# Variables Glossary

This chapter lists common variables used by BitBake and gives an overview of their function and contents.

Following are some points regarding the variables listed in this glossary:

- The variables listed in this glossary are specific to BitBake. Consequently, the descriptions are limited to that context.

- Also, variables exist in other systems that use BitBake (e.g. The Yocto Project and OpenEmbedded) that have names identical to those found in this glossary. For such cases, the variables in those systems extend the functionality of the variable as it is described here in this glossary.

- Finally, there are variables mentioned in this glossary that do not appear in the BitBake glossary. These other variables are variables used in systems that use BitBake.

A B C D E F G H I L M O P R S T

A

ASSUME_PROVIDED

  Lists recipe names (`PN` values) BitBake does not attempt to build. Instead, BitBake assumes these recipes have already been built.

  In OpenEmbedded-Core, `ASSUME_PROVIDED` mostly specifies native tools that should not be built. An example is `git-native`, which when specified allows for the Git binary from the host to be used rather than building `git-native`.

B

B

  The directory in which BitBake executes functions during a recipe's build process.

BB_ALLOWED_NETWORKS

  Specifies a space-delimited list of hosts that the fetcher is allowed to use to obtain the required source code. Following are considerations surrounding this variable:

  - This host list is only used if `BB_NO_NETWORK` is either not set or set to "0".

  - Limited support for the "`*`" wildcard character for matching against the beginning of host names exists. For example, the following setting matches `git.gnu.org`, `ftp.gnu.org`, and `foo.git.gnu.org`.

             BB_ALLOWED_NETWORKS = "*.gnu.org"

    Important

    The use of the "`*`" character only works at the beginning of a host name and it must be isolated from the remainder of the host name. You cannot use the wildcard character in any other location of the name or combined with the front part of the name.

    For example, `*.foo.bar` is supported, while `*aa.foo.bar` is not.

  - Mirrors not in the host list are skipped and logged in debug.

  - Attempts to access networks not in the host list cause a failure.

  Using `BB_ALLOWED_NETWORKS` in conjunction with `PREMIRRORS` is very useful. Adding the host you want to use to `PREMIRRORS` results in the source code being fetched from an allowed location and avoids raising an error when a host that is not allowed is in a `SRC_URI` statement. This is because the fetcher does not attempt to use the host listed in `SRC_URI` after a successful fetch from the `PREMIRRORS` occurs.
BB_CONSOLELOG

  Specifies the path to a log file into which BitBake's user interface writes output during the build.

BB_CURRENTTASK

  Contains the name of the currently running task. The name does not include the `do_` prefix.

BB_DANGLINGAPPENDS_WARNONLY

  Defines how BitBake handles situations where an append file (`.bbappend`) has no corresponding recipe file (`.bb`). This condition often occurs when layers get out of sync (e.g. `oe-core` bumps a recipe version and the old recipe no longer exists and the other layer has not been updated to the new version of the recipe yet).

  The default fatal behavior is safest because it is the sane reaction given something is out of sync. It is important to realize when your changes are no longer being applied.

BB_DEFAULT_TASK

  The default task to use when none is specified (e.g. with the `-c` command line option). The task name specified should not include the `do_` prefix.

BB_DISKMON_DIRS

  Monitors disk space and available inodes during the build and allows you to control the build based on these parameters.

  Disk space monitoring is disabled by default. When setting this variable, use the following form:

           BB_DISKMON_DIRS = "<action>,<dir>,<threshold> [...]"

           where:

              <action> is:
                 ABORT:     Immediately abort the build when
                            a threshold is broken.
                 STOPTASKS: Stop the build after the currently
                            executing tasks have finished when
                            a threshold is broken.
                 WARN:      Issue a warning but continue the
                            build when a threshold is broken.
                            Subsequent warnings are issued as
                            defined by the
                            BB_DISKMON_WARNINTERVAL variable,
                            which must be defined.

              <dir> is:
                 Any directory you choose. You can specify one or
                 more directories to monitor by separating the
                 groupings with a space.  If two directories are
                 on the same device, only the first directory
                 is monitored.

              <threshold> is:
                 Either the minimum available disk space,
                 the minimum number of free inodes, or
                 both.  You must specify at least one.  To
                 omit one or the other, simply omit the value.
                 Specify the threshold using G, M, K for Gbytes,
                 Mbytes, and Kbytes, respectively. If you do
                 not specify G, M, or K, Kbytes is assumed by
                 default.  Do not use GB, MB, or KB.

