Apptainer Cache

Apptainer handles images as standard .sif files on your disk. To save the network bandwidth and the time, it automatically maintains a local image cache. When you pull an image from a remote registry (like Docker Hub or NVIDIA NGC), Apptainer saves a copy in a hidden directory. If you accidentally delete your local .sif file and try to pull it again, Apptainer will instantly grab it from your local cache instead of downloading gigabytes of data over a network.

To inspect how much total space you are consuming, run this command apptainer cache list . By default, this only shows the total file count and size. To see the specific images names, creation dates and where they were pulled from, add the verbose -v flag. apptainer cache list -v

Note

Under the TYPE column, images from Apptainer Hub appears as shub, while standard Docker/NGC images appear as blob or library/oci

Similarly, if your cluster storage quota is running low, you can clear out cached files using the apptainer cache clean. Running this command will ask to wipe everything. However, if you want to see what exactly would be reomved without actually deleting it, you can use -n or --dry-run flag. Moreover, to wipe out only a specific type of cached image (e.g. clearing out old Apptainer Hub templates while keeping your heavy Docker/NGC layers), you can use apptainer cache clean --type=shub command