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+.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
+
+*******
+Classes
+*******
+
+Class files are used to abstract common functionality and share it
+amongst multiple recipe (``.bb``) files. To use a class file, you simply
+make sure the recipe inherits the class. In most cases, when a recipe
+inherits a class it is enough to enable its features. There are cases,
+however, where in the recipe you might need to set variables or override
+some default behavior.
+
+Any :term:`Metadata` usually found in a recipe can also be
+placed in a class file. Class files are identified by the extension
+``.bbclass`` and are usually placed in a ``classes/`` directory beneath
+the ``meta*/`` directory found in the :term:`Source Directory`.
+Class files can also be pointed to by
+:term:`BUILDDIR` (e.g. ``build/``) in the same way as
+``.conf`` files in the ``conf`` directory. Class files are searched for
+in :term:`BBPATH` using the same method by which ``.conf``
+files are searched.
+
+This chapter discusses only the most useful and important classes. Other
+classes do exist within the ``meta/classes`` directory in the Source
+Directory. You can reference the ``.bbclass`` files directly for more
+information.
+
+.. _ref-classes-allarch:
+
+``allarch.bbclass``
+===================
+
+The ``allarch`` class is inherited by recipes that do not produce
+architecture-specific output. The class disables functionality that is
+normally needed for recipes that produce executable binaries (such as
+building the cross-compiler and a C library as pre-requisites, and
+splitting out of debug symbols during packaging).
+
+.. note::
+
+   Unlike some distro recipes (e.g. Debian), OpenEmbedded recipes that
+   produce packages that depend on tunings through use of the
+   :term:`RDEPENDS` and
+   :term:`TUNE_PKGARCH` variables, should never be
+   configured for all architectures using ``allarch``. This is the case
+   even if the recipes do not produce architecture-specific output.
+
+   Configuring such recipes for all architectures causes the
+   ``do_package_write_*`` tasks to
+   have different signatures for the machines with different tunings.
+   Additionally, unnecessary rebuilds occur every time an image for a
+   different ``MACHINE`` is built even when the recipe never changes.
+
+By default, all recipes inherit the :ref:`base <ref-classes-base>` and
+:ref:`package <ref-classes-package>` classes, which enable
+functionality needed for recipes that produce executable output. If your
+recipe, for example, only produces packages that contain configuration
+files, media files, or scripts (e.g. Python and Perl), then it should
+inherit the ``allarch`` class.
+
+.. _ref-classes-archiver:
+
+``archiver.bbclass``
+====================
+
+The ``archiver`` class supports releasing source code and other
+materials with the binaries.
+
+For more details on the source archiver, see the
+":ref:`dev-manual/common-tasks:maintaining open source license compliance during your product's lifecycle`"
+section in the Yocto Project Development Tasks Manual. You can also see
+the :term:`ARCHIVER_MODE` variable for information
+about the variable flags (varflags) that help control archive creation.
+
+.. _ref-classes-autotools:
+
+``autotools*.bbclass``
+======================
+
+The ``autotools*`` classes support Autotooled packages.
+
+The ``autoconf``, ``automake``, and ``libtool`` packages bring
+standardization. This class defines a set of tasks (e.g. ``configure``,
+``compile`` and so forth) that work for all Autotooled packages. It
+should usually be enough to define a few standard variables and then
+simply ``inherit autotools``. These classes can also work with software
+that emulates Autotools. For more information, see the
+":ref:`dev-manual/common-tasks:autotooled package`" section
+in the Yocto Project Development Tasks Manual.
+
+By default, the ``autotools*`` classes use out-of-tree builds (i.e.
+``autotools.bbclass`` building with ``B != S``).
+
+If the software being built by a recipe does not support using
+out-of-tree builds, you should have the recipe inherit the
+``autotools-brokensep`` class. The ``autotools-brokensep`` class behaves
+the same as the ``autotools`` class but builds with :term:`B`
+== :term:`S`. This method is useful when out-of-tree build
+support is either not present or is broken.
+
+.. note::
+
+   It is recommended that out-of-tree support be fixed and used if at
+   all possible.
+
+It's useful to have some idea of how the tasks defined by the
+``autotools*`` classes work and what they do behind the scenes.
+
+-  :ref:`ref-tasks-configure` - Regenerates the
+   configure script (using ``autoreconf``) and then launches it with a
+   standard set of arguments used during cross-compilation. You can pass
+   additional parameters to ``configure`` through the ``EXTRA_OECONF``
+   or :term:`PACKAGECONFIG_CONFARGS`
+   variables.
+
+-  :ref:`ref-tasks-compile` - Runs ``make`` with
+   arguments that specify the compiler and linker. You can pass
+   additional arguments through the ``EXTRA_OEMAKE`` variable.
+
+-  :ref:`ref-tasks-install` - Runs ``make install`` and
+   passes in ``${``\ :term:`D`\ ``}`` as ``DESTDIR``.
+
+.. _ref-classes-base:
+
+``base.bbclass``
+================
+
+The ``base`` class is special in that every ``.bb`` file implicitly
+inherits the class. This class contains definitions for standard basic
+tasks such as fetching, unpacking, configuring (empty by default),
+compiling (runs any ``Makefile`` present), installing (empty by default)
+and packaging (empty by default). These classes are often overridden or
+extended by other classes such as the
+:ref:`autotools <ref-classes-autotools>` class or the
+:ref:`package <ref-classes-package>` class.
+
+The class also contains some commonly used functions such as
+``oe_runmake``, which runs ``make`` with the arguments specified in
+:term:`EXTRA_OEMAKE` variable as well as the
+arguments passed directly to ``oe_runmake``.
+
+.. _ref-classes-bash-completion:
+
+``bash-completion.bbclass``
+===========================
+
+Sets up packaging and dependencies appropriate for recipes that build
+software that includes bash-completion data.
+
+.. _ref-classes-bin-package:
+
+``bin_package.bbclass``
+=======================
+
+The ``bin_package`` class is a helper class for recipes that extract the
+contents of a binary package (e.g. an RPM) and install those contents
+rather than building the binary from source. The binary package is
+extracted and new packages in the configured output package format are
+created. Extraction and installation of proprietary binaries is a good
+example use for this class.
+
+.. note::
+
+   For RPMs and other packages that do not contain a subdirectory, you
+   should specify an appropriate fetcher parameter to point to the
+   subdirectory. For example, if BitBake is using the Git fetcher (``git://``),
+   the "subpath" parameter limits the checkout to a specific subpath
+   of the tree. Here is an example where ``${BP}`` is used so that the files
+   are extracted into the subdirectory expected by the default value of
+   ``S``:
+   ::
+
+           SRC_URI = "git://example.com/downloads/somepackage.rpm;subpath=${BP}"
+
+
+   See the ":ref:`bitbake-user-manual/bitbake-user-manual-fetching:fetchers`" section in the BitBake User Manual for
+   more information on supported BitBake Fetchers.
+
+.. _ref-classes-binconfig:
+
+``binconfig.bbclass``
+=====================
+
+The ``binconfig`` class helps to correct paths in shell scripts.
+
+Before ``pkg-config`` had become widespread, libraries shipped shell
+scripts to give information about the libraries and include paths needed
+to build software (usually named ``LIBNAME-config``). This class assists
+any recipe using such scripts.
+
+During staging, the OpenEmbedded build system installs such scripts into
+the ``sysroots/`` directory. Inheriting this class results in all paths
+in these scripts being changed to point into the ``sysroots/`` directory
+so that all builds that use the script use the correct directories for
+the cross compiling layout. See the
+:term:`BINCONFIG_GLOB` variable for more
+information.
+
+.. _ref-classes-binconfig-disabled:
+
+``binconfig-disabled.bbclass``
+==============================
+
+An alternative version of the :ref:`binconfig <ref-classes-binconfig>`
+class, which disables binary configuration scripts by making them return
+an error in favor of using ``pkg-config`` to query the information. The
+scripts to be disabled should be specified using the
+:term:`BINCONFIG` variable within the recipe inheriting
+the class.
+
+.. _ref-classes-blacklist:
+
+``blacklist.bbclass``
+=====================
+
+The ``blacklist`` class prevents the OpenEmbedded build system from
+building specific recipes (blacklists them). To use this class, inherit
+the class globally and set :term:`PNBLACKLIST` for
+each recipe you wish to blacklist. Specify the :term:`PN`
+value as a variable flag (varflag) and provide a reason, which is
+reported, if the package is requested to be built as the value. For
+example, if you want to blacklist a recipe called "exoticware", you add
+the following to your ``local.conf`` or distribution configuration:
+::
+
+   INHERIT += "blacklist"
+   PNBLACKLIST[exoticware] = "Not supported by our organization."
+
+.. _ref-classes-buildhistory:
+
+``buildhistory.bbclass``
+========================
+
+The ``buildhistory`` class records a history of build output metadata,
+which can be used to detect possible regressions as well as used for
+analysis of the build output. For more information on using Build
+History, see the
+":ref:`dev-manual/common-tasks:maintaining build output quality`"
+section in the Yocto Project Development Tasks Manual.
+
+.. _ref-classes-buildstats:
+
+``buildstats.bbclass``
+======================
+
+The ``buildstats`` class records performance statistics about each task
+executed during the build (e.g. elapsed time, CPU usage, and I/O usage).
+
+When you use this class, the output goes into the
+:term:`BUILDSTATS_BASE` directory, which defaults
+to ``${TMPDIR}/buildstats/``. You can analyze the elapsed time using
+``scripts/pybootchartgui/pybootchartgui.py``, which produces a cascading
+chart of the entire build process and can be useful for highlighting
+bottlenecks.
+
+Collecting build statistics is enabled by default through the
+:term:`USER_CLASSES` variable from your
+``local.conf`` file. Consequently, you do not have to do anything to
+enable the class. However, if you want to disable the class, simply
+remove "buildstats" from the ``USER_CLASSES`` list.
+
+.. _ref-classes-buildstats-summary:
+
+``buildstats-summary.bbclass``
+==============================
+
+When inherited globally, prints statistics at the end of the build on
+sstate re-use. In order to function, this class requires the
+:ref:`buildstats <ref-classes-buildstats>` class be enabled.
+
+.. _ref-classes-ccache:
+
+``ccache.bbclass``
+==================
+
+The ``ccache`` class enables the C/C++ Compiler Cache for the build.
+This class is used to give a minor performance boost during the build.
+However, using the class can lead to unexpected side-effects. Thus, it
+is recommended that you do not use this class. See
+http://ccache.samba.org/ for information on the C/C++ Compiler
+Cache.
+
+.. _ref-classes-chrpath:
+
+``chrpath.bbclass``
+===================
+
+The ``chrpath`` class is a wrapper around the "chrpath" utility, which
+is used during the build process for ``nativesdk``, ``cross``, and
+``cross-canadian`` recipes to change ``RPATH`` records within binaries
+in order to make them relocatable.
+
+.. _ref-classes-clutter:
+
+``clutter.bbclass``
+===================
+
+The ``clutter`` class consolidates the major and minor version naming
+and other common items used by Clutter and related recipes.
+
+.. note::
+
+   Unlike some other classes related to specific libraries, recipes
+   building other software that uses Clutter do not need to inherit this
+   class unless they use the same recipe versioning scheme that the
+   Clutter and related recipes do.
+
+.. _ref-classes-cmake:
+
+``cmake.bbclass``
+=================
+
+The ``cmake`` class allows for recipes that need to build software using
+the `CMake <https://cmake.org/overview/>`__ build system. You can use
+the :term:`EXTRA_OECMAKE` variable to specify
+additional configuration options to be passed using the ``cmake``
+command line.
+
+On the occasion that you would be installing custom CMake toolchain
+files supplied by the application being built, you should install them
+to the preferred CMake Module directory: ``${D}${datadir}/cmake/``
+Modules during
+:ref:`ref-tasks-install`.
+
+.. _ref-classes-cml1:
+
+``cml1.bbclass``
+================
+
+The ``cml1`` class provides basic support for the Linux kernel style
+build configuration system.
+
+.. _ref-classes-compress_doc:
+
+``compress_doc.bbclass``
+========================
+
+Enables compression for man pages and info pages. This class is intended
+to be inherited globally. The default compression mechanism is gz (gzip)
+but you can select an alternative mechanism by setting the
+:term:`DOC_COMPRESS` variable.
+
+.. _ref-classes-copyleft_compliance:
+
+``copyleft_compliance.bbclass``
+===============================
+
+The ``copyleft_compliance`` class preserves source code for the purposes
+of license compliance. This class is an alternative to the ``archiver``
+class and is still used by some users even though it has been deprecated
+in favor of the :ref:`archiver <ref-classes-archiver>` class.
+
+.. _ref-classes-copyleft_filter:
+
+``copyleft_filter.bbclass``
+===========================
+
+A class used by the :ref:`archiver <ref-classes-archiver>` and
+:ref:`copyleft_compliance <ref-classes-copyleft_compliance>` classes
+for filtering licenses. The ``copyleft_filter`` class is an internal
+class and is not intended to be used directly.