  Here are some examples:

           BB_DISKMON_DIRS = "ABORT,${TMPDIR},1G,100K WARN,${SSTATE_DIR},1G,100K"
           BB_DISKMON_DIRS = "STOPTASKS,${TMPDIR},1G"
           BB_DISKMON_DIRS = "ABORT,${TMPDIR},,100K"

  The first example works only if you also set the `BB_DISKMON_WARNINTERVAL` variable. This example causes the build system to immediately abort when either the disk space in `${TMPDIR}` drops below 1 Gbyte or the available free inodes drops below 100 Kbytes. Because two directories are provided with the variable, the build system also issues a warning when the disk space in the `${SSTATE_DIR}` directory drops below 1 Gbyte or the number of free inodes drops below 100 Kbytes. Subsequent warnings are issued during intervals as defined by the `BB_DISKMON_WARNINTERVAL` variable.

  The second example stops the build after all currently executing tasks complete when the minimum disk space in the `${TMPDIR}` directory drops below 1 Gbyte. No disk monitoring occurs for the free inodes in this case.

  The final example immediately aborts the build when the number of free inodes in the `${TMPDIR}` directory drops below 100 Kbytes. No disk space monitoring for the directory itself occurs in this case.

BB_DISKMON_WARNINTERVAL

  Defines the disk space and free inode warning intervals.

  If you are going to use the `BB_DISKMON_WARNINTERVAL` variable, you must also use the `BB_DISKMON_DIRS` variable and define its action as "WARN". During the build, subsequent warnings are issued each time disk space or number of free inodes further reduces by the respective interval.

  If you do not provide a `BB_DISKMON_WARNINTERVAL` variable and you do use `BB_DISKMON_DIRS` with the "WARN" action, the disk monitoring interval defaults to the following:

           BB_DISKMON_WARNINTERVAL = "50M,5K"

  When specifying the variable in your configuration file, use the following form:

           BB_DISKMON_WARNINTERVAL = "<disk_space_interval>,<disk_inode_interval>"

           where:

              <disk_space_interval> is:
                 An interval of memory expressed in either
                 G, M, or K for Gbytes, Mbytes, or Kbytes,
                 respectively. You cannot use GB, MB, or KB.

              <disk_inode_interval> is:
                 An interval of free inodes expressed in either
                 G, M, or K for Gbytes, Mbytes, or Kbytes,
                 respectively. You cannot use GB, MB, or KB.

  Here is an example:

           BB_DISKMON_DIRS = "WARN,${SSTATE_DIR},1G,100K"
           BB_DISKMON_WARNINTERVAL = "50M,5K"

  These variables cause BitBake to issue subsequent warnings each time the available disk space further reduces by 50 Mbytes or the number of free inodes further reduces by 5 Kbytes in the `${SSTATE_DIR}` directory. Subsequent warnings based on the interval occur each time a respective interval is reached beyond the initial warning (i.e. 1 Gbytes and 100 Kbytes).
BB_ENV_WHITELIST

  Specifies the internal whitelist of variables to allow through from the external environment into BitBake's datastore. If the value of this variable is not specified (which is the default), the following list is used: `BBPATH`, `BB_PRESERVE_ENV`, `BB_ENV_WHITELIST`, and `BB_ENV_EXTRAWHITE`.

  You must set this variable in the external environment in order for it to work.
BB_ENV_EXTRAWHITE

  Specifies an additional set of variables to allow through (whitelist) from the external environment into BitBake's datastore. This list of variables are on top of the internal list set in `BB_ENV_WHITELIST`.

  You must set this variable in the external environment in order for it to work.
BB_FETCH_PREMIRRORONLY

  When set to "1", causes BitBake's fetcher module to only search `PREMIRRORS` for files. BitBake will not search the main `SRC_URI` or `MIRRORS`.

BB_FILENAME

  Contains the filename of the recipe that owns the currently running task. For example, if the `do_fetch` task that resides in the `my-recipe.bb` is executing, the `BB_FILENAME` variable contains "/foo/path/my-recipe.bb".

BB_GENERATE_MIRROR_TARBALLS

  Causes tarballs of the Git repositories, including the Git metadata, to be placed in the `DL_DIR` directory. Anyone wishing to create a source mirror would want to enable this variable.

  For performance reasons, creating and placing tarballs of the Git repositories is not the default action by BitBake.

           BB_GENERATE_MIRROR_TARBALLS = "1"

BB_HASHCONFIG_WHITELIST

  Lists variables that are excluded from base configuration checksum, which is used to determine if the cache can be reused.

  One of the ways BitBake determines whether to re-parse the main metadata is through checksums of the variables in the datastore of the base configuration data. There are variables that you typically want to exclude when checking whether or not to re-parse and thus rebuild the cache. As an example, you would usually exclude `TIME` and `DATE` because these variables are always changing. If you did not exclude them, BitBake would never reuse the cache.

