# Variables Glossary

This chapter lists common variables used in the OpenEmbedded build system and gives an overview of their function and contents.

A B C D E F H I K L M P R S T W

### A

ALLOW_EMPTY

  Specifies if an output package should still be produced if it is empty. By default, BitBake does not produce empty packages. This default behavior can cause issues when there is an `RDEPENDS` or some other runtime hard-requirement on the existence of the package.

  Like all package-controlling variables, you must always use them in conjunction with a package name override. Here is an example:

           ALLOW_EMPTY_${PN} = "1"

AUTHOR

  The email address used to contact the original author or authors in order to send patches, forward bugs, etc.

AUTOREV

  When `SRCREV` is set to the value of this variable, it specifies that the latest source revision in the repository should be used. Here is an example:

           SRCREV = "${AUTOREV}"

### B

B

  The Build Directory. The OpenEmbedded build system places generated objects into the Build Directory during a recipe's build process. By default, this directory is the same as the `S` directory:

           B = ${WORKDIR}/${BPN}-{PV}/

  You can separate the (`S`) directory and the directory pointed to by the `B` variable. Most autotools-based recipes support separating these directories. The build system defaults to using separate directories for `gcc` and some kernel recipes.
BAD_RECOMMENDATIONS

  A list of packages not to install despite being recommended by a recipe. Support for this variable exists only when using the `ipk` packaging backend.

BBCLASSEXTEND

  Allows you to extend a recipe so that it builds variants of the software. Common variants for recipes exist such as "natives" like `quilt-native`, which is a copy of quilt built to run on the build system; "crosses" such as `gcc-cross`, which is a compiler built to run on the build machine but produces binaries that run on the target `MACHINE`; "nativesdk", which targets the SDK machine instead of `MACHINE`; and "mulitlibs" in the form "`multilib:<multilib_name>`".

  To build a different variant of the recipe with a minimal amount of code, it usually is as simple as adding the following to your recipe:

           BBCLASSEXTEND =+ "native nativesdk"
           BBCLASSEXTEND =+ "multilib:<multilib_name>"

BBMASK

  Prevents BitBake from processing recipes and recipe append files. You can use the `BBMASK` variable to "hide" these `.bb` and `.bbappend` files. BitBake ignores any recipe or recipe append files that match the expression. It is as if BitBake does not see them at all. Consequently, matching files are not parsed or otherwise used by BitBake.

  The value you provide is passed to python's regular expression compiler. For complete syntax information, see python's documentation at . The expression is compared against the full paths to the files. For example, the following uses a complete regular expression to tell BitBake to ignore all recipe and recipe append files in the `.*/meta-ti/recipes-misc/` directory:

           BBMASK = ".*/meta-ti/recipes-misc/"

  Use the `BBMASK` variable from within the `conf/local.conf` file found in the Build Directory.

BB_NUMBER_THREADS

  The maximum number of tasks BitBake should run in parallel at any one time. If your host development system supports multiple cores a good rule of thumb is to set this variable to twice the number of cores.

BBFILE_COLLECTIONS

  Lists the names of configured layers. These names are used to find the other `BBFILE_*` variables. Typically, each layer will append its name to this variable in its `conf/layer.conf` file.

BBFILE_PATTERN

  Variable that expands to match files from `BBFILES` in a particular layer. This variable is used in the `conf/layer.conf` file and must be suffixed with the name of the specific layer (e.g. `BBFILE_PATTERN_emenlow`).

BBFILE_PRIORITY

  Assigns the priority for recipe files in each layer.

  This variable is useful in situations where the same recipe appears in more than one layer. Setting this variable allows you to prioritize a layer against other layers that contain the same recipe - effectively letting you control the precedence for the multiple layers. The precedence established through this variable stands regardless of a recipe's version (`PV` variable). For example, a layer that has a recipe with a higher `PV` value but for which the `BBFILE_PRIORITY` is set to have a lower precedence still has a lower precedence.

  A larger value for the `BBFILE_PRIORITY` variable results in a higher precedence. For example, the value 6 has a higher precedence than the value 5. If not specified, the `BBFILE_PRIORITY` variable is set based on layer dependencies (see the `LAYERDEPENDS` variable for more information. The default priority, if unspecified for a layer with no dependencies, is the lowest defined priority + 1 (or 1 if no priorities are defined).

  You can use the command `bitbake-layers show_layers` to list all configured layers along with their priorities.

BBFILES

  List of recipe files used by BitBake to build software

BBPATH

  Used by BitBake to locate `.bbclass` and configuration files. This variable is analogous to the `PATH` variable.

BBINCLUDELOGS

  Variable that controls how BitBake displays logs on build failure.

BBLAYERS

  Lists the layers to enable during the build. This variable is defined in the `bblayers.conf` configuration file in the Build Directory. Here is an example:

           BBLAYERS = " \
             /home/scottrif/poky/meta \
             /home/scottrif/poky/meta-yocto \
             /home/scottrif/poky/meta-yocto-bsp \
             /home/scottrif/poky/meta-mykernel \
             "

  This example enables four layers, one of which is a custom, user-defined layer named `meta-mykernel`.
BP

  The base recipe name and version but without any special recipe name suffix (i.e. `-native`, `lib64-`, and so forth). `BP` is comprised of the following:

           ${BPN}-${PV}

BPN

  The bare name of the recipe. This variable is a version of the `PN` variable but removes common suffixes such as "-native" and "-cross" as well as removes common prefixes such as multilib's "lib64-" and "lib32-". The exact list of suffixes removed is specified by the `SPECIAL_PKGSUFFIX` variable. The exact list of prefixes removed is specified by the `MLPREFIX` variable. Prefixes are removed for multilib and nativesdk cases.

### C

CFLAGS

  Flags passed to C compiler for the target system. This variable evaluates to the same as `TARGET_CFLAGS`.

COMPATIBLE_MACHINE

  A regular expression which evaluates to match the machines the recipe works with. It stops recipes being run on machines for which they are not compatible. This is particularly useful with kernels. It also helps to increase parsing speed as further parsing of the recipe is skipped if it is found the current machine is not compatible.

CONFFILES

  Identifies editable or configurable files that are part of a package. If the Package Management System (PMS) is being used to update packages on the target system, it is possible that configuration files you have changed after the original installation and that you now want to remain unchanged are overwritten. In other words, editable files might exist in the package that you do not want reset as part of the package update process. You can use the `CONFFILES` variable to list the files in the package that you wish to prevent the PMS from overwriting during this update process.

  To use the `CONFFILES` variable, provide a package name override that identifies the resulting package. Then, provide a space-separated list of files. Here is an example:

        CONFFILES_${PN} += "${sysconfdir}/file1 \
           ${sysconfdir}/file2 ${sysconfdir}/file3"

  A relationship exists between the `CONFFILES` and `FILES` variables. The files listed within `CONFFILES` must be a subset of the files listed within `FILES`. Because the configuration files you provide with `CONFFILES` are simply being identified so that the PMS will not overwrite them, it makes sense that the files must already be included as part of the package through the `FILES` variable.

  When specifying paths as part of the `CONFFILES` variable, it is good practice to use appropriate path variables. For example, `${sysconfdir}` rather than `/etc` or `${bindir}` rather than `/usr/bin`. You can find a list of these variables at the top of the `/meta/conf/bitbake.conf` file in the Source Directory.

