show how to combine
                        the partial filesystem with the full filesystem.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Configure the system to include gdbserver in
                        the target filesystem:</emphasis></para>

                        <para>Make the following addition in either your
                        <filename>local.conf</filename> file or in an image
                        recipe:
                        <literallayout class='monospaced'>
     IMAGE_INSTALL_append = “ gdbserver"
                        </literallayout>
                        The change makes sure the <filename>gdbserver</filename>
                        package is included.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Build the environment:</emphasis></para>

                        <para>Use the following command to construct the image
                        and the companion Debug Filesystem:
                        <literallayout class='monospaced'>
     $ bitbake <replaceable>image</replaceable>
                        </literallayout>
                        Build the cross GDB component and make it available
                        for debugging.
                        Build the SDK that matches the image.
                        Building the SDK is best for a production build
                        that can be used later for debugging, especially
                        during long term maintenance:
                        <literallayout class='monospaced'>
     $ bitbake -c populate_sdk <replaceable>image</replaceable>
                        </literallayout></para>

                        <para>Alternatively, you can build the minimal
                        toolchain components that match the target.
                        Doing so creates a smaller than typical SDK and only
                        contains a minimal set of components with which to
                        build simple test applications, as well as run the
                        debugger:
                        <literallayout class='monospaced'>
     $ bitbake meta-toolchain
                        </literallayout></para>

                        <para>A final method is to build Gdb itself within
                        the build system:
                        <literallayout class='monospaced'>
     $ bitbake gdb-cross-<replaceable>architecture</replaceable>
                        </literallayout>
                        Doing so produces a temporary copy of
                        <filename>cross-gdb</filename> you can use for
                        debugging during development.
                        While this is the quickest approach, the two previous
                        methods in this step are better when considering
                        long-term maintenance strategies.
                        <note>
                            If you run
                            <filename>bitbake gdb-cross</filename>, the
                            OpenEmbedded build system suggests the actual
                            image (e.g. <filename>gdb-cross-i586</filename>).
                            The suggestion is usually the actual name you want
                            to use.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Set up the</emphasis>&nbsp;<filename>debugfs</filename></para>

                        <para>Run the following commands to set up the
                        <filename>debugfs</filename>:
                        <literallayout class='monospaced'>
     $ mkdir debugfs
     $ cd debugfs
     $ tar xvfj <replaceable>build-dir</replaceable>/tmp-glibc/deploy/images/<replaceable>machine</replaceable>/<replaceable>image</replaceable>.rootfs.tar.bz2
     $ tar xvfj <replaceable>build-dir</replaceable>/tmp-glibc/deploy/images/<replaceable>machine</replaceable>/<replaceable>image</replaceable>-dbg.rootfs.tar.bz2
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Set up GDB</emphasis></para>

                        <para>Install the SDK (if you built one) and then
                        source the correct environment file.
                        Sourcing the environment file puts the SDK in your
                        <filename>PATH</filename> environment variable.</para>

                        <para>If you are using the build system, Gdb is
                        located in
                        <replaceable>build-dir</replaceable>/tmp/sysroots/<replaceable>host</replaceable>/usr/bin/<replaceable>architecture</replaceable>/<replaceable>architecture</replaceable>-gdb
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Boot the target:</emphasis></para>

                        <para>For information on how to run QEMU, see the
                        <ulink url='http://wiki.qemu.org/Documentation/GettingStartedDevelopers'>QEMU Documentation</ulink>.
                        <note>
                            Be sure to verify that your host can access the
                            target via TCP.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Debug a program:</emphasis></para>

                        <para>Debugging a program involves running gdbserver
                        on the target and then running Gdb on the host.
                        The example in this step debugs
                        <filename>gzip</filename>:
                        <literallayout class='monospaced'>
     root@qemux86:~# gdbserver localhost:1234 /bin/gzip —help
                        </literallayout>
                        For additional gdbserver options, see the
                        <ulink url='https://www.gnu.org/software/gdb/documentation/'>GDB Server Documentation</ulink>.
                        </para>

                        <para>After running gdbserver on the target, you need
                        to run Gdb on the host and configure it and connect to
                        the target.
                        Use these commands:
                        <literallayout class='monospaced'>
     $ cd <replaceable>directory-holding-the-debugfs-directory</replaceable>
     $ <replaceable>arch</replaceable>-gdb

     (gdb) set sysroot debugfs
     (gdb) set substitute-path /usr/src/debug debugfs/usr/src/debug
     (gdb) target remote <replaceable>IP-of-target</replaceable>:1234
                        </literallayout>
                        At this point, everything should automatically load
                        (i.e. matching binaries, symbols and headers).
                        <note>
                            The Gdb <filename>set</filename> commands in the
                            previous example can be placed into the users
                           <filename>~/.gdbinit</filename> file.
                            Upon starting, Gdb automatically runs whatever
                            commands are in that file.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Deploying without a full image
                        rebuild:</emphasis></para>

                        <para>In many cases, during development you want a
                        quick method to deploy a new binary to the target and
                        debug it, without waiting for a full image build.
                        </para>

                        <para>One approach to solving this situation is to
                        just build the component you want to debug.
                        Once you have built the component, copy the
                        executable directly to both the target and the
                        host <filename>debugfs</filename>.</para>

                        <para>If the binary is processed through the debug
                        splitting in OpenEmbedded, you should also
                        copy the debug items (i.e. <filename>.debug</filename>
                        contents and corresponding
                        <filename>/usr/src/debug</filename> files)
                        from the work directory.
                        Here is an example:
                        <literallayout class='monospaced'>
     $ bitbake bash
     $ bitbake -c devshell bash
     $ cd ..
     $ scp packages-split/bash/bin/bash <replaceable>target</replaceable>:/bin/bash
     $ cp -a packages-split/bash-dbg/* <replaceable>path</replaceable>/debugfs
                        </literallayout>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='debugging-with-the-gnu-project-debugger-gdb-on-the-target'>
            <title>Debugging with the GNU Project Debugger (GDB) on the Target</title>

            <para>
                The previous section addressed using GDB remotely for debugging
                purposes, which is the most usual case due to the inherent
                hardware limitations on many embedded devices.
                However, debugging in the target hardware itself is also
                possible with more powerful devices.
                This section describes what you need to do in order to support
                using GDB to debug on the target hardware.
            </para>

            <para>
                To support this kind of debugging, you need do the following:
                <itemizedlist>
                    <listitem><para>
                        Ensure that GDB is on the target.
                        You can do this by adding "gdb" to
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>:
                        <literallayout class='monospaced'>
     IMAGE_INSTALL_append = " gdb"
                        </literallayout>
                        Alternatively, you can add "tools-debug" to
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>:
                        <literallayout class='monospaced'>
     IMAGE_FEATURES_append = " tools-debug"
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Ensure that debug symbols are present.
                        You can make sure these symbols are present by
                        installing <filename>-dbg</filename>:
                        <literallayout class='monospaced'>
     IMAGE_INSTALL_append = " <replaceable>packagename</replaceable>-dbg"
                        </literallayout>
                        Alternatively, you can do the following to include all
                        the debug symbols:
                        <literallayout class='monospaced'>
     IMAGE_FEATURES_append = " dbg-pkgs"
                        </literallayout>
                        </para></listitem>
                </itemizedlist>
                <note>
                    To improve the debug information accuracy, you can reduce
                    the level of optimization used by the compiler.
                    For example, when adding the following line to your
                    <filename>local.conf</filename> file, you will reduce
                    optimization from
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-FULL_OPTIMIZATION'><filename>FULL_OPTIMIZATION</filename></ulink>
                    of "-O2" to
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DEBUG_OPTIMIZATION'><filename>DEBUG_OPTIMIZATION</filename></ulink>
                    of "-O -fno-omit-frame-pointer":
                    <literallayout class='monospaced'>
     DEBUG_BUILD = "1"
                    </literallayout>
                    Consider that this will reduce the application's performance
                    and is recommended only for debugging purposes.
                </note>
            </para>
        </section>

        <section id='dev-other-debugging-others'>
            <title>Other Debugging Tips</title>