BB_HASHBASE_WHITELIST

  Lists variables that are excluded from checksum and dependency data. Variables that are excluded can therefore change without affecting the checksum mechanism. A common example would be the variable for the path of the build. BitBake's output should not (and usually does not) depend on the directory in which it was built.

BB_HASHCHECK_FUNCTION

  Specifies the name of the function to call during the "setscene" part of the task's execution in order to validate the list of task hashes. The function returns the list of setscene tasks that should be executed.

  At this point in the execution of the code, the objective is to quickly verify if a given setscene function is likely to work or not. It's easier to check the list of setscene functions in one pass than to call many individual tasks. The returned list need not be completely accurate. A given setscene task can still later fail. However, the more accurate the data returned, the more efficient the build will be.

BB_INVALIDCONF

  Used in combination with the `ConfigParsed` event to trigger re-parsing the base metadata (i.e. all the recipes). The `ConfigParsed` event can set the variable to trigger the re-parse. You must be careful to avoid recursive loops with this functionality.

BB_LOGCONFIG

  Specifies the name of a config file that contains the user logging configuration. See Logging for additional information

BB_LOGFMT

  Specifies the name of the log files saved into `${``T``}`. By default, the `BB_LOGFMT` variable is undefined and the log file names get created using the following form:

           log.{task}.{pid}

  If you want to force log files to take a specific name, you can set this variable in a configuration file.
BB_NICE_LEVEL

  Allows BitBake to run at a specific priority (i.e. nice level). System permissions usually mean that BitBake can reduce its priority but not raise it again. See `BB_TASK_NICE_LEVEL` for additional information.

BB_NO_NETWORK

  Disables network access in the BitBake fetcher modules. With this access disabled, any command that attempts to access the network becomes an error.

  Disabling network access is useful for testing source mirrors, running builds when not connected to the Internet, and when operating in certain kinds of firewall environments.

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.

BB_NUMBER_PARSE_THREADS

  Sets the number of threads BitBake uses when parsing. By default, the number of threads is equal to the number of cores on the system.

BB_ORIGENV

  Contains a copy of the original external environment in which BitBake was run. The copy is taken before any whitelisted variable values are filtered into BitBake's datastore.

  The contents of this variable is a datastore object that can be queried using the normal datastore operations.
BB_PRESERVE_ENV

  Disables whitelisting and instead allows all variables through from the external environment into BitBake's datastore.

  You must set this variable in the external environment in order for it to work.
BB_RUNFMT

  Specifies the name of the executable script files (i.e. run files) saved into `${``T``}`. By default, the `BB_RUNFMT` variable is undefined and the run file names get created using the following form:

           run.{task}.{pid}

  If you want to force run files to take a specific name, you can set this variable in a configuration file.
BB_RUNTASK

  Contains the name of the currently executing task. The value includes the "do_" prefix. For example, if the currently executing task is `do_config`, the value is "do_config".

BB_SCHEDULER

  Selects the name of the scheduler to use for the scheduling of BitBake tasks. Three options exist:

  - basic - The basic framework from which everything derives. Using this option causes tasks to be ordered numerically as they are parsed.

  - speed - Executes tasks first that have more tasks depending on them. The "speed" option is the default.

  - completion - Causes the scheduler to try to complete a given recipe once its build has started.

BB_SCHEDULERS

  Defines custom schedulers to import. Custom schedulers need to be derived from the `RunQueueScheduler` class.

  For information how to select a scheduler, see the `BB_SCHEDULER` variable.

BB_SETSCENE_DEPVALID

  Specifies a function BitBake calls that determines whether BitBake requires a setscene dependency to be met.

  When running a setscene task, BitBake needs to know which dependencies of that setscene task also need to be run. Whether dependencies also need to be run is highly dependent on the metadata. The function specified by this variable returns a "True" or "False" depending on whether the dependency needs to be met.

BB_SETSCENE_VERIFY_FUNCTION2

  Specifies a function to call that verifies the list of planned task execution before the main task execution happens. The function is called once BitBake has a list of setscene tasks that have run and either succeeded or failed.

  The function allows for a task list check to see if they make sense. Even if BitBake was planning to skip a task, the returned value of the function can force BitBake to run the task, which is necessary under certain metadata defined circumstances.

BB_SIGNATURE_EXCLUDE_FLAGS

  Lists variable flags (varflags) that can be safely excluded from checksum and dependency data for keys in the datastore. When generating checksum or dependency data for keys in the datastore, the flags set against that key are normally included in the checksum.

  For more information on varflags, see the "Variable Flags" section.

BB_SIGNATURE_HANDLER

  Defines the name of the signature handler BitBake uses. The signature handler defines the way stamp files are created and handled, if and how the signature is incorporated into the stamps, and how the signature itself is generated.

