Lifecycle details

Each part is built in four separate steps, each with its own input and output locations:

  1. PULL — The source and external dependencies (such as package dependencies) for the part are retrieved from their stated location and placed into a package cache area.

  2. BUILD — The part is built according to the particular part plugin and build override.

  3. STAGE — The specified outputs from the BUILD step are copied into a unified staging area for all parts.

  4. PRIME — The specified files are copied from the staging area to the priming area for use in the final payload. This is distinct from STAGE in that the STAGE step allows files that are used in the BUILD steps of dependent parts to be accessed, while the PRIME step occurs after all parts have been staged.

Note

While craft-parts offers an OVERLAY step as well, charmcraft does not use it. This is a distinction between how Charmcraft and Rockcraft work.

Step order

While each part’s steps are guaranteed to run in the order above, they are not necessarily run immediately following each other, especially if multiple parts are included in a project. While specifics are implementation-dependent, the general rules for combining parts are:

  1. PULL all parts before running further steps.

  2. BUILD any unbuilt parts whose dependencies have been staged. If a part has no dependencies, this part is built in the first iteration.

  3. STAGE any newly-built parts.

  4. Repeat the BUILD and STAGE steps until all parts have been staged.

  5. PRIME all parts.

Further Information

Further information can be found in the Craft-parts documentation.