            <para>
                Here are some other tips that you might find useful:
                <itemizedlist>
                    <listitem><para>
                        When adding new packages, it is worth watching for
                        undesirable items making their way into compiler command
                        lines.
                        For example, you do not want references to local system
                        files like
                        <filename>/usr/lib/</filename> or
                        <filename>/usr/include/</filename>.
                        </para></listitem>
                    <listitem><para>
                        If you want to remove the <filename>psplash</filename>
                        boot splashscreen,
                        add <filename>psplash=false</filename> to  the kernel
                        command line.
                        Doing so prevents <filename>psplash</filename> from
                        loading and thus allows you to see the console.
                        It is also possible to switch out of the splashscreen by
                        switching the virtual console (e.g. Fn+Left or Fn+Right
                        on a Zaurus).
                        </para></listitem>
                    <listitem><para>
                        Removing
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
                        (usually <filename>tmp/</filename>, within the
                        <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>)
                        can often fix temporary build issues.
                        Removing <filename>TMPDIR</filename> is usually a
                        relatively cheap operation, because task output will be
                        cached in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>
                        (usually <filename>sstate-cache/</filename>, which is
                        also in the Build Directory).
                        <note>
                            Removing <filename>TMPDIR</filename> might be a
                            workaround rather than a fix.
                            Consequently, trying to determine the underlying
                            cause of an issue before removing the directory is
                            a good idea.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        Understanding how a feature is used in practice within
                        existing recipes can be very helpful.
                        It is recommended that you configure some method that
                        allows you to quickly search through files.</para>

                        <para>Using GNU Grep, you can use the following shell
                        function to recursively search through common
                        recipe-related files, skipping binary files,
                        <filename>.git</filename> directories, and the
                        Build Directory (assuming its name starts with
                        "build"):
                        <literallayout class='monospaced'>
     g() {
         grep -Ir \
              --exclude-dir=.git \
              --exclude-dir='build*' \
              --include='*.bb*' \
              --include='*.inc*' \
              --include='*.conf*' \
              --include='*.py*' \
              "$@"
     }
                        </literallayout>
                        Following are some usage examples:
                        <literallayout class='monospaced'>
     $ g FOO    # Search recursively for "FOO"
     $ g -i foo # Search recursively for "foo", ignoring case
     $ g -w FOO # Search recursively for "FOO" as a word, ignoring e.g. "FOOBAR"
                        </literallayout>
                        If figuring out how some feature works requires a lot of
                        searching, it might indicate that the documentation
                        should be extended or improved.
                        In such cases, consider filing a documentation bug using
                        the Yocto Project implementation of
                        <ulink url='https://bugzilla.yoctoproject.org/'>Bugzilla</ulink>.
                        For information on how to submit a bug against
                        the Yocto Project, see the Yocto Project Bugzilla
                        <ulink url='&YOCTO_WIKI_URL;/wiki/Bugzilla_Configuration_and_Bug_Tracking'>wiki page</ulink>
                        and the
                        "<link linkend='submitting-a-defect-against-the-yocto-project'>Submitting a Defect Against the Yocto Project</link>"
                        section.
                        <note>
                            The manuals might not be the right place to document
                            variables that are purely internal and have a
                            limited scope (e.g. internal variables used to
                            implement a single <filename>.bbclass</filename>
                            file).
                        </note>
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id='making-changes-to-the-yocto-project'>
        <title>Making Changes to the Yocto Project</title>

        <para>
            Because the Yocto Project is an open-source, community-based
            project, you can effect changes to the project.
            This section presents procedures that show you how to submit
            a defect against the project and how to submit a change.
        </para>

        <section id='submitting-a-defect-against-the-yocto-project'>
            <title>Submitting a Defect Against the Yocto Project</title>

            <para>
                Use the Yocto Project implementation of
                <ulink url='http://www.bugzilla.org/about/'>Bugzilla</ulink>
                to submit a defect (bug) against the Yocto Project.
                For additional information on this implementation of Bugzilla see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#resources-bugtracker'>Yocto Project Bugzilla</ulink>"
                section in the Yocto Project Reference Manual.
                For more detail on any of the following steps, see the Yocto Project
                <ulink url='&YOCTO_WIKI_URL;/wiki/Bugzilla_Configuration_and_Bug_Tracking'>Bugzilla wiki page</ulink>.
            </para>

            <para>
                Use the following general steps to submit a bug"

                <orderedlist>
                    <listitem><para>
                        Open the Yocto Project implementation of
                        <ulink url='&YOCTO_BUGZILLA_URL;'>Bugzilla</ulink>.
                        </para></listitem>
                    <listitem><para>
                        Click "File a Bug" to enter a new bug.
                        </para></listitem>
                    <listitem><para>
                        Choose the appropriate "Classification", "Product", and
                        "Component" for which the bug was found.
                        Bugs for the Yocto Project fall into one of several
                        classifications, which in turn break down into several
                        products and components.
                        For example, for a bug against the
                        <filename>meta-intel</filename> layer, you would choose
                        "Build System, Metadata &amp; Runtime", "BSPs", and
                        "bsps-meta-intel", respectively.
                        </para></listitem>
                    <listitem><para>
                        Choose the "Version" of the Yocto Project for which you found
                        the bug (e.g. &DISTRO;).
                        </para></listitem>
                    <listitem><para>
                        Determine and select the "Severity" of the bug.
                        The severity indicates how the bug impacted your work.
                        </para></listitem>
                    <listitem><para>
                        Choose the "Hardware" that the bug impacts.
                        </para></listitem>
                    <listitem><para>
                        Choose the "Architecture" that the bug impacts.
                        </para></listitem>
                    <listitem><para>
                        Choose a "Documentation change" item for the bug.
                        Fixing a bug might or might not affect the Yocto Project
                        documentation.
                        If you are unsure of the impact to the documentation, select
                        "Don't Know".
                        </para></listitem>
                    <listitem><para>
                        Provide a brief "Summary" of the bug.
                        Try to limit your summary to just a line or two and be sure
                        to capture the essence of the bug.
                        </para></listitem>
                    <listitem><para>
                        Provide a detailed "Description" of the bug.
                        You should provide as much detail as you can about the context,
                        behavior, output, and so forth that surrounds the bug.
                        You can even attach supporting files for output from logs by
                        using the "Add an attachment" button.
                        </para></listitem>
                    <listitem><para>
                        Click the "Submit Bug" button submit the bug.
                        A new Bugzilla number is assigned to the bug and the defect
                        is logged in the bug tracking system.
                        </para></listitem>
                </orderedlist>
                Once you file a bug, the bug is processed by the Yocto Project Bug
                Triage Team and further details concerning the bug are assigned
                (e.g. priority and owner).
                You are the "Submitter" of the bug and any further categorization,
                progress, or comments on the bug result in Bugzilla sending you an
                automated email concerning the particular change or progress to the
                bug.
            </para>
        </section>

        <section id='how-to-submit-a-change'>
            <title>Submitting a Change to the Yocto Project</title>

            <para>
                Contributions to the Yocto Project and OpenEmbedded are very welcome.
                Because the system is extremely configurable and flexible, we recognize
                that developers will want to extend, configure or optimize it for
                their specific uses.
            </para>

            <para>
                The Yocto Project uses a mailing list and a patch-based workflow
                that is similar to the Linux kernel but contains important
                differences.
                In general, a mailing list exists through which you can submit
                patches.
                You should send patches to the appropriate mailing list so that they
                can be reviewed and merged by the appropriate maintainer.
                The specific mailing list you need to use depends on the
                location of the code you are changing.
                Each component (e.g. layer) should have a
                <filename>README</filename> file that indicates where to send
                the changes and which process to follow.
            </para>

            <para>
                You can send the patch to the mailing list using whichever approach
                you feel comfortable with to generate the patch.
                Once sent, the patch is usually reviewed by the community at large.
                If somebody has concerns with the patch, they will usually voice
                their concern over the mailing list.
                If a patch does not receive any negative reviews, the maintainer of
                the affected layer typically takes the patch, tests it, and then
                based on successful testing, merges the patch.
            </para>