  A new signature handler can be added by injecting a class derived from the `SignatureGenerator` class into the global namespace.

BB_SRCREV_POLICY

  Defines the behavior of the fetcher when it interacts with source control systems and dynamic source revisions. The `BB_SRCREV_POLICY` variable is useful when working without a network.

  The variable can be set using one of two policies:

  - cache - Retains the value the system obtained previously rather than querying the source control system each time.

  - clear - Queries the source controls system every time. With this policy, there is no cache. The "clear" policy is the default.

BB_STAMP_POLICY

  Defines the mode used for how timestamps of stamp files are compared. You can set the variable to one of the following modes:

  - perfile - Timestamp comparisons are only made between timestamps of a specific recipe. This is the default mode.

  - full - Timestamp comparisons are made for all dependencies.

  - whitelist - Identical to "full" mode except timestamp comparisons are made for recipes listed in the `BB_STAMP_WHITELIST` variable.

  Stamp policies are largely obsolete with the introduction of setscene tasks.
BB_STAMP_WHITELIST

  Lists files whose stamp file timestamps are compared when the stamp policy mode is set to "whitelist". For information on stamp policies, see the `BB_STAMP_POLICY` variable.

BB_STRICT_CHECKSUM

  Sets a more strict checksum mechanism for non-local URLs. Setting this variable to a value causes BitBake to report an error if it encounters a non-local URL that does not have at least one checksum specified.

BB_TASK_IONICE_LEVEL

  Allows adjustment of a task's Input/Output priority. During Autobuilder testing, random failures can occur for tasks due to I/O starvation. These failures occur during various QEMU runtime timeouts. You can use the `BB_TASK_IONICE_LEVEL` variable to adjust the I/O priority of these tasks.

  This variable works similarly to the `BB_TASK_NICE_LEVEL` variable except with a task's I/O priorities.

  Set the variable as follows:

           BB_TASK_IONICE_LEVEL = "class.prio"

  For class, the default value is "2", which is a best effort. You can use "1" for realtime and "3" for idle. If you want to use realtime, you must have superuser privileges.

  For prio, you can use any value from "0", which is the highest priority, to "7", which is the lowest. The default value is "4". You do not need any special privileges to use this range of priority values.

  In order for your I/O priority settings to take effect, you need the Completely Fair Queuing (CFQ) Scheduler selected for the backing block device. To select the scheduler, use the following command form where device is the device (e.g. sda, sdb, and so forth):

            $ sudo sh -c “echo cfq > /sys/block/device/queu/scheduler

BB_TASK_NICE_LEVEL

  Allows specific tasks to change their priority (i.e. nice level).

  You can use this variable in combination with task overrides to raise or lower priorities of specific tasks. For example, on the Yocto Project autobuilder, QEMU emulation in images is given a higher priority as compared to build tasks to ensure that images do not suffer timeouts on loaded systems.

BB_TASKHASH

  Within an executing task, this variable holds the hash of the task as returned by the currently enabled signature generator.

BB_VERBOSE_LOGS

  Controls how verbose BitBake is during builds. If set, shell scripts echo commands and shell script output appears on standard out (stdout).

BB_WORKERCONTEXT

  Specifies if the current context is executing a task. BitBake sets this variable to "1" when a task is being executed. The value is not set when the task is in server context during parsing or event handling.

BBCLASSEXTEND

  Allows you to extend a recipe so that it builds variants of the software. Some examples of these variants for recipes from the OpenEmbedded-Core metadata are "natives" such as `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 variable to your recipe. Here are two examples. The "native" variants are from the OpenEmbedded-Core metadata:

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

  Internally, the `BBCLASSEXTEND` mechanism generates recipe variants by rewriting variable values and applying overrides such as `_class-native`. For example, to generate a native version of a recipe, a `DEPENDS` on "foo" is rewritten to a `DEPENDS` on "foo-native".

  Even when using `BBCLASSEXTEND`, the recipe is only parsed once. Parsing once adds some limitations. For example, it is not possible to include a different file depending on the variant, since `include` statements are processed when the recipe is parsed.

BBDEBUG

  Sets the BitBake debug output level to a specific value as incremented by the `-D` command line option.

  You must set this variable in the external environment in order for it to work.
BBFILE_COLLECTIONS

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

BBFILE_PATTERN

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

BBFILE_PRIORITY

  Assigns the priority for recipe files in each layer.

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

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

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

  A space-separated list of recipe files BitBake uses to build software.

  When specifying recipe files, you can pattern match using Python's `glob` syntax. For details on the syntax, see the documentation by following the previous link.

