poky/documentation/ref-manual/terms.rst - openbmc/openbmc - Gitiles

 .. SPDX-License-Identifier: CC-BY-SA-2.0-UK

 *******************
 Yocto Project Terms
 *******************

 Following is a list of terms and definitions users new to the Yocto Project
 development environment might find helpful. While some of these terms are
 universal, the list includes them just in case:

 .. glossary::

    :term:`Append Files`
       Files that append build information to a recipe file.  Append files are
       known as BitBake append files and ``.bbappend`` files. The OpenEmbedded
       build system expects every append file to have a corresponding recipe
       (``.bb``) file. Furthermore, the append file and corresponding recipe file
       must use the same root filename.  The filenames can differ only in the
       file type suffix used (e.g. ``formfactor_0.0.bb`` and
       ``formfactor_0.0.bbappend``).

       Information in append files extends or overrides the information in the
       similarly-named recipe file. For an example of an append file in use, see
       the    ":ref:`dev-manual/common-tasks:appending other layers metadata with your layer`"
       section in the Yocto Project Development Tasks Manual.

       When you name an append file, you can use the "``%``" wildcard character
       to allow for matching recipe names. For example, suppose you have an
       append file named as follows::

          busybox_1.21.%.bbappend

       That append file
       would match any ``busybox_1.21.x.bb`` version of the recipe. So,
       the append file would match any of the following recipe names:

       .. code-block:: shell

          busybox_1.21.1.bb
          busybox_1.21.2.bb
          busybox_1.21.3.bb
          busybox_1.21.10.bb
          busybox_1.21.25.bb

       .. note::

          The use of the "%" character is limited in that it only works
          directly in front of the .bbappend portion of the append file's
          name. You cannot use the wildcard character in any other location of
          the name.

    :term:`BitBake`
       The task executor and scheduler used by the OpenEmbedded build system to
       build images. For more information on BitBake, see the :doc:`BitBake User
       Manual <bitbake:index>`.

    :term:`Board Support Package (BSP)`
       A group of drivers, definitions, and other components that provide support
       for a specific hardware configuration. For more information on BSPs, see
       the :doc:`/bsp-guide/index`.

    :term:`Build Directory`
       This term refers to the area used by the OpenEmbedded build system for
       builds. The area is created when you ``source`` the setup environment
       script that is found in the Source Directory
       (i.e. :ref:`ref-manual/structure:\`\`oe-init-build-env\`\``). The
       :term:`TOPDIR` variable points to the Build Directory.

       You have a lot of flexibility when creating the Build Directory.
       Following are some examples that show how to create the directory.  The
       examples assume your :term:`Source Directory` is named ``poky``:

          -  Create the Build Directory inside your Source Directory and let
             the name of the Build Directory default to ``build``:

             .. code-block:: shell

                $ cd poky
                $ source oe-init-build-env

          -  Create the Build Directory inside your home directory and
             specifically name it ``test-builds``:

             .. code-block:: shell

                $ source poky/oe-init-build-env test-builds

          -  Provide a directory path and specifically name the Build
             Directory. Any intermediate folders in the pathname must exist.
             This next example creates a Build Directory named
             ``YP-&DISTRO;`` within the existing directory ``mybuilds``:

             .. code-block:: shell

                $ source poky/oe-init-build-env mybuilds/YP-&DISTRO;

       .. note::

          By default, the Build Directory contains :term:`TMPDIR`, which is a
          temporary directory the build system uses for its work. :term:`TMPDIR` cannot
          be under NFS. Thus, by default, the Build Directory cannot be under
          NFS. However, if you need the Build Directory to be under NFS, you can
          set this up by setting :term:`TMPDIR` in your ``local.conf`` file to use a local
          drive. Doing so effectively separates :term:`TMPDIR` from :term:`TOPDIR`, which is the
          Build Directory.

    :term:`Build Host`
       The system used to build images in a Yocto Project Development
       environment. The build system is sometimes referred to as the development
       host.

    :term:`Classes`
       Files that provide for logic encapsulation and inheritance so that
       commonly used patterns can be defined once and then easily used in
       multiple recipes. For reference information on the Yocto Project classes,
       see the ":ref:`ref-manual/classes:Classes`" chapter. Class files end with the
       ``.bbclass`` filename extension.