+
+.. _ref-classes-core-image:
+
+``core-image.bbclass``
+======================
+
+The ``core-image`` class provides common definitions for the
+``core-image-*`` image recipes, such as support for additional
+:term:`IMAGE_FEATURES`.
+
+.. _ref-classes-cpan:
+
+``cpan*.bbclass``
+=================
+
+The ``cpan*`` classes support Perl modules.
+
+Recipes for Perl modules are simple. These recipes usually only need to
+point to the source's archive and then inherit the proper class file.
+Building is split into two methods depending on which method the module
+authors used.
+
+-  Modules that use old ``Makefile.PL``-based build system require
+   ``cpan.bbclass`` in their recipes.
+
+-  Modules that use ``Build.PL``-based build system require using
+   ``cpan_build.bbclass`` in their recipes.
+
+Both build methods inherit the ``cpan-base`` class for basic Perl
+support.
+
+.. _ref-classes-cross:
+
+``cross.bbclass``
+=================
+
+The ``cross`` class provides support for the recipes that build the
+cross-compilation tools.
+
+.. _ref-classes-cross-canadian:
+
+``cross-canadian.bbclass``
+==========================
+
+The ``cross-canadian`` class provides support for the recipes that build
+the Canadian Cross-compilation tools for SDKs. See the
+":ref:`overview-manual/concepts:cross-development toolchain generation`"
+section in the Yocto Project Overview and Concepts Manual for more
+discussion on these cross-compilation tools.
+
+.. _ref-classes-crosssdk:
+
+``crosssdk.bbclass``
+====================
+
+The ``crosssdk`` class provides support for the recipes that build the
+cross-compilation tools used for building SDKs. See the
+":ref:`overview-manual/concepts:cross-development toolchain generation`"
+section in the Yocto Project Overview and Concepts Manual for more
+discussion on these cross-compilation tools.
+
+.. _ref-classes-debian:
+
+``debian.bbclass``
+==================
+
+The ``debian`` class renames output packages so that they follow the
+Debian naming policy (i.e. ``glibc`` becomes ``libc6`` and
+``glibc-devel`` becomes ``libc6-dev``.) Renaming includes the library
+name and version as part of the package name.
+
+If a recipe creates packages for multiple libraries (shared object files
+of ``.so`` type), use the :term:`LEAD_SONAME`
+variable in the recipe to specify the library on which to apply the
+naming scheme.
+
+.. _ref-classes-deploy:
+
+``deploy.bbclass``
+==================
+
+The ``deploy`` class handles deploying files to the
+:term:`DEPLOY_DIR_IMAGE` directory. The main
+function of this class is to allow the deploy step to be accelerated by
+shared state. Recipes that inherit this class should define their own
+:ref:`ref-tasks-deploy` function to copy the files to be
+deployed to :term:`DEPLOYDIR`, and use ``addtask`` to
+add the task at the appropriate place, which is usually after
+:ref:`ref-tasks-compile` or
+:ref:`ref-tasks-install`. The class then takes care of
+staging the files from ``DEPLOYDIR`` to ``DEPLOY_DIR_IMAGE``.
+
+.. _ref-classes-devshell:
+
+``devshell.bbclass``
+====================
+
+The ``devshell`` class adds the ``do_devshell`` task. Distribution
+policy dictates whether to include this class. See the ":ref:`dev-manual/common-tasks:using a development shell`"
+section in the Yocto Project Development Tasks Manual for more
+information about using ``devshell``.
+
+.. _ref-classes-devupstream:
+
+``devupstream.bbclass``
+=======================
+
+The ``devupstream`` class uses
+:term:`BBCLASSEXTEND` to add a variant of the
+recipe that fetches from an alternative URI (e.g. Git) instead of a
+tarball. Following is an example:
+::
+
+   BBCLASSEXTEND = "devupstream:target"
+   SRC_URI_class-devupstream = "git://git.example.com/example"
+   SRCREV_class-devupstream = "abcd1234"
+
+Adding the above statements to your recipe creates a variant that has
+:term:`DEFAULT_PREFERENCE` set to "-1".
+Consequently, you need to select the variant of the recipe to use it.
+Any development-specific adjustments can be done by using the
+``class-devupstream`` override. Here is an example:
+::
+
+   DEPENDS_append_class-devupstream = " gperf-native"
+   do_configure_prepend_class-devupstream() {
+       touch ${S}/README
+   }
+
+The class
+currently only supports creating a development variant of the target
+recipe, not ``native`` or ``nativesdk`` variants.
+
+The ``BBCLASSEXTEND`` syntax (i.e. ``devupstream:target``) provides
+support for ``native`` and ``nativesdk`` variants. Consequently, this
+functionality can be added in a future release.
+
+Support for other version control systems such as Subversion is limited
+due to BitBake's automatic fetch dependencies (e.g.
+``subversion-native``).
+
+.. _ref-classes-distutils:
+
+``distutils*.bbclass``
+======================
+
+The ``distutils*`` classes support recipes for Python version 2.x
+extensions, which are simple. These recipes usually only need to point
+to the source's archive and then inherit the proper class. Building is
+split into two methods depending on which method the module authors
+used.
+
+-  Extensions that use an Autotools-based build system require Autotools
+   and the classes based on ``distutils`` in their recipes.
+
+-  Extensions that use build systems based on ``distutils`` require the
+   ``distutils`` class in their recipes.
+
+-  Extensions that use build systems based on ``setuptools`` require the
+   :ref:`setuptools <ref-classes-setuptools>` class in their recipes.
+
+The ``distutils-common-base`` class is required by some of the
+``distutils*`` classes to provide common Python2 support.
+
+.. _ref-classes-distutils3:
+
+``distutils3*.bbclass``
+=======================
+
+The ``distutils3*`` classes support recipes for Python version 3.x
+extensions, which are simple. These recipes usually only need to point
+to the source's archive and then inherit the proper class. Building is
+split into three methods depending on which method the module authors
+used.
+
+-  Extensions that use an Autotools-based build system require Autotools
+   and ``distutils``-based classes in their recipes.
+
+-  Extensions that use ``distutils``-based build systems require the
+   ``distutils`` class in their recipes.
+
+-  Extensions that use build systems based on ``setuptools3`` require
+   the :ref:`setuptools3 <ref-classes-setuptools>` class in their
+   recipes.
+
+The ``distutils3*`` classes either inherit their corresponding
+``distutils*`` class or replicate them using a Python3 version instead
+(e.g. ``distutils3-base`` inherits ``distutils-common-base``, which is
+the same as ``distutils-base`` but inherits ``python3native`` instead of
+``pythonnative``).
+
+.. _ref-classes-externalsrc:
+
+``externalsrc.bbclass``
+=======================
+
+The ``externalsrc`` class supports building software from source code
+that is external to the OpenEmbedded build system. Building software
+from an external source tree means that the build system's normal fetch,
+unpack, and patch process is not used.
+
+By default, the OpenEmbedded build system uses the :term:`S`
+and :term:`B` variables to locate unpacked recipe source code
+and to build it, respectively. When your recipe inherits the
+``externalsrc`` class, you use the
+:term:`EXTERNALSRC` and
+:term:`EXTERNALSRC_BUILD` variables to
+ultimately define ``S`` and ``B``.
+
+By default, this class expects the source code to support recipe builds
+that use the :term:`B` variable to point to the directory in
+which the OpenEmbedded build system places the generated objects built
+from the recipes. By default, the ``B`` directory is set to the
+following, which is separate from the source directory (``S``):
+::
+
+   ${WORKDIR}/${BPN}/{PV}/
+
+See these variables for more information:
+:term:`WORKDIR`, :term:`BPN`, and
+:term:`PV`,
+
+For more information on the ``externalsrc`` class, see the comments in
+``meta/classes/externalsrc.bbclass`` in the :term:`Source Directory`.
+For information on how to use the
+``externalsrc`` class, see the
+":ref:`dev-manual/common-tasks:building software from an external source`"
+section in the Yocto Project Development Tasks Manual.
+
+.. _ref-classes-extrausers:
+
+``extrausers.bbclass``
+======================
+
+The ``extrausers`` class allows additional user and group configuration
+to be applied at the image level. Inheriting this class either globally
+or from an image recipe allows additional user and group operations to
+be performed using the
+:term:`EXTRA_USERS_PARAMS` variable.
+
+.. note::
+
+   The user and group operations added using the
+   extrausers
+   class are not tied to a specific recipe outside of the recipe for the
+   image. Thus, the operations can be performed across the image as a
+   whole. Use the
+   useradd
+   class to add user and group configuration to a specific recipe.
+
+Here is an example that uses this class in an image recipe:
+::
+
+   inherit extrausers
+   EXTRA_USERS_PARAMS = "\
+       useradd -p '' tester; \
+       groupadd developers; \
+       userdel nobody; \
+       groupdel -g video; \
+       groupmod -g 1020 developers; \
+       usermod -s /bin/sh tester; \
+       "
+
+Here is an example that adds two users named "tester-jim" and "tester-sue" and assigns
+passwords:
+::
+
+   inherit extrausers
+   EXTRA_USERS_PARAMS = "\
+       useradd -P tester01 tester-jim; \
+       useradd -P tester01 tester-sue; \
+       "
+
+Finally, here is an example that sets the root password to "1876*18":
+::
+
+   inherit extrausers
+   EXTRA_USERS_PARAMS = "\
+       usermod -P 1876*18 root; \
+       "
+
+.. _ref-classes-features_check:
+
+``features_check.bbclass``
+=================================
+
+The ``features_check`` class allows individual recipes to check
+for required and conflicting
+:term:`DISTRO_FEATURES`, :term:`MACHINE_FEATURES` or :term:`COMBINED_FEATURES`.
+
+This class provides support for the following variables:
+
+- :term:`REQUIRED_DISTRO_FEATURES`
+- :term:`CONFLICT_DISTRO_FEATURES`
+- :term:`ANY_OF_DISTRO_FEATURES`
+- ``REQUIRED_MACHINE_FEATURES``
+- ``CONFLICT_MACHINE_FEATURES``
+- ``ANY_OF_MACHINE_FEATURES``
+- ``REQUIRED_COMBINED_FEATURES``
+- ``CONFLICT_COMBINED_FEATURES``
+- ``ANY_OF_COMBINED_FEATURES``
+
+If any conditions specified in the recipe using the above
+variables are not met, the recipe will be skipped, and if the
+build system attempts to build the recipe then an error will be
+triggered.
+
+.. _ref-classes-fontcache:
+
+``fontcache.bbclass``
+=====================
+
+The ``fontcache`` class generates the proper post-install and
+post-remove (postinst and postrm) scriptlets for font packages. These
+scriptlets call ``fc-cache`` (part of ``Fontconfig``) to add the fonts
+to the font information cache. Since the cache files are
+architecture-specific, ``fc-cache`` runs using QEMU if the postinst
+scriptlets need to be run on the build host during image creation.
+
+If the fonts being installed are in packages other than the main
+package, set :term:`FONT_PACKAGES` to specify the
+packages containing the fonts.
+
+.. _ref-classes-fs-uuid:
+
+``fs-uuid.bbclass``
+===================
+
+The ``fs-uuid`` class extracts UUID from
+``${``\ :term:`ROOTFS`\ ``}``, which must have been built
+by the time that this function gets called. The ``fs-uuid`` class only
+works on ``ext`` file systems and depends on ``tune2fs``.
+
+.. _ref-classes-gconf:
+
+``gconf.bbclass``
+=================
+
+The ``gconf`` class provides common functionality for recipes that need
+to install GConf schemas. The schemas will be put into a separate
+package (``${``\ :term:`PN`\ ``}-gconf``) that is created
+automatically when this class is inherited. This package uses the
+appropriate post-install and post-remove (postinst/postrm) scriptlets to
+register and unregister the schemas in the target image.
+
+.. _ref-classes-gettext:
+
+``gettext.bbclass``
+===================
+
+The ``gettext`` class provides support for building software that uses
+the GNU ``gettext`` internationalization and localization system. All
+recipes building software that use ``gettext`` should inherit this
+class.
+
+.. _ref-classes-gnomebase:
+
+``gnomebase.bbclass``
+=====================
+
+The ``gnomebase`` class is the base class for recipes that build
+software from the GNOME stack. This class sets
+:term:`SRC_URI` to download the source from the GNOME
+mirrors as well as extending :term:`FILES` with the typical
+GNOME installation paths.
+
+.. _ref-classes-gobject-introspection:
+
+``gobject-introspection.bbclass``
+=================================
+
+Provides support for recipes building software that supports GObject
+introspection. This functionality is only enabled if the
+"gobject-introspection-data" feature is in
+:term:`DISTRO_FEATURES` as well as
+"qemu-usermode" being in
+:term:`MACHINE_FEATURES`.
+
+.. note::
+
+   This functionality is backfilled by default and, if not applicable,
+   should be disabled through ``DISTRO_FEATURES_BACKFILL_CONSIDERED`` or
+   ``MACHINE_FEATURES_BACKFILL_CONSIDERED``, respectively.