CONFIG_SITE

  A list of files that contains `autoconf` test results relevant to the current build. This variable is used by the Autotools utilities when running `configure`.

CORE_IMAGE_EXTRA_INSTALL

  Specifies the list of packages to be added to the image. This variable should only be set in the `local.conf` configuration file found in the Build Directory.

  This variable replaces `POKY_EXTRA_INSTALL`, which is no longer supported.

### D

D

  The destination directory.

DEBUG_BUILD

  Specifies to build packages with debugging information. This influences the value of the `SELECTED_OPTIMIZATION` variable.

DEBUG_OPTIMIZATION

  The options to pass in `TARGET_CFLAGS` and `CFLAGS` when compiling a system for debugging. This variable defaults to "-O -fno-omit-frame-pointer -g".

DEFAULT_PREFERENCE

  Specifies the priority of recipes.

DEPENDS

  Lists a recipe's build-time dependencies (i.e. other recipe files). The system ensures that all the dependencies listed have been built and have their contents in the appropriate sysroots before the recipe's configure task is executed.

DESCRIPTION

  The package description used by package managers. If not set, `DESCRIPTION` takes the value of the `SUMMARY` variable.

DESTDIR

  the destination directory.

DISTRO

  The short name of the distribution. This variable corresponds to a file with the extension `.conf` located in a `conf/distro` directory within the metadata that contains the distribution configuration. The value must not contain spaces, and is typically all lower-case.

  If the variable is blank, a set of default configuration will be used, which is specified within `meta/conf/distro/defaultsetup.conf`.

DISTRO_EXTRA_RDEPENDS

  Specifies a list of distro-specific packages to add to all images. This variable takes affect through `packagegroup-base` so the variable only really applies to the more full-featured images that include `packagegroup-base`. You can use this variable to keep distro policy out of generic images. As with all other distro variables, you set this variable in the distro `.conf` file.

DISTRO_EXTRA_RRECOMMENDS

  Specifies a list of distro-specific packages to add to all images if the packages exist. The packages might not exist or be empty (e.g. kernel modules). The list of packages are automatically installed but can be removed by the user.

DISTRO_FEATURES

  The features enabled for the distribution. For a list of features supported by the Yocto Project as shipped, see the "Distro" section.

DISTRO_FEATURES_BACKFILL

  Features to be added to `DISTRO_FEATURES` if not also present in `DISTRO_FEATURES_BACKFILL_CONSIDERED`.

  This variable is set in the `meta/conf/bitbake.conf` file. It is not intended to be user-configurable. It is best to just reference the variable to see which distro features are being backfilled for all distro configurations. See the Feature backfilling section for more information.

DISTRO_FEATURES_BACKFILL_CONSIDERED

  Features from `DISTRO_FEATURES_BACKFILL` that should not backfilled (i.e. added to `DISTRO_FEATURES`) during the build. See the "Feature Backfilling" section for more information.

DISTRO_NAME

  The long name of the distribution.

DISTRO_PN_ALIAS

  Alias names used for the recipe in various Linux distributions.

  See the "Handling a Package Name Alias" section in the Yocto Project Development Manual for more information.

DISTRO_VERSION

  the version of the distribution.

DL_DIR

  The central download directory used by the build process to store downloads. You can set this directory by defining the `DL_DIR` variable in the `/conf/local.conf` file. This directory is self-maintaining and you should not have to touch it. By default, the directory is `downloads` in the Build Directory.

           #DL_DIR ?= "${TOPDIR}/downloads"

  To specify a different download directory, simply uncomment the line and provide your directory.

  During a first build, the system downloads many different source code tarballs from various upstream projects. Downloading can take a while, particularly if your network connection is slow. Tarballs are all stored in the directory defined by `DL_DIR` and the build system looks there first to find source tarballs.

  When wiping and rebuilding, you can preserve this directory to speed up this part of subsequent builds.

  You can safely share this directory between multiple builds on the same development machine. For additional information on how the build process gets source files when working behind a firewall or proxy server, see the "FAQ" chapter.

### E

ENABLE_BINARY_LOCALE_GENERATION

  Variable that controls which locales for `eglibc` are to be generated during the build (useful if the target device has 64Mbytes of RAM or less).

EXTENDPE

  Used with file and pathnames to create a prefix for a recipe's version based on the recipe's `PE` value. If `PE` is set and greater than zero for a recipe, `EXTENDPE` becomes that value (e.g if `PE` is equal to "1" then `EXTENDPE` becomes "1_"). If a recipe's `PE` is not set (the default) or is equal to zero, `EXTENDPE` becomes "".

  See the `STAMP` variable for an example.

EXTRA_IMAGE_FEATURES

  Allows extra packages to be added to the generated images. You set this variable in the `local.conf` configuration file. Note that some image features are also added using the `IMAGE_FEATURES` variable generally configured in image recipes. You can use this variable to add more features in addition to those. Here are some examples of features you can add:

      "dbg-pkgs" - Adds -dbg packages for all installed packages
                   including symbol information for debugging and
                   profiling.

      "dev-pkgs" - Adds -dev packages for all installed packages.
                   This is useful if you want to develop against
                   the libraries in the image.

      "tools-sdk" - Adds development tools such as gcc, make,
                    pkgconfig and so forth.

      "tools-debug" - Adds debugging tools such as gdb and
                      strace.

      "tools-profile" - Adds profiling tools such as oprofile,
                        exmap, lttng and valgrind (x86 only).

      "tools-testapps" - Adds useful testing tools such as
                         ts_print, aplay, arecord and so
                         forth.

      "debug-tweaks" - Makes an image suitable for development.
                       For example, ssh root access has a blank
                       password.  You should remove this feature
                       before you produce a production image.

  There are other valid features too, see the Images section for more details.

EXTRA_IMAGEDEPENDS

  A list of recipes to be built that do not provide packages to be installed in the root filesystem.

  Sometimes a recipe is required to build the final image but is not needed in the root filesystem. You can use the `EXTRA_IMAGEDEPENDS` variable to list these recipes and thus, specify the dependencies. A typical example is a required bootloader in a machine configuration.

  To add packages to the root filesystem, see the various `*DEPENDS` and `*RECOMMENDS` variables.

EXTRA_OECMAKE

  Additional `cmake` options.

EXTRA_OECONF

  Additional `configure` script options.

EXTRA_OEMAKE

  Additional GNU `make` options.

### F

FILES

  The list of directories or files that are placed in packages.

  To use the `FILES` variable, provide a package name override that identifies the resulting package. Then, provide a space-separated list of files or paths that identifies the files you want included as part of the resulting package. Here is an example:

        FILES_${PN} += "${bindir}/mydir1/ ${bindir}/mydir2/myfile"

  When specifying paths as part of the `FILES` variable, it is good practice to use appropriate path variables. For example, `${sysconfdir}` rather than `/etc` or `${bindir}` rather than `/usr/bin`. You can find a list of these variables at the top of the `/meta/conf/bitbake.conf` file in the Source Directory.

  If some of the files you provide with the `FILES` variable are editable and you know they should not be overwritten during the package update process by the Package Management System (PMS), you can identify these files so that the PMS will not overwrite them. See the `CONFFILES` variable for information on how to identify these files to the PMS.

