27 Conserving Disk Space

27.1 Conserving Disk Space During Builds

To help conserve disk space during builds, you can add the following statement to your project’s local.conf configuration file found in the Build Directory:

INHERIT += "rm_work"

Adding this statement deletes the work directory used for building a recipe once the recipe is built. For more information on “rm_work”, see the rm_work.bbclass class in the Yocto Project Reference Manual.

When you inherit this class and build a core-image-sato image for a qemux86-64 machine from an Ubuntu 22.04 x86-64 system, you end up with a final disk usage of 22 Gbytes instead of &MIN_DISK_SPACE; Gbytes. However, &MIN_DISK_SPACE_RM_WORK; Gbytes of initial free disk space are still needed to create temporary files before they can be deleted.

27.2 Purging Obsolete Shared State Cache Files

After multiple build iterations, the Shared State (sstate) cache can contain multiple cache files for a given package, consuming a substantial amount of disk space. However, only the most recent ones are likely to be reused.

The following command is a quick way to purge all the cache files which haven’t been used for a least a specified number of days:

find build/sstate-cache -type f -mtime +$DAYS -delete

The above command relies on the fact that BitBake touches the sstate cache files as it accesses them, when it has write access to the cache.

You could use -atime instead of -mtime if the partition isn’t mounted with the noatime option for a read only cache.

For more advanced needs, OpenEmbedded-Core also offers a more elaborate command. It has the ability to purge all but the newest cache files on each architecture, and also to remove files that it considers unreachable by exploring a set of build configurations. However, this command requires a full build environment to be available and doesn’t work well covering multiple releases. It won’t work either on limited environments such as BSD based NAS:

sstate-cache-management.sh --remove-duplicated --cache-dir=build/sstate-cache

This command will ask you to confirm the deletions it identifies. Run sstate-cache-management.sh for more details about this script.


As this command is much more cautious and selective, removing only cache files, it will execute much slower than the simple find command described above. Therefore, it may not be your best option to trim huge cache directories.