            <para id='figuring-out-the-mailing-list-to-use'>
                The "poky" repository, which is the Yocto Project's reference build
                environment, is a hybrid repository that contains several
                individual pieces (e.g. BitBake, Metadata, documentation,
                and so forth) built using the combo-layer tool.
                The upstream location used for submitting changes varies by
                component:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Core Metadata:</emphasis>
                        Send your patch to the
                        <ulink url='http://lists.openembedded.org/mailman/listinfo/openembedded-core'>openembedded-core</ulink>
                        mailing list.  For example, a change to anything under
                        the <filename>meta</filename> or
                        <filename>scripts</filename> directories should be sent
                        to this mailing list.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>BitBake:</emphasis>
                        For changes to BitBake (i.e. anything under the
                        <filename>bitbake</filename> directory), send your patch
                        to the
                        <ulink url='http://lists.openembedded.org/mailman/listinfo/bitbake-devel'>bitbake-devel</ulink>
                        mailing list.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>"meta-*" trees:</emphasis>
                        These trees contain Metadata.
                        Use the
                        <ulink url='https://lists.yoctoproject.org/listinfo/poky'>poky</ulink>
                        mailing list.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                For changes to other layers hosted in the Yocto Project source
                repositories (i.e. <filename>yoctoproject.org</filename>), tools,
                and the Yocto Project documentation, use the
                <ulink url='https://lists.yoctoproject.org/listinfo/yocto'>Yocto Project</ulink>
                general mailing list.
                <note>
                    Sometimes a layer's documentation specifies to use a
                    particular mailing list.
                    If so, use that list.
                </note>
                For additional recipes that do not fit into the core Metadata, you
                should determine which layer the recipe should go into and submit
                the change in the manner recommended by the documentation (e.g.
                the <filename>README</filename> file) supplied with the layer.
                If in doubt, please ask on the Yocto general mailing list or on
                the openembedded-devel mailing list.
            </para>

            <para>
                You can also push a change upstream and request a maintainer to
                pull the change into the component's upstream repository.
                You do this by pushing to a contribution repository that is upstream.
                See the
                "<ulink url='&YOCTO_DOCS_OM_URL;#gs-git-workflows-and-the-yocto-project'>Git Workflows and the Yocto Project</ulink>"
                section in the Yocto Project Overview and Concepts Manual for additional
                concepts on working in the Yocto Project development environment.
            </para>

            <para>
                Two commonly used testing repositories exist for
                OpenEmbedded-Core:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>"ross/mut" branch:</emphasis>
                        The "mut" (master-under-test) tree
                        exists in the <filename>poky-contrib</filename> repository
                        in the
                        <ulink url='&YOCTO_GIT_URL;'>Yocto Project source repositories</ulink>.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>"master-next" branch:</emphasis>
                        This branch is part of the main
                        "poky" repository in the Yocto Project source repositories.
                        </para></listitem>
                </itemizedlist>
                Maintainers use these branches to test submissions prior to merging
                patches.
                Thus, you can get an idea of the status of a patch based on
                whether the patch has been merged into one of these branches.
                <note>
                    This system is imperfect and changes can sometimes get lost in the
                    flow.
                    Asking about the status of a patch or change is reasonable if the
                    change has been idle for a while with no feedback.
                    The Yocto Project does have plans to use
                    <ulink url='https://en.wikipedia.org/wiki/Patchwork_(software)'>Patchwork</ulink>
                    to track the status of patches and also to automatically preview
                    patches.
                </note>
            </para>

            <para>
                The following sections provide procedures for submitting a change.
            </para>

            <section id='pushing-a-change-upstream'>
                <title>Using Scripts to Push a Change Upstream and Request a Pull</title>

                <para>
                    Follow this procedure to push a change to an upstream "contrib"
                    Git repository:
                    <note>
                        You can find general Git information on how to push a change
                        upstream in the
                        <ulink url='http://git-scm.com/book/en/v2/Distributed-Git-Distributed-Workflows'>Git Community Book</ulink>.
                    </note>
                    <orderedlist>
                        <listitem><para>
                            <emphasis>Make Your Changes Locally:</emphasis>
                            Make your changes in your local Git repository.
                            You should make small, controlled, isolated changes.
                            Keeping changes small and isolated aids review,
                            makes merging/rebasing easier and keeps the change
                            history clean should anyone need to refer to it in
                            future.
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Stage Your Changes:</emphasis>
                            Stage your changes by using the <filename>git add</filename>
                            command on each file you changed.
                            </para></listitem>
                        <listitem><para id='making-sure-you-have-correct-commit-information'>
                            <emphasis>Commit Your Changes:</emphasis>
                            Commit the change by using the
                            <filename>git commit</filename> command.
                            Make sure your commit information follows standards by
                            following these accepted conventions:
                            <itemizedlist>
                                <listitem><para>
                                    Be sure to include a "Signed-off-by:" line in the
                                    same style as required by the Linux kernel.
                                    Adding this line signifies that you, the submitter,
                                    have agreed to the Developer's Certificate of
                                    Origin 1.1 as follows:
                                    <literallayout class='monospaced'>
     Developer's Certificate of Origin 1.1

     By making a contribution to this project, I certify that:

     (a) The contribution was created in whole or in part by me and I
         have the right to submit it under the open source license
         indicated in the file; or

     (b) The contribution is based upon previous work that, to the best
         of my knowledge, is covered under an appropriate open source
         license and I have the right under that license to submit that
         work with modifications, whether created in whole or in part
         by me, under the same open source license (unless I am
         permitted to submit under a different license), as indicated
         in the file; or

     (c) The contribution was provided directly to me by some other
         person who certified (a), (b) or (c) and I have not modified
         it.

     (d) I understand and agree that this project and the contribution
         are public and that a record of the contribution (including all
         personal information I submit with it, including my sign-off) is
         maintained indefinitely and may be redistributed consistent with
         this project or the open source license(s) involved.
                                    </literallayout>
                                    </para></listitem>
                                <listitem><para>
                                    Provide a single-line summary of the change.
                                    and,
                                    if more explanation is needed, provide more
                                    detail in the body of the commit.
                                    This summary is typically viewable in the
                                    "shortlist" of changes.
                                    Thus, providing something short and descriptive
                                    that gives the reader a summary of the change is
                                    useful when viewing a list of many commits.
                                    You should prefix this short description with the
                                    recipe name (if changing a recipe), or else with
                                    the short form path to the file being changed.
                                    </para></listitem>
                                <listitem><para>
                                    For the body of the commit message, provide
                                    detailed information that describes what you
                                    changed, why you made the change, and the approach
                                    you used.
                                    It might also be helpful if you mention how you
                                    tested the change.
                                    Provide as much detail as you can in the body of
                                    the commit message.
                                    <note>
                                        You do not need to provide a more detailed
                                        explanation of a change if the change is
                                        minor to the point of the single line
                                        summary providing all the information.
                                    </note>
                                    </para></listitem>
                                <listitem><para>
                                    If the change addresses a specific bug or issue
                                    that is associated with a bug-tracking ID,
                                    include a reference to that ID in your detailed
                                    description.
                                    For example, the Yocto Project uses a specific
                                    convention for bug references - any commit that
                                    addresses a specific bug should use the following
                                    form for the detailed description.
                                    Be sure to use the actual bug-tracking ID from
                                    Bugzilla for
                                    <replaceable>bug-id</replaceable>:
                                    <literallayout class='monospaced'>
     Fixes [YOCTO #<replaceable>bug-id</replaceable>]

     <replaceable>detailed description of change</replaceable>
                                    </literallayout>
                                    </para></listitem>
                            </itemizedlist>
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Push Your Commits to a "Contrib" Upstream:</emphasis>
                            If you have arranged for permissions to push to an
                            upstream contrib repository, push the change to that
                            repository:
                            <literallayout class='monospaced'>
     $ git push <replaceable>upstream_remote_repo</replaceable> <replaceable>local_branch_name</replaceable>
                            </literallayout>
                            For example, suppose you have permissions to push into the
                            upstream <filename>meta-intel-contrib</filename>
                            repository and you are working in a local branch named
                            <replaceable>your_name</replaceable><filename>/README</filename>.
                            The following command pushes your local commits to the
                            <filename>meta-intel-contrib</filename> upstream
                            repository and puts the commit in a branch named
                            <replaceable>your_name</replaceable><filename>/README</filename>:
                            <literallayout class='monospaced'>
     $ git push meta-intel-contrib <replaceable>your_name</replaceable>/README
                            </literallayout>
                            </para></listitem>
                        <listitem><para id='push-determine-who-to-notify'>
                            <emphasis>Determine Who to Notify:</emphasis>
                            Determine the maintainer or the mailing list
                            that you need to notify for the change.</para>