    :term:`Configuration File`
       Files that hold global definitions of variables, user-defined variables,
       and hardware configuration information. These files tell the OpenEmbedded
       build system what to build and what to put into the image to support a
       particular platform.

       Configuration files end with a ``.conf`` filename extension. The
       :file:`conf/local.conf` configuration file in the :term:`Build Directory`
       contains user-defined variables that affect every build. The
       :file:`meta-poky/conf/distro/poky.conf` configuration file defines Yocto
       "distro" configuration variables used only when building with this
       policy. Machine configuration files, which are located throughout the
       :term:`Source Directory`, define variables for specific hardware and are
       only used when building for that target (e.g. the
       :file:`machine/beaglebone.conf` configuration file defines variables for
       the Texas Instruments ARM Cortex-A8 development board).

    :term:`Container Layer`
       A flexible definition that typically refers to a single Git checkout
       which contains multiple (and typically related) sub-layers which can
       be included independently in your project's ``bblayers.conf`` file.

       In some cases, such as with OpenEmbedded's
       `meta-openembedded <https://github.com/openembedded/meta-openembedded>`_
       layer, the top level ``meta-openembedded/`` directory is not itself an actual layer,
       so you would never explicitly include it in a ``bblayers.conf`` file;
       rather, you would include any number of its layer subdirectories, such as
       `meta-openembedded/meta-oe <https://github.com/openembedded/meta-openembedded/tree/master/meta-oe>`_,
       `meta-openembedded/meta-python <https://github.com/openembedded/meta-openembedded/tree/master/meta-python>`_
       and so on.

       On the other hand, some container layers (such as
       :yocto_git:`meta-security </meta-security>`)
       have a top-level directory that is itself an actual layer, as well as
       a variety of sub-layers, both of which could be included in your
       ``bblayers.conf`` file.

       In either case, the phrase "container layer" is simply used to describe
       a directory structure which contains multiple valid OpenEmbedded layers.

    :term:`Cross-Development Toolchain`
       In general, a cross-development toolchain is a collection of software
       development tools and utilities that run on one architecture and allow you
       to develop software for a different, or targeted, architecture. These
       toolchains contain cross-compilers, linkers, and debuggers that are
       specific to the target architecture.

       The Yocto Project supports two different cross-development toolchains:

       - A toolchain only used by and within BitBake when building an image for a
         target architecture.

       - A relocatable toolchain used outside of BitBake by developers when
         developing applications that will run on a targeted device.

       Creation of these toolchains is simple and automated. For information on
       toolchain concepts as they apply to the Yocto Project, see the
       ":ref:`overview-manual/concepts:Cross-Development
       Toolchain Generation`" section in the Yocto Project Overview and Concepts
       Manual. You can also find more information on using the relocatable
       toolchain in the :doc:`/sdk-manual/index` manual.

    :term:`Extensible Software Development Kit (eSDK)`
       A custom SDK for application developers. This eSDK allows developers to
       incorporate their library and programming changes back into the image to
       make their code available to other application developers.

       For information on the eSDK, see the :doc:`/sdk-manual/index` manual.

    :term:`Image`
       An image is an artifact of the BitBake build process given a collection of
       recipes and related Metadata. Images are the binary output that run on
       specific hardware or QEMU and are used for specific use-cases. For a list
       of the supported image types that the Yocto Project provides, see the
       ":ref:`ref-manual/images:Images`" chapter.

    :term:`Layer`
       A collection of related recipes. Layers allow you to consolidate related
       metadata to customize your build. Layers also isolate information used
       when building for multiple architectures.  Layers are hierarchical in
       their ability to override previous specifications. You can include any
       number of available layers from the Yocto Project and customize the build
       by adding your layers after them. You can search the Layer Index for
       layers used within Yocto Project.

       For introductory information on layers, see the
       ":ref:`overview-manual/yp-intro:The Yocto Project Layer
       Model`" section in the Yocto Project Overview and Concepts Manual. For
       more detailed information on layers, see the
       ":ref:`dev-manual/common-tasks:Understanding and Creating
       Layers`" section in the Yocto Project Development Tasks Manual. For a
       discussion specifically on BSP Layers, see the ":ref:`bsp-guide/bsp:BSP
       Layers`" section in the Yocto Project Board Support Packages (BSP)
       Developer's Guide.