FILESEXTRAPATHS

  Extends the search path the OpenEmbedded build system uses when looking for files and patches as it processes recipes. The directories BitBake uses when it processes recipes is defined by the `FILESPATH` variable. You can add directories to the search path by defining the `FILESEXTRAPATHS` variable.

  To add paths to the search order, provide a list of directories and separate each path using a colon character as follows:

           FILESEXTRAPATHS_prepend := "path_1:path_2:path_3:"

  Typically, you want your directories searched first. To make sure that happens, use `_prepend` and the immediate expansion (`:=`) operator as shown in the previous example. Finally, to maintain the integrity of the `FILESPATH` variable, you must include the appropriate beginning or ending (as needed) colon character.

  The `FILESEXTRAPATHS` variable is intended for use in `.bbappend` files to include any additional files provided in that layer. You typically accomplish this with the following:

           FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

FILESPATH

  The default set of directories the OpenEmbedded build system uses when searching for patches and files. During the build process, BitBake searches each directory in `FILESPATH` in the specified order when looking for files and patches specified by each `file://` URI in a recipe.

  The default value for the `FILESPATH` variable is defined in the `base.bbclass` class found in `meta/classes` in the Source Directory:

      FILESPATH = "${@base_set_filespath([ "${FILE_DIRNAME}/${PF}", \
         "${FILE_DIRNAME}/${P}", "${FILE_DIRNAME}/${PN}", \
         "${FILE_DIRNAME}/${BP}", "${FILE_DIRNAME}/${BPN}", \
         "${FILE_DIRNAME}/files", "${FILE_DIRNAME}" ], d)}"

  Do not hand-edit the `FILESPATH` variable. If you want to extend the set of pathnames that BitBake uses when searching for files and patches, use the `FILESEXTRAPATHS` variable.
FILESYSTEM_PERMS_TABLES

  Allows you to define your own file permissions settings table as part of your configuration for the packaging process. For example, suppose you need a consistent set of custom permissions for a set of groups and users across an entire work project. It is best to do this in the packages themselves but this is not always possible.

  By default, the OpenEmbedded build system uses the `fs-perms.txt`, which is located in the `meta/files` folder in the Source Directory. If you create your own file permissions setting table, you should place it in your layer or the distros layer.

  You define the `FILESYSTEM_PERMS_TABLES` variable in the `conf/local.conf` file, which is found in the Build Directory, to point to your custom `fs-perms.txt`. You can specify more than a single file permissions setting table. The paths you specify to these files must be defined within the `BBPATH` variable.

  For guidance on how to create your own file permissions settings table file, examine the existing `fs-perms.txt`.

FULL_OPTIMIZATION

  The options to pass in `TARGET_CFLAGS` and `CFLAGS` when compiling an optimized system. This variable defaults to "-fexpensive-optimizations -fomit-frame-pointer -frename-registers -O2".

### H

HOMEPAGE

  Website where more information about the software the recipe is building can be found.

### I

IMAGE_FEATURES

  The list of features to include in an image. Typically, you configure this variable in an image recipe. Note that you can also add extra features to the image by using the `EXTRA_IMAGE_FEATURES` variable. See the "Images" section for the full list of features that can be included in images built by the OpenEmbedded build system.

IMAGE_FSTYPES

  Formats of root filesystem images that you want to have created.

IMAGE_INSTALL

  Specifies the packages to install into an image. The `IMAGE_INSTALL` variable is a mechanism for an image recipe and you should use it with care to avoid ordering issues.

  Image recipes set `IMAGE_INSTALL` to specify the packages to install into an image through `image.bbclass`. Additionally, "helper" classes exist, such as `core-image.bbclass`, that can take `IMAGE_FEATURES` lists and turn these into auto-generated entries in `IMAGE_INSTALL` in addition to its default contents.

  Using `IMAGE_INSTALL` with the `+=` operator from the `/conf/local.conf` file or from within an image recipe is not recommended as it can cause ordering issues. Since `core-image.bbclass` sets `IMAGE_INSTALL` to a default value using the `?=` operator, using a `+=` operation against `IMAGE_INSTALL` will result in unexpected behavior when used in `/conf/local.conf`. Furthermore, the same operation from with an image recipe may or may not succeed depending on the specific situation. In both these cases, the behavior is contrary to how most users expect the `+=` operator to work.

  When you use this variable, it is best to use it as follows:

           IMAGE_INSTALL_append = " package-name"

  Be sure to include the space between the quotation character and the start of the package name.
IMAGE_OVERHEAD_FACTOR

  Defines a multiplier that the build system applies to the initial image size for cases when the multiplier times the returned disk usage value for the image is greater than the sum of `IMAGE_ROOTFS_SIZE` and `IMAGE_ROOTFS_EXTRA_SPACE`. The result of the multiplier applied to the initial image size creates free disk space in the image as overhead. By default, the build process uses a multiplier of 1.3 for this variable. This default value results in 30% free disk space added to the image when this method is used to determine the final generated image size. You should be aware that post install scripts and the package management system uses disk space inside this overhead area. Consequently, the multiplier does not produce an image with all the theoretical free disk space. See `IMAGE_ROOTFS_SIZE` for information on how the build system determines the overall image size.

  The default 30% free disk space typically gives the image enough room to boot and allows for basic post installs while still leaving a small amount of free disk space. If 30% free space is inadequate, you can increase the default value. For example, the following setting gives you 50% free space added to the image:

           IMAGE_OVERHEAD_FACTOR = "1.5"

  Alternatively, you can ensure a specific amount of free disk space is added to the image by using `IMAGE_ROOTFS_EXTRA_SPACE` the variable.

IMAGE_ROOTFS_EXTRA_SPACE

  Defines additional free disk space created in the image in Kbytes. By default, this variable is set to "0". This free disk space is added to the image after the build system determines the image size as described in `IMAGE_ROOTFS_SIZE`.

  This variable is particularly useful when you want to ensure that a specific amount of free disk space is available on a device after an image is installed and running. For example, to be sure 5 Gbytes of free disk space is available, set the variable as follows:

           IMAGE_ROOTFS_EXTRA_SPACE = "5242880"

IMAGE_ROOTFS_SIZE

  Defines the size in Kbytes for the generated image. The OpenEmbedded build system determines the final size for the generated image using an algorithm that takes into account the initial disk space used for the generated image, a requested size for the image, and requested additional free disk space to be added to the image. Programatically, the build system determines the final size of the generated image as follows:

          if (image-du * overhead) < rootfs-size:
      	internal-rootfs-size = rootfs-size + xspace
          else:
      	internal-rootfs-size = (image-du * overhead) + xspace

          where:

            image-du = Returned value of the du command on
                       the image.

            overhead = IMAGE_OVERHEAD_FACTOR

            rootfs-size = IMAGE_ROOTFS_SIZE

            internal-rootfs-size = Initial root filesystem
                                   size before any modifications.

            xspace = IMAGE_ROOTFS_EXTRA_SPACE

INC_PR

  Helps define the recipe revision for recipes that share a common `include` file. You can think of this variable as part of the recipe revision as set from within an include file.