                            <para>Before submitting any change, you need to be sure
                            who the maintainer is or what mailing list that you need
                            to notify.
                            Use either these methods to find out:
                            <itemizedlist>
                                <listitem><para>
                                    <emphasis>Maintenance File:</emphasis>
                                    Examine the <filename>maintainers.inc</filename>
                                    file, which is located in the
                                    <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                                    at
                                    <filename>meta/conf/distro/include</filename>,
                                    to see who is responsible for code.
                                    </para></listitem>
                                <listitem><para>
                                    <emphasis>Search by File:</emphasis>
                                    Using <ulink url='&YOCTO_DOCS_OM_URL;#git'>Git</ulink>,
                                    you can enter the following command to bring up a
                                    short list of all commits against a specific file:
                                    <literallayout class='monospaced'>
     git shortlog -- <replaceable>filename</replaceable>
                                    </literallayout>
                                    Just provide the name of the file for which you
                                    are interested.
                                    The information returned is not ordered by history
                                    but does include a list of everyone who has
                                    committed grouped by name.
                                    From the list, you can see who is responsible for
                                    the bulk of the changes against the file.
                                    </para></listitem>
                                <listitem><para>
                                    <emphasis>Examine the List of Mailing Lists:</emphasis>
                                    For a list of the Yocto Project and related mailing
                                    lists, see the
                                    "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing lists</ulink>"
                                    section in the Yocto Project Reference Manual.
                                    </para></listitem>
                            </itemizedlist>
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Make a Pull Request:</emphasis>
                            Notify the maintainer or the mailing list that you have
                            pushed a change by making a pull request.</para>

                            <para>The Yocto Project provides two scripts that
                            conveniently let you generate and send pull requests to the
                            Yocto Project.
                            These scripts are <filename>create-pull-request</filename>
                            and <filename>send-pull-request</filename>.
                            You can find these scripts in the
                            <filename>scripts</filename> directory within the
                            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                            (e.g. <filename>~/poky/scripts</filename>).
                            </para>

                            <para>Using these scripts correctly formats the requests
                            without introducing any whitespace or HTML formatting.
                            The maintainer that receives your patches either directly
                            or through the mailing list needs to be able to save and
                            apply them directly from your emails.
                            Using these scripts is the preferred method for sending
                            patches.</para>

                            <para>First, create the pull request.
                            For example, the following command runs the script,
                            specifies the upstream repository in the contrib directory
                            into which you pushed the change, and provides a subject
                            line in the created patch files:
                            <literallayout class='monospaced'>
     $ ~/poky/scripts/create-pull-request -u meta-intel-contrib -s "Updated Manual Section Reference in README"
                            </literallayout>
                            Running this script forms
                            <filename>*.patch</filename> files in a folder named
                            <filename>pull-</filename><replaceable>PID</replaceable>
                            in the current directory.
                            One of the patch files is a cover letter.</para>

                            <para>Before running the
                            <filename>send-pull-request</filename> script, you must
                            edit the cover letter patch to insert information about
                            your change.
                            After editing the cover letter, send the pull request.
                            For example, the following command runs the script and
                            specifies the patch directory and email address.
                            In this example, the email address is a mailing list:
                            <literallayout class='monospaced'>
     $ ~/poky/scripts/send-pull-request -p ~/meta-intel/pull-10565 -t meta-intel@yoctoproject.org
                            </literallayout>
                            You need to follow the prompts as the script is
                            interactive.
                            <note>
                                For help on using these scripts, simply provide the
                                <filename>-h</filename> argument as follows:
                                <literallayout class='monospaced'>
     $ poky/scripts/create-pull-request -h
     $ poky/scripts/send-pull-request -h
                                </literallayout>
                            </note>
                            </para></listitem>
                    </orderedlist>
                </para>
            </section>

            <section id='submitting-a-patch'>
                <title>Using Email to Submit a Patch</title>

                <para>
                    You can submit patches without using the
                    <filename>create-pull-request</filename> and
                    <filename>send-pull-request</filename> scripts described in the
                    previous section.
                    However, keep in mind, the preferred method is to use the scripts.
                </para>

                <para>
                    Depending on the components changed, you need to submit the email
                    to a specific mailing list.
                    For some guidance on which mailing list to use, see the
                    <link linkend='figuring-out-the-mailing-list-to-use'>list</link>
                    at the beginning of this section.
                    For a description of all the available mailing lists, see the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing Lists</ulink>"
                    section in the Yocto Project Reference Manual.
                </para>

                <para>
                    Here is the general procedure on how to submit a patch through
                    email without using the scripts:
                    <orderedlist>
                        <listitem><para>
                            <emphasis>Make Your Changes Locally:</emphasis>
                            Make your changes in your local Git repository.
                            You should make small, controlled, isolated changes.
                            Keeping changes small and isolated aids review,
                            makes merging/rebasing easier and keeps the change
                            history clean should anyone need to refer to it in
                            future.
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Stage Your Changes:</emphasis>
                            Stage your changes by using the <filename>git add</filename>
                            command on each file you changed.
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Commit Your Changes:</emphasis>
                            Commit the change by using the
                            <filename>git commit --signoff</filename> command.
                            Using the <filename>--signoff</filename> option identifies
                            you as the person making the change and also satisfies
                            the Developer's Certificate of Origin (DCO) shown earlier.
                            </para>

                            <para>When you form a commit, you must follow certain
                            standards established by the Yocto Project development
                            team.
                            See
                            <link linkend='making-sure-you-have-correct-commit-information'>Step 3</link>
                            in the previous section for information on how to
                            provide commit information that meets Yocto Project
                            commit message standards.
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Format the Commit:</emphasis>
                            Format the commit into an email message.
                            To format commits, use the
                            <filename>git format-patch</filename> command.
                            When you provide the command, you must include a revision
                            list or a number of patches as part of the command.
                            For example, either of these two commands takes your most
                            recent single commit and formats it as an email message in
                            the current directory:
                            <literallayout class='monospaced'>
     $ git format-patch -1
                            </literallayout>
                            or
                            <literallayout class='monospaced'>
     $ git format-patch HEAD~
                            </literallayout></para>

                            <para>After the command is run, the current directory
                            contains a numbered <filename>.patch</filename> file for
                            the commit.</para>

                            <para>If you provide several commits as part of the
                            command, the <filename>git format-patch</filename> command
                            produces a series of numbered files in the current
                            directory – one for each commit.
                            If you have more than one patch, you should also use the
                            <filename>--cover</filename> option with the command,
                            which generates a cover letter as the first "patch" in
                            the series.
                            You can then edit the cover letter to provide a
                            description for the series of patches.
                            For information on the
                            <filename>git format-patch</filename> command,
                            see <filename>GIT_FORMAT_PATCH(1)</filename> displayed
                            using the <filename>man git-format-patch</filename>
                            command.
                            <note>
                                If you are or will be a frequent contributor to the
                                Yocto Project or to OpenEmbedded, you might consider
                                requesting a contrib area and the necessary associated
                                rights.
                            </note>
                            </para></listitem>
                        <listitem><para>
                            <emphasis>Import the Files Into Your Mail Client:</emphasis>
                            Import the files into your mail client by using the
                            <filename>git send-email</filename> command.
                            <note>
                                In order to use <filename>git send-email</filename>,
                                you must have the proper Git packages installed on
                                your host.
                                For Ubuntu, Debian, and Fedora the package is
                                <filename>git-email</filename>.
                            </note></para>