    :term:`Metadata`
       A key element of the Yocto Project is the Metadata that
       is used to construct a Linux distribution and is contained in the
       files that the :term:`OpenEmbedded Build System`
       parses when building an image. In general, Metadata includes recipes,
       configuration files, and other information that refers to the build
       instructions themselves, as well as the data used to control what
       things get built and the effects of the build. Metadata also includes
       commands and data used to indicate what versions of software are
       used, from where they are obtained, and changes or additions to the
       software itself (patches or auxiliary files) that are used to fix
       bugs or customize the software for use in a particular situation.
       OpenEmbedded-Core is an important set of validated metadata.

       In the context of the kernel ("kernel Metadata"), the term refers to
       the kernel config fragments and features contained in the
       :yocto_git:`yocto-kernel-cache </yocto-kernel-cache>`
       Git repository.

    :term:`OpenEmbedded-Core (OE-Core)`
       OE-Core is metadata comprised of
       foundational recipes, classes, and associated files that are meant to
       be common among many different OpenEmbedded-derived systems,
       including the Yocto Project. OE-Core is a curated subset of an
       original repository developed by the OpenEmbedded community that has
       been pared down into a smaller, core set of continuously validated
       recipes. The result is a tightly controlled and an quality-assured
       core set of recipes.

       You can see the Metadata in the ``meta`` directory of the Yocto
       Project :yocto_git:`Source Repositories </poky>`.

    :term:`OpenEmbedded Build System`
       The build system specific to the Yocto
       Project. The OpenEmbedded build system is based on another project
       known as "Poky", which uses :term:`BitBake` as the task
       executor. Throughout the Yocto Project documentation set, the
       OpenEmbedded build system is sometimes referred to simply as "the
       build system". If other build systems, such as a host or target build
       system are referenced, the documentation clearly states the
       difference.

       .. note::

          For some historical information about Poky, see the :term:`Poky` term.

    :term:`Package`
       In the context of the Yocto Project, this term refers to a
       recipe's packaged output produced by BitBake (i.e. a "baked recipe").
       A package is generally the compiled binaries produced from the
       recipe's sources. You "bake" something by running it through BitBake.

       It is worth noting that the term "package" can, in general, have
       subtle meanings. For example, the packages referred to in the
       ":ref:`ref-manual/system-requirements:required packages for the build host`"
       section are compiled binaries that, when installed, add functionality to
       your Linux distribution.

       Another point worth noting is that historically within the Yocto
       Project, recipes were referred to as packages --- thus, the existence
       of several BitBake variables that are seemingly mis-named, (e.g.
       :term:`PR`, :term:`PV`, and
       :term:`PE`).

    :term:`Package Groups`
       Arbitrary groups of software Recipes. You use
       package groups to hold recipes that, when built, usually accomplish a
       single task. For example, a package group could contain the recipes
       for a company's proprietary or value-add software. Or, the package
       group could contain the recipes that enable graphics. A package group
       is really just another recipe. Because package group files are
       recipes, they end with the ``.bb`` filename extension.

    :term:`Poky`
       Poky, which is pronounced *Pock*-ee, is a reference embedded
       distribution and a reference test configuration. Poky provides the
       following:

       -  A base-level functional distro used to illustrate how to customize
          a distribution.

       -  A means by which to test the Yocto Project components (i.e. Poky
          is used to validate the Yocto Project).

       -  A vehicle through which you can download the Yocto Project.

       Poky is not a product level distro. Rather, it is a good starting
       point for customization.

       .. note::

          Poky began as an open-source project initially developed by
          OpenedHand. OpenedHand developed Poky from the existing
          OpenEmbedded build system to create a commercially supportable
          build system for embedded Linux. After Intel Corporation acquired
          OpenedHand, the poky project became the basis for the Yocto
          Project's build system.

    :term:`Recipe`
       A set of instructions for building packages. A recipe
       describes where you get source code, which patches to apply, how to
       configure the source, how to compile it and so on. Recipes also
       describe dependencies for libraries or for other recipes. Recipes
       represent the logical unit of execution, the software to build, the
       images to build, and use the ``.bb`` file extension.