+
+.. _ref-classes-grub-efi:
+
+``grub-efi.bbclass``
+====================
+
+The ``grub-efi`` class provides ``grub-efi``-specific functions for
+building bootable images.
+
+This class supports several variables:
+
+-  :term:`INITRD`: Indicates list of filesystem images to
+   concatenate and use as an initial RAM disk (initrd) (optional).
+
+-  :term:`ROOTFS`: Indicates a filesystem image to include
+   as the root filesystem (optional).
+
+-  :term:`GRUB_GFXSERIAL`: Set this to "1" to have
+   graphics and serial in the boot menu.
+
+-  :term:`LABELS`: A list of targets for the automatic
+   configuration.
+
+-  :term:`APPEND`: An override list of append strings for
+   each ``LABEL``.
+
+-  :term:`GRUB_OPTS`: Additional options to add to the
+   configuration (optional). Options are delimited using semi-colon
+   characters (``;``).
+
+-  :term:`GRUB_TIMEOUT`: Timeout before executing
+   the default ``LABEL`` (optional).
+
+.. _ref-classes-gsettings:
+
+``gsettings.bbclass``
+=====================
+
+The ``gsettings`` class provides common functionality for recipes that
+need to install GSettings (glib) schemas. The schemas are assumed to be
+part of the main package. Appropriate post-install and post-remove
+(postinst/postrm) scriptlets are added to register and unregister the
+schemas in the target image.
+
+.. _ref-classes-gtk-doc:
+
+``gtk-doc.bbclass``
+===================
+
+The ``gtk-doc`` class is a helper class to pull in the appropriate
+``gtk-doc`` dependencies and disable ``gtk-doc``.
+
+.. _ref-classes-gtk-icon-cache:
+
+``gtk-icon-cache.bbclass``
+==========================
+
+The ``gtk-icon-cache`` class generates the proper post-install and
+post-remove (postinst/postrm) scriptlets for packages that use GTK+ and
+install icons. These scriptlets call ``gtk-update-icon-cache`` to add
+the fonts to GTK+'s icon cache. Since the cache files are
+architecture-specific, ``gtk-update-icon-cache`` is run using QEMU if
+the postinst scriptlets need to be run on the build host during image
+creation.
+
+.. _ref-classes-gtk-immodules-cache:
+
+``gtk-immodules-cache.bbclass``
+===============================
+
+The ``gtk-immodules-cache`` class generates the proper post-install and
+post-remove (postinst/postrm) scriptlets for packages that install GTK+
+input method modules for virtual keyboards. These scriptlets call
+``gtk-update-icon-cache`` to add the input method modules to the cache.
+Since the cache files are architecture-specific,
+``gtk-update-icon-cache`` is run using QEMU if the postinst scriptlets
+need to be run on the build host during image creation.
+
+If the input method modules being installed are in packages other than
+the main package, set
+:term:`GTKIMMODULES_PACKAGES` to specify
+the packages containing the modules.
+
+.. _ref-classes-gzipnative:
+
+``gzipnative.bbclass``
+======================
+
+The ``gzipnative`` class enables the use of different native versions of
+``gzip`` and ``pigz`` rather than the versions of these tools from the
+build host.
+
+.. _ref-classes-icecc:
+
+``icecc.bbclass``
+=================
+
+The ``icecc`` class supports
+`Icecream <https://github.com/icecc/icecream>`__, which facilitates
+taking compile jobs and distributing them among remote machines.
+
+The class stages directories with symlinks from ``gcc`` and ``g++`` to
+``icecc``, for both native and cross compilers. Depending on each
+configure or compile, the OpenEmbedded build system adds the directories
+at the head of the ``PATH`` list and then sets the ``ICECC_CXX`` and
+``ICEC_CC`` variables, which are the paths to the ``g++`` and ``gcc``
+compilers, respectively.
+
+For the cross compiler, the class creates a ``tar.gz`` file that
+contains the Yocto Project toolchain and sets ``ICECC_VERSION``, which
+is the version of the cross-compiler used in the cross-development
+toolchain, accordingly.
+
+The class handles all three different compile stages (i.e native
+,cross-kernel and target) and creates the necessary environment
+``tar.gz`` file to be used by the remote machines. The class also
+supports SDK generation.
+
+If :term:`ICECC_PATH` is not set in your
+``local.conf`` file, then the class tries to locate the ``icecc`` binary
+using ``which``. If :term:`ICECC_ENV_EXEC` is set
+in your ``local.conf`` file, the variable should point to the
+``icecc-create-env`` script provided by the user. If you do not point to
+a user-provided script, the build system uses the default script
+provided by the recipe ``icecc-create-env-native.bb``.
+
+.. note::
+
+   This script is a modified version and not the one that comes with
+   icecc.
+
+If you do not want the Icecream distributed compile support to apply to
+specific recipes or classes, you can effectively "blacklist" them by
+listing the recipes and classes using the
+:term:`ICECC_USER_PACKAGE_BL` and
+:term:`ICECC_USER_CLASS_BL`, variables,
+respectively, in your ``local.conf`` file. Doing so causes the
+OpenEmbedded build system to handle these compilations locally.
+
+Additionally, you can list recipes using the
+:term:`ICECC_USER_PACKAGE_WL` variable in
+your ``local.conf`` file to force ``icecc`` to be enabled for recipes
+using an empty :term:`PARALLEL_MAKE` variable.
+
+Inheriting the ``icecc`` class changes all sstate signatures.
+Consequently, if a development team has a dedicated build system that
+populates :term:`SSTATE_MIRRORS` and they want to
+reuse sstate from ``SSTATE_MIRRORS``, then all developers and the build
+system need to either inherit the ``icecc`` class or nobody should.
+
+At the distribution level, you can inherit the ``icecc`` class to be
+sure that all builders start with the same sstate signatures. After
+inheriting the class, you can then disable the feature by setting the
+:term:`ICECC_DISABLED` variable to "1" as follows:
+::
+
+   INHERIT_DISTRO_append = " icecc"
+   ICECC_DISABLED ??= "1"
+
+This practice
+makes sure everyone is using the same signatures but also requires
+individuals that do want to use Icecream to enable the feature
+individually as follows in your ``local.conf`` file:
+::
+
+   ICECC_DISABLED = ""
+
+.. _ref-classes-image:
+
+``image.bbclass``
+=================
+
+The ``image`` class helps support creating images in different formats.
+First, the root filesystem is created from packages using one of the
+``rootfs*.bbclass`` files (depending on the package format used) and
+then one or more image files are created.
+
+-  The ``IMAGE_FSTYPES`` variable controls the types of images to
+   generate.
+
+-  The ``IMAGE_INSTALL`` variable controls the list of packages to
+   install into the image.
+
+For information on customizing images, see the
+":ref:`dev-manual/common-tasks:customizing images`" section
+in the Yocto Project Development Tasks Manual. For information on how
+images are created, see the
+":ref:`overview-manual/concepts:images`" section in the
+Yocto Project Overview and Concpets Manual.
+
+.. _ref-classes-image-buildinfo:
+
+``image-buildinfo.bbclass``
+===========================
+
+The ``image-buildinfo`` class writes information to the target
+filesystem on ``/etc/build``.
+
+.. _ref-classes-image_types:
+
+``image_types.bbclass``
+=======================
+
+The ``image_types`` class defines all of the standard image output types
+that you can enable through the
+:term:`IMAGE_FSTYPES` variable. You can use this
+class as a reference on how to add support for custom image output
+types.
+
+By default, the :ref:`image <ref-classes-image>` class automatically
+enables the ``image_types`` class. The ``image`` class uses the
+``IMGCLASSES`` variable as follows:
+::
+
+   IMGCLASSES = "rootfs_${IMAGE_PKGTYPE} image_types ${IMAGE_CLASSES}"
+   IMGCLASSES += "${@['populate_sdk_base', 'populate_sdk_ext']['linux' in d.getVar("SDK_OS")]}"
+   IMGCLASSES += "${@bb.utils.contains_any('IMAGE_FSTYPES', 'live iso hddimg', 'image-live', '', d)}"
+   IMGCLASSES += "${@bb.utils.contains('IMAGE_FSTYPES', 'container', 'image-container', '', d)}"
+   IMGCLASSES += "image_types_wic"
+   IMGCLASSES += "rootfs-postcommands"
+   IMGCLASSES += "image-postinst-intercepts"
+   inherit ${IMGCLASSES}
+
+The ``image_types`` class also handles conversion and compression of images.
+
+.. note::
+
+   To build a VMware VMDK image, you need to add "wic.vmdk" to
+   ``IMAGE_FSTYPES``. This would also be similar for Virtual Box Virtual Disk
+   Image ("vdi") and QEMU Copy On Write Version 2 ("qcow2") images.
+
+.. _ref-classes-image-live:
+
+``image-live.bbclass``
+======================
+
+This class controls building "live" (i.e. HDDIMG and ISO) images. Live
+images contain syslinux for legacy booting, as well as the bootloader
+specified by :term:`EFI_PROVIDER` if
+:term:`MACHINE_FEATURES` contains "efi".
+
+Normally, you do not use this class directly. Instead, you add "live" to
+:term:`IMAGE_FSTYPES`.
+
+.. _ref-classes-image-mklibs:
+
+``image-mklibs.bbclass``
+========================
+
+The ``image-mklibs`` class enables the use of the ``mklibs`` utility
+during the :ref:`ref-tasks-rootfs` task, which optimizes
+the size of libraries contained in the image.
+
+By default, the class is enabled in the ``local.conf.template`` using
+the :term:`USER_CLASSES` variable as follows:
+::
+
+   USER_CLASSES ?= "buildstats image-mklibs image-prelink"
+
+.. _ref-classes-image-prelink:
+
+``image-prelink.bbclass``
+=========================
+
+The ``image-prelink`` class enables the use of the ``prelink`` utility
+during the :ref:`ref-tasks-rootfs` task, which optimizes
+the dynamic linking of shared libraries to reduce executable startup
+time.
+
+By default, the class is enabled in the ``local.conf.template`` using
+the :term:`USER_CLASSES` variable as follows:
+::
+
+   USER_CLASSES ?= "buildstats image-mklibs image-prelink"
+
+.. _ref-classes-insane:
+
+``insane.bbclass``
+==================
+
+The ``insane`` class adds a step to the package generation process so
+that output quality assurance checks are generated by the OpenEmbedded
+build system. A range of checks are performed that check the build's
+output for common problems that show up during runtime. Distribution
+policy usually dictates whether to include this class.
+
+You can configure the sanity checks so that specific test failures
+either raise a warning or an error message. Typically, failures for new
+tests generate a warning. Subsequent failures for the same test would
+then generate an error message once the metadata is in a known and good
+condition. See the ":doc:`/ref-manual/qa-checks`" Chapter for a list of all the warning
+and error messages you might encounter using a default configuration.
+
+Use the :term:`WARN_QA` and
+:term:`ERROR_QA` variables to control the behavior of
+these checks at the global level (i.e. in your custom distro
+configuration). However, to skip one or more checks in recipes, you
+should use :term:`INSANE_SKIP`. For example, to skip
+the check for symbolic link ``.so`` files in the main package of a
+recipe, add the following to the recipe. You need to realize that the
+package name override, in this example ``${PN}``, must be used:
+::
+
+   INSANE_SKIP_${PN} += "dev-so"
+
+Please keep in mind that the QA checks
+exist in order to detect real or potential problems in the packaged
+output. So exercise caution when disabling these checks.
+
+The following list shows the tests you can list with the ``WARN_QA`` and
+``ERROR_QA`` variables:
+
+-  ``already-stripped:`` Checks that produced binaries have not
+   already been stripped prior to the build system extracting debug
+   symbols. It is common for upstream software projects to default to
+   stripping debug symbols for output binaries. In order for debugging
+   to work on the target using ``-dbg`` packages, this stripping must be
+   disabled.
+
+-  ``arch:`` Checks the Executable and Linkable Format (ELF) type, bit
+   size, and endianness of any binaries to ensure they match the target
+   architecture. This test fails if any binaries do not match the type
+   since there would be an incompatibility. The test could indicate that
+   the wrong compiler or compiler options have been used. Sometimes
+   software, like bootloaders, might need to bypass this check.
+
+-  ``buildpaths:`` Checks for paths to locations on the build host
+   inside the output files. Currently, this test triggers too many false
+   positives and thus is not normally enabled.
+
+-  ``build-deps:`` Determines if a build-time dependency that is
+   specified through :term:`DEPENDS`, explicit
+   :term:`RDEPENDS`, or task-level dependencies exists
+   to match any runtime dependency. This determination is particularly
+   useful to discover where runtime dependencies are detected and added
+   during packaging. If no explicit dependency has been specified within
+   the metadata, at the packaging stage it is too late to ensure that
+   the dependency is built, and thus you can end up with an error when
+   the package is installed into the image during the
+   :ref:`ref-tasks-rootfs` task because the auto-detected
+   dependency was not satisfied. An example of this would be where the
+   :ref:`update-rc.d <ref-classes-update-rc.d>` class automatically
+   adds a dependency on the ``initscripts-functions`` package to
+   packages that install an initscript that refers to
+   ``/etc/init.d/functions``. The recipe should really have an explicit
+   ``RDEPENDS`` for the package in question on ``initscripts-functions``
+   so that the OpenEmbedded build system is able to ensure that the
+   ``initscripts`` recipe is actually built and thus the
+   ``initscripts-functions`` package is made available.