                            <para>The <filename>git send-email</filename> command
                            sends email by using a local or remote Mail Transport Agent
                            (MTA) such as <filename>msmtp</filename>,
                            <filename>sendmail</filename>, or through a direct
                            <filename>smtp</filename> configuration in your Git
                            <filename>~/.gitconfig</filename> file.
                            If you are submitting patches through email only, it is
                            very important that you submit them without any whitespace
                            or HTML formatting that either you or your mailer
                            introduces.
                            The maintainer that receives your patches needs to be able
                            to save and apply them directly from your emails.
                            A good way to verify that what you are sending will be
                            applicable by the maintainer is to do a dry run and send
                            them to yourself and then save and apply them as the
                            maintainer would.</para>

                            <para>The <filename>git send-email</filename> command is
                            the preferred method for sending your patches using
                            email since there is no risk of compromising whitespace
                            in the body of the message, which can occur when you use
                            your own mail client.
                            The command also has several options that let you
                            specify recipients and perform further editing of the
                            email message.
                            For information on how to use the
                            <filename>git send-email</filename> command,
                            see <filename>GIT-SEND-EMAIL(1)</filename> displayed using
                            the <filename>man git-send-email</filename> command.
                            </para></listitem>
                    </orderedlist>
                </para>
            </section>
        </section>
    </section>

    <section id='working-with-licenses'>
        <title>Working With Licenses</title>

        <para>
            As mentioned in the
            "<ulink url='&YOCTO_DOCS_OM_URL;#licensing'>Licensing</ulink>"
            section in the Yocto Project Overview and Concepts Manual,
            open source projects are open to the public and they
            consequently have different licensing structures in place.
            This section describes the mechanism by which the
            <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink>
            tracks changes to licensing text and covers how to maintain open
            source license compliance during your project's lifecycle.
            The section also describes how to enable commercially licensed
            recipes, which by default are disabled.
        </para>

        <section id="usingpoky-configuring-LIC_FILES_CHKSUM">
            <title>Tracking License Changes</title>

            <para>
                The license of an upstream project might change in the future.
                In order to prevent these changes going unnoticed, the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
                variable tracks changes to the license text. The checksums are
                validated at the end of the configure step, and if the
                checksums do not match, the build will fail.
            </para>

            <section id="usingpoky-specifying-LIC_FILES_CHKSUM">
                <title>Specifying the <filename>LIC_FILES_CHKSUM</filename> Variable</title>

                <para>
                    The <filename>LIC_FILES_CHKSUM</filename>
                    variable contains checksums of the license text in the
                    source code for the recipe.
                    Following is an example of how to specify
                    <filename>LIC_FILES_CHKSUM</filename>:
                    <literallayout class='monospaced'>
     LIC_FILES_CHKSUM = "file://COPYING;md5=xxxx \
                         file://licfile1.txt;beginline=5;endline=29;md5=yyyy \
                         file://licfile2.txt;endline=50;md5=zzzz \
                         ..."
                    </literallayout>
                    <note><title>Notes</title>
                        <itemizedlist>
                            <listitem><para>
                                When using "beginline" and "endline", realize
                                that line numbering begins with one and not
                                zero.
                                Also, the included lines are inclusive (i.e.
                                lines five through and including 29 in the
                                previous example for
                                <filename>licfile1.txt</filename>).
                                </para></listitem>
                            <listitem><para>
                                When a license check fails, the selected license
                                text is included as part of the QA message.
                                Using this output, you can determine the exact
                                start and finish for the needed license text.
                                </para></listitem>
                        </itemizedlist>
                    </note>
                </para>

                <para>
                    The build system uses the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
                    variable as the default directory when searching files
                    listed in <filename>LIC_FILES_CHKSUM</filename>.
                    The previous example employs the default directory.
                </para>

                <para>
                    Consider this next example:
                    <literallayout class='monospaced'>
     LIC_FILES_CHKSUM = "file://src/ls.c;beginline=5;endline=16;\
                                         md5=bb14ed3c4cda583abc85401304b5cd4e"
     LIC_FILES_CHKSUM = "file://${WORKDIR}/license.html;md5=5c94767cedb5d6987c902ac850ded2c6"
                    </literallayout>
                </para>

                <para>
                    The first line locates a file in
                    <filename>${S}/src/ls.c</filename> and isolates lines five
                    through 16 as license text.
                    The second line refers to a file in
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>.
                </para>

                <para>
                    Note that <filename>LIC_FILES_CHKSUM</filename> variable is
                    mandatory for all recipes, unless the
                    <filename>LICENSE</filename> variable is set to "CLOSED".
                </para>
            </section>

            <section id="usingpoky-LIC_FILES_CHKSUM-explanation-of-syntax">
                <title>Explanation of Syntax</title>

                <para>
                    As mentioned in the previous section, the
                    <filename>LIC_FILES_CHKSUM</filename> variable lists all
                    the important files that contain the license text for the
                    source code.
                    It is possible to specify a checksum for an entire file,
                    or a specific section of a file (specified by beginning and
                    ending line numbers with the "beginline" and "endline"
                    parameters, respectively).
                    The latter is useful for source files with a license
                    notice header, README documents, and so forth.
                    If you do not use the "beginline" parameter, then it is
                    assumed that the text begins on the first line of the file.
                    Similarly, if you do not use the "endline" parameter,
                    it is assumed that the license text ends with the last
                    line of the file.
                </para>

                <para>
                    The "md5" parameter stores the md5 checksum of the license
                    text.
                    If the license text changes in any way as compared to
                    this parameter then a mismatch occurs.
                    This mismatch triggers a build failure and notifies
                    the developer.
                    Notification allows the developer to review and address
                    the license text changes.
                    Also note that if a mismatch occurs during the build,
                    the correct md5 checksum is placed in the build log and
                    can be easily copied to the recipe.
                </para>

                <para>
                    There is no limit to how many files you can specify using
                    the <filename>LIC_FILES_CHKSUM</filename> variable.
                    Generally, however, every project requires a few
                    specifications for license tracking.
                    Many projects have a "COPYING" file that stores the
                    license information for all the source code files.
                    This practice allows you to just track the "COPYING"
                    file as long as it is kept up to date.
                    <note><title>Tips</title>
                        <itemizedlist>
                            <listitem><para>
                                If you specify an empty or invalid "md5"
                                parameter,
                                <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink>
                                returns an md5 mis-match
                                error and displays the correct "md5" parameter
                                value during the build.
                                The correct parameter is also captured in
                                the build log.
                                </para></listitem>
                            <listitem><para>
                                If the whole file contains only license text,
                                you do not need to use the "beginline" and
                               "endline" parameters.
                               </para></listitem>
                        </itemizedlist>
                    </note>
                </para>
            </section>
        </section>

        <section id="enabling-commercially-licensed-recipes">
            <title>Enabling Commercially Licensed Recipes</title>

            <para>
                By default, the OpenEmbedded build system disables
                components that have commercial or other special licensing
                requirements.
                Such requirements are defined on a
                recipe-by-recipe basis through the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE_FLAGS'><filename>LICENSE_FLAGS</filename></ulink>
                variable definition in the affected recipe.
                For instance, the
                <filename>poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly</filename>
                recipe contains the following statement:
                <literallayout class='monospaced'>
     LICENSE_FLAGS = "commercial"
                </literallayout>
                Here is a slightly more complicated example that contains both
                an explicit recipe name and version (after variable expansion):
                <literallayout class='monospaced'>
     LICENSE_FLAGS = "license_${PN}_${PV}"
                </literallayout>
	            In order for a component restricted by a
                <filename>LICENSE_FLAGS</filename> definition to be enabled and
                included in an image, it needs to have a matching entry in the
                global
	            <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE_FLAGS_WHITELIST'><filename>LICENSE_FLAGS_WHITELIST</filename></ulink>
                variable, which is a variable typically defined in your
                <filename>local.conf</filename> file.
                For example, to enable the
                <filename>poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly</filename>
	            package, you could add either the string
	            "commercial_gst-plugins-ugly" or the more general string
	            "commercial" to <filename>LICENSE_FLAGS_WHITELIST</filename>.
                See the
                "<link linkend='license-flag-matching'>License Flag Matching</link>"
                section for a full
                explanation of how <filename>LICENSE_FLAGS</filename> matching
                works.
                Here is the example:
                <literallayout class='monospaced'>
     LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly"
                </literallayout>
	            Likewise, to additionally enable the package built from the
                recipe containing
	            <filename>LICENSE_FLAGS = "license_${PN}_${PV}"</filename>,
                and assuming that the actual recipe name was
                <filename>emgd_1.10.bb</filename>, the following string would
                enable that package as well as the original
                <filename>gst-plugins-ugly</filename> package:
                <literallayout class='monospaced'>
     LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly license_emgd_1.10"
                </literallayout>
	            As a convenience, you do not need to specify the complete
                license string in the whitelist for every package.
                You can use an abbreviated form, which consists
                of just the first portion or portions of the license
                string before the initial underscore character or characters.
                A partial string will match any license that contains the
                given string as the first portion of its license.
                For example, the following whitelist string will also match
                both of the packages previously mentioned as well as any other
                packages that have licenses starting with "commercial" or
                "license".
                <literallayout class='monospaced'>
     LICENSE_FLAGS_WHITELIST = "commercial license"
                </literallayout>
            </para>