    :term:`Reference Kit`
       A working example of a system, which includes a
       :term:`BSP<Board Support Package (BSP)>` as well as a
       :term:`build host<Build Host>` and other components, that can
       work on specific hardware.

    :term:`Source Directory`
      This term refers to the directory structure
      created as a result of creating a local copy of the ``poky`` Git
      repository ``git://git.yoctoproject.org/poky`` or expanding a
      released ``poky`` tarball.

      .. note::

         Creating a local copy of the
         poky
         Git repository is the recommended method for setting up your
         Source Directory.

      Sometimes you might hear the term "poky directory" used to refer to
      this directory structure.

      .. note::

         The OpenEmbedded build system does not support file or directory
         names that contain spaces. Be sure that the Source Directory you
         use does not contain these types of names.

      The Source Directory contains BitBake, Documentation, Metadata and
      other files that all support the Yocto Project. Consequently, you
      must have the Source Directory in place on your development system in
      order to do any development using the Yocto Project.

      When you create a local copy of the Git repository, you can name the
      repository anything you like. Throughout much of the documentation,
      "poky" is used as the name of the top-level folder of the local copy
      of the poky Git repository. So, for example, cloning the ``poky`` Git
      repository results in a local Git repository whose top-level folder
      is also named "poky".

      While it is not recommended that you use tarball extraction to set up
      the Source Directory, if you do, the top-level directory name of the
      Source Directory is derived from the Yocto Project release tarball.
      For example, downloading and unpacking poky tarballs from
      :yocto_dl:`/releases/yocto/&DISTRO_REL_TAG;/`
      results in a Source Directory whose root folder is named poky.


      It is important to understand the differences between the Source
      Directory created by unpacking a released tarball as compared to
      cloning ``git://git.yoctoproject.org/poky``. When you unpack a
      tarball, you have an exact copy of the files based on the time of
      release --- a fixed release point. Any changes you make to your local
      files in the Source Directory are on top of the release and will
      remain local only. On the other hand, when you clone the ``poky`` Git
      repository, you have an active development repository with access to
      the upstream repository's branches and tags. In this case, any local
      changes you make to the local Source Directory can be later applied
      to active development branches of the upstream ``poky`` Git
      repository.

      For more information on concepts related to Git repositories,
      branches, and tags, see the
      ":ref:`overview-manual/development-environment:repositories, tags, and branches`"
      section in the Yocto Project Overview and Concepts Manual.

    :term:`Sysroot`
       When cross-compiling, the target file system may be differently laid
       out and contain different things compared to the host system. The concept
       of a *sysroot* is directory which looks like the target filesystem and
       can be used to cross-compile against.

       In the context of cross-compiling toolchains, a *sysroot*
       typically contains C library and kernel headers, plus the
       compiled binaries for the C library. A *multilib toolchain*
       can contain multiple variants of the C library binaries,
       each compiled for a target instruction set (such as ``armv5``,
       ``armv7`` and ``armv8``), and possibly optimized for a specific CPU core.

       In the more specific context of the OpenEmbedded build System and
       of the Yocto Project, each recipe has two sysroots:

       -  A *target sysroot* contains all the **target** libraries and headers
          needed to build the recipe.

       -  A *native sysroot* contains all the **host** files and executables
          needed to build the recipe.

       See the :term:`SYSROOT_* <SYSROOT_DESTDIR>` variables controlling
       how sysroots are created and stored.

    :term:`Task`
       A per-recipe unit of execution for BitBake (e.g.
       :ref:`ref-tasks-compile`,
       :ref:`ref-tasks-fetch`,
       :ref:`ref-tasks-patch`, and so forth).
       One of the major benefits of the build system is that, since each
       recipe will typically spawn the execution of numerous tasks,
       it is entirely possible that many tasks can execute in parallel,
       either tasks from separate recipes or independent tasks within
       the same recipe, potentially up to the parallelism of your
       build system.

    :term:`Toaster`
       A web interface to the Yocto Project's :term:`OpenEmbedded Build System`.
       The interface enables you to
       configure and run your builds. Information about builds is collected
       and stored in a database. For information on Toaster, see the
       :doc:`/toaster-manual/index`.