BBINCLUDED

  Contains a space-separated list of all of all files that BitBake's parser included during parsing of the current file.

BBINCLUDELOGS

  If set to a value, enables printing the task log when reporting a failed task.

BBINCLUDELOGS_LINES

  If `BBINCLUDELOGS` is set, specifies the maximum number of lines from the task log file to print when reporting a failed task. If you do not set `BBINCLUDELOGS_LINES`, the entire log is printed.

BBLAYERS

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

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

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

  Sets the base location where layers are stored. This setting is used in conjunction with `bitbake-layers layerindex-fetch` and tells `bitbake-layers` where to place the fetched layers.

BBMASK

  Prevents BitBake from processing recipes and recipe append files.

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

  The values you provide are passed to Python's regular expression compiler. Consequently, the syntax follows Python's Regular Expression (re) syntax. The expressions are compared against the full paths to the files. For complete syntax information, see Python's documentation at .

  The following example 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/"

  If you want to mask out multiple directories or recipes, you can specify multiple regular expression fragments. This next example masks out multiple directories and individual recipes:

           BBMASK += "/meta-ti/recipes-misc/ meta-ti/recipes-ti/packagegroup/"
           BBMASK += "/meta-oe/recipes-support/"
           BBMASK += "/meta-foo/.*/openldap"
           BBMASK += "opencv.*\.bbappend"
           BBMASK += "lzma"

  When specifying a directory name, use the trailing slash character to ensure you match just that directory name.
BBMULTICONFIG
BBMULTICONFIG[doc] = "Enables BitBake to perform multiple configuration builds and lists each separate configuration (multiconfig)."

  Enables BitBake to perform multiple configuration builds and lists each separate configuration (multiconfig). You can use this variable to cause BitBake to build multiple targets where each target has a separate configuration. Define `BBMULTICONFIG` in your `conf/local.conf` configuration file.

  As an example, the following line specifies three multiconfigs, each having a separate configuration file:

           BBMULTIFONFIG = "configA configB configC"

  Each configuration file you use must reside in the build directory within a directory named `conf/multiconfig` (e.g. build_directory`/conf/multiconfig/configA.conf`).

  For information on how to use `BBMULTICONFIG` in an environment that supports building targets with multiple configurations, see the "Executing a Multiple Configuration Build" section.

BBPATH

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

  If you run BitBake from a directory outside of the build directory, you must be sure to set `BBPATH` to point to the build directory. Set the variable as you would any environment variable and then run BitBake:

           $ BBPATH="build_directory"
           $ export BBPATH
           $ bitbake target

BBSERVER

  Points to the server that runs memory-resident BitBake. The variable is only used when you employ memory-resident BitBake.

BBTARGETS

  Allows you to use a configuration file to add to the list of command-line target recipes you want to build.

BBVERSIONS

  Allows a single recipe to build multiple versions of a project from a single recipe file. You also able to specify conditional metadata using the `OVERRIDES` mechanism for a single version or for an optionally named range of versions.

  For more information on `BBVERSIONS`, see the "Variants - Class Extension Mechanism" section.

BITBAKE_UI

  Used to specify the UI module to use when running BitBake. Using this variable is equivalent to using the `-u` command-line option.

  You must set this variable in the external environment in order for it to work.
BUILDNAME

  A name assigned to the build. The name defaults to a datetime stamp of when the build was started but can be defined by the metadata.

BZRDIR

  The directory in which files checked out of a Bazaar system are stored.

C

CACHE

  Specifies the directory BitBake uses to store a cache of the metadata so it does not need to be parsed every time BitBake is started.

CVSDIR

  The directory in which files checked out under the CVS system are stored.

D

DEFAULT_PREFERENCE

  Specifies a weak bias for recipe selection priority.

  The most common usage of this is variable is to set it to "-1" within a recipe for a development version of a piece of software. Using the variable in this way causes the stable version of the recipe to build by default in the absence of `PREFERRED_VERSION` being used to build the development version.

  The bias provided by `DEFAULT_PREFERENCE` is weak and is overridden by `BBFILE_PRIORITY` if that variable is different between two layers that contain different versions of the same recipe.
DEPENDS

  Lists a recipe's build-time dependencies (i.e. other recipe files).

  Consider this simple example for two recipes named "a" and "b" that produce similarly named packages. In this example, the `DEPENDS` statement appears in the "a" recipe:

           DEPENDS = "b"

  Here, the dependency is such that the `do_configure` task for recipe "a" depends on the `do_populate_sysroot` task of recipe "b". This means anything that recipe "b" puts into sysroot is available when recipe "a" is configuring itself.

  For information on runtime dependencies, see the `RDEPENDS` variable.

DESCRIPTION

  A long description for the recipe.