+
+-  ``compile-host-path:`` Checks the
+   :ref:`ref-tasks-compile` log for indications that
+   paths to locations on the build host were used. Using such paths
+   might result in host contamination of the build output.
+
+-  ``debug-deps:`` Checks that all packages except ``-dbg`` packages
+   do not depend on ``-dbg`` packages, which would cause a packaging
+   bug.
+
+-  ``debug-files:`` Checks for ``.debug`` directories in anything but
+   the ``-dbg`` package. The debug files should all be in the ``-dbg``
+   package. Thus, anything packaged elsewhere is incorrect packaging.
+
+-  ``dep-cmp:`` Checks for invalid version comparison statements in
+   runtime dependency relationships between packages (i.e. in
+   :term:`RDEPENDS`,
+   :term:`RRECOMMENDS`,
+   :term:`RSUGGESTS`,
+   :term:`RPROVIDES`,
+   :term:`RREPLACES`, and
+   :term:`RCONFLICTS` variable values). Any invalid
+   comparisons might trigger failures or undesirable behavior when
+   passed to the package manager.
+
+-  ``desktop:`` Runs the ``desktop-file-validate`` program against any
+   ``.desktop`` files to validate their contents against the
+   specification for ``.desktop`` files.
+
+-  ``dev-deps:`` Checks that all packages except ``-dev`` or
+   ``-staticdev`` packages do not depend on ``-dev`` packages, which
+   would be a packaging bug.
+
+-  ``dev-so:`` Checks that the ``.so`` symbolic links are in the
+   ``-dev`` package and not in any of the other packages. In general,
+   these symlinks are only useful for development purposes. Thus, the
+   ``-dev`` package is the correct location for them. Some very rare
+   cases do exist for dynamically loaded modules where these symlinks
+   are needed instead in the main package.
+
+-  ``file-rdeps:`` Checks that file-level dependencies identified by
+   the OpenEmbedded build system at packaging time are satisfied. For
+   example, a shell script might start with the line ``#!/bin/bash``.
+   This line would translate to a file dependency on ``/bin/bash``. Of
+   the three package managers that the OpenEmbedded build system
+   supports, only RPM directly handles file-level dependencies,
+   resolving them automatically to packages providing the files.
+   However, the lack of that functionality in the other two package
+   managers does not mean the dependencies do not still need resolving.
+   This QA check attempts to ensure that explicitly declared
+   :term:`RDEPENDS` exist to handle any file-level
+   dependency detected in packaged files.
+
+-  ``files-invalid:`` Checks for :term:`FILES` variable
+   values that contain "//", which is invalid.
+
+-  ``host-user-contaminated:`` Checks that no package produced by the
+   recipe contains any files outside of ``/home`` with a user or group
+   ID that matches the user running BitBake. A match usually indicates
+   that the files are being installed with an incorrect UID/GID, since
+   target IDs are independent from host IDs. For additional information,
+   see the section describing the
+   :ref:`ref-tasks-install` task.
+
+-  ``incompatible-license:`` Report when packages are excluded from
+   being created due to being marked with a license that is in
+   :term:`INCOMPATIBLE_LICENSE`.
+
+-  ``install-host-path:`` Checks the
+   :ref:`ref-tasks-install` log for indications that
+   paths to locations on the build host were used. Using such paths
+   might result in host contamination of the build output.
+
+-  ``installed-vs-shipped:`` Reports when files have been installed
+   within ``do_install`` but have not been included in any package by
+   way of the :term:`FILES` variable. Files that do not
+   appear in any package cannot be present in an image later on in the
+   build process. Ideally, all installed files should be packaged or not
+   installed at all. These files can be deleted at the end of
+   ``do_install`` if the files are not needed in any package.
+
+-  ``invalid-chars:`` Checks that the recipe metadata variables
+   :term:`DESCRIPTION`,
+   :term:`SUMMARY`, :term:`LICENSE`, and
+   :term:`SECTION` do not contain non-UTF-8 characters.
+   Some package managers do not support such characters.
+
+-  ``invalid-packageconfig:`` Checks that no undefined features are
+   being added to :term:`PACKAGECONFIG`. For
+   example, any name "foo" for which the following form does not exist:
+   ::
+
+      PACKAGECONFIG[foo] = "..."
+
+-  ``la:`` Checks ``.la`` files for any ``TMPDIR`` paths. Any ``.la``
+   file containing these paths is incorrect since ``libtool`` adds the
+   correct sysroot prefix when using the files automatically itself.
+
+-  ``ldflags:`` Ensures that the binaries were linked with the
+   :term:`LDFLAGS` options provided by the build system.
+   If this test fails, check that the ``LDFLAGS`` variable is being
+   passed to the linker command.
+
+-  ``libdir:`` Checks for libraries being installed into incorrect
+   (possibly hardcoded) installation paths. For example, this test will
+   catch recipes that install ``/lib/bar.so`` when ``${base_libdir}`` is
+   "lib32". Another example is when recipes install
+   ``/usr/lib64/foo.so`` when ``${libdir}`` is "/usr/lib".
+
+-  ``libexec:`` Checks if a package contains files in
+   ``/usr/libexec``. This check is not performed if the ``libexecdir``
+   variable has been set explicitly to ``/usr/libexec``.
+
+-  ``packages-list:`` Checks for the same package being listed
+   multiple times through the :term:`PACKAGES` variable
+   value. Installing the package in this manner can cause errors during
+   packaging.
+
+-  ``perm-config:`` Reports lines in ``fs-perms.txt`` that have an
+   invalid format.
+
+-  ``perm-line:`` Reports lines in ``fs-perms.txt`` that have an
+   invalid format.
+
+-  ``perm-link:`` Reports lines in ``fs-perms.txt`` that specify
+   'link' where the specified target already exists.
+
+-  ``perms:`` Currently, this check is unused but reserved.
+
+-  ``pkgconfig:`` Checks ``.pc`` files for any
+   :term:`TMPDIR`/:term:`WORKDIR` paths.
+   Any ``.pc`` file containing these paths is incorrect since
+   ``pkg-config`` itself adds the correct sysroot prefix when the files
+   are accessed.
+
+-  ``pkgname:`` Checks that all packages in
+   :term:`PACKAGES` have names that do not contain
+   invalid characters (i.e. characters other than 0-9, a-z, ., +, and
+   -).
+
+-  ``pkgv-undefined:`` Checks to see if the ``PKGV`` variable is
+   undefined during :ref:`ref-tasks-package`.
+
+-  ``pkgvarcheck:`` Checks through the variables
+   :term:`RDEPENDS`,
+   :term:`RRECOMMENDS`,
+   :term:`RSUGGESTS`,
+   :term:`RCONFLICTS`,
+   :term:`RPROVIDES`,
+   :term:`RREPLACES`, :term:`FILES`,
+   :term:`ALLOW_EMPTY`, ``pkg_preinst``,
+   ``pkg_postinst``, ``pkg_prerm`` and ``pkg_postrm``, and reports if
+   there are variable sets that are not package-specific. Using these
+   variables without a package suffix is bad practice, and might
+   unnecessarily complicate dependencies of other packages within the
+   same recipe or have other unintended consequences.
+
+-  ``pn-overrides:`` Checks that a recipe does not have a name
+   (:term:`PN`) value that appears in
+   :term:`OVERRIDES`. If a recipe is named such that
+   its ``PN`` value matches something already in ``OVERRIDES`` (e.g.
+   ``PN`` happens to be the same as :term:`MACHINE` or
+   :term:`DISTRO`), it can have unexpected consequences.
+   For example, assignments such as ``FILES_${PN} = "xyz"`` effectively
+   turn into ``FILES = "xyz"``.
+
+-  ``rpaths:`` Checks for rpaths in the binaries that contain build
+   system paths such as ``TMPDIR``. If this test fails, bad ``-rpath``
+   options are being passed to the linker commands and your binaries
+   have potential security issues.
+
+-  ``split-strip:`` Reports that splitting or stripping debug symbols
+   from binaries has failed.
+
+-  ``staticdev:`` Checks for static library files (``*.a``) in
+   non-``staticdev`` packages.
+
+-  ``symlink-to-sysroot:`` Checks for symlinks in packages that point
+   into :term:`TMPDIR` on the host. Such symlinks will
+   work on the host, but are clearly invalid when running on the target.
+
+-  ``textrel:`` Checks for ELF binaries that contain relocations in
+   their ``.text`` sections, which can result in a performance impact at
+   runtime. See the explanation for the ``ELF binary`` message in
+   ":doc:`/ref-manual/qa-checks`" for more information regarding runtime performance
+   issues.
+
+-  ``unlisted-pkg-lics:`` Checks that all declared licenses applying
+   for a package are also declared on the recipe level (i.e. any license
+   in ``LICENSE_*`` should appear in :term:`LICENSE`).
+
+-  ``useless-rpaths:`` Checks for dynamic library load paths (rpaths)
+   in the binaries that by default on a standard system are searched by
+   the linker (e.g. ``/lib`` and ``/usr/lib``). While these paths will
+   not cause any breakage, they do waste space and are unnecessary.
+
+-  ``var-undefined:`` Reports when variables fundamental to packaging
+   (i.e. :term:`WORKDIR`,
+   :term:`DEPLOY_DIR`, :term:`D`,
+   :term:`PN`, and :term:`PKGD`) are undefined
+   during :ref:`ref-tasks-package`.
+
+-  ``version-going-backwards:`` If Build History is enabled, reports
+   when a package being written out has a lower version than the
+   previously written package under the same name. If you are placing
+   output packages into a feed and upgrading packages on a target system
+   using that feed, the version of a package going backwards can result
+   in the target system not correctly upgrading to the "new" version of
+   the package.
+
+   .. note::
+
+      If you are not using runtime package management on your target
+      system, then you do not need to worry about this situation.
+
+-  ``xorg-driver-abi:`` Checks that all packages containing Xorg
+   drivers have ABI dependencies. The ``xserver-xorg`` recipe provides
+   driver ABI names. All drivers should depend on the ABI versions that
+   they have been built against. Driver recipes that include
+   ``xorg-driver-input.inc`` or ``xorg-driver-video.inc`` will
+   automatically get these versions. Consequently, you should only need
+   to explicitly add dependencies to binary driver recipes.
+
+.. _ref-classes-insserv:
+
+``insserv.bbclass``
+===================
+
+The ``insserv`` class uses the ``insserv`` utility to update the order
+of symbolic links in ``/etc/rc?.d/`` within an image based on
+dependencies specified by LSB headers in the ``init.d`` scripts
+themselves.
+
+.. _ref-classes-kernel:
+
+``kernel.bbclass``
+==================
+
+The ``kernel`` class handles building Linux kernels. The class contains
+code to build all kernel trees. All needed headers are staged into the
+``STAGING_KERNEL_DIR`` directory to allow out-of-tree module builds
+using the :ref:`module <ref-classes-module>` class.
+
+This means that each built kernel module is packaged separately and
+inter-module dependencies are created by parsing the ``modinfo`` output.
+If all modules are required, then installing the ``kernel-modules``
+package installs all packages with modules and various other kernel
+packages such as ``kernel-vmlinux``.
+
+The ``kernel`` class contains logic that allows you to embed an initial
+RAM filesystem (initramfs) image when you build the kernel image. For
+information on how to build an initramfs, see the
+":ref:`dev-manual/common-tasks:building an initial ram filesystem (initramfs) image`" section in
+the Yocto Project Development Tasks Manual.
+
+Various other classes are used by the ``kernel`` and ``module`` classes
+internally including the :ref:`kernel-arch <ref-classes-kernel-arch>`,
+:ref:`module-base <ref-classes-module-base>`, and
+:ref:`linux-kernel-base <ref-classes-linux-kernel-base>` classes.
+
+.. _ref-classes-kernel-arch:
+
+``kernel-arch.bbclass``
+=======================
+
+The ``kernel-arch`` class sets the ``ARCH`` environment variable for
+Linux kernel compilation (including modules).
+
+.. _ref-classes-kernel-devicetree:
+
+``kernel-devicetree.bbclass``
+=============================
+
+The ``kernel-devicetree`` class, which is inherited by the
+:ref:`kernel <ref-classes-kernel>` class, supports device tree
+generation.
+
+.. _ref-classes-kernel-fitimage:
+
+``kernel-fitimage.bbclass``
+===========================
+
+The ``kernel-fitimage`` class provides support to pack a kernel Image,
+device trees and a RAM disk into a single FIT image. In theory, a FIT
+image can support any number of kernels, RAM disks and device-trees.