    :term:`Upstream`
       A reference to source code or repositories that are not
       local to the development system but located in a remote area that is
       controlled by the maintainer of the source code. For example, in
       order for a developer to work on a particular piece of code, they
       need to first get a copy of it from an "upstream" source.
	.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

	*******************
	Yocto Project Terms
	*******************

	Following is a list of terms and definitions users new to the Yocto Project
	development environment might find helpful. While some of these terms are
	universal, the list includes them just in case:

	.. glossary::

	:term:`Append Files`
	Files that append build information to a recipe file. Append files are
	known as BitBake append files and ``.bbappend`` files. The OpenEmbedded
	build system expects every append file to have a corresponding recipe
	(``.bb``) file. Furthermore, the append file and corresponding recipe file
	must use the same root filename. The filenames can differ only in the
	file type suffix used (e.g. ``formfactor_0.0.bb`` and
	``formfactor_0.0.bbappend``).

	Information in append files extends or overrides the information in the
	similarly-named recipe file. For an example of an append file in use, see
	the ":ref:`dev-manual/common-tasks:appending other layers metadata with your layer`"
	section in the Yocto Project Development Tasks Manual.

	When you name an append file, you can use the "``%``" wildcard character
	to allow for matching recipe names. For example, suppose you have an
	append file named as follows::

	busybox_1.21.%.bbappend

	That append file
	would match any ``busybox_1.21.x.bb`` version of the recipe. So,
	the append file would match any of the following recipe names:

	.. code-block:: shell

	busybox_1.21.1.bb
	busybox_1.21.2.bb
	busybox_1.21.3.bb
	busybox_1.21.10.bb
	busybox_1.21.25.bb

	.. note::

	The use of the "%" character is limited in that it only works
	directly in front of the .bbappend portion of the append file's
	name. You cannot use the wildcard character in any other location of
	the name.

	:term:`BitBake`
	The task executor and scheduler used by the OpenEmbedded build system to
	build images. For more information on BitBake, see the :doc:`BitBake User
	Manual <bitbake:index>`.

	:term:`Board Support Package (BSP)`
	A group of drivers, definitions, and other components that provide support
	for a specific hardware configuration. For more information on BSPs, see
	the :doc:`/bsp-guide/index`.

	:term:`Build Directory`
	This term refers to the area used by the OpenEmbedded build system for
	builds. The area is created when you ``source`` the setup environment
	script that is found in the Source Directory
	(i.e. :ref:`ref-manual/structure:\`\`oe-init-build-env\`\``). The
	:term:`TOPDIR` variable points to the Build Directory.

	You have a lot of flexibility when creating the Build Directory.
	Following are some examples that show how to create the directory. The
	examples assume your :term:`Source Directory` is named ``poky``:

	- Create the Build Directory inside your Source Directory and let
	the name of the Build Directory default to ``build``:

	.. code-block:: shell

	$ cd poky
	$ source oe-init-build-env

	- Create the Build Directory inside your home directory and
	specifically name it ``test-builds``:

	.. code-block:: shell

	$ source poky/oe-init-build-env test-builds

	- Provide a directory path and specifically name the Build
	Directory. Any intermediate folders in the pathname must exist.
	This next example creates a Build Directory named
	``YP-&DISTRO;`` within the existing directory ``mybuilds``:

	.. code-block:: shell

	$ source poky/oe-init-build-env mybuilds/YP-&DISTRO;

	.. note::

	By default, the Build Directory contains :term:`TMPDIR`, which is a
	temporary directory the build system uses for its work. :term:`TMPDIR` cannot
	be under NFS. Thus, by default, the Build Directory cannot be under
	NFS. However, if you need the Build Directory to be under NFS, you can
	set this up by setting :term:`TMPDIR` in your ``local.conf`` file to use a local
	drive. Doing so effectively separates :term:`TMPDIR` from :term:`TOPDIR`, which is the
	Build Directory.

	:term:`Build Host`
	The system used to build images in a Yocto Project Development
	environment. The build system is sometimes referred to as the development
	host.

	:term:`Classes`
	Files that provide for logic encapsulation and inheritance so that
	commonly used patterns can be defined once and then easily used in
	multiple recipes. For reference information on the Yocto Project classes,
	see the ":ref:`ref-manual/classes:Classes`" chapter. Class files end with the
	``.bbclass`` filename extension.