  Suppose, for example, you have a set of recipes that are used across several projects. And, within each of those recipes the revision (its `PR` value) is set accordingly. In this case, when the revision of those recipes changes the burden is on you to find all those recipes and be sure that they get changed to reflect the updated version of the recipe. In this scenario, it can get complicated when recipes used in many places and that provide common functionality are upgraded to a new revision.

  A more efficient way of dealing with this situation is to set the `INC_PR` variable inside the `include` files that the recipes share and then expand the `INC_PR` variable within the recipes to help define the recipe revision.

  The following provides an example that shows how to use the `INC_PR` variable given a common `include` file that defines the variable. Once the variable is defined in the `include` file, you can use the variable to set the `PR` values in each recipe. You will notice that when you set a recipe's `PR` you can provide more granular revisioning by appending values to the `INC_PR` variable:

      recipes-graphics/xorg-font/xorg-font-common.inc:INC_PR = "r2"
      recipes-graphics/xorg-font/encodings_1.0.4.bb:PR = "${INC_PR}.1"
      recipes-graphics/xorg-font/font-util_1.3.0.bb:PR = "${INC_PR}.0"
      recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"

  The first line of the example establishes the baseline revision to be used for all recipes that use the `include` file. The remaining lines in the example are from individual recipes and show how the `PR` value is set.
INHIBIT_PACKAGE_STRIP

  Causes the build to not strip binaries in resulting packages.

INHERIT

  Causes the named class to be inherited at this point during parsing. The variable is only valid in configuration files.

INITSCRIPT_PACKAGES

  A list of the packages that contain initscripts. If multiple packages are specified, you need to append the package name to the other `INITSCRIPT_*` as an override.

  This variable is used in recipes when using `update-rc.d.bbclass`. The variable is optional and defaults to the `PN` variable.

INITSCRIPT_NAME

  The filename of the initscript (as installed to `${etcdir}/init.d)`.

  This variable is used in recipes when using `update-rc.d.bbclass`. The variable is Mandatory.

INITSCRIPT_PARAMS

  Specifies the options to pass to `update-rc.d`. An example is `start 99 5 2 . stop 20 0 1 6 .`, which gives the script a runlevel of 99, starts the script in initlevels 2 and 5, and stops the script in levels 0, 1 and 6.

  The variable is mandatory and is used in recipes when using `update-rc.d.bbclass`.

### K

KBRANCH

  A regular expression used by the build process to explicitly identify the kernel branch that is validated, patched and configured during a build. The `KBRANCH` variable is optional. You can use it to trigger checks to ensure the exact kernel branch you want is being used by the build process.

  Values for this variable are set in the kernel's recipe file and the kernel's append file. For example, if you are using the Yocto Project kernel that is based on the Linux 3.4 kernel, the kernel recipe file is the `meta/recipes-kernel/linux/linux-yocto_3.4.bb` file. Following is the default value for `KBRANCH` and the default override for the architectures the Yocto Project supports:

           KBRANCH_DEFAULT = "standard/base"
           KBRANCH = "${KBRANCH_DEFAULT}"

  This branch exists in the `linux-yocto-3.4` kernel Git repository .

  This variable is also used from the kernel's append file to identify the kernel branch specific to a particular machine or target hardware. The kernel's append file is located in the BSP layer for a given machine. For example, the kernel append file for the Crown Bay BSP is in the `meta-intel` Git repository and is named `meta-crownbay/recipes-kernel/linux/linux-yocto_3.4.bbappend`. Here are the related statements from the append file:

           COMPATIBLE_MACHINE_crownbay = "crownbay"
           KMACHINE_crownbay  = "crownbay"
           KBRANCH_crownbay  = "standard/crownbay"

           COMPATIBLE_MACHINE_crownbay-noemgd = "crownbay-noemgd"
           KMACHINE_crownbay-noemgd  = "crownbay"
           KBRANCH_crownbay-noemgd  = "standard/crownbay"

  The `KBRANCH_*` statements identify the kernel branch to use when building for the Crown Bay BSP. In this case there are two identical statements: one for each type of Crown Bay machine.
KERNEL_FEATURES

  Includes additional metadata from the Yocto Project kernel Git repository. In the OpenEmbedded build system, the default Board Support Packages (BSPs) metadata is provided through the `KMACHINE` and `KBRANCH` variables. You can use the `KERNEL_FEATURES` variable to further add metadata for all BSPs.

  The metadata you add through this variable includes config fragments and features descriptions, which usually includes patches as well as config fragments. You typically override the `KERNEL_FEATURES` variable for a specific machine. In this way, you can provide validated, but optional, sets of kernel configurations and features.

  For example, the following adds `netfilter` to all the Yocto Project kernels and adds sound support to the `qemux86` machine:

           # Add netfilter to all linux-yocto kernels
           KERNEL_FEATURES="features/netfilter"

           # Add sound support to the qemux86 machine
           KERNEL_FEATURES_append_qemux86=" cfg/sound"

KERNEL_IMAGETYPE

  The type of kernel to build for a device, usually set by the machine configuration files and defaults to "zImage". This variable is used when building the kernel and is passed to `make` as the target to build.

KMACHINE

  The machine as known by the kernel. Sometimes the machine name used by the kernel does not match the machine name used by the OpenEmbedded build system. For example, the machine name that the OpenEmbedded build system understands as `qemuarm` goes by a different name in the Linux Yocto kernel. The kernel understands that machine as `arm_versatile926ejs`. For cases like these, the `KMACHINE` variable maps the kernel machine name to the OpenEmbedded build system machine name.

  Kernel machine names are initially defined in the Yocto Linux Kernel in the `meta` branch. From the `meta` branch, look in the `meta/cfg/kernel-cache/bsp/<bsp_name>/<bsp-name>-<kernel-type>.scc` file. For example, from the `meta` branch in the `linux-yocto-3.0` kernel, the `meta/cfg/kernel-cache/bsp/cedartrail/cedartrail-standard.scc` file has the following:

           define KMACHINE cedartrail
           define KTYPE standard
           define KARCH i386

           include ktypes/standard
           branch cedartrail

           include cedartrail.scc

  You can see that the kernel understands the machine name for the Cedar Trail BSP as `cedartrail`.

  If you look in the Cedar Trail BSP layer in the `meta-intel` source repository at `meta-cedartrail/recipes-kernel/linux/linux-yocto_3.0.bbappend`, you will find the following statements among others:

           COMPATIBLE_MACHINE_cedartrail = "cedartrail"
           KMACHINE_cedartrail  = "cedartrail"
           KBRANCH_cedartrail  = "yocto/standard/cedartrail"
           KERNEL_FEATURES_append_cedartrail += "bsp/cedartrail/cedartrail-pvr-merge.scc"
           KERNEL_FEATURES_append_cedartrail += "cfg/efi-ext.scc"

           COMPATIBLE_MACHINE_cedartrail-nopvr = "cedartrail"
           KMACHINE_cedartrail-nopvr  = "cedartrail"
           KBRANCH_cedartrail-nopvr  = "yocto/standard/cedartrail"
           KERNEL_FEATURES_append_cedartrail-nopvr += " cfg/smp.scc"

  The `KMACHINE` statements in the kernel's append file make sure that the OpenEmbedded build system and the Yocto Linux kernel understand the same machine names.