+However, ``kernel-fitimage`` currently only supports
+limited usescases: just one kernel image, an optional RAM disk, and
+any number of device tree.
+
+To create a FIT image, it is required that :term:`KERNEL_CLASSES`
+is set to "kernel-fitimage" and :term:`KERNEL_IMAGETYPE`
+is set to "fitImage".
+
+The options for the device tree compiler passed to mkimage -D feature
+when creating the FIT image are specified using the
+:term:`UBOOT_MKIMAGE_DTCOPTS` variable.
+
+Only a single kernel can be added to the FIT image created by
+``kernel-fitimage`` and the kernel image in FIT is mandatory. The
+address where the kernel image is to be loaded by U-boot is
+specified by :term:`UBOOT_LOADADDRESS` and the entrypoint by
+:term:`UBOOT_ENTRYPOINT`.
+
+Multiple device trees can be added to the FIT image created by
+``kernel-fitimage`` and the device tree is optional.
+The address where the device tree is to be loaded by U-boot is
+specified by :term:`UBOOT_DTBO_LOADADDRESS` for device tree overlays
+and by :term:`UBOOT_DTB_LOADADDRESS` for device tree binaries.
+
+Only a single RAM disk can be added to the FIT image created by
+``kernel-fitimage`` and the RAM disk in FIT is optional.
+The address where the RAM disk image is to be loaded by U-boot
+is specified by :term:`UBOOT_RD_LOADADDRESS` and the entrypoint by
+:term:`UBOOT_RD_ENTRYPOINT`. The ramdisk is added to FIT image when
+:term:`INITRAMFS_IMAGE` is specified.
+
+The FIT image generated by ``kernel-fitimage`` class is signed when the
+variables :term:`UBOOT_SIGN_ENABLE`, :term:`UBOOT_MKIMAGE_DTCOPTS`,
+:term:`UBOOT_SIGN_KEYDIR` and :term:`UBOOT_SIGN_KEYNAME` are set
+appropriately. The default values used for :term:`FIT_HASH_ALG` and
+:term:`FIT_SIGN_ALG` in ``kernel-fitimage`` are "sha256" and
+"rsa2048" respectively. The keys for signing fitImage can be generated using
+the ``kernel-fitimage`` class when both :term:`FIT_GENERATE_KEYS` and
+:term:`UBOOT_SIGN_ENABLE` are set to "1".
+
+
+.. _ref-classes-kernel-grub:
+
+``kernel-grub.bbclass``
+=======================
+
+The ``kernel-grub`` class updates the boot area and the boot menu with
+the kernel as the priority boot mechanism while installing a RPM to
+update the kernel on a deployed target.
+
+.. _ref-classes-kernel-module-split:
+
+``kernel-module-split.bbclass``
+===============================
+
+The ``kernel-module-split`` class provides common functionality for
+splitting Linux kernel modules into separate packages.
+
+.. _ref-classes-kernel-uboot:
+
+``kernel-uboot.bbclass``
+========================
+
+The ``kernel-uboot`` class provides support for building from
+vmlinux-style kernel sources.
+
+.. _ref-classes-kernel-uimage:
+
+``kernel-uimage.bbclass``
+=========================
+
+The ``kernel-uimage`` class provides support to pack uImage.
+
+.. _ref-classes-kernel-yocto:
+
+``kernel-yocto.bbclass``
+========================
+
+The ``kernel-yocto`` class provides common functionality for building
+from linux-yocto style kernel source repositories.
+
+.. _ref-classes-kernelsrc:
+
+``kernelsrc.bbclass``
+=====================
+
+The ``kernelsrc`` class sets the Linux kernel source and version.
+
+.. _ref-classes-lib_package:
+
+``lib_package.bbclass``
+=======================
+
+The ``lib_package`` class supports recipes that build libraries and
+produce executable binaries, where those binaries should not be
+installed by default along with the library. Instead, the binaries are
+added to a separate ``${``\ :term:`PN`\ ``}-bin`` package to
+make their installation optional.
+
+.. _ref-classes-libc*:
+
+``libc*.bbclass``
+=================
+
+The ``libc*`` classes support recipes that build packages with ``libc``:
+
+-  The ``libc-common`` class provides common support for building with
+   ``libc``.
+
+-  The ``libc-package`` class supports packaging up ``glibc`` and
+   ``eglibc``.
+
+.. _ref-classes-license:
+
+``license.bbclass``
+===================
+
+The ``license`` class provides license manifest creation and license
+exclusion. This class is enabled by default using the default value for
+the :term:`INHERIT_DISTRO` variable.
+
+.. _ref-classes-linux-kernel-base:
+
+``linux-kernel-base.bbclass``
+=============================
+
+The ``linux-kernel-base`` class provides common functionality for
+recipes that build out of the Linux kernel source tree. These builds
+goes beyond the kernel itself. For example, the Perf recipe also
+inherits this class.
+
+.. _ref-classes-linuxloader:
+
+``linuxloader.bbclass``
+=======================
+
+Provides the function ``linuxloader()``, which gives the value of the
+dynamic loader/linker provided on the platform. This value is used by a
+number of other classes.
+
+.. _ref-classes-logging:
+
+``logging.bbclass``
+===================
+
+The ``logging`` class provides the standard shell functions used to log
+messages for various BitBake severity levels (i.e. ``bbplain``,
+``bbnote``, ``bbwarn``, ``bberror``, ``bbfatal``, and ``bbdebug``).
+
+This class is enabled by default since it is inherited by the ``base``
+class.
+
+.. _ref-classes-meta:
+
+``meta.bbclass``
+================
+
+The ``meta`` class is inherited by recipes that do not build any output
+packages themselves, but act as a "meta" target for building other
+recipes.
+
+.. _ref-classes-metadata_scm:
+
+``metadata_scm.bbclass``
+========================
+
+The ``metadata_scm`` class provides functionality for querying the
+branch and revision of a Source Code Manager (SCM) repository.
+
+The :ref:`base <ref-classes-base>` class uses this class to print the
+revisions of each layer before starting every build. The
+``metadata_scm`` class is enabled by default because it is inherited by
+the ``base`` class.
+
+.. _ref-classes-migrate_localcount:
+
+``migrate_localcount.bbclass``
+==============================
+
+The ``migrate_localcount`` class verifies a recipe's localcount data and
+increments it appropriately.
+
+.. _ref-classes-mime:
+
+``mime.bbclass``
+================
+
+The ``mime`` class generates the proper post-install and post-remove
+(postinst/postrm) scriptlets for packages that install MIME type files.
+These scriptlets call ``update-mime-database`` to add the MIME types to
+the shared database.
+
+.. _ref-classes-mirrors:
+
+``mirrors.bbclass``
+===================
+
+The ``mirrors`` class sets up some standard
+:term:`MIRRORS` entries for source code mirrors. These
+mirrors provide a fall-back path in case the upstream source specified
+in :term:`SRC_URI` within recipes is unavailable.
+
+This class is enabled by default since it is inherited by the
+:ref:`base <ref-classes-base>` class.
+
+.. _ref-classes-module:
+
+``module.bbclass``
+==================
+
+The ``module`` class provides support for building out-of-tree Linux
+kernel modules. The class inherits the
+:ref:`module-base <ref-classes-module-base>` and
+:ref:`kernel-module-split <ref-classes-kernel-module-split>` classes,
+and implements the :ref:`ref-tasks-compile` and
+:ref:`ref-tasks-install` tasks. The class provides
+everything needed to build and package a kernel module.
+
+For general information on out-of-tree Linux kernel modules, see the
+":ref:`kernel-dev/common:incorporating out-of-tree modules`"
+section in the Yocto Project Linux Kernel Development Manual.
+
+.. _ref-classes-module-base:
+
+``module-base.bbclass``
+=======================
+
+The ``module-base`` class provides the base functionality for building
+Linux kernel modules. Typically, a recipe that builds software that
+includes one or more kernel modules and has its own means of building
+the module inherits this class as opposed to inheriting the
+:ref:`module <ref-classes-module>` class.
+
+.. _ref-classes-multilib*:
+
+``multilib*.bbclass``
+=====================
+
+The ``multilib*`` classes provide support for building libraries with
+different target optimizations or target architectures and installing
+them side-by-side in the same image.
+
+For more information on using the Multilib feature, see the
+":ref:`dev-manual/common-tasks:combining multiple versions of library files into one image`"
+section in the Yocto Project Development Tasks Manual.
+
+.. _ref-classes-native:
+
+``native.bbclass``
+==================
+
+The ``native`` class provides common functionality for recipes that
+build tools to run on the :term:`Build Host` (i.e. tools that use the compiler
+or other tools from the build host).
+
+You can create a recipe that builds tools that run natively on the host
+a couple different ways:
+
+-  Create a myrecipe\ ``-native.bb`` recipe that inherits the ``native``
+   class. If you use this method, you must order the inherit statement
+   in the recipe after all other inherit statements so that the
+   ``native`` class is inherited last.
+
+   .. note::
+
+      When creating a recipe this way, the recipe name must follow this
+      naming convention:
+      ::
+
+         myrecipe-native.bb
+
+
+      Not using this naming convention can lead to subtle problems
+      caused by existing code that depends on that naming convention.
+
+-  Create or modify a target recipe that contains the following:
+   ::
+
+      BBCLASSEXTEND = "native"
+
+   Inside the
+   recipe, use ``_class-native`` and ``_class-target`` overrides to
+   specify any functionality specific to the respective native or target
+   case.
+
+Although applied differently, the ``native`` class is used with both
+methods. The advantage of the second method is that you do not need to
+have two separate recipes (assuming you need both) for native and
+target. All common parts of the recipe are automatically shared.
+
+.. _ref-classes-nativesdk:
+
+``nativesdk.bbclass``
+=====================
+
+The ``nativesdk`` class provides common functionality for recipes that
+wish to build tools to run as part of an SDK (i.e. tools that run on
+:term:`SDKMACHINE`).
+
+You can create a recipe that builds tools that run on the SDK machine a
+couple different ways:
+
+-  Create a ``nativesdk-``\ myrecipe\ ``.bb`` recipe that inherits the
+   ``nativesdk`` class. If you use this method, you must order the
+   inherit statement in the recipe after all other inherit statements so
+   that the ``nativesdk`` class is inherited last.
+
+-  Create a ``nativesdk`` variant of any recipe by adding the following:
+   ::
+
+       BBCLASSEXTEND = "nativesdk"
+
+   Inside the
+   recipe, use ``_class-nativesdk`` and ``_class-target`` overrides to
+   specify any functionality specific to the respective SDK machine or
+   target case.
+
+.. note::
+
+   When creating a recipe, you must follow this naming convention:
+   ::
+
+           nativesdk-myrecipe.bb
+
+
+   Not doing so can lead to subtle problems because code exists that
+   depends on the naming convention.
+
+Although applied differently, the ``nativesdk`` class is used with both
+methods. The advantage of the second method is that you do not need to
+have two separate recipes (assuming you need both) for the SDK machine
+and the target. All common parts of the recipe are automatically shared.
+
+.. _ref-classes-nopackages:
+
+``nopackages.bbclass``
+======================
+
+Disables packaging tasks for those recipes and classes where packaging
+is not needed.
+
+.. _ref-classes-npm:
+
+``npm.bbclass``
+===============
+
+Provides support for building Node.js software fetched using the `node
+package manager (NPM) <https://en.wikipedia.org/wiki/Npm_(software)>`__.
+
+.. note::
+
+   Currently, recipes inheriting this class must use the ``npm://``
+   fetcher to have dependencies fetched and packaged automatically.
+
+For information on how to create NPM packages, see the
+":ref:`dev-manual/common-tasks:creating node package manager (npm) packages`"
+section in the Yocto Project Development Tasks Manual.
+
+.. _ref-classes-oelint:
+
+``oelint.bbclass``
+==================
+
+The ``oelint`` class is an obsolete lint checking tool that exists in
+``meta/classes`` in the :term:`Source Directory`.
+
+A number of classes exist that could be generally useful in OE-Core but
+are never actually used within OE-Core itself. The ``oelint`` class is
+one such example. However, being aware of this class can reduce the
+proliferation of different versions of similar classes across multiple
+layers.
+
+.. _ref-classes-own-mirrors:
+
+``own-mirrors.bbclass``
+=======================
+
+The ``own-mirrors`` class makes it easier to set up your own
+:term:`PREMIRRORS` from which to first fetch source
+before attempting to fetch it from the upstream specified in
+:term:`SRC_URI` within each recipe.
+
+To use this class, inherit it globally and specify
+:term:`SOURCE_MIRROR_URL`. Here is an example:
+::
+
+   INHERIT += "own-mirrors"
+   SOURCE_MIRROR_URL = "http://example.com/my-source-mirror"
+
+You can specify only a single URL
+in ``SOURCE_MIRROR_URL``.