	:term:`Configuration File`
	Files that hold global definitions of variables, user-defined variables,
	and hardware configuration information. These files tell the OpenEmbedded
	build system what to build and what to put into the image to support a
	particular platform.

	Configuration files end with a ``.conf`` filename extension. The
	:file:`conf/local.conf` configuration file in the :term:`Build Directory`
	contains user-defined variables that affect every build. The
	:file:`meta-poky/conf/distro/poky.conf` configuration file defines Yocto
	"distro" configuration variables used only when building with this
	policy. Machine configuration files, which are located throughout the
	:term:`Source Directory`, define variables for specific hardware and are
	only used when building for that target (e.g. the
	:file:`machine/beaglebone.conf` configuration file defines variables for
	the Texas Instruments ARM Cortex-A8 development board).

	:term:`Container Layer`
	A flexible definition that typically refers to a single Git checkout
	which contains multiple (and typically related) sub-layers which can
	be included independently in your project's ``bblayers.conf`` file.

	In some cases, such as with OpenEmbedded's
	`meta-openembedded <https://github.com/openembedded/meta-openembedded>`_
	layer, the top level ``meta-openembedded/`` directory is not itself an actual layer,
	so you would never explicitly include it in a ``bblayers.conf`` file;
	rather, you would include any number of its layer subdirectories, such as
	`meta-openembedded/meta-oe <https://github.com/openembedded/meta-openembedded/tree/master/meta-oe>`_,
	`meta-openembedded/meta-python <https://github.com/openembedded/meta-openembedded/tree/master/meta-python>`_
	and so on.

	On the other hand, some container layers (such as
	:yocto_git:`meta-security </meta-security>`)
	have a top-level directory that is itself an actual layer, as well as
	a variety of sub-layers, both of which could be included in your
	``bblayers.conf`` file.

	In either case, the phrase "container layer" is simply used to describe
	a directory structure which contains multiple valid OpenEmbedded layers.

	:term:`Cross-Development Toolchain`
	In general, a cross-development toolchain is a collection of software
	development tools and utilities that run on one architecture and allow you
	to develop software for a different, or targeted, architecture. These
	toolchains contain cross-compilers, linkers, and debuggers that are
	specific to the target architecture.

	The Yocto Project supports two different cross-development toolchains:

	- A toolchain only used by and within BitBake when building an image for a
	target architecture.

	- A relocatable toolchain used outside of BitBake by developers when
	developing applications that will run on a targeted device.

	Creation of these toolchains is simple and automated. For information on
	toolchain concepts as they apply to the Yocto Project, see the
	":ref:`overview-manual/concepts:Cross-Development
	Toolchain Generation`" section in the Yocto Project Overview and Concepts
	Manual. You can also find more information on using the relocatable
	toolchain in the :doc:`/sdk-manual/index` manual.

	:term:`Extensible Software Development Kit (eSDK)`
	A custom SDK for application developers. This eSDK allows developers to
	incorporate their library and programming changes back into the image to
	make their code available to other application developers.

	For information on the eSDK, see the :doc:`/sdk-manual/index` manual.

	:term:`Image`
	An image is an artifact of the BitBake build process given a collection of
	recipes and related Metadata. Images are the binary output that run on
	specific hardware or QEMU and are used for specific use-cases. For a list
	of the supported image types that the Yocto Project provides, see the
	":ref:`ref-manual/images:Images`" chapter.

	:term:`Layer`
	A collection of related recipes. Layers allow you to consolidate related
	metadata to customize your build. Layers also isolate information used
	when building for multiple architectures. Layers are hierarchical in
	their ability to override previous specifications. You can include any
	number of available layers from the Yocto Project and customize the build
	by adding your layers after them. You can search the Layer Index for
	layers used within Yocto Project.

	For introductory information on layers, see the
	":ref:`overview-manual/yp-intro:The Yocto Project Layer
	Model`" section in the Yocto Project Overview and Concepts Manual. For
	more detailed information on layers, see the
	":ref:`dev-manual/common-tasks:Understanding and Creating
	Layers`" section in the Yocto Project Development Tasks Manual. For a
	discussion specifically on BSP Layers, see the ":ref:`bsp-guide/bsp:BSP
	Layers`" section in the Yocto Project Board Support Packages (BSP)
	Developer's Guide.

