Parts and Steps

Parts and steps are the basic data types craft-parts will work with. Together, they define the lifecycle of a project (i.e. how to process each step of each part in order to obtain the final primed result).


When the LifecycleManager is invoked, parts are defined in a dictionary under the parts key. If the dictionary contains other keys, they will be ignored.


Steps are used to establish plan targets and in informational data structures such as StepInfo. They are defined by the Step enumeration, containing entries for the lifecycle steps PULL, OVERLAY, BUILD, STAGE, and PRIME.

Step execution environment

Craft-parts defines the following environment for use during step processing and execution of user-defined scriptlets:

  • CRAFT_ARCH_TRIPLET: The the machine-vendor-os platform triplet definition.

  • CRAFT_TARGET_ARCH: The architecture we’re building for.

  • CRAFT_PARALLEL_BUILD_COUNT: The maximum number of concurrent build jobs to execute.

  • CRAFT_PROJECT_DIR: The path to the current project’s subtree in the filesystem.

  • CRAFT_PART_NAME: The name of the part currently being processed.

  • CRAFT_PART_SRC: The path to the part source directory. This is where sources are located after the PULL step.

  • CRAFT_PART_SRC_WORK: The path to the part source subdirectory, if any. Defaults to the part source directory.

  • CRAFT_PART_BUILD: The path to the part build directory. This is where parts are built during the BUILD step.

  • CRAFT_PART_BUILD_WORK: The path to the part build subdirectory in case of out-of-tree builds. Defaults to the part source directory.

  • CRAFT_PART_INSTALL: The path to the part install directory. This is where built artifacts are installed after the BUILD step.

  • CRAFT_OVERLAY: The path to the part’s layer directory during the OVERLAY step if overlays are enabled.

  • CRAFT_STAGE: The path to the project’s staging directory. This is where installed artifacts are migrated after the STAGE step.

  • CRAFT_PRIME: The path to the final primed payload directory after the PRIME step.