+
+.. _ref-classes-package:
+
+``package.bbclass``
+===================
+
+The ``package`` class supports generating packages from a build's
+output. The core generic functionality is in ``package.bbclass``. The
+code specific to particular package types resides in these
+package-specific classes:
+:ref:`package_deb <ref-classes-package_deb>`,
+:ref:`package_rpm <ref-classes-package_rpm>`,
+:ref:`package_ipk <ref-classes-package_ipk>`, and
+:ref:`package_tar <ref-classes-package_tar>`.
+
+.. note::
+
+   The
+   package_tar
+   class is broken and not supported. It is recommended that you do not
+   use this class.
+
+You can control the list of resulting package formats by using the
+``PACKAGE_CLASSES`` variable defined in your ``conf/local.conf``
+configuration file, which is located in the :term:`Build Directory`.
+When defining the variable, you can
+specify one or more package types. Since images are generated from
+packages, a packaging class is needed to enable image generation. The
+first class listed in this variable is used for image generation.
+
+If you take the optional step to set up a repository (package feed) on
+the development host that can be used by DNF, you can install packages
+from the feed while you are running the image on the target (i.e.
+runtime installation of packages). For more information, see the
+":ref:`dev-manual/common-tasks:using runtime package management`"
+section in the Yocto Project Development Tasks Manual.
+
+The package-specific class you choose can affect build-time performance
+and has space ramifications. In general, building a package with IPK
+takes about thirty percent less time as compared to using RPM to build
+the same or similar package. This comparison takes into account a
+complete build of the package with all dependencies previously built.
+The reason for this discrepancy is because the RPM package manager
+creates and processes more :term:`Metadata` than the IPK package
+manager. Consequently, you might consider setting ``PACKAGE_CLASSES`` to
+"package_ipk" if you are building smaller systems.
+
+Before making your package manager decision, however, you should
+consider some further things about using RPM:
+
+-  RPM starts to provide more abilities than IPK due to the fact that it
+   processes more Metadata. For example, this information includes
+   individual file types, file checksum generation and evaluation on
+   install, sparse file support, conflict detection and resolution for
+   Multilib systems, ACID style upgrade, and repackaging abilities for
+   rollbacks.
+
+-  For smaller systems, the extra space used for the Berkeley Database
+   and the amount of metadata when using RPM can affect your ability to
+   perform on-device upgrades.
+
+You can find additional information on the effects of the package class
+at these two Yocto Project mailing list links:
+
+-  :yocto_lists:`/pipermail/poky/2011-May/006362.html`
+
+-  :yocto_lists:`/pipermail/poky/2011-May/006363.html`
+
+.. _ref-classes-package_deb:
+
+``package_deb.bbclass``
+=======================
+
+The ``package_deb`` class provides support for creating packages that
+use the Debian (i.e. ``.deb``) file format. The class ensures the
+packages are written out in a ``.deb`` file format to the
+``${``\ :term:`DEPLOY_DIR_DEB`\ ``}`` directory.
+
+This class inherits the :ref:`package <ref-classes-package>` class and
+is enabled through the :term:`PACKAGE_CLASSES`
+variable in the ``local.conf`` file.
+
+.. _ref-classes-package_ipk:
+
+``package_ipk.bbclass``
+=======================
+
+The ``package_ipk`` class provides support for creating packages that
+use the IPK (i.e. ``.ipk``) file format. The class ensures the packages
+are written out in a ``.ipk`` file format to the
+``${``\ :term:`DEPLOY_DIR_IPK`\ ``}`` directory.
+
+This class inherits the :ref:`package <ref-classes-package>` class and
+is enabled through the :term:`PACKAGE_CLASSES`
+variable in the ``local.conf`` file.
+
+.. _ref-classes-package_rpm:
+
+``package_rpm.bbclass``
+=======================
+
+The ``package_rpm`` class provides support for creating packages that
+use the RPM (i.e. ``.rpm``) file format. The class ensures the packages
+are written out in a ``.rpm`` file format to the
+``${``\ :term:`DEPLOY_DIR_RPM`\ ``}`` directory.
+
+This class inherits the :ref:`package <ref-classes-package>` class and
+is enabled through the :term:`PACKAGE_CLASSES`
+variable in the ``local.conf`` file.
+
+.. _ref-classes-package_tar:
+
+``package_tar.bbclass``
+=======================
+
+The ``package_tar`` class provides support for creating tarballs. The
+class ensures the packages are written out in a tarball format to the
+``${``\ :term:`DEPLOY_DIR_TAR`\ ``}`` directory.
+
+This class inherits the :ref:`package <ref-classes-package>` class and
+is enabled through the :term:`PACKAGE_CLASSES`
+variable in the ``local.conf`` file.
+
+.. note::
+
+   You cannot specify the ``package_tar`` class first using the
+   ``PACKAGE_CLASSES`` variable. You must use ``.deb``, ``.ipk``, or ``.rpm``
+   file formats for your image or SDK.
+
+.. _ref-classes-packagedata:
+
+``packagedata.bbclass``
+=======================
+
+The ``packagedata`` class provides common functionality for reading
+``pkgdata`` files found in :term:`PKGDATA_DIR`. These
+files contain information about each output package produced by the
+OpenEmbedded build system.
+
+This class is enabled by default because it is inherited by the
+:ref:`package <ref-classes-package>` class.
+
+.. _ref-classes-packagegroup:
+
+``packagegroup.bbclass``
+========================
+
+The ``packagegroup`` class sets default values appropriate for package
+group recipes (e.g. ``PACKAGES``, ``PACKAGE_ARCH``, ``ALLOW_EMPTY``, and
+so forth). It is highly recommended that all package group recipes
+inherit this class.
+
+For information on how to use this class, see the
+":ref:`dev-manual/common-tasks:customizing images using custom package groups`"
+section in the Yocto Project Development Tasks Manual.
+
+Previously, this class was called the ``task`` class.
+
+.. _ref-classes-patch:
+
+``patch.bbclass``
+=================
+
+The ``patch`` class provides all functionality for applying patches
+during the :ref:`ref-tasks-patch` task.
+
+This class is enabled by default because it is inherited by the
+:ref:`base <ref-classes-base>` class.
+
+.. _ref-classes-perlnative:
+
+``perlnative.bbclass``
+======================
+
+When inherited by a recipe, the ``perlnative`` class supports using the
+native version of Perl built by the build system rather than using the
+version provided by the build host.
+
+.. _ref-classes-pixbufcache:
+
+``pixbufcache.bbclass``
+=======================
+
+The ``pixbufcache`` class generates the proper post-install and
+post-remove (postinst/postrm) scriptlets for packages that install
+pixbuf loaders, which are used with ``gdk-pixbuf``. These scriptlets
+call ``update_pixbuf_cache`` to add the pixbuf loaders to the cache.
+Since the cache files are architecture-specific, ``update_pixbuf_cache``
+is run using QEMU if the postinst scriptlets need to be run on the build
+host during image creation.
+
+If the pixbuf loaders being installed are in packages other than the
+recipe's main package, set
+:term:`PIXBUF_PACKAGES` to specify the packages
+containing the loaders.
+
+.. _ref-classes-pkgconfig:
+
+``pkgconfig.bbclass``
+=====================
+
+The ``pkgconfig`` class provides a standard way to get header and
+library information by using ``pkg-config``. This class aims to smooth
+integration of ``pkg-config`` into libraries that use it.
+
+During staging, BitBake installs ``pkg-config`` data into the
+``sysroots/`` directory. By making use of sysroot functionality within
+``pkg-config``, the ``pkgconfig`` class no longer has to manipulate the
+files.
+
+.. _ref-classes-populate-sdk:
+
+``populate_sdk.bbclass``
+========================
+
+The ``populate_sdk`` class provides support for SDK-only recipes. For
+information on advantages gained when building a cross-development
+toolchain using the :ref:`ref-tasks-populate_sdk`
+task, see the ":ref:`sdk-manual/appendix-obtain:building an sdk installer`"
+section in the Yocto Project Application Development and the Extensible
+Software Development Kit (eSDK) manual.
+
+.. _ref-classes-populate-sdk-*:
+
+``populate_sdk_*.bbclass``
+==========================
+
+The ``populate_sdk_*`` classes support SDK creation and consist of the
+following classes:
+
+-  ``populate_sdk_base``: The base class supporting SDK creation under
+   all package managers (i.e. DEB, RPM, and opkg).
+
+-  ``populate_sdk_deb``: Supports creation of the SDK given the Debian
+   package manager.
+
+-  ``populate_sdk_rpm``: Supports creation of the SDK given the RPM
+   package manager.
+
+-  ``populate_sdk_ipk``: Supports creation of the SDK given the opkg
+   (IPK format) package manager.
+
+-  ``populate_sdk_ext``: Supports extensible SDK creation under all
+   package managers.
+
+The ``populate_sdk_base`` class inherits the appropriate
+``populate_sdk_*`` (i.e. ``deb``, ``rpm``, and ``ipk``) based on
+:term:`IMAGE_PKGTYPE`.
+
+The base class ensures all source and destination directories are
+established and then populates the SDK. After populating the SDK, the
+``populate_sdk_base`` class constructs two sysroots:
+``${``\ :term:`SDK_ARCH`\ ``}-nativesdk``, which
+contains the cross-compiler and associated tooling, and the target,
+which contains a target root filesystem that is configured for the SDK
+usage. These two images reside in :term:`SDK_OUTPUT`,
+which consists of the following:
+::
+
+   ${SDK_OUTPUT}/${SDK_ARCH}-nativesdk-pkgs
+   ${SDK_OUTPUT}/${SDKTARGETSYSROOT}/target-pkgs
+
+Finally, the base populate SDK class creates the toolchain environment
+setup script, the tarball of the SDK, and the installer.
+
+The respective ``populate_sdk_deb``, ``populate_sdk_rpm``, and
+``populate_sdk_ipk`` classes each support the specific type of SDK.
+These classes are inherited by and used with the ``populate_sdk_base``
+class.
+
+For more information on the cross-development toolchain generation, see
+the ":ref:`overview-manual/concepts:cross-development toolchain generation`"
+section in the Yocto Project Overview and Concepts Manual. For
+information on advantages gained when building a cross-development
+toolchain using the :ref:`ref-tasks-populate_sdk`
+task, see the
+":ref:`sdk-manual/appendix-obtain:building an sdk installer`"
+section in the Yocto Project Application Development and the Extensible
+Software Development Kit (eSDK) manual.
+
+.. _ref-classes-prexport:
+
+``prexport.bbclass``
+====================
+
+The ``prexport`` class provides functionality for exporting
+:term:`PR` values.
+
+.. note::
+
+   This class is not intended to be used directly. Rather, it is enabled
+   when using "``bitbake-prserv-tool export``".
+
+.. _ref-classes-primport:
+
+``primport.bbclass``
+====================
+
+The ``primport`` class provides functionality for importing
+:term:`PR` values.
+
+.. note::
+
+   This class is not intended to be used directly. Rather, it is enabled
+   when using "``bitbake-prserv-tool import``".
+
+.. _ref-classes-prserv:
+
+``prserv.bbclass``
+==================
+
+The ``prserv`` class provides functionality for using a :ref:`PR
+service <dev-manual/common-tasks:working with a pr service>` in order to
+automatically manage the incrementing of the :term:`PR`
+variable for each recipe.
+
+This class is enabled by default because it is inherited by the
+:ref:`package <ref-classes-package>` class. However, the OpenEmbedded
+build system will not enable the functionality of this class unless
+:term:`PRSERV_HOST` has been set.
+
+.. _ref-classes-ptest:
+
+``ptest.bbclass``
+=================
+
+The ``ptest`` class provides functionality for packaging and installing
+runtime tests for recipes that build software that provides these tests.
+
+This class is intended to be inherited by individual recipes. However,
+the class' functionality is largely disabled unless "ptest" appears in
+:term:`DISTRO_FEATURES`. See the
+":ref:`dev-manual/common-tasks:testing packages with ptest`"
+section in the Yocto Project Development Tasks Manual for more information
+on ptest.
+
+.. _ref-classes-ptest-gnome:
+
+``ptest-gnome.bbclass``
+=======================
+
+Enables package tests (ptests) specifically for GNOME packages, which
+have tests intended to be executed with ``gnome-desktop-testing``.
+
+For information on setting up and running ptests, see the
+":ref:`dev-manual/common-tasks:testing packages with ptest`"
+section in the Yocto Project Development Tasks Manual.
+
+.. _ref-classes-python-dir:
+
+``python-dir.bbclass``
+======================
+
+The ``python-dir`` class provides the base version, location, and site
+package location for Python.
+
+.. _ref-classes-python3native:
+
+``python3native.bbclass``
+=========================
+
+The ``python3native`` class supports using the native version of Python
+3 built by the build system rather than support of the version provided
+by the build host.
+
+.. _ref-classes-pythonnative:
+
+``pythonnative.bbclass``
+========================
+
+When inherited by a recipe, the ``pythonnative`` class supports using
+the native version of Python built by the build system rather than using
+the version provided by the build host.
