# Reference: Variables Glossary

This section lists common variables used in the Yocto Project 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}

AUTHOR

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

AUTOREV

  Specifies to use the current (newest) source revision. This variable is with the `SRCREV` variable.

### B

B

  The directory in which the Yocto Project build system places generated objects 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 source directory (`S`) and the directory pointed to by the `B` variable. Most autotools-based recipes support separating these directories. The Yocto Project 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 for images that use the `ipkg` packaging system.

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 Yocto Project 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 package appears in more than one layer. Setting this variable allows you to prioritize a layer against other layers that contain the same package - effectively letting you control the precedence for the multiple layers. The precedence established through this variable stands regardless of a layer's package version (`PV` variable). For example, a layer that has a package 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 Yocto Project build. This variable is defined in the `bblayers.conf` configuration file in the Yocto Project build directory. Here is an example:

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

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

  Bare name of package with any suffixes like -cross -native removed.

### 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 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 Yocto Project files 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 Yocto Project 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

  A list of build-time dependencies for a given recipe. The variable indicates recipes that must have been staged before a particular recipe can configure.

DESCRIPTION

  The package description used by package managers.

DESTDIR

  the destination directory.

DISTRO

  The short name of the distribution.

DISTRO_EXTRA_RRECOMMENDS

  The list of packages which extend usability of the image. Those packages will automatically be installed but can be removed by user.

DISTRO_FEATURES

  The features of the distribution.

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 Yocto Project 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" appendix.

### 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).

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 application targets too, see
                       meta/classes/poky-image.bbclass
                       and meta/packages/tasks/task-poky.bb
                       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 package. Then, provide a space-separated list of files or paths that identifies the files you want included as part of the 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 Yocto Project files 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 Yocto Project 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 search 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 Yocto Project 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 Yocto Project Files:

      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 Yocto Project uses the `fs-perms.txt`, which is located in the `meta/files` directory of the Yocto Project files 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 Yocto Project's 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 info about package can be found

### I

IMAGE_FEATURES

  The list of features present in images. Typically, you configure this variable in image recipes. Note that you can add extra features to the image by using the `EXTRA_IMAGE_FEATURES` variable. See the "Reference: Images" section for the list of features present in images built by the Yocto Project.

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 Yocto Project 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

  Defines the Package revision. You manually combine values for `INC_PR` into the `PR` field of the parent recipe. When you change this variable, you change the `PR` value for every person that includes the file.

  The following example shows how to use the `INC_PR` variable given a common `.inc` file that defines the variable. Once defined, you can use the variable to set the `PR` value:

       recipes-graphics/xorg-font/font-util_1.1.1.bb:PR - "$(INC_PR).1"
       recipes-graphics/xorg-font/xorg-font-common.inc:INC_PR - "r1"
       recipes-graphics/xorg-font/encondings_1.0.3.bb:PR - "$(INC_PR).1"
       recipes-graphics/xorg-font/fiont-alias_1.0.2.bb:PR - "$(INC_PR).0"

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

KERNEL_FEATURES

  Includes additional metadata from the Linux Yocto kernel Git repository. In the Yocto Project 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 Linux Yocto 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.

### 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 package source licenses.

LICENSE_DIR

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

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

### M

MACHINE

  Specifies the target device.

MACHINE_ESSENTIAL_EXTRA_RDEPENDS

  A list of required packages to install as part of the package 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 `task-core-boot`, including the `core-image-minimal` image.

  This variable is similar to the `MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS` variable with the exception that the package 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.

  For example, suppose you are building a runtime package that depends on a certain disk driver. In this case, you would use the following:

           MACHINE_ESSENTIAL_EXTRA_RDEPENDS += "<disk_driver>"

MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS

  A list of recommended packages to install as part of the package being built. The build process does not depend 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 `task-core-boot`, including the `core-image-minimal` image.

  This variable is similar to the `MACHINE_ESSENTIAL_EXTRA_RDEPENDS` variable with the exception that the package 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. However, because this is one of the "essential" variables, the resulting image might not boot on the machine. Or, if the machine does boot using the image, the machine might not be fully functional.

  Consider an example where you have a custom kernel with a disk driver built into the kernel itself, rather than using the driver built as a module. If you include the package that has the driver module as part of the variable's list, the build process will not find that package. However, because these packages are "recommends" packages, the build will not fail due to the missing package. Not accounting for any other problems, the custom kernel would still boot the machine.