            <section id="license-flag-matching">
                <title>License Flag Matching</title>

                <para>
		            License flag matching allows you to control what recipes
                    the OpenEmbedded build system includes in the build.
                    Fundamentally, the build system attempts to match
                    <filename>LICENSE_FLAGS</filename> strings found in recipes
                    against <filename>LICENSE_FLAGS_WHITELIST</filename>
                    strings found in the whitelist.
                    A match causes the build system to include a recipe in the
                    build, while failure to find a match causes the build
                    system to exclude a recipe.
                </para>

                <para>
                    In general, license flag matching is simple.
                    However, understanding some concepts will help you
                    correctly and effectively use matching.
                </para>

                <para>
                    Before a flag
                    defined by a particular recipe is tested against the
                    contents of the whitelist, the expanded string
                    <filename>_${PN}</filename> is appended to the flag.
                    This expansion makes each
                    <filename>LICENSE_FLAGS</filename> value recipe-specific.
                    After expansion, the string is then matched against the
                    whitelist.
                    Thus, specifying
                    <filename>LICENSE_FLAGS = "commercial"</filename>
                    in recipe "foo", for example, results in the string
                    <filename>"commercial_foo"</filename>.
                    And, to create a match, that string must appear in the
                    whitelist.
                </para>

                <para>
                    Judicious use of the <filename>LICENSE_FLAGS</filename>
                    strings and the contents of the
                    <filename>LICENSE_FLAGS_WHITELIST</filename> variable
                    allows you a lot of flexibility for including or excluding
                    recipes based on licensing.
                    For example, you can broaden the matching capabilities by
                    using license flags string subsets in the whitelist.
                    <note>
                        When using a string subset, be sure to use the part of
                        the expanded string that precedes the appended
                        underscore character (e.g.
                        <filename>usethispart_1.3</filename>,
                        <filename>usethispart_1.4</filename>, and so forth).
                    </note>
                    For example, simply specifying the string "commercial" in
                    the whitelist matches any expanded
                    <filename>LICENSE_FLAGS</filename> definition that starts
                    with the string "commercial" such as "commercial_foo" and
                    "commercial_bar", which are the strings the build system
                    automatically generates for hypothetical recipes named
                    "foo" and "bar" assuming those recipes simply specify the
                    following:
                    <literallayout class='monospaced'>
     LICENSE_FLAGS = "commercial"
                    </literallayout>
                    Thus, you can choose to exhaustively
                    enumerate each license flag in the whitelist and
                    allow only specific recipes into the image, or
                    you can use a string subset that causes a broader range of
                    matches to allow a range of recipes into the image.
                </para>

                <para>
                    This scheme works even if the
                    <filename>LICENSE_FLAGS</filename> string already
                    has <filename>_${PN}</filename> appended.
                    For example, the build system turns the license flag
                    "commercial_1.2_foo" into "commercial_1.2_foo_foo" and
                    would match both the general "commercial" and the specific
                    "commercial_1.2_foo" strings found in the whitelist, as
                    expected.
                </para>

                <para>
                    Here are some other scenarios:
                    <itemizedlist>
                        <listitem><para>
                            You can specify a versioned string in the recipe
                            such as "commercial_foo_1.2" in a "foo" recipe.
                            The build system expands this string to
                            "commercial_foo_1.2_foo".
                            Combine this license flag with a whitelist that has
                            the string "commercial" and you match the flag
                            along with any other flag that starts with the
                            string "commercial".
                            </para></listitem>
                        <listitem><para>
                            Under the same circumstances, you can use
                            "commercial_foo" in the whitelist and the build
                            system not only matches "commercial_foo_1.2" but
                            also matches any license flag with the string
                            "commercial_foo", regardless of the version.
                            </para></listitem>
                        <listitem><para>
                            You can be very specific and use both the
                            package and version parts in the whitelist (e.g.
                            "commercial_foo_1.2") to specifically match a
                            versioned recipe.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id="other-variables-related-to-commercial-licenses">
                <title>Other Variables Related to Commercial Licenses</title>

                <para>
                    Other helpful variables related to commercial
                    license handling exist and are defined in the
                    <filename>poky/meta/conf/distro/include/default-distrovars.inc</filename> file:
                    <literallayout class='monospaced'>
     COMMERCIAL_AUDIO_PLUGINS ?= ""
     COMMERCIAL_VIDEO_PLUGINS ?= ""
                    </literallayout>
                    If you want to enable these components, you can do so by
                    making sure you have statements similar to the following
                    in your <filename>local.conf</filename> configuration file:
                    <literallayout class='monospaced'>
     COMMERCIAL_AUDIO_PLUGINS = "gst-plugins-ugly-mad \
        gst-plugins-ugly-mpegaudioparse"
     COMMERCIAL_VIDEO_PLUGINS = "gst-plugins-ugly-mpeg2dec \
        gst-plugins-ugly-mpegstream gst-plugins-bad-mpegvideoparse"
     LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly commercial_gst-plugins-bad commercial_qmmp"
                    </literallayout>
                    Of course, you could also create a matching whitelist
                    for those components using the more general "commercial"
                    in the whitelist, but that would also enable all the
                    other packages with <filename>LICENSE_FLAGS</filename>
                    containing "commercial", which you may or may not want:
                    <literallayout class='monospaced'>
     LICENSE_FLAGS_WHITELIST = "commercial"
                    </literallayout>
                </para>

                <para>
                    Specifying audio and video plugins as part of the
                    <filename>COMMERCIAL_AUDIO_PLUGINS</filename> and
                    <filename>COMMERCIAL_VIDEO_PLUGINS</filename> statements
                    (along with the enabling
                    <filename>LICENSE_FLAGS_WHITELIST</filename>) includes the
                    plugins or components into built images, thus adding
                    support for media formats or components.
                </para>
            </section>
        </section>

        <section id='maintaining-open-source-license-compliance-during-your-products-lifecycle'>
            <title>Maintaining Open Source License Compliance During Your Product's Lifecycle</title>

            <para>
                One of the concerns for a development organization using open source
                software is how to maintain compliance with various open source
                licensing during the lifecycle of the product.
                While this section does not provide legal advice or
                comprehensively cover all scenarios, it does
                present methods that you can use to
                assist you in meeting the compliance requirements during a software
                release.
            </para>

            <para>
                With hundreds of different open source licenses that the Yocto
                Project tracks, it is difficult to know the requirements of each
                and every license.
                However, the requirements of the major FLOSS licenses can begin
                to be covered by
                assuming that three main areas of concern exist:
                <itemizedlist>
                    <listitem><para>Source code must be provided.</para></listitem>
                    <listitem><para>License text for the software must be
                        provided.</para></listitem>
                    <listitem><para>Compilation scripts and modifications to the
                        source code must be provided.
                        </para></listitem>
                </itemizedlist>
                There are other requirements beyond the scope of these
                three and the methods described in this section
                (e.g. the mechanism through which source code is distributed).
            </para>

