yocto project glossary

Appendix F. Reference: Variables Glossary

Table of Contents

Glossary

This section lists common variables used in the Yocto Project and gives an overview of their function and contents.

Glossary

AB 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 anRDEPENDS 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 theSRCREV 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 theS directory:

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

You can separate the source directory (S) and the directory pointed to by theB variable. Most autotools-based recipes support separating these directories. The Yocto Project defaults to using separate directories forgcc 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 theipkg 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" likequilt-native, which is a copy of quilt built to run on the build system; "crosses" such asgcc-cross, which is a compiler built to run on the build machine but produces binaries that run on the targetMACHINE; "nativesdk", which targets the SDK machine instead ofMACHINE; 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 theBBMASK 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 athttp://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 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 itsconf/layer.conf file.

BBFILE_PATTERN

Variable that expands to match files from BBFILES in a particular layer. This variable is used in theconf/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 higherPV 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, theBBFILE_PRIORITY variable is set based on layer dependencies (see theLAYERDEPENDS 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).

Tip

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 thePATH 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 thebblayers.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 namedmeta-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 asTARGET_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 theCONFFILES 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 withinCONFFILES must be a subset of the files listed withinFILES. Because the configuration files you provide withCONFFILES 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 theFILES variable.

Note

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 runningconfigure.

CORE_IMAGE_EXTRA_INSTALL

Specifies the list of packages to be added to the image. This variable should only be set in thelocal.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 theSELECTED_OPTIMIZATION variable.

DEBUG_OPTIMIZATION

The options to pass in TARGET_CFLAGS andCFLAGS 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 theDL_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 isdownloads 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 byDL_DIR and the build system looks there first to find source tarballs.

Note

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 thelocal.conf configuration file. Note that some image features are also added using theIMAGE_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 theEXTRA_IMAGEDEPENDS variable to list these recipes and thus, specify the dependencies. A typical example is a required bootloader in a machine configuration.

Note

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"                    

Note

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 theFILESPATH variable. You can add directories to the search path by defining theFILESEXTRAPATHS 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 theFILESPATH 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 inFILESPATH in the specified order when looking for files and patches specified by eachfile:// URI in a recipe.

The default value for the FILESPATH variable is defined in thebase.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 theFILESEXTRAPATHS 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 themeta/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 theconf/local.conf file, which is found in the Yocto Project's build directory, to point to your customfs-perms.txt. You can specify more than a single file permissions setting table. The paths you specify to these files must be defined within theBBPATH variable.

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

FULL_OPTIMIZATION

The options to pass in TARGET_CFLAGS andCFLAGS 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 theEXTRA_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 throughimage.bbclass. Additionally, "helper" classes exist, such ascore-image.bbclass, that can take IMAGE_FEATURES lists and turn these into auto-generated entries inIMAGE_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. Sincecore-image.bbclass sets IMAGE_INSTALL to a default value using the?= operator, using a += operation againstIMAGE_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 ofIMAGE_ROOTFS_SIZE andIMAGE_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. SeeIMAGE_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 usingIMAGE_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 inIMAGE_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 thePR 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 thePR 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 otherINITSCRIPT_* as an override.

This variable is used in recipes when using update-rc.d.bbclass. The variable is optional and defaults to thePN 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 isstart 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 theKMACHINE and KBRANCH variables. You can use theKERNEL_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 theKERNEL_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 theqemux86 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 tomake 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 againstLAYERVERSION_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 theconf/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 withinLAYERDEPENDS for another layer in order to depend on a specific version of the layer. This variable is used in theconf/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 usesCOMMON_LICENSE_DIR to define the directory that holds common license text used during the build. TheLICENSE_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 thecore-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 thecore-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 ontask-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'sconf 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, seePackaging - 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 namedexpat_2.0.1.bb, then PV will be2.0.1. 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 followingRDEPENDS statement:

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

In the example, the package name (${PN}-dev) must appear as it would in thePACKAGES namespace before any renaming of the output package by classes likedebian.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 apkg-config information file, the build process uses this file to add items to theRDEPENDS 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 thePACKAGES namespace before any renaming of the output package by classes likedebian.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 ofpoky/build. In this case, the working directory the build system uses to build thedb 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 unlessDEBUG_BUILD = "1". In this case the value ofDEBUG_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 occursgetty 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 changesPACKAGE_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 asipkg, 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 supportsarm and i586.

TARGET_CFLAGS

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

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" foreglibc-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 replacesPOKYLIBC, which is no longer supported.

You can select eglibc or uclibc.

Note

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

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 inmeta/conf/distro/include/tcmode-* is used.

By default, TCMODE is set to "default", which choosestcmode-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, theTMPDIR variable is named tmp within theYocto Project Build Directory.

If you want to establish this directory in a location other than the default, you can uncomment the following statement in theconf/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 theTMPDIR 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 defaultYocto Project Build Directory of poky/build. In this case, the working directory the build system uses to build thev86d 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 theacl package, which is dependent on a MIPS-based device, is the following:

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