  This append file uses two `KMACHINE` statements. The first is not really necessary but does ensure that the machine known to the OpenEmbedded build system as `cedartrail` maps to the machine in the kernel also known as `cedartrail`:

           KMACHINE_cedartrail  = "cedartrail"

  The second statement is a good example of why the `KMACHINE` variable is needed. In this example, the OpenEmbedded build system uses the `cedartrail-nopvr` machine name to refer to the Cedar Trail BSP that does not support the propriatory PowerVR driver. The kernel, however, uses the machine name `cedartrail`. Thus, the append file must map the `cedartrail-nopvr` machine name to the kernel's `cedartrail` name:

           KMACHINE_cedartrail-nopvr  = "cedartrail"

  BSPs that ship with the Yocto Project release provide all mappings between the Yocto Project kernel machine names and the OpenEmbedded machine names. Be sure to use the `KMACHINE` if you create a BSP and the machine name you use is different than that used in the kernel.

### L

LAYERDEPENDS

  Lists the layers that this recipe depends upon, separated by spaces. Optionally, you can specify a specific layer version for a dependency by adding it to the end of the layer name with a colon, (e.g. "anotherlayer:3" to be compared against `LAYERVERSION_anotherlayer` in this case). An error will be produced if any dependency is missing or the version numbers do not match exactly (if specified). This variable is used in the `conf/layer.conf` file and must be suffixed with the name of the specific layer (e.g. `LAYERDEPENDS_mylayer`).

LAYERDIR

  When used inside the `layer.conf` configuration file, this variable provides the path of the current layer. This variable requires immediate expansion (see the BitBake manual) as lazy expansion can result in the expansion happening in the wrong directory and therefore giving the wrong value.

LAYERVERSION

  Optionally specifies the version of a layer as a single number. You can use this within `LAYERDEPENDS` for another layer in order to depend on a specific version of the layer. This variable is used in the `conf/layer.conf` file and must be suffixed with the name of the specific layer (e.g. `LAYERVERSION_mylayer`).

LIC_FILES_CHKSUM

  Checksums of the license text in the recipe source code.

  This variable tracks changes in license text of the source code files. If the license text is changed, it will trigger a build failure, which gives the developer an opportunity to review any license change.

  This variable must be defined for all recipes (unless `LICENSE` is set to "CLOSED")

  For more information, see the Tracking License Changes section

LICENSE

  The list of source licenses for the recipe. Follow these rules:

  - Do not use spaces within individual license names.

  - Separate license names using | (pipe) when there is a choice between licenses.

  - Separate license names using & (ampersand) when multiple licenses exist that cover different parts of the source.

  - You can use spaces between license names.

  Here are some examples:

           LICENSE = "LGPLv2.1 | GPLv3"
           LICENSE = "MPL-1 & LGPLv2.1"
           LICENSE = "GPLv2+"

  The first example is from the recipes for Qt, which the user may choose to distribute under either the LGPL version 2.1 or GPL version 3. The second example is from Cairo where two licenses cover different parts of the source code. The final example is from `sysstat`, which presents a single license.
LICENSE_PATH

  Path to additional licenses used during the build. By default, the OpenEmbedded build system uses `COMMON_LICENSE_DIR` to define the directory that holds common license text used during the build. The `LICENSE_PATH` variable allows you to extend that location to other areas that have additional licenses:

        LICENSE_PATH += "/path/to/additional/common/licenses"

### M

MACHINE

  Specifies the target device for which the image is built. You define `MACHINE` in the `local.conf` file found in the Build Directory. By default, `MACHINE` is set to "qemux86", which is an x86-based architecture machine to be emulated using QEMU:

           MACHINE ?= "qemux86"

  The variable corresponds to a machine configuration file of the same name, through which machine-specific configurations are set. Thus, when `MACHINE` is set to "qemux86" there exists the corresponding `qemux86.conf` machine configuration file, which can be found in the Source Directory in `meta/conf/machine`.

  The list of machines supported by the Yocto Project as shipped include the following:

           MACHINE ?= "qemuarm"
           MACHINE ?= "qemumips"
           MACHINE ?= "qemuppc"
           MACHINE ?= "qemux86"
           MACHINE ?= "qemux86-64"
           MACHINE ?= "atom-pc"
           MACHINE ?= "beagleboard"
           MACHINE ?= "mpc8315e-rdb"
           MACHINE ?= "routerstationpro"

  The last four are Yocto Project reference hardware boards, which are provided in the `meta-yocto-bsp` layer.

  Adding additional Board Support Package (BSP) layers to your configuration adds new possible settings for `MACHINE`.

MACHINE_ESSENTIAL_EXTRA_RDEPENDS

  A list of required machine-specific packages to install as part of the image being built. The build process depends on these packages being present. Furthermore, because this is a "machine essential" variable, the list of packages are essential for the machine to boot. The impact of this variable affects images based on `packagegroup-core-boot`, including the `core-image-minimal` image.

  This variable is similar to the `MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS` variable with the exception that the image being built has a build dependency on the variable's list of packages. In other words, the image will not build if a file in this list is not found.

  As an example, suppose the machine for which you are building requires `example-init` to be run during boot to initialize the hardware. In this case, you would use the following in the machine's `.conf` configuration file:

           MACHINE_ESSENTIAL_EXTRA_RDEPENDS += "example-init"

MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS

  A list of recommended machine-specific packages to install as part of the image being built. The build process does not depend on these packages being present. However, because this is a "machine essential" variable, the list of packages are essential for the machine to boot. The impact of this variable affects images based on `packagegroup-core-boot`, including the `core-image-minimal` image.

  This variable is similar to the `MACHINE_ESSENTIAL_EXTRA_RDEPENDS` variable with the exception that the image being built does not have a build dependency on the variable's list of packages. In other words, the image will still build if a package in this list is not found. Typically, this variable is used to handle essential kernel modules, whose functionality may be selected to be built into the kernel rather than as a module, in which case a package will not be produced.

  Consider an example where you have a custom kernel where a specific touchscreen driver is required for the machine to be usable. However, the driver can be built as a module or into the kernel depending on the kernel configuration. If the driver is built as a module, you want it to be installed. But, when the driver is built into the kernel, you still want the build to succeed. This variable sets up a "recommends" relationship so that in the latter case, the build will not fail due to the missing package. To accomplish this, assuming the package for the module was called `kernel-module-ab123`, you would use the following in the machine's `.conf` configuration file:

           MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS += "kernel-module-ab123"

  Some examples of these machine essentials are flash, screen, keyboard, mouse, or touchscreen drivers (depending on the machine).

MACHINE_EXTRA_RDEPENDS

  A list of machine-specific packages to install as part of the image being built that are not essential for the machine to boot. However, the build process for more fully-featured images depends on the packages being present.

  This variable affects all images based on `packagegroup-base`, which does not include the `core-image-minimal` or `core-image-basic` images.

  The variable is similar to the `MACHINE_EXTRA_RRECOMMENDS` variable with the exception that the image being built has a build dependency on the variable's list of packages. In other words, the image will not build if a file in this list is not found.

  An example is a machine that has WiFi capability but is not essential For the machine to boot the image. However, if you are building a more fully-featured image, you want to enable the WiFi. The package containing the firmware for the WiFi hardware is always expected to exist, so it is acceptable for the build process to depend upon finding the package. In this case, assuming the package for the firmware was called `wifidriver-firmware`, you would use the following in the `.conf` file for the machine:

           MACHINE_EXTRA_RDEPENDS += "wifidriver-firmware"

MACHINE_EXTRA_RRECOMMENDS

  A list of machine-specific packages to install as part of the image being built that are not essential for booting the machine. The image being built has no build dependency on this list of packages.