DL_DIR

  The central download directory used by the build process to store downloads. By default, `DL_DIR` gets files suitable for mirroring for everything except Git repositories. If you want tarballs of Git repositories, use the `BB_GENERATE_MIRROR_TARBALLS` variable.

E

EXCLUDE_FROM_WORLD

  Directs BitBake to exclude a recipe from world builds (i.e. `bitbake world`). During world builds, BitBake locates, parses and builds all recipes found in every layer exposed in the `bblayers.conf` configuration file.

  To exclude a recipe from a world build using this variable, set the variable to "1" in the recipe.

  Recipes added to `EXCLUDE_FROM_WORLD` may still be built during a world build in order to satisfy dependencies of other recipes. Adding a recipe to `EXCLUDE_FROM_WORLD` only ensures that the recipe is not explicitly added to the list of build targets in a world build.

F

FAKEROOT

  Contains the command to use when running a shell script in a fakeroot environment. The `FAKEROOT` variable is obsolete and has been replaced by the other `FAKEROOT*` variables. See these entries in the glossary for more information.

FAKEROOTBASEENV

  Lists environment variables to set when executing the command defined by `FAKEROOTCMD` that starts the bitbake-worker process in the fakeroot environment.

FAKEROOTCMD

  Contains the command that starts the bitbake-worker process in the fakeroot environment.

FAKEROOTDIRS

  Lists directories to create before running a task in the fakeroot environment.

FAKEROOTENV

  Lists environment variables to set when running a task in the fakeroot environment. For additional information on environment variables and the fakeroot environment, see the `FAKEROOTBASEENV` variable.

FAKEROOTNOENV

  Lists environment variables to set when running a task that is not in the fakeroot environment. For additional information on environment variables and the fakeroot environment, see the `FAKEROOTENV` variable.

FETCHCMD

  Defines the command the BitBake fetcher module executes when running fetch operations. You need to use an override suffix when you use the variable (e.g. `FETCHCMD_git` or `FETCHCMD_svn`).

FILE

  Points at the current file. BitBake sets this variable during the parsing process to identify the file being parsed. BitBake also sets this variable when a recipe is being executed to identify the recipe file.

FILESPATH

  Specifies directories BitBake uses when searching for patches and files. The "local" fetcher module uses these directories when handling `file://` URLs. The variable behaves like a shell `PATH` environment variable. The value is a colon-separated list of directories that are searched left-to-right in order.

G

GITDIR

  The directory in which a local copy of a Git repository is stored when it is cloned.

H

HGDIR

  The directory in which files checked out of a Mercurial system are stored.

HOMEPAGE

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

I

INHERIT

  Causes the named class or classes to be inherited globally. Anonymous functions in the class or classes are not executed for the base configuration and in each individual recipe. The OpenEmbedded build system ignores changes to `INHERIT` in individual recipes.

  For more information on `INHERIT`, see the "`INHERIT` Configuration Directive" section.

L

LAYERDEPENDS

  Lists the layers, separated by spaces, upon which this recipe depends. 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). BitBake produces an error if any dependency is missing or the version numbers do not match exactly (if specified).

  You use this variable in the `conf/layer.conf` file. You must also use the specific layer name as a suffix to the variable (e.g. `LAYERDEPENDS_mylayer`).

LAYERDIR

  When used inside the `layer.conf` configuration file, this variable provides the path of the current layer. This variable is not available outside of `layer.conf` and references are expanded immediately when parsing of the file completes.

LAYERDIR_RE

  When used inside the `layer.conf` configuration file, this variable provides the path of the current layer, escaped for use in a regular expression (`BBFILE_PATTERN`). This variable is not available outside of `layer.conf` and references are expanded immediately when parsing of the file completes.

LAYERVERSION

  Optionally specifies the version of a layer as a single number. You can use this variable within `LAYERDEPENDS` for another layer in order to depend on a specific version of the layer.

  You use this variable in the `conf/layer.conf` file. You must also use the specific layer name as a suffix to the variable (e.g. `LAYERDEPENDS_mylayer`).

LICENSE

  The list of source licenses for the recipe.

M

MIRRORS

  Specifies additional paths from which BitBake gets source code. When the build system searches for source code, it first tries the local download directory. If that location fails, the build system tries locations defined by `PREMIRRORS`, the upstream source, and then locations specified by `MIRRORS` in that order.

MULTI_PROVIDER_WHITELIST

  Allows you to suppress BitBake warnings caused when building two separate recipes that provide the same output.

  BitBake normally issues a warning when building two different recipes where each provides the same output. This scenario is usually something the user does not want. However, cases do exist where it makes sense, particularly in the `virtual/*` namespace. You can use this variable to suppress BitBake's warnings.