            <para>
                As different organizations have different methods of complying with
                open source licensing, this section is not meant to imply that
                there is only one single way to meet your compliance obligations,
                but rather to describe one method of achieving compliance.
                The remainder of this section describes methods supported to meet the
                previously mentioned three requirements.
                Once you take steps to meet these requirements,
                and prior to releasing images, sources, and the build system,
                you should audit all artifacts to ensure completeness.
                <note>
                    The Yocto Project generates a license manifest during
                    image creation that is located
                    in <filename>${DEPLOY_DIR}/licenses/<replaceable>image_name-datestamp</replaceable></filename>
                    to assist with any audits.
                </note>
            </para>

            <section id='providing-the-source-code'>
                <title>Providing the Source Code</title>

                <para>
                    Compliance activities should begin before you generate the
                    final image.
                    The first thing you should look at is the requirement that
                    tops the list for most compliance groups - providing
                    the source.
                    The Yocto Project has a few ways of meeting this
                    requirement.
                </para>

                <para>
                    One of the easiest ways to meet this requirement is
                    to provide the entire
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>
                    used by the build.
                    This method, however, has a few issues.
                    The most obvious is the size of the directory since it includes
                    all sources used in the build and not just the source used in
                    the released image.
                    It will include toolchain source, and other artifacts, which
                    you would not generally release.
                    However, the more serious issue for most companies is accidental
                    release of proprietary software.
                    The Yocto Project provides an
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-archiver'><filename>archiver</filename></ulink>
                    class to help avoid some of these concerns.
                </para>

                <para>
                    Before you employ <filename>DL_DIR</filename> or the
                    <filename>archiver</filename> class, you need to decide how
                    you choose to provide source.
                    The source <filename>archiver</filename> class can generate
                    tarballs and SRPMs and can create them with various levels of
                    compliance in mind.
                </para>

                <para>
                    One way of doing this (but certainly not the only way) is to
                    release just the source as a tarball.
                    You can do this by adding the following to the
                    <filename>local.conf</filename> file found in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
                    <literallayout class='monospaced'>
     INHERIT += "archiver"
     ARCHIVER_MODE[src] = "original"
                    </literallayout>
                    During the creation of your image, the source from all
                    recipes that deploy packages to the image is placed within
                    subdirectories of
                    <filename>DEPLOY_DIR/sources</filename> based on the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                    for each recipe.
                    Releasing the entire directory enables you to comply with
                    requirements concerning providing the unmodified source.
                    It is important to note that the size of the directory can
                    get large.
                </para>

                <para>
                    A way to help mitigate the size issue is to only release
                    tarballs for licenses that require the release of
                    source.
                    Let us assume you are only concerned with GPL code as
                    identified by running the following script:
                    <literallayout class='monospaced'>
     # Script to archive a subset of packages matching specific license(s)
     # Source and license files are copied into sub folders of package folder
     # Must be run from build folder
     #!/bin/bash
     src_release_dir="source-release"
     mkdir -p $src_release_dir
     for a in tmp/deploy/sources/*; do
        for d in $a/*; do
           # Get package name from path
           p=`basename $d`
           p=${p%-*}
           p=${p%-*}
           # Only archive GPL packages (update *GPL* regex for your license check)
           numfiles=`ls tmp/deploy/licenses/$p/*GPL* 2> /dev/null | wc -l`
           if [ $numfiles -gt 1 ]; then
              echo Archiving $p
              mkdir -p $src_release_dir/$p/source
              cp $d/* $src_release_dir/$p/source 2> /dev/null
              mkdir -p $src_release_dir/$p/license
              cp tmp/deploy/licenses/$p/* $src_release_dir/$p/license 2> /dev/null
           fi
        done
     done
                    </literallayout>
                    At this point, you could create a tarball from the
                    <filename>gpl_source_release</filename> directory and
                    provide that to the end user.
                    This method would be a step toward achieving compliance
                    with section 3a of GPLv2 and with section 6 of GPLv3.
                </para>
            </section>

            <section id='providing-license-text'>
                <title>Providing License Text</title>

                <para>
                    One requirement that is often overlooked is inclusion
                    of license text.
                    This requirement also needs to be dealt with prior to
                    generating the final image.
                    Some licenses require the license text to accompany
                    the binary.
                    You can achieve this by adding the following to your
                    <filename>local.conf</filename> file:
                    <literallayout class='monospaced'>
     COPY_LIC_MANIFEST = "1"
     COPY_LIC_DIRS = "1"
     LICENSE_CREATE_PACKAGE = "1"
                    </literallayout>
                    Adding these statements to the configuration file ensures
                    that the licenses collected during package generation
                    are included on your image.
                    <note>
                        <para>Setting all three variables to "1" results in the
                        image having two copies of the same license file.
                        One copy resides in
                        <filename>/usr/share/common-licenses</filename> and
                        the other resides in
                        <filename>/usr/share/license</filename>.</para>

                        <para>The reason for this behavior is because
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-COPY_LIC_DIRS'><filename>COPY_LIC_DIRS</filename></ulink>
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-COPY_LIC_MANIFEST'><filename>COPY_LIC_MANIFEST</filename></ulink>
                        add a copy of the license when the image is built but do
                        not offer a path for adding licenses for newly installed
                        packages to an image.
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE_CREATE_PACKAGE'><filename>LICENSE_CREATE_PACKAGE</filename></ulink>
                        adds a separate package and an upgrade path for adding
                        licenses to an image.</para>
                    </note>
                </para>

                <para>
                    As the source <filename>archiver</filename> class has already
                    archived the original
                    unmodified source that contains the license files,
                    you would have already met the requirements for inclusion
                    of the license information with source as defined by the GPL
                    and other open source licenses.
                </para>
            </section>

            <section id='providing-compilation-scripts-and-source-code-modifications'>
                <title>Providing Compilation Scripts and Source Code Modifications</title>

                <para>
                    At this point, we have addressed all we need to
                    prior to generating the image.
                    The next two requirements are addressed during the final
                    packaging of the release.
                </para>

                <para>
                    By releasing the version of the OpenEmbedded build system
                    and the layers used during the build, you will be providing both
                    compilation scripts and the source code modifications in one
                    step.
                </para>

                <para>
                    If the deployment team has a
                    <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP layer</ulink>
                    and a distro layer, and those those layers are used to patch,
                    compile, package, or modify (in any way) any open source
                    software included in your released images, you
                    might be required to release those layers under section 3 of
                    GPLv2 or section 1 of GPLv3.
                    One way of doing that is with a clean
                    checkout of the version of the Yocto Project and layers used
                    during your build.
                    Here is an example:
                    <literallayout class='monospaced'>
     # We built using the &DISTRO_NAME_NO_CAP; branch of the poky repo
     $ git clone -b &DISTRO_NAME_NO_CAP; git://git.yoctoproject.org/poky
     $ cd poky
     # We built using the release_branch for our layers
     $ git clone -b release_branch git://git.mycompany.com/meta-my-bsp-layer
     $ git clone -b release_branch git://git.mycompany.com/meta-my-software-layer
     # clean up the .git repos
     $ find . -name ".git" -type d -exec rm -rf {} \;
                    </literallayout>
                    One thing a development organization might want to consider
                    for end-user convenience is to modify
                    <filename>meta-poky/conf/bblayers.conf.sample</filename> to
                    ensure that when the end user utilizes the released build
                    system to build an image, the development organization's
                    layers are included in the <filename>bblayers.conf</filename>
                    file automatically:
                    <literallayout class='monospaced'>
     # POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf
     # changes incompatibly
     POKY_BBLAYERS_CONF_VERSION = "2"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       ##OEROOT##/meta \
       ##OEROOT##/meta-poky \
       ##OEROOT##/meta-yocto-bsp \
       ##OEROOT##/meta-mylayer \
       "
                    </literallayout>
                    Creating and providing an archive of the
                    <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink>
                    layers (recipes, configuration files, and so forth)
                    enables you to meet your
                    requirements to include the scripts to control compilation
                    as well as any modifications to the original source.
                </para>
            </section>
        </section>

        <section id='copying-licenses-that-do-not-exist'>
            <title>Copying Licenses that Do Not Exist</title>

            <para>
                Some packages, such as the linux-firmware package, have many
                licenses that are not in any way common.
                You can avoid adding a lot of these types of common license
                files, which are only applicable to a specific package, by using
                the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-NO_GENERIC_LICENSE'><filename>NO_GENERIC_LICENSE</filename></ulink>
                variable.
                Using this variable also avoids QA errors when you use a
                non-common, non-CLOSED license in a recipe.
            </para>