  This variable affects only images based on `packagegroup-base`, which does not include the `core-image-minimal` or `core-image-basic` images.

  This variable is similar to the `MACHINE_EXTRA_RDEPENDS` variable with the exception that the image being built does not have a build dependency on the variable's list of packages. In other words, the image will build if a file in this list is not found.

  An example is a machine that has WiFi capability but is not essential For the machine to boot the image. However, if you are building a more fully-featured image, you want to enable WiFi. In this case, the package containing the WiFi kernel module will not be produced if the WiFi driver is built into the kernel, in which case you still want the build to succeed instead of failing as a result of the package not being found. To accomplish this, assuming the package for the module was called `kernel-module-examplewifi`, you would use the following in the `.conf` file for the machine:

           MACHINE_EXTRA_RRECOMMENDS += "kernel-module-examplewifi"

MACHINE_FEATURES

  Specifies the list of hardware features the MACHINE supports. For a list of features supported by the Yocto Project as shipped, see the "Machine" section.

MACHINE_FEATURES_BACKFILL

  Features to be added to `MACHINE_FEATURES` if not also present in `MACHINE_FEATURES_BACKFILL_CONSIDERED`.

  This variable is set in the `meta/conf/bitbake.conf` file. It is not intended to be user-configurable. It is best to just reference the variable to see which machine features are being backfilled for all machine configurations. See the Feature backfilling section for more information.

MACHINE_FEATURES_BACKFILL_CONSIDERED

  Features from `MACHINE_FEATURES_BACKFILL` that should not be backfilled (i.e. added to `MACHINE_FEATURES`) during the build. See the Feature backfilling section for more information.

MAINTAINER

  The email address of the distribution maintainer.

MLPREFIX

  Specifies a prefix has been added to `PN` to create a special version of a recipe or package, such as a multilib version. The variable is used in places where the prefix needs to be added to or removed from a the name (e.g. the `BPN` variable). `MLPREFIX` gets set when a prefix has been added to `PN`.

MULTIMACH_TARGET_SYS

  Separates files for different machines such that you can build for multiple target machines using the same output directories. See the `STAMP` variable for an example.

### P

P

  The recipe name and version. `P` is comprised of the following:

           ${PN}-${PV}

PACKAGE_ARCH

  The architecture of the resulting package or packages.

PACKAGE_BEFORE_PN

  Enables easily adding packages to `PACKAGES` before `${PN}` so that the packages can pick up files that would normally be included in the default package.

PACKAGE_CLASSES

  This variable, which is set in the `local.conf` configuration file found in the `conf` folder of the Source Directory, specifies the package manager to use when packaging data. You can provide one or more arguments for the variable with the first argument being the package manager used to create images:

           PACKAGE_CLASSES ?= "package_rpm package_deb package_ipk"

  For information on build performance effects as a result of the package manager use, see Packaging - `package*.bbclass` in this manual.
PACKAGE_EXTRA_ARCHS

  Specifies the list of architectures compatible with the device CPU. This variable is useful when you build for several different devices that use miscellaneous processors such as XScale and ARM926-EJS).

PACKAGECONFIG

  This variable provides a means of enabling or disabling features of a recipe on a per-recipe basis. The `PACKAGECONFIG` variable itself specifies a space-separated list of the features to enable, while the named flags set on the variable specify for each feature the additional build dependencies (`DEPENDS`) that should be added if the feature is enabled, and any extra arguments that should be added to the configure script argument list (`EXTRA_OECONF`) if the feature is enabled or disabled.

  For example, the following taken from the `librsvg` recipe will add `--with-croco` to the configure script arguments and `libcroco` to `DEPENDS` by default. However, if "croco" is removed from `PACKAGECONFIG` (for example, by using a `.bbappend` file in another layer), then `--without-croco` will be added to the configure script arguments instead:

           PACKAGECONFIG ??= "croco"
           PACKAGECONFIG[croco] = "--with-croco,--without-croco,libcroco"

PACKAGES

  The list of packages to be created from the recipe. The default value is the following:

           ${PN}-dbg ${PN}-staticdev ${PN}-dev ${PN}-doc ${PN}-locale ${PACKAGE_BEFORE_PN} ${PN}

PARALLEL_MAKE

  Specifies extra options that are passed to the `make` command during the compile tasks. This variable is usually in the form `-j 4`, where the number represents the maximum number of parallel threads make can run. If you development host supports multiple cores a good rule of thumb is to set this variable to twice the number of cores on the host.

PF

  Specifies the recipe or package name and includes all version and revision numbers (i.e. `eglibc-2.13-r20+svnr15508/` and `bash-4.2-r1/`). This variable is comprised of the following:

           ${PN}-${EXTENDPE}${PV}-${PR}

PN

  This variable can have two separate functions depending on the context: a recipe name or a resulting package name.

  `PN` refers to a recipe name in the context of a file used by the OpenEmbedded build system as input to create a package. The name is normally extracted from the recipe file name. For example, if the recipe is named `expat_2.0.1.bb`, then the default value of `PN` will be "expat".

  The variable refers to a package name in the context of a file created or produced by the OpenEmbedded build system.

  If applicable, the `PN` variable also contains any special suffix or prefix. For example, using `bash` to build packages for the native machine, `PN` is `bash-native`. Using `bash` to build packages for the target and for Multilib, `PN` would be `bash` and `lib64-bash`, respectively.

PR

  The revision of the recipe. The default value for this variable is "r0".

PRINC

  Causes the `PR` variable of `.bbappend` files to dynamically increment. This increment minimizes the impact of layer ordering.

  In order to ensure multiple `.bbappend` files can co-exist, `PRINC` should be self referencing. This variable defaults to 0.

  Following is an example that increments `PR` by two:

           PRINC := "${@int(PRINC) + 2}"

  It is adviseable not to use strings such as ".= '.1'" with the variable because this usage is very sensitive to layer ordering. Explicit assignments should be avoided as they cannot adequately represent multiple `.bbappend` files.
PV

  The version of the recipe. The version is normally extracted from the recipe filename. For example, if the recipe is named `expat_2.0.1.bb`, then the default value of `PV` will be "2.0.1". `PV` is generally not overridden within a recipe unless it is building an unstable (i.e. development) version from a source code repository (e.g. Git or Subversion).

PE

  the epoch of the recipe. The default value is "0". The field is used to make upgrades possible when the versioning scheme changes in some backwards incompatible way.

PREFERRED_PROVIDER

  If multiple recipes provide an item, this variable determines which recipe should be given preference. The variable must always be suffixed with the name of the provided item, and should be set to the `PN` of the recipe to which you want to give precedence. Here is an example:

           PREFERRED_PROVIDER_virtual/xserver = "xserver-xf86"

PREFERRED_VERSION

  If there are multiple versions of recipes available, this variable determines which recipe should be given preference. The variable must always be suffixed with the `PN` for which to select, and should be set to the `PV` to which you want to give precedence. You can use the "`%`" character as a wildcard to match any number of characters, which can be useful when specifying versions that contain long revision number that could potentially change. Here are two examples:

           PREFERRED_VERSION_python = "2.6.6"
           PREFERRED_VERSION_linux-yocto = "3.0+git%"

### R

RCONFLICTS

  The list of packages that conflict with a package. Note that the package will not be installed if the conflicting packages are not first removed.

