4 Variable Context

Variables might only have an impact or can be used in certain contexts. Some should only be used in global files like .conf, while others are intended only for local files like .bb. This chapter aims to describe some important variable contexts.

4.1 BitBake’s own configuration

Variables starting with BB_ usually configure the behaviour of BitBake itself. For example, one could configure:

• System resources, like disk space to be used (BB_DISKMON_DIRS), or the number of tasks to be run in parallel by BitBake (BB_NUMBER_THREADS).

• How the fetchers shall behave, e.g., BB_FETCH_PREMIRRORONLY is used by BitBake to determine if BitBake’s fetcher shall search only PREMIRRORS for files.

Those variables are usually configured globally.

4.2 BitBake configuration

There are variables:

• Like B or T, that are used to specify directories used by BitBake during the build of a particular recipe. Those variables are specified in bitbake.conf. Some, like B, are quite often overwritten in recipes.

• Starting with FAKEROOT, to configure how the fakeroot command is handled. Those are usually set by bitbake.conf and might get adapted in a bbclass.

• Detailing where BitBake will store and fetch information from, for data reuse between build runs like CACHE, DL_DIR or PERSISTENT_DIR. Those are usually global.

4.3 Layers and files

Variables starting with LAYER configure how BitBake handles layers. Additionally, variables starting with BB configure how layers and files are handled. For example:

• LAYERDEPENDS is used to configure on which layers a given layer depends.

• The configured layers are contained in BBLAYERS and files in BBFILES.

Those variables are often used in the files layer.conf and bblayers.conf.

4.4 Recipes and packages

Variables handling recipes and packages can be split into:

• PN, PV or PF for example, contain information about the name or revision of a recipe or package. Usually, the default set in bitbake.conf is used, but those are from time to time overwritten in recipes.

• SUMMARY, DESCRIPTION, LICENSE or HOMEPAGE contain the expected information and should be set specifically for every recipe.

• In recipes, variables are also used to control build and runtime dependencies between recipes/packages with other recipes/packages. The most common should be: PROVIDES, RPROVIDES, DEPENDS, and RDEPENDS.

• There are further variables starting with SRC that specify the sources in a recipe like SRC_URI or SRCDATE. Those are also usually set in recipes.

• Which version or provider of a recipe should be given preference when multiple recipes would provide the same item, is controlled by variables starting with PREFERRED_. Those are normally set in the configuration files of a MACHINE or DISTRO.