  To use the variable, list provider names (e.g. recipe names, `virtual/kernel`, and so forth).

O

OVERRIDES

  BitBake uses `OVERRIDES` to control what variables are overridden after BitBake parses recipes and configuration files.

  Following is a simple example that uses an overrides list based on machine architectures:

           OVERRIDES = "arm:x86:mips:powerpc"

  You can find information on how to use `OVERRIDES` in the "Conditional Syntax (Overrides)" section.

P

P4DIR

  The directory in which a local copy of a Perforce depot is stored when it is fetched.

PACKAGES

  The list of packages the recipe creates.

PACKAGES_DYNAMIC

  A promise that your recipe satisfies runtime dependencies for optional modules that are found in other recipes. `PACKAGES_DYNAMIC` does not actually satisfy the dependencies, it only states that they should be satisfied. For example, if a hard, runtime dependency (`RDEPENDS`) of another package is satisfied during the build through the `PACKAGES_DYNAMIC` variable, but a package with the module name is never actually produced, then the other package will be broken.

PE

  The epoch of the recipe. By default, this variable is unset. The variable is used to make upgrades possible when the versioning scheme changes in some backwards incompatible way.

PERSISTENT_DIR

  Specifies the directory BitBake uses to store data that should be preserved between builds. In particular, the data stored is the data that uses BitBake's persistent data API and the data used by the PR Server and PR Service.

PF

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

PN

  The recipe name.

PR

  The revision of the recipe.

PREFERRED_PROVIDER

  Determines which recipe should be given preference when multiple recipes provide the same item. You should always suffix the variable with the name of the provided item, and you should set it to the `PN` of the recipe to which you want to give precedence. Some examples:

           PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
           PREFERRED_PROVIDER_virtual/xserver = "xserver-xf86"
           PREFERRED_PROVIDER_virtual/libgl ?= "mesa"

PREFERRED_PROVIDERS

  Determines which recipe should be given preference for cases where multiple recipes provide the same item. Functionally, `PREFERRED_PROVIDERS` is identical to `PREFERRED_PROVIDER`. However, the `PREFERRED_PROVIDERS` variable lets you define preferences for multiple situations using the following form:

           PREFERRED_PROVIDERS = "xxx:yyy aaa:bbb ..."

  This form is a convenient replacement for the following:

           PREFERRED_PROVIDER_xxx = "yyy"
           PREFERRED_PROVIDER_aaa = "bbb"

PREFERRED_VERSION

  If there are multiple versions of recipes available, this variable determines which recipe should be given preference. You must always suffix the variable with the `PN` you want to select, and you should set `PV` accordingly for precedence.

  The `PREFERRED_VERSION` variable supports limited wildcard use through the "`%`" character. You can use the character to match any number of characters, which can be useful when specifying versions that contain long revision numbers that potentially change. Here are two examples:

           PREFERRED_VERSION_python = "2.7.3"
           PREFERRED_VERSION_linux-yocto = "4.12%"

  Important

  The use of the "`%`" character is limited in that it only works at the end of the string. You cannot use the wildcard character in any other location of the string.
PREMIRRORS

  Specifies additional paths from which BitBake gets source code. When the build system searches for source code, it first tries the local download directory. If that location fails, the build system tries locations defined by `PREMIRRORS`, the upstream source, and then locations specified by `MIRRORS` in that order.

  Typically, you would add a specific server for the build system to attempt before any others by adding something like the following to your configuration:

           PREMIRRORS_prepend = "\
           git://.*/.* http://www.yoctoproject.org/sources/ \n \
           ftp://.*/.* http://www.yoctoproject.org/sources/ \n \
           http://.*/.* http://www.yoctoproject.org/sources/ \n \
           https://.*/.* http://www.yoctoproject.org/sources/ \n"

  These changes cause the build system to intercept Git, FTP, HTTP, and HTTPS requests and direct them to the `http://` sources mirror. You can use `file://` URLs to point to local directories or network shares as well.
PROVIDES

  A list of aliases by which a particular recipe can be known. By default, a recipe's own `PN` is implicitly already in its `PROVIDES` list. If a recipe uses `PROVIDES`, the additional aliases are synonyms for the recipe and can be useful satisfying dependencies of other recipes during the build as specified by `DEPENDS`.

  Consider the following example `PROVIDES` statement from a recipe file `libav_0.8.11.bb`:

           PROVIDES += "libpostproc"

  The `PROVIDES` statement results in the "libav" recipe also being known as "libpostproc".