+
+.. _ref-classes-qemu:
+
+``qemu.bbclass``
+================
+
+The ``qemu`` class provides functionality for recipes that either need
+QEMU or test for the existence of QEMU. Typically, this class is used to
+run programs for a target system on the build host using QEMU's
+application emulation mode.
+
+.. _ref-classes-recipe_sanity:
+
+``recipe_sanity.bbclass``
+=========================
+
+The ``recipe_sanity`` class checks for the presence of any host system
+recipe prerequisites that might affect the build (e.g. variables that
+are set or software that is present).
+
+.. _ref-classes-relocatable:
+
+``relocatable.bbclass``
+=======================
+
+The ``relocatable`` class enables relocation of binaries when they are
+installed into the sysroot.
+
+This class makes use of the :ref:`chrpath <ref-classes-chrpath>` class
+and is used by both the :ref:`cross <ref-classes-cross>` and
+:ref:`native <ref-classes-native>` classes.
+
+.. _ref-classes-remove-libtool:
+
+``remove-libtool.bbclass``
+==========================
+
+The ``remove-libtool`` class adds a post function to the
+:ref:`ref-tasks-install` task to remove all ``.la`` files
+installed by ``libtool``. Removing these files results in them being
+absent from both the sysroot and target packages.
+
+If a recipe needs the ``.la`` files to be installed, then the recipe can
+override the removal by setting ``REMOVE_LIBTOOL_LA`` to "0" as follows:
+::
+
+   REMOVE_LIBTOOL_LA = "0"
+
+.. note::
+
+   The ``remove-libtool`` class is not enabled by default.
+
+.. _ref-classes-report-error:
+
+``report-error.bbclass``
+========================
+
+The ``report-error`` class supports enabling the :ref:`error reporting
+tool <dev-manual/common-tasks:using the error reporting tool>`",
+which allows you to submit build error information to a central database.
+
+The class collects debug information for recipe, recipe version, task,
+machine, distro, build system, target system, host distro, branch,
+commit, and log. From the information, report files using a JSON format
+are created and stored in
+``${``\ :term:`LOG_DIR`\ ``}/error-report``.
+
+.. _ref-classes-rm-work:
+
+``rm_work.bbclass``
+===================
+
+The ``rm_work`` class supports deletion of temporary workspace, which
+can ease your hard drive demands during builds.
+
+The OpenEmbedded build system can use a substantial amount of disk space
+during the build process. A portion of this space is the work files
+under the ``${TMPDIR}/work`` directory for each recipe. Once the build
+system generates the packages for a recipe, the work files for that
+recipe are no longer needed. However, by default, the build system
+preserves these files for inspection and possible debugging purposes. If
+you would rather have these files deleted to save disk space as the
+build progresses, you can enable ``rm_work`` by adding the following to
+your ``local.conf`` file, which is found in the :term:`Build Directory`.
+::
+
+   INHERIT += "rm_work"
+
+If you are
+modifying and building source code out of the work directory for a
+recipe, enabling ``rm_work`` will potentially result in your changes to
+the source being lost. To exclude some recipes from having their work
+directories deleted by ``rm_work``, you can add the names of the recipe
+or recipes you are working on to the ``RM_WORK_EXCLUDE`` variable, which
+can also be set in your ``local.conf`` file. Here is an example:
+::
+
+   RM_WORK_EXCLUDE += "busybox glibc"
+
+.. _ref-classes-rootfs*:
+
+``rootfs*.bbclass``
+===================
+
+The ``rootfs*`` classes support creating the root filesystem for an
+image and consist of the following classes:
+
+-  The ``rootfs-postcommands`` class, which defines filesystem
+   post-processing functions for image recipes.
+
+-  The ``rootfs_deb`` class, which supports creation of root filesystems
+   for images built using ``.deb`` packages.
+
+-  The ``rootfs_rpm`` class, which supports creation of root filesystems
+   for images built using ``.rpm`` packages.
+
+-  The ``rootfs_ipk`` class, which supports creation of root filesystems
+   for images built using ``.ipk`` packages.
+
+-  The ``rootfsdebugfiles`` class, which installs additional files found
+   on the build host directly into the root filesystem.
+
+The root filesystem is created from packages using one of the
+``rootfs*.bbclass`` files as determined by the
+:term:`PACKAGE_CLASSES` variable.
+
+For information on how root filesystem images are created, see the
+":ref:`overview-manual/concepts:image generation`"
+section in the Yocto Project Overview and Concepts Manual.
+
+.. _ref-classes-sanity:
+
+``sanity.bbclass``
+==================
+
+The ``sanity`` class checks to see if prerequisite software is present
+on the host system so that users can be notified of potential problems
+that might affect their build. The class also performs basic user
+configuration checks from the ``local.conf`` configuration file to
+prevent common mistakes that cause build failures. Distribution policy
+usually determines whether to include this class.
+
+.. _ref-classes-scons:
+
+``scons.bbclass``
+=================
+
+The ``scons`` class supports recipes that need to build software that
+uses the SCons build system. You can use the
+:term:`EXTRA_OESCONS` variable to specify
+additional configuration options you want to pass SCons command line.
+
+.. _ref-classes-sdl:
+
+``sdl.bbclass``
+===============
+
+The ``sdl`` class supports recipes that need to build software that uses
+the Simple DirectMedia Layer (SDL) library.
+
+.. _ref-classes-setuptools:
+
+``setuptools.bbclass``
+======================
+
+The ``setuptools`` class supports Python version 2.x extensions that use
+build systems based on ``setuptools``. If your recipe uses these build
+systems, the recipe needs to inherit the ``setuptools`` class.
+
+.. _ref-classes-setuptools3:
+
+``setuptools3.bbclass``
+=======================
+
+The ``setuptools3`` class supports Python version 3.x extensions that
+use build systems based on ``setuptools3``. If your recipe uses these
+build systems, the recipe needs to inherit the ``setuptools3`` class.
+
+.. _ref-classes-sign_rpm:
+
+``sign_rpm.bbclass``
+====================
+
+The ``sign_rpm`` class supports generating signed RPM packages.
+
+.. _ref-classes-sip:
+
+``sip.bbclass``
+===============
+
+The ``sip`` class supports recipes that build or package SIP-based
+Python bindings.
+
+.. _ref-classes-siteconfig:
+
+``siteconfig.bbclass``
+======================
+
+The ``siteconfig`` class provides functionality for handling site
+configuration. The class is used by the
+:ref:`autotools <ref-classes-autotools>` class to accelerate the
+:ref:`ref-tasks-configure` task.
+
+.. _ref-classes-siteinfo:
+
+``siteinfo.bbclass``
+====================
+
+The ``siteinfo`` class provides information about the targets that might
+be needed by other classes or recipes.
+
+As an example, consider Autotools, which can require tests that must
+execute on the target hardware. Since this is not possible in general
+when cross compiling, site information is used to provide cached test
+results so these tests can be skipped over but still make the correct
+values available. The ``meta/site directory`` contains test results
+sorted into different categories such as architecture, endianness, and
+the ``libc`` used. Site information provides a list of files containing
+data relevant to the current build in the ``CONFIG_SITE`` variable that
+Autotools automatically picks up.
+
+The class also provides variables like ``SITEINFO_ENDIANNESS`` and
+``SITEINFO_BITS`` that can be used elsewhere in the metadata.
+
+.. _ref-classes-sstate:
+
+``sstate.bbclass``
+==================
+
+The ``sstate`` class provides support for Shared State (sstate). By
+default, the class is enabled through the
+:term:`INHERIT_DISTRO` variable's default value.
+
+For more information on sstate, see the
+":ref:`overview-manual/concepts:shared state cache`"
+section in the Yocto Project Overview and Concepts Manual.
+
+.. _ref-classes-staging:
+
+``staging.bbclass``
+===================
+
+The ``staging`` class installs files into individual recipe work
+directories for sysroots. The class contains the following key tasks:
+
+-  The :ref:`ref-tasks-populate_sysroot` task,
+   which is responsible for handing the files that end up in the recipe
+   sysroots.
+
+-  The
+   :ref:`ref-tasks-prepare_recipe_sysroot`
+   task (a "partner" task to the ``populate_sysroot`` task), which
+   installs the files into the individual recipe work directories (i.e.
+   :term:`WORKDIR`).
+
+The code in the ``staging`` class is complex and basically works in two
+stages:
+
+-  *Stage One:* The first stage addresses recipes that have files they
+   want to share with other recipes that have dependencies on the
+   originating recipe. Normally these dependencies are installed through
+   the :ref:`ref-tasks-install` task into
+   ``${``\ :term:`D`\ ``}``. The ``do_populate_sysroot`` task
+   copies a subset of these files into ``${SYSROOT_DESTDIR}``. This
+   subset of files is controlled by the
+   :term:`SYSROOT_DIRS`,
+   :term:`SYSROOT_DIRS_NATIVE`, and
+   :term:`SYSROOT_DIRS_BLACKLIST`
+   variables.
+
+   .. note::
+
+      Additionally, a recipe can customize the files further by
+      declaring a processing function in the ``SYSROOT_PREPROCESS_FUNCS``
+      variable.
+
+   A shared state (sstate) object is built from these files and the
+   files are placed into a subdirectory of
+   :ref:`structure-build-tmp-sysroots-components`.
+   The files are scanned for hardcoded paths to the original
+   installation location. If the location is found in text files, the
+   hardcoded locations are replaced by tokens and a list of the files
+   needing such replacements is created. These adjustments are referred
+   to as "FIXMEs". The list of files that are scanned for paths is
+   controlled by the :term:`SSTATE_SCAN_FILES`
+   variable.
+
+-  *Stage Two:* The second stage addresses recipes that want to use
+   something from another recipe and declare a dependency on that recipe
+   through the :term:`DEPENDS` variable. The recipe will
+   have a
+   :ref:`ref-tasks-prepare_recipe_sysroot`
+   task and when this task executes, it creates the ``recipe-sysroot``
+   and ``recipe-sysroot-native`` in the recipe work directory (i.e.
+   :term:`WORKDIR`). The OpenEmbedded build system
+   creates hard links to copies of the relevant files from
+   ``sysroots-components`` into the recipe work directory.
+
+   .. note::
+
+      If hard links are not possible, the build system uses actual
+      copies.
+
+   The build system then addresses any "FIXMEs" to paths as defined from
+   the list created in the first stage.
+
+   Finally, any files in ``${bindir}`` within the sysroot that have the
+   prefix "``postinst-``" are executed.
+
+   .. note::
+
+      Although such sysroot post installation scripts are not
+      recommended for general use, the files do allow some issues such
+      as user creation and module indexes to be addressed.
+
+   Because recipes can have other dependencies outside of ``DEPENDS``
+   (e.g. ``do_unpack[depends] += "tar-native:do_populate_sysroot"``),
+   the sysroot creation function ``extend_recipe_sysroot`` is also added
+   as a pre-function for those tasks whose dependencies are not through
+   ``DEPENDS`` but operate similarly.
+
+   When installing dependencies into the sysroot, the code traverses the
+   dependency graph and processes dependencies in exactly the same way
+   as the dependencies would or would not be when installed from sstate.
+   This processing means, for example, a native tool would have its
+   native dependencies added but a target library would not have its
+   dependencies traversed or installed. The same sstate dependency code
+   is used so that builds should be identical regardless of whether
+   sstate was used or not. For a closer look, see the
+   ``setscene_depvalid()`` function in the
+   :ref:`sstate <ref-classes-sstate>` class.
+
+   The build system is careful to maintain manifests of the files it
+   installs so that any given dependency can be installed as needed. The
+   sstate hash of the installed item is also stored so that if it
+   changes, the build system can reinstall it.
+
+.. _ref-classes-syslinux:
+
+``syslinux.bbclass``
+====================
+
+The ``syslinux`` class provides syslinux-specific functions for building
+bootable images.
+
+The class supports the following variables:
+
+-  :term:`INITRD`: Indicates list of filesystem images to
+   concatenate and use as an initial RAM disk (initrd). This variable is
+   optional.
+
+-  :term:`ROOTFS`: Indicates a filesystem image to include
+   as the root filesystem. This variable is optional.
+
+-  :term:`AUTO_SYSLINUXMENU`: Enables creating
+   an automatic menu when set to "1".
+
+-  :term:`LABELS`: Lists targets for automatic
+   configuration.
+
+-  :term:`APPEND`: Lists append string overrides for each
+   label.
+
+-  :term:`SYSLINUX_OPTS`: Lists additional options
+   to add to the syslinux file. Semicolon characters separate multiple
+   options.
+
+-  :term:`SYSLINUX_SPLASH`: Lists a background
+   for the VGA boot menu when you are using the boot menu.
+
+-  :term:`SYSLINUX_DEFAULT_CONSOLE`: Set
+   to "console=ttyX" to change kernel boot default console.
+
+-  :term:`SYSLINUX_SERIAL`: Sets an alternate
+   serial port. Or, turns off serial when the variable is set with an
+   empty string.
+
+-  :term:`SYSLINUX_SERIAL_TTY`: Sets an
+   alternate "console=tty..." kernel boot argument.