	:term:`Metadata`
	A key element of the Yocto Project is the Metadata that
	is used to construct a Linux distribution and is contained in the
	files that the :term:`OpenEmbedded Build System`
	parses when building an image. In general, Metadata includes recipes,
	configuration files, and other information that refers to the build
	instructions themselves, as well as the data used to control what
	things get built and the effects of the build. Metadata also includes
	commands and data used to indicate what versions of software are
	used, from where they are obtained, and changes or additions to the
	software itself (patches or auxiliary files) that are used to fix
	bugs or customize the software for use in a particular situation.
	OpenEmbedded-Core is an important set of validated metadata.

	In the context of the kernel ("kernel Metadata"), the term refers to
	the kernel config fragments and features contained in the
	:yocto_git:`yocto-kernel-cache </yocto-kernel-cache>`
	Git repository.

	:term:`OpenEmbedded-Core (OE-Core)`
	OE-Core is metadata comprised of
	foundational recipes, classes, and associated files that are meant to
	be common among many different OpenEmbedded-derived systems,
	including the Yocto Project. OE-Core is a curated subset of an
	original repository developed by the OpenEmbedded community that has
	been pared down into a smaller, core set of continuously validated
	recipes. The result is a tightly controlled and an quality-assured
	core set of recipes.

	You can see the Metadata in the ``meta`` directory of the Yocto
	Project :yocto_git:`Source Repositories </poky>`.

	:term:`OpenEmbedded Build System`
	The build system specific to the Yocto
	Project. The OpenEmbedded build system is based on another project
	known as "Poky", which uses :term:`BitBake` as the task
	executor. Throughout the Yocto Project documentation set, the
	OpenEmbedded build system is sometimes referred to simply as "the
	build system". If other build systems, such as a host or target build
	system are referenced, the documentation clearly states the
	difference.

	.. note::

	For some historical information about Poky, see the :term:`Poky` term.

	:term:`Package`
	In the context of the Yocto Project, this term refers to a
	recipe's packaged output produced by BitBake (i.e. a "baked recipe").
	A package is generally the compiled binaries produced from the
	recipe's sources. You "bake" something by running it through BitBake.

	It is worth noting that the term "package" can, in general, have
	subtle meanings. For example, the packages referred to in the
	":ref:`ref-manual/system-requirements:required packages for the build host`"
	section are compiled binaries that, when installed, add functionality to
	your Linux distribution.

	Another point worth noting is that historically within the Yocto
	Project, recipes were referred to as packages --- thus, the existence
	of several BitBake variables that are seemingly mis-named, (e.g.
	:term:`PR`, :term:`PV`, and
	:term:`PE`).

	:term:`Package Groups`
	Arbitrary groups of software Recipes. You use
	package groups to hold recipes that, when built, usually accomplish a
	single task. For example, a package group could contain the recipes
	for a company's proprietary or value-add software. Or, the package
	group could contain the recipes that enable graphics. A package group
	is really just another recipe. Because package group files are
	recipes, they end with the ``.bb`` filename extension.

	:term:`Poky`
	Poky, which is pronounced Pock-ee, is a reference embedded
	distribution and a reference test configuration. Poky provides the
	following:

	- A base-level functional distro used to illustrate how to customize
	a distribution.

	- A means by which to test the Yocto Project components (i.e. Poky
	is used to validate the Yocto Project).

	- A vehicle through which you can download the Yocto Project.

	Poky is not a product level distro. Rather, it is a good starting
	point for customization.

	.. note::

	Poky began as an open-source project initially developed by
	OpenedHand. OpenedHand developed Poky from the existing
	OpenEmbedded build system to create a commercially supportable
	build system for embedded Linux. After Intel Corporation acquired
	OpenedHand, the poky project became the basis for the Yocto
	Project's build system.

	:term:`Recipe`
	A set of instructions for building packages. A recipe
	describes where you get source code, which patches to apply, how to
	configure the source, how to compile it and so on. Recipes also
	describe dependencies for libraries or for other recipes. Recipes
	represent the logical unit of execution, the software to build, the
	images to build, and use the ``.bb`` file extension.

	:term:`Reference Kit`
	A working example of a system, which includes a
	:term:`BSP<Board Support Package (BSP)>` as well as a
	:term:`build host<Build Host>` and other components, that can
	work on specific hardware.

