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"
                   

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

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}"
                    

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.

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.

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>"
                    

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 http://docs.python.org/release/2.3/lib/re-syntax.html. 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.

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.

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.

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).

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).

List of recipe files used by BitBake to build software

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

Variable that controls how BitBake displays logs on build failure.

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.

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}
                    

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.

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

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.

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.

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.

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.

The destination directory.

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

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".

Specifies the priority of recipes.

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.

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

the destination directory.

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.

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.

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.

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

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.

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.

The long name of the distribution.

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.

the version of the distribution.

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.

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.

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).

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.

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.

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.

Additional cmake options.

Additional configure script options.

Additional GNU make options.

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"
                    

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.

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}:"
                    

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.

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.

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".

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

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.

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

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.

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.

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"
                    

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
                    

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.

Causes the build to not strip binaries in resulting packages.

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

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.

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.

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.

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 http://git.yoctoproject.org/cgit.cgi/linux-yocto-3.4/refs/heads.

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.

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"
                    

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.

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.

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).

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.

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).

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

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

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.

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"
                    

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.

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"
                    

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).

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"
                    

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"
                    

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.

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.

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.

The email address of the distribution maintainer.

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.

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.

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

     ${PN}-${PV}
                    

The architecture of the resulting package or packages.

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.

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.

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).

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"
                    

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}
                    

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.

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}
                    

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.

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

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.

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).

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.

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"
                    

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%" 
                    

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"
                   

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:

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.

The list of packages that are replaced with this package.

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
                    

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

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

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

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.

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

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

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.

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:

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

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

Here are some additional options worth mentioning:

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.

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).

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.

The directory for the shared state.

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"
                    

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

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.

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.

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.

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

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

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.

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.

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.

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.

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"
                    

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

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:

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