            <para>
                The following is an example that uses the
                <filename>LICENSE.Abilis.txt</filename>
                file as the license from the fetched source:
                <literallayout class='monospaced'>
     NO_GENERIC_LICENSE[Firmware-Abilis] = "LICENSE.Abilis.txt"
                </literallayout>
            </para>
        </section>
    </section>

    <section id='using-the-error-reporting-tool'>
        <title>Using the Error Reporting Tool</title>

        <para>
            The error reporting tool allows you to
            submit errors encountered during builds to a central database.
            Outside of the build environment, you can use a web interface to
            browse errors, view statistics, and query for errors.
            The tool works using a client-server system where the client
            portion is integrated with the installed Yocto Project
            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
            (e.g. <filename>poky</filename>).
            The server receives the information collected and saves it in a
            database.
        </para>

        <para>
            A live instance of the error reporting server exists at
            <ulink url='http://errors.yoctoproject.org'></ulink>.
            This server exists so that when you want to get help with
            build failures, you can submit all of the information on the
            failure easily and then point to the URL in your bug report
            or send an email to the mailing list.
            <note>
                If you send error reports to this server, the reports become
                publicly visible.
            </note>
        </para>

        <section id='enabling-and-using-the-tool'>
            <title>Enabling and Using the Tool</title>

            <para>
                By default, the error reporting tool is disabled.
                You can enable it by inheriting the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-report-error'><filename>report-error</filename></ulink>
                class by adding the following statement to the end of
                your <filename>local.conf</filename> file in your
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                <literallayout class='monospaced'>
     INHERIT += "report-error"
                </literallayout>
            </para>

            <para>
                By default, the error reporting feature stores information in
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LOG_DIR'><filename>LOG_DIR</filename></ulink><filename>}/error-report</filename>.
                However, you can specify a directory to use by adding the following
                to your <filename>local.conf</filename> file:
                <literallayout class='monospaced'>
     ERR_REPORT_DIR = "path"
                </literallayout>
                Enabling error reporting causes the build process to collect
                the errors and store them in a file as previously described.
                When the build system encounters an error, it includes a
                command as part of the console output.
                You can run the command to send the error file to the server.
                For example, the following command sends the errors to an
                upstream server:
                <literallayout class='monospaced'>
     $ send-error-report /home/brandusa/project/poky/build/tmp/log/error-report/error_report_201403141617.txt
                </literallayout>
                In the previous example, the errors are sent to a public
                database available at
                <ulink url='http://errors.yoctoproject.org'></ulink>, which is
                used by the entire community.
                If you specify a particular server, you can send the errors
                to a different database.
                Use the following command for more information on available
                options:
                <literallayout class='monospaced'>
     $ send-error-report --help
                </literallayout>
            </para>

            <para>
                When sending the error file, you are prompted to review the
                data being sent as well as to provide a name and optional
                email address.
                Once you satisfy these prompts, the command returns a link
                from the server that corresponds to your entry in the database.
                For example, here is a typical link:
                <literallayout class='monospaced'>
     http://errors.yoctoproject.org/Errors/Details/9522/
                </literallayout>
                Following the link takes you to a web interface where you can
                browse, query the errors, and view statistics.
             </para>
        </section>

        <section id='disabling-the-tool'>
            <title>Disabling the Tool</title>

            <para>
                To disable the error reporting feature, simply remove or comment
                out the following statement from the end of your
                <filename>local.conf</filename> file in your
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                <literallayout class='monospaced'>
     INHERIT += "report-error"
                </literallayout>
            </para>
        </section>

        <section id='setting-up-your-own-error-reporting-server'>
            <title>Setting Up Your Own Error Reporting Server</title>

            <para>
                If you want to set up your own error reporting server, you
                can obtain the code from the Git repository at
                <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/error-report-web/'></ulink>.
                Instructions on how to set it up are in the README document.
            </para>
        </section>
     </section>

    <section id="dev-using-wayland-and-weston">
        <title>Using Wayland and Weston</title>

        <para>
            <ulink url='http://en.wikipedia.org/wiki/Wayland_(display_server_protocol)'>Wayland</ulink>
            is a computer display server protocol that
            provides a method for compositing window managers to communicate
            directly with applications and video hardware and expects them to
            communicate with input hardware using other libraries.
            Using Wayland with supporting targets can result in better control
            over graphics frame rendering than an application might otherwise
            achieve.
        </para>

        <para>
            The Yocto Project provides the Wayland protocol libraries and the
            reference
            <ulink url='http://en.wikipedia.org/wiki/Wayland_(display_server_protocol)#Weston'>Weston</ulink>
            compositor as part of its release.
            You can find the integrated packages in the
            <filename>meta</filename> layer of the
            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
            Specifically, you can find the recipes that build both Wayland
            and Weston at <filename>meta/recipes-graphics/wayland</filename>.
        </para>

        <para>
            You can build both the Wayland and Weston packages for use only
            with targets that accept the
            <ulink url='https://en.wikipedia.org/wiki/Mesa_(computer_graphics)'>Mesa 3D and Direct Rendering Infrastructure</ulink>,
            which is also known as Mesa DRI.
            This implies that you cannot build and use the packages if your
            target uses, for example, the
            <trademark class='registered'>Intel</trademark> Embedded Media
            and Graphics Driver
            (<trademark class='registered'>Intel</trademark> EMGD) that
            overrides Mesa DRI.
            <note>
                Due to lack of EGL support, Weston 1.0.3 will not run
                directly on the emulated QEMU hardware.
                However, this version of Weston will run under X emulation
                without issues.
            </note>
        </para>

        <para>
            This section describes what you need to do to implement Wayland and
            use the Weston compositor when building an image for a supporting
            target.
        </para>

        <section id="enabling-wayland-in-an-image">
            <title>Enabling Wayland in an Image</title>

            <para>
                To enable Wayland, you need to enable it to be built and enable
                it to be included (installed) in the image.
            </para>

            <section id="enable-building">
                <title>Building</title>

                <para>
                    To cause Mesa to build the <filename>wayland-egl</filename>
                    platform and Weston to build Wayland with Kernel Mode
                    Setting
                    (<ulink url='https://wiki.archlinux.org/index.php/Kernel_Mode_Setting'>KMS</ulink>)
                    support, include the "wayland" flag in the
                    <ulink url="&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES"><filename>DISTRO_FEATURES</filename></ulink>
                    statement in your <filename>local.conf</filename> file:
                    <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " wayland"
                    </literallayout>
                    <note>
                        If X11 has been enabled elsewhere, Weston will build
                        Wayland with X11 support
                    </note>
                </para>
            </section>

            <section id="enable-installation-in-an-image">
                <title>Installing</title>

                <para>
                    To install the Wayland feature into an image, you must
                    include the following
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-CORE_IMAGE_EXTRA_INSTALL'><filename>CORE_IMAGE_EXTRA_INSTALL</filename></ulink>
                    statement in your <filename>local.conf</filename> file:
                    <literallayout class='monospaced'>
     CORE_IMAGE_EXTRA_INSTALL += "wayland weston"
                    </literallayout>
                </para>
            </section>
        </section>

        <section id="running-weston">
            <title>Running Weston</title>

            <para>
                To run Weston inside X11, enabling it as described earlier and
                building a Sato image is sufficient.
                If you are running your image under Sato, a Weston Launcher
                appears in the "Utility" category.
            </para>

            <para>
                Alternatively, you can run Weston through the command-line
                interpretor (CLI), which is better suited for development work.
                To run Weston under the CLI, you need to do the following after
                your image is built:
                <orderedlist>
                    <listitem><para>
                        Run these commands to export
                        <filename>XDG_RUNTIME_DIR</filename>:
                        <literallayout class='monospaced'>
     mkdir -p /tmp/$USER-weston
     chmod 0700 /tmp/$USER-weston
     export XDG_RUNTIME_DIR=/tmp/$USER-weston
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Launch Weston in the shell:
                        <literallayout class='monospaced'>
     weston
                        </literallayout></para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>
</chapter>

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