  Like all package-controlling variables, you must always use them in conjunction with a package name override. Here is an example:

           RCONFLICTS_${PN} = "another-conflicting-package-name"

RDEPENDS

  Lists a package's run-time dependencies (i.e. other packages) that must be installed for the package to be built. In other words, in order for the package to be built and run correctly, it depends on the listed packages. If a package in this list cannot be found, it is probable that a dependency error would occur before the build.

  The names of the variables you list with `RDEPENDS` must be the names of other packages as listed in the `PACKAGES` variable. You should not list recipe names (`PN`).

  Because the `RDEPENDS` variable applies to packages being built, you should always attach a package name to the variable to specify the particular run-time package that has the dependency. For example, suppose you are building a development package that depends on the `perl` package. In this case, you would use the following `RDEPENDS` statement:

           RDEPENDS_${PN}-dev += "perl"

  In the example, the package name (`${PN}-dev`) must appear as it would in the `PACKAGES` namespace before any renaming of the output package by classes like `debian.bbclass`.

  In many cases you do not need to explicitly add dependencies to `RDEPENDS` since some automatic handling occurs:

  - `shlibdeps`: If a run-time package contains a shared library (`.so`), the build processes the library in order to determine other libraries to which it is dynamically linked. The build process adds these libraries to `RDEPENDS` when creating the run-time package.

  - `pcdeps`: If the package ships a `pkg-config` information file, the build process uses this file to add items to the `RDEPENDS` variable to create the run-time packages.

RRECOMMENDS

  A list of packages that extend the usability of a package being built. The package being built does not depend on this list of packages in order to successfully build, but needs them for the extended usability. To specify runtime dependencies for packages, see the `RDEPENDS` variable.

  The OpenEmbedded build process automatically installs the list of packages as part of the built package. However, you can remove them later if you want. If, during the build, a package from the list cannot be found, the build process continues without an error.

  Because the `RRECOMMENDS` variable applies to packages being built, you should always attach an override to the variable to specify the particular package whose usability is being extended. For example, suppose you are building a development package that is extended to support wireless functionality. In this case, you would use the following:

           RRECOMMENDS_${PN}-dev += "<wireless_package_name>"

  In the example, the package name (`${PN}-dev`) must appear as it would in the `PACKAGES` namespace before any renaming of the output package by classes like `debian.bbclass`.
RREPLACES

  The list of packages that are replaced with this package.

### S

S

  The location in the Build Directory where unpacked package source code resides. This location is within the working directory (`WORKDIR`), which is not static. The unpacked source location depends on the package name (`PN`) and package version (`PV`) as follows:

       ${WORKDIR}/${PN}-${PV}

  As an example, assume a Source Directory top-level folder named `poky` and a default Build Directory at `poky/build`. In this case, the working directory the build system uses to build the `db` package is the following:

       ~/poky/build/tmp/work/qemux86-poky-linux/db-5.1.19-r3/db-5.1.19

SDKIMAGE_FEATURES

  Equivalent to `IMAGE_FEATURES`. However, this variable applies to the SDK generated from an image using `bitbake -c populate_sdk imagename`).

SECTION

  The section in which packages should be categorized. Package management utilities can make use of this variable.

SELECTED_OPTIMIZATION

  The variable takes the value of `FULL_OPTIMIZATION` unless `DEBUG_BUILD` = "1". In this case the value of `DEBUG_OPTIMIZATION` is used.

SERIAL_CONSOLE

  The speed and device for the serial port used to attach the serial console. This variable is given to the kernel as the "console" parameter and after booting occurs `getty` is started on that port so remote login is possible.

SITEINFO_ENDIANNESS

  Specifies the endian byte order of the target system. The value should be either "le" for little-endian or "be" for big-endian.

SITEINFO_BITS

  Specifies the number of bits for the target system CPU. The value should be either "32" or "64".

SPECIAL_PKGSUFFIX

  A list of prefixes for `PN` used by the OpenEmbedded build system to create variants of recipes or packages. The list specifies the prefixes to strip off during certain circumstances such as the generation of the `BPN` variable.

SRC_URI

  The list of source files - local or remote. This variable tells the OpenEmbedded build system which bits to pull in for the build and how to pull them in. For example, if the recipe only needs to fetch a tarball from the internet, the recipe uses a single `SRC_URI` entry. On the other hand, if the recipe needs to fetch a tarball, apply two patches, and include a custom file, the recipe would include four instances of the variable.

  The following list explains the available URI protocols:

  - `file://` - Fetches files, which is usually a file shipped with the metadata, from the local machine. The path is relative to the `FILESPATH` variable. Thus, the build system searches, in order, from the following directories, which are assumed to be a subdirectories of the directory in which the recipe file resides:

    - `${PN}` - The recipe name with any special suffix or prefix, if applicable. For example, using `bash` to build for the native machine, `PN` is `bash-native`. Using `bash` to build for the target and for Multilib, `PN` would be `bash` and `lib64-bash`, respectively.

    - `${PF}` - `${PN}-${EXTENDPE}${PV}-${PR}`. The recipe name including all version and revision numbers (i.e. `eglibc-2.13-r20+svnr15508/` and `bash-4.2-r1/`).

    - `${P}` - `${PN}-${PV}`. The recipe name and version (i.e. `bash-4.2`).

    - `${BPN}` - The base recipe name without any special suffix or version numbers.

    - `${BP}` - `${BPN}-${PV}`. The base recipe name and version but without any special package name suffix.

    - Files - Files beneath the directory in which the recipe resides.

    - Directory - The directory itself in which the recipe resides.

  - `bzr://` - Fetches files from a Bazaar revision control repository.

  - `git://` - Fetches files from a Git revision control repository.

  - `osc://` - Fetches files from an OSC (OpenSuse Build service) revision control repository.

  - `repo://` - Fetches files from a repo (Git) repository.

  - `svk://` - Fetches files from an SVK revision control repository.

  - `http://` - Fetches files from the Internet using `http`.

  - `https://` - Fetches files from the Internet using `https`.

  - `ftp://` - Fetches files from the Internet using `ftp`.

  - `cvs://` - Fetches files from a CVS revision control repository.

  - `hg://` - Fetches files from a Mercurial (`hg`) revision control repository.

  - `p4://` - Fetches files from a Perforce (`p4`) revision control repository.

  - `ssh://` - Fetches files from a secure shell.

  - `svn://` - Fetches files from a Subversion (`svn`) revision control repository.

  Standard and recipe-specific options for `SRC_URI` exist. Here are standard options:

  - `apply` - Whether to apply the patch or not. The default action is to apply the patch.

  - `striplevel` - Which striplevel to use when applying the patch. The default level is 1.

  Here are options specific to recipes building code from a revision control system:

  - `mindate` - Only applies the patch if `SRCDATE` is equal to or greater than `mindate`.

  - `maxdate` - Only applies the patch if `SRCDATE` is not later than `mindate`.