+
+.. _ref-classes-systemd:
+
+``systemd.bbclass``
+===================
+
+The ``systemd`` class provides support for recipes that install systemd
+unit files.
+
+The functionality for this class is disabled unless you have "systemd"
+in :term:`DISTRO_FEATURES`.
+
+Under this class, the recipe or Makefile (i.e. whatever the recipe is
+calling during the :ref:`ref-tasks-install` task)
+installs unit files into
+``${``\ :term:`D`\ ``}${systemd_unitdir}/system``. If the unit
+files being installed go into packages other than the main package, you
+need to set :term:`SYSTEMD_PACKAGES` in your
+recipe to identify the packages in which the files will be installed.
+
+You should set :term:`SYSTEMD_SERVICE` to the
+name of the service file. You should also use a package name override to
+indicate the package to which the value applies. If the value applies to
+the recipe's main package, use ``${``\ :term:`PN`\ ``}``. Here
+is an example from the connman recipe:
+::
+
+   SYSTEMD_SERVICE_${PN} = "connman.service"
+
+Services are set up to start on boot automatically
+unless you have set
+:term:`SYSTEMD_AUTO_ENABLE` to "disable".
+
+For more information on ``systemd``, see the
+":ref:`dev-manual/common-tasks:selecting an initialization manager`"
+section in the Yocto Project Development Tasks Manual.
+
+.. _ref-classes-systemd-boot:
+
+``systemd-boot.bbclass``
+========================
+
+The ``systemd-boot`` class provides functions specific to the
+systemd-boot bootloader for building bootable images. This is an
+internal class and is not intended to be used directly.
+
+.. note::
+
+   The ``systemd-boot`` class is a result from merging the ``gummiboot`` class
+   used in previous Yocto Project releases with the ``systemd`` project.
+
+Set the :term:`EFI_PROVIDER` variable to
+"systemd-boot" to use this class. Doing so creates a standalone EFI
+bootloader that is not dependent on systemd.
+
+For information on more variables used and supported in this class, see
+the :term:`SYSTEMD_BOOT_CFG`,
+:term:`SYSTEMD_BOOT_ENTRIES`, and
+:term:`SYSTEMD_BOOT_TIMEOUT` variables.
+
+You can also see the `Systemd-boot
+documentation <http://www.freedesktop.org/wiki/Software/systemd/systemd-boot/>`__
+for more information.
+
+.. _ref-classes-terminal:
+
+``terminal.bbclass``
+====================
+
+The ``terminal`` class provides support for starting a terminal session.
+The :term:`OE_TERMINAL` variable controls which
+terminal emulator is used for the session.
+
+Other classes use the ``terminal`` class anywhere a separate terminal
+session needs to be started. For example, the
+:ref:`patch <ref-classes-patch>` class assuming
+:term:`PATCHRESOLVE` is set to "user", the
+:ref:`cml1 <ref-classes-cml1>` class, and the
+:ref:`devshell <ref-classes-devshell>` class all use the ``terminal``
+class.
+
+.. _ref-classes-testimage*:
+
+``testimage*.bbclass``
+======================
+
+The ``testimage*`` classes support running automated tests against
+images using QEMU and on actual hardware. The classes handle loading the
+tests and starting the image. To use the classes, you need to perform
+steps to set up the environment.
+
+.. note::
+
+   Best practices include using :term:`IMAGE_CLASSES` rather than
+   :term:`INHERIT` to inherit the ``testimage`` class for automated image
+   testing.
+
+The tests are commands that run on the target system over ``ssh``. Each
+test is written in Python and makes use of the ``unittest`` module.
+
+The ``testimage.bbclass`` runs tests on an image when called using the
+following:
+::
+
+   $ bitbake -c testimage image
+
+The ``testimage-auto`` class
+runs tests on an image after the image is constructed (i.e.
+:term:`TESTIMAGE_AUTO` must be set to "1").
+
+For information on how to enable, run, and create new tests, see the
+":ref:`dev-manual/common-tasks:performing automated runtime testing`"
+section in the Yocto Project Development Tasks Manual.
+
+.. _ref-classes-testsdk:
+
+``testsdk.bbclass``
+===================
+
+This class supports running automated tests against software development
+kits (SDKs). The ``testsdk`` class runs tests on an SDK when called
+using the following:
+::
+
+   $ bitbake -c testsdk image
+
+.. note::
+
+   Best practices include using :term:`IMAGE_CLASSES` rather than
+   :term:`INHERIT` to inherit the ``testsdk`` class for automated SDK
+   testing.
+
+.. _ref-classes-texinfo:
+
+``texinfo.bbclass``
+===================
+
+This class should be inherited by recipes whose upstream packages invoke
+the ``texinfo`` utilities at build-time. Native and cross recipes are
+made to use the dummy scripts provided by ``texinfo-dummy-native``, for
+improved performance. Target architecture recipes use the genuine
+Texinfo utilities. By default, they use the Texinfo utilities on the
+host system.
+
+.. note::
+
+   If you want to use the Texinfo recipe shipped with the build system,
+   you can remove "texinfo-native" from :term:`ASSUME_PROVIDED` and makeinfo
+   from :term:`SANITY_REQUIRED_UTILITIES`.
+
+.. _ref-classes-toaster:
+
+``toaster.bbclass``
+===================
+
+The ``toaster`` class collects information about packages and images and
+sends them as events that the BitBake user interface can receive. The
+class is enabled when the Toaster user interface is running.
+
+This class is not intended to be used directly.
+
+.. _ref-classes-toolchain-scripts:
+
+``toolchain-scripts.bbclass``
+=============================
+
+The ``toolchain-scripts`` class provides the scripts used for setting up
+the environment for installed SDKs.
+
+.. _ref-classes-typecheck:
+
+``typecheck.bbclass``
+=====================
+
+The ``typecheck`` class provides support for validating the values of
+variables set at the configuration level against their defined types.
+The OpenEmbedded build system allows you to define the type of a
+variable using the "type" varflag. Here is an example:
+::
+
+   IMAGE_FEATURES[type] = "list"
+
+.. _ref-classes-uboot-config:
+
+``uboot-config.bbclass``
+========================
+
+The ``uboot-config`` class provides support for U-Boot configuration for
+a machine. Specify the machine in your recipe as follows:
+::
+
+   UBOOT_CONFIG ??= <default>
+   UBOOT_CONFIG[foo] = "config,images"
+
+You can also specify the machine using this method:
+::
+
+   UBOOT_MACHINE = "config"
+
+See the :term:`UBOOT_CONFIG` and :term:`UBOOT_MACHINE` variables for additional
+information.
+
+.. _ref-classes-uninative:
+
+``uninative.bbclass``
+=====================
+
+Attempts to isolate the build system from the host distribution's C
+library in order to make re-use of native shared state artifacts across
+different host distributions practical. With this class enabled, a
+tarball containing a pre-built C library is downloaded at the start of
+the build. In the Poky reference distribution this is enabled by default
+through ``meta/conf/distro/include/yocto-uninative.inc``. Other
+distributions that do not derive from poky can also
+"``require conf/distro/include/yocto-uninative.inc``" to use this.
+Alternatively if you prefer, you can build the uninative-tarball recipe
+yourself, publish the resulting tarball (e.g. via HTTP) and set
+``UNINATIVE_URL`` and ``UNINATIVE_CHECKSUM`` appropriately. For an
+example, see the ``meta/conf/distro/include/yocto-uninative.inc``.
+
+The ``uninative`` class is also used unconditionally by the extensible
+SDK. When building the extensible SDK, ``uninative-tarball`` is built
+and the resulting tarball is included within the SDK.
+
+.. _ref-classes-update-alternatives:
+
+``update-alternatives.bbclass``
+===============================
+
+The ``update-alternatives`` class helps the alternatives system when
+multiple sources provide the same command. This situation occurs when
+several programs that have the same or similar function are installed
+with the same name. For example, the ``ar`` command is available from
+the ``busybox``, ``binutils`` and ``elfutils`` packages. The
+``update-alternatives`` class handles renaming the binaries so that
+multiple packages can be installed without conflicts. The ``ar`` command
+still works regardless of which packages are installed or subsequently
+removed. The class renames the conflicting binary in each package and
+symlinks the highest priority binary during installation or removal of
+packages.
+
+To use this class, you need to define a number of variables:
+
+-  :term:`ALTERNATIVE`
+
+-  :term:`ALTERNATIVE_LINK_NAME`
+
+-  :term:`ALTERNATIVE_TARGET`
+
+-  :term:`ALTERNATIVE_PRIORITY`
+
+These variables list alternative commands needed by a package, provide
+pathnames for links, default links for targets, and so forth. For
+details on how to use this class, see the comments in the
+:yocto_git:`update-alternatives.bbclass </poky/tree/meta/classes/update-alternatives.bbclass>`
+file.
+
+.. note::
+
+   You can use the ``update-alternatives`` command directly in your recipes.
+   However, this class simplifies things in most cases.
+
+.. _ref-classes-update-rc.d:
+
+``update-rc.d.bbclass``
+=======================
+
+The ``update-rc.d`` class uses ``update-rc.d`` to safely install an
+initialization script on behalf of the package. The OpenEmbedded build
+system takes care of details such as making sure the script is stopped
+before a package is removed and started when the package is installed.
+
+Three variables control this class: ``INITSCRIPT_PACKAGES``,
+``INITSCRIPT_NAME`` and ``INITSCRIPT_PARAMS``. See the variable links
+for details.
+
+.. _ref-classes-useradd:
+
+``useradd*.bbclass``
+====================
+
+The ``useradd*`` classes support the addition of users or groups for
+usage by the package on the target. For example, if you have packages
+that contain system services that should be run under their own user or
+group, you can use these classes to enable creation of the user or
+group. The ``meta-skeleton/recipes-skeleton/useradd/useradd-example.bb``
+recipe in the :term:`Source Directory` provides a simple
+example that shows how to add three users and groups to two packages.
+See the ``useradd-example.bb`` recipe for more information on how to use
+these classes.
+
+The ``useradd_base`` class provides basic functionality for user or
+groups settings.
+
+The ``useradd*`` classes support the
+:term:`USERADD_PACKAGES`,
+:term:`USERADD_PARAM`,
+:term:`GROUPADD_PARAM`, and
+:term:`GROUPMEMS_PARAM` variables.
+
+The ``useradd-staticids`` class supports the addition of users or groups
+that have static user identification (``uid``) and group identification
+(``gid``) values.
+
+The default behavior of the OpenEmbedded build system for assigning
+``uid`` and ``gid`` values when packages add users and groups during
+package install time is to add them dynamically. This works fine for
+programs that do not care what the values of the resulting users and
+groups become. In these cases, the order of the installation determines
+the final ``uid`` and ``gid`` values. However, if non-deterministic
+``uid`` and ``gid`` values are a problem, you can override the default,
+dynamic application of these values by setting static values. When you
+set static values, the OpenEmbedded build system looks in
+:term:`BBPATH` for ``files/passwd`` and ``files/group``
+files for the values.
+
+To use static ``uid`` and ``gid`` values, you need to set some
+variables. See the :term:`USERADDEXTENSION`,
+:term:`USERADD_UID_TABLES`,
+:term:`USERADD_GID_TABLES`, and
+:term:`USERADD_ERROR_DYNAMIC` variables.
+You can also see the :ref:`useradd <ref-classes-useradd>` class for
+additional information.
+
+.. note::
+
+   You do not use the ``useradd-staticids`` class directly. You either enable
+   or disable the class by setting the ``USERADDEXTENSION`` variable. If you
+   enable or disable the class in a configured system, :term:`TMPDIR` might
+   contain incorrect ``uid`` and ``gid`` values. Deleting the ``TMPDIR``
+   directory will correct this condition.
+
+.. _ref-classes-utility-tasks:
+
+``utility-tasks.bbclass``
+=========================
+
+The ``utility-tasks`` class provides support for various "utility" type
+tasks that are applicable to all recipes, such as
+:ref:`ref-tasks-clean` and
+:ref:`ref-tasks-listtasks`.
+
+This class is enabled by default because it is inherited by the
+:ref:`base <ref-classes-base>` class.
+
+.. _ref-classes-utils:
+
+``utils.bbclass``
+=================
+
+The ``utils`` class provides some useful Python functions that are
+typically used in inline Python expressions (e.g. ``${@...}``). One
+example use is for ``bb.utils.contains()``.
+
+This class is enabled by default because it is inherited by the
+:ref:`base <ref-classes-base>` class.
+
+.. _ref-classes-vala:
+
+``vala.bbclass``
+================
+
+The ``vala`` class supports recipes that need to build software written
+using the Vala programming language.
+
+.. _ref-classes-waf:
+
+``waf.bbclass``
+===============
+
+The ``waf`` class supports recipes that need to build software that uses
+the Waf build system. You can use the
+:term:`EXTRA_OECONF` or
+:term:`PACKAGECONFIG_CONFARGS` variables
+to specify additional configuration options to be passed on the Waf
+command line.