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

  For example, suppose you are building a runtime package that depends on a mouse driver. In this case, you would use the following:

           MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS += "<mouse_driver>"

MACHINE_EXTRA_RDEPENDS

  A list of optional but non-machine essential packages to install as part of the package being built. Even though these packages are not essential for the machine to boot, the build process depends on them being present. The impact of this variable affects all images based on `task-base`, which does not include the `core-image-minimal` or `core-image-basic` images.

  This variable is similar to the `MACHINE_EXTRA_RRECOMMENDS` variable with the exception that the package 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 might or might not have a WiFi card. The package containing the WiFi support is not essential for the machine to boot the image. If it is not there, the machine will boot but not be able to use the WiFi functionality. However, if you include the package with the WiFi support as part of the variable's package list, the build process depends on finding the package. In this case, you would use the following:

           MACHINE_EXTRA_RDEPENDS += "<wifi_driver>"

MACHINE_EXTRA_RRECOMMENDS

  A list of optional but non-machine essential packages to install as part of the package being built. The package being built has no build dependency on the list of packages with this variable. The impact of this variable affects only images based on `task-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 package 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 might or might not have a WiFi card. The package containing the WiFi support is not essential for the machine to boot the image. If it is not there, the machine will boot but not be able to use the WiFi functionality. You are free to either include or not include the the package with the WiFi support as part of the variable's package list, the build process does not depend on finding the package. If you include the package, you would use the following:

           MACHINE_EXTRA_RRECOMMENDS += "<wifi_driver>"

MACHINE_FEATURES

  Specifies the list of device features. See the Machine section for more information.

MAINTAINER

  The email address of the distribution maintainer.

### P

PACKAGE_ARCH

  The architecture of the resulting package.

PACKAGE_CLASSES

  This variable, which is set in the `local.conf` configuration file found in the Yocto Project file's `conf` 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).

PACKAGES

  The list of packages to be created from the recipe. The default value is "${PN}-dbg ${PN} ${PN}-doc ${PN}-dev".

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.

PN

  The name of the package.

PR

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

PV

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

PE

  the epoch of the package. 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 this package. Note that the package will not be installed if the conflicting packages are not first removed.

RDEPENDS

  A list of packages that must be installed as part of a package being built. The package being built has a runtime dependency on the packages in the variable's list. In other words, in order for the package being built to run correctly, it depends on these listed packages. If a package in this list cannot be found during the build, the build will not complete.

  Because the `RDEPENDS` variable applies to packages being built, you should always attach an override to the variable to specify the particular runtime 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`.

  Some automatic handling occurs around the `RDEPENDS` variable:

  - `shlibdeps`: If a runtime 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` to create the runtime 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 runtime 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 Yocto Project 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 Yocto Project 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 Yocto Project Files top-level directory named `poky` and a default Yocto Project Build Directory of `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

SECTION

  The section where package should be put. Package managers use 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.

SSTATE_DIR

  The directory for the shared state.

SITEINFO_ENDIANNESS

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

SITEINFO_BITS

  Specifies the number of bits for the target system CPU. The variable is either "32" or "64".

SRC_URI

  The list of source files - local or remote.

SRC_URI_OVERRIDES_PACKAGE_ARCH

  By default, the Yocto Project automatically detects whether `SRC_URI` contains files that are machine-specific. If so, the Yocto Project 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.

STAGING_KERNEL_DIR

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

STAMP

  The directory (usually `TMPDIR/stamps`) with timestamps of executed tasks.

SUMMARY

  The short (72 characters or less) summary of the binary package for packaging systems such as `ipkg`, `rpm` or `debian`. By default, this variable inherits `DESCRIPTION`.

### T

TARGET_ARCH

  The architecture of the device being built. While a number of values are possible, the Yocto Project 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 from the Yocto Project or a few supported combinations of the upstream GCC or CodeSourcery Labs toolchain. The variable determines which of the files in `meta/conf/distro/include/tcmode-*` is used.

  By default, `TCMODE` is set to "default", which chooses `tcmode-default.inc`. 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 Yocto Project build system uses when it does its work building images. By default, the `TMPDIR` variable is named `tmp` within the Yocto Project 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 Yocto Project Files:

           #TMPDIR = "${TOPDIR}/tmp"

TOPDIR

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

### W

WORKDIR

  The pathname of the working directory in which the Yocto Project build system builds packages. 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 package name - `PN`
  - The package version - `PV`
  - The package 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 Yocto Project Files top-level directory named `poky` and a default Yocto Project Build Directory of `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 Yocto Project Files top-level directory named `poky` and a default Yocto Project build directory of `poky/build`. In this case, the working directory the build system uses to build the `acl` package, which is dependent on a MIPS-based device, is the following:

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