  In addition to providing recipes under alternate names, the `PROVIDES` mechanism is also used to implement virtual targets. A virtual target is a name that corresponds to some particular functionality (e.g. a Linux kernel). Recipes that provide the functionality in question list the virtual target in `PROVIDES`. Recipes that depend on the functionality in question can include the virtual target in `DEPENDS` to leave the choice of provider open.

  Conventionally, virtual targets have names on the form "virtual/function" (e.g. "virtual/kernel"). The slash is simply part of the name and has no syntactical significance.

PRSERV_HOST

  The network based `PR` service host and port.

  Following is an example of how the `PRSERV_HOST` variable is set:

           PRSERV_HOST = "localhost:0"

  You must set the variable if you want to automatically start a local PR service. You can set `PRSERV_HOST` to other values to use a remote PR service.
PV

  The version of the recipe.

R

RDEPENDS

  Lists a package's runtime dependencies (i.e. other packages) that must be installed in order for the built package to run correctly. If a package in this list cannot be found during the build, you will get a build error.

  Because the `RDEPENDS` variable applies to packages being built, you should always use the variable in a form with an attached package name. 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 development package depends on the `perl` package. Thus, the `RDEPENDS` variable has the `${PN}-dev` package name as part of the variable.

  BitBake supports specifying versioned dependencies. Although the syntax varies depending on the packaging format, BitBake hides these differences from you. Here is the general syntax to specify versions with the `RDEPENDS` variable:

           RDEPENDS_${PN} = "package (operator version)"

  For `operator`, you can specify the following:

           =
           <
           >
           <=
           >=

  For example, the following sets up a dependency on version 1.2 or greater of the package `foo`:

           RDEPENDS_${PN} = "foo (>= 1.2)"

  For information on build-time dependencies, see the `DEPENDS` variable.

REPODIR

  The directory in which a local copy of a `google-repo` directory is stored when it is synced.

RPROVIDES

  A list of package name aliases that a package also provides. These aliases are useful for satisfying runtime dependencies of other packages both during the build and on the target (as specified by `RDEPENDS`).

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

           RPROVIDES_${PN} = "widget-abi-2"

RRECOMMENDS

  A list of packages that extends 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.

  BitBake supports specifying versioned recommends. Although the syntax varies depending on the packaging format, BitBake hides these differences from you. Here is the general syntax to specify versions with the `RRECOMMENDS` variable:

           RRECOMMENDS_${PN} = "package (operator version)"

  For `operator`, you can specify the following:

           =
           <
           >
           <=
           >=

  For example, the following sets up a recommend on version 1.2 or greater of the package `foo`:

           RRECOMMENDS_${PN} = "foo (>= 1.2)"

S

SECTION

  The section in which packages should be categorized.

SRC_URI

  The list of source files - local or remote. This variable tells BitBake which bits to pull for the build and how to pull them. For example, if the recipe or append file needs to fetch a single tarball from the Internet, the recipe or append file uses a `SRC_URI` entry that specifies that tarball. On the other hand, if the recipe or append file needs to fetch a tarball and include a custom file, the recipe or append file needs an `SRC_URI` variable that specifies all those sources.

  The following list explains the available URI protocols:

  - `file://` - Fetches files, which are usually files shipped with the metadata, from the local machine. The path is relative to the `FILESPATH` variable.

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

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

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

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

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

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

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

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

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

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

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

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

  Here are some additional options worth mentioning:

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

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

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

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

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 only when using Subversion, Git, Mercurial and Bazaar. If you want to build a fixed revision and you want 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.

SRCREV_FORMAT

  Helps construct valid `SRCREV` values when multiple source controlled URLs are used in `SRC_URI`.

  The system needs help constructing these values under these circumstances. Each component in the `SRC_URI` is assigned a name and these are referenced in the `SRCREV_FORMAT` variable. Consider an example with URLs named "machine" and "meta". In this case, `SRCREV_FORMAT` could look like "machine_meta" and those names would have the SCM versions substituted into each position. Only one `AUTOINC` placeholder is added and if needed. And, this placeholder is placed at the start of the returned string.

STAMP

  Specifies the base path used to create recipe stamp files. The path to an actual stamp file is constructed by evaluating this string and then appending additional information.

STAMPCLEAN

  Specifies the base path used to create recipe stamp files. Unlike the `STAMP` variable, `STAMPCLEAN` can contain wildcards to match the range of files a clean operation should remove. BitBake uses a clean operation to remove any other stamps it should be removing when creating a new stamp.

SUMMARY

  A short summary for the recipe, which is 72 characters or less.

SVNDIR

  The directory in which files checked out of a Subversion system are stored.

T

T

  Points to a directory were BitBake places temporary files, which consist mostly of task logs and scripts, when building a particular recipe.

TOPDIR

  Points to the build directory. BitBake automatically sets this variable.