  - `minrev` - Only applies the patch if `SRCREV` is equal to or greater than `minrev`.

  - `maxrev` - Only applies the patch if `SRCREV` is not later than `maxrev`.

  - `rev` - Only applies the patch if `SRCREV` is equal to `rev`.

  - `notrev` - Only applies the patch if `SRCREV` is not equal to `rev`.

  Here are some additional options worth mentioning:

  - `unpack` - Controls whether or not to unpack the file if it is an archive. The default action is to upack the file.

  - `subdir` - Places the file (or extracts its contents) into the specified subdirectory of `WORKDIR`. This option is useful for unusual tarballs or other archives that don't have their files already in a subdirectory within the archive.

  - `name` - Specifies a name to be used for association with `SRC_URI` checksums when you have more than one file specified in `SRC_URI`.

  - `downloadfilename` - Specifies the filename used when storing the downloaded file.

SRC_URI_OVERRIDES_PACKAGE_ARCH

  By default, the OpenEmbedded build system automatically detects whether `SRC_URI` contains files that are machine-specific. If so, the build system automatically changes `PACKAGE_ARCH`. Setting this variable to "0" disables this behavior.

SRCDATE

  The date of the source code used to build the package. This variable applies only if the source was fetched from a Source Code Manager (SCM).

SRCREV

  The revision of the source code used to build the package. This variable applies to Subversion, Git, Mercurial and Bazaar only. Note that if you wish to build a fixed revision and you wish to avoid performing a query on the remote repository every time BitBake parses your recipe, you should specify a `SRCREV` that is a full revision identifier and not just a tag.

SSTATE_DIR

  The directory for the shared state.

SSTATE_MIRRORS

  Configures the OpenEmbedded build system to search other mirror locations for prebuilt cache data objects before building out the data. This variable works like fetcher `MIRRORS`/`PREMIRRORS` and points to the cache locations to check for the shared objects.

  You can specify a filesystem directory or a remote URL such as HTTP or FTP. The locations you specify need to contain the shared state cache (sstate-cache) results from previous builds. The sstate-cache you point to can also be from builds on other machines.

  If a mirror uses the same structure as `SSTATE_DIR`, you need to add "PATH" at the end as shown in the examples below. The build system substitues the correct path within the directory structure.

           SSTATE_MIRRORS ?= "\
           file://.* http://someserver.tld/share/sstate/PATH \n \
           file://.* file:///some/local/dir/sstate/PATH"

STAGING_KERNEL_DIR

  The directory with kernel headers that are required to build out-of-tree modules.

STAMP

  Specifies the base path used to create recipe stamp files. The path to an actual stamp file is constructed by evaluating this string and then appending additional information. Currently, the default assignment for `STAMP` as set in the `meta/conf/bitbake.conf` file is:

           STAMP = "${TMPDIR}/stamps/${MULTIMACH_TARGET_SYS}/${PN}-${EXTENDPE}${PV}-${PR}"

  See `TMPDIR`, `MULTIMACH_TARGET_SYS`, `PN`, `EXTENDPE`, `PV`, and `PR` for related variable information.
SUMMARY

  The short (72 characters or less) summary of the binary package for packaging systems such as `opkg`, `rpm` or `dpkg`. By default, `SUMMARY` is used to define the `DESCRIPTION` variable if `DESCRIPTION` is not set in the recipe.

### T

T

  This variable points to a directory were Bitbake places temporary files when building a particular package. It is typically set as follows:

           T = ${WORKDIR}/temp

  The `WORKDIR` is the directory into which Bitbake unpacks and builds the package. The default `bitbake.conf` file sets this variable.

  The `T` variable is not to be confused with the `TMPDIR` variable, which points to the root of the directory tree where Bitbake places the output of an entire build.

TARGET_ARCH

  The architecture of the device being built. While a number of values are possible, the OpenEmbedded build system primarily supports `arm` and `i586`.

TARGET_CFLAGS

  Flags passed to the C compiler for the target system. This variable evaluates to the same as `CFLAGS`.

TARGET_FPU

  Specifies the method for handling FPU code. For FPU-less targets, which include most ARM CPUs, the variable must be set to "soft". If not, the kernel emulation gets used, which results in a performance penalty.

TARGET_OS

  Specifies the target's operating system. The variable can be set to "linux" for `eglibc`-based systems and to "linux-uclibc" for `uclibc`. For ARM/EABI targets, there are also "linux-gnueabi" and "linux-uclibc-gnueabi" values possible.

TCLIBC

  Specifies which variant of the GNU standard C library (`libc`) to use during the build process. This variable replaces `POKYLIBC`, which is no longer supported.

  You can select `eglibc` or `uclibc`.

  This release of the Yocto Project does not support the `glibc` implementation of `libc`.

TCMODE

  The toolchain selector. This variable replaces `POKYMODE`, which is no longer supported.

  The `TCMODE` variable selects the external toolchain built using the OpenEmbedded build system or a few supported combinations of the upstream GCC or CodeSourcery Labs toolchain. The variable identifies the `tcmode-*` files used in the `meta/conf/distro/include` directory, which is found in the Source Directory.

  By default, `TCMODE` is set to "default", which chooses the `tcmode-default.inc` file. The variable is similar to `TCLIBC`, which controls the variant of the GNU standard C library (`libc`) used during the build process: `eglibc` or `uclibc`.

TMPDIR

  This variable is the temporary directory the OpenEmbedded build system uses when it does its work building images. By default, the `TMPDIR` variable is named `tmp` within the Build Directory.

  If you want to establish this directory in a location other than the default, you can uncomment the following statement in the `conf/local.conf` file in the Source Directory:

           #TMPDIR = "${TOPDIR}/tmp"

TOPDIR

  This variable is the Build Directory. BitBake automatically sets this variable. The OpenEmbedded build system uses the Build Directory when building images.

### W

WORKDIR

  The pathname of the working directory in which the OpenEmbedded build system builds a recipe. This directory is located within the `TMPDIR` directory structure and changes as different packages are built.

  The actual `WORKDIR` directory depends on several things:

  - The temporary directory - `TMPDIR`
  - The package architecture - `PACKAGE_ARCH`
  - The target machine - `MACHINE`
  - The target operating system - `TARGET_OS`
  - The recipe name - `PN`
  - The recipe version - `PV`
  - The recipe revision - `PR`

  For packages that are not dependent on a particular machine, `WORKDIR` is defined as follows:

       ${TMPDIR}/work/${PACKAGE_ARCH}-poky-${TARGET_OS}/${PN}-${PV}-${PR}

  As an example, assume a Source Directory top-level folder name `poky` and a default Build Directory at `poky/build`. In this case, the working directory the build system uses to build the `v86d` package is the following:

           ~/poky/build/tmp/work/qemux86-poky-linux/v86d-01.9-r0

  For packages that are dependent on a particular machine, `WORKDIR` is defined slightly different:

       ${TMPDIR}/work/${MACHINE}-poky-${TARGET_OS}/${PN}-${PV}-${PR}

  As an example, again assume a Source Directory top-level folder named `poky` and a default Build Directory at `poky/build`. In this case, the working directory the build system uses to build the `acl` recipe, which is being built for a MIPS-based device, is the following:

           ~/poky/build/tmp/work/mips-poky-linux/acl-2.2.51-r2