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BitBake is the task executor and scheduler used by the OpenEmbedded build system to build images. BitBake is a generic task execution engine that allows shell and Python tasks to be run efficiently and in parallel while working within complex inter-task dependency constraints. BitBake stores the output of each task in a directory, the shared state cache. Its location is controlled by the SSTATE_DIR variable. This cache is use to speed up compilation.

Panel
Usage:

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  bitbake

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[options]

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[recipename/target

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Bitbake executes all the layers starting with a prefix ‘meta’.

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  • conf/ : Configuration files - image specific and layer configuration.
  • downloads/ : This folder stores the downloaded upstream tarballs of the packages used in the builds, facilitating fast rebuilds. If the content of this folder is deleted, the builds will go and refetch the source tars again.
  • sstate-cache/ : Shared state cache, it is the local prebuilt store used by all builds. It will be populated when you do the builds. It is important to keep this directory safe for sstate reuse.
  • tmp/ : Holds all the build.
  • tmp/buildstats/ : Build statistics for all packages built (CPU usage, elapsed time, host, timestamps).
  • tmp/deploy/ : Final output of the build.
  • tmp/deploy/images/ : Contains the complete images built by the OpenEmbedded build system. These images are used to flash the target.
  • tmp/work/ : Set of specific work directories, split by architecture. They are used to unpack, configure and build the packages. Contains the patched sources, generated objects and logs.
  • tmp/sysroots/ : Shared libraries and headers used to compile packages for the target but also for the host.

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Note
 build-<machine> (e.g. build-oem-platform) - This is the object/build directory, all objects and intermediate files for all components are stored in this folder. if you want to do a clean build you can delete this folder, then run ./meta-cmf/setup-environment and rebuild. The build will be very fast since it will reuse the sstate (prebuilts) during this build, assuming the sstate-cache directory was populated with previous builds already.

Meta-layers

Meta-layer contains configuration, recipes, classes, patches.

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