	:term:`Source Directory`
	This term refers to the directory structure
	created as a result of creating a local copy of the ``poky`` Git
	repository ``git://git.yoctoproject.org/poky`` or expanding a
	released ``poky`` tarball.

	.. note::

	Creating a local copy of the
	poky
	Git repository is the recommended method for setting up your
	Source Directory.

	Sometimes you might hear the term "poky directory" used to refer to
	this directory structure.

	.. note::

	The OpenEmbedded build system does not support file or directory
	names that contain spaces. Be sure that the Source Directory you
	use does not contain these types of names.

	The Source Directory contains BitBake, Documentation, Metadata and
	other files that all support the Yocto Project. Consequently, you
	must have the Source Directory in place on your development system in
	order to do any development using the Yocto Project.

	When you create a local copy of the Git repository, you can name the
	repository anything you like. Throughout much of the documentation,
	"poky" is used as the name of the top-level folder of the local copy
	of the poky Git repository. So, for example, cloning the ``poky`` Git
	repository results in a local Git repository whose top-level folder
	is also named "poky".

	While it is not recommended that you use tarball extraction to set up
	the Source Directory, if you do, the top-level directory name of the
	Source Directory is derived from the Yocto Project release tarball.
	For example, downloading and unpacking poky tarballs from
	:yocto_dl:`/releases/yocto/&DISTRO_REL_TAG;/`
	results in a Source Directory whose root folder is named poky.


	It is important to understand the differences between the Source
	Directory created by unpacking a released tarball as compared to
	cloning ``git://git.yoctoproject.org/poky``. When you unpack a
	tarball, you have an exact copy of the files based on the time of
	release --- a fixed release point. Any changes you make to your local
	files in the Source Directory are on top of the release and will
	remain local only. On the other hand, when you clone the ``poky`` Git
	repository, you have an active development repository with access to
	the upstream repository's branches and tags. In this case, any local
	changes you make to the local Source Directory can be later applied
	to active development branches of the upstream ``poky`` Git
	repository.

	For more information on concepts related to Git repositories,
	branches, and tags, see the
	":ref:`overview-manual/development-environment:repositories, tags, and branches`"
	section in the Yocto Project Overview and Concepts Manual.

	:term:`Sysroot`
	When cross-compiling, the target file system may be differently laid
	out and contain different things compared to the host system. The concept
	of a sysroot is directory which looks like the target filesystem and
	can be used to cross-compile against.

	In the context of cross-compiling toolchains, a sysroot
	typically contains C library and kernel headers, plus the
	compiled binaries for the C library. A multilib toolchain
	can contain multiple variants of the C library binaries,
	each compiled for a target instruction set (such as ``armv5``,
	``armv7`` and ``armv8``), and possibly optimized for a specific CPU core.

	In the more specific context of the OpenEmbedded build System and
	of the Yocto Project, each recipe has two sysroots:

	- A target sysroot contains all the target libraries and headers
	needed to build the recipe.

	- A native sysroot contains all the host files and executables
	needed to build the recipe.

	See the :term:`SYSROOT_* <SYSROOT_DESTDIR>` variables controlling
	how sysroots are created and stored.

	:term:`Task`
	A per-recipe unit of execution for BitBake (e.g.
	:ref:`ref-tasks-compile`,
	:ref:`ref-tasks-fetch`,
	:ref:`ref-tasks-patch`, and so forth).
	One of the major benefits of the build system is that, since each
	recipe will typically spawn the execution of numerous tasks,
	it is entirely possible that many tasks can execute in parallel,
	either tasks from separate recipes or independent tasks within
	the same recipe, potentially up to the parallelism of your
	build system.

	:term:`Toaster`
	A web interface to the Yocto Project's :term:`OpenEmbedded Build System`.
	The interface enables you to
	configure and run your builds. Information about builds is collected
	and stored in a database. For information on Toaster, see the
	:doc:`/toaster-manual/index`.

	:term:`Upstream`
	A reference to source code or repositories that are not
	local to the development system but located in a remote area that is
	controlled by the maintainer of the source code. For example, in
	order for a developer to work on a particular piece of code, they
	need to first get a copy of it from an "upstream" source.