When you pull or build an image from a remote source, Apptainer caches the SIF images and the layers used to build the image. The next time the same image is pulled or run, Apptainer uses the cached version, avoiding re-downloads if the image is frequently used in a job script.

By default on TACC Vista, this cache is located in the scratch file system at /scratch/<number>/<user>/apptainer_cache. It's an ideal location because container images can be very large, and the scratch file system is not subject to quotas and is designed for temporary storage. On other systems, you can check where your cache lives by echoing the APPTAINER_CACHEDIR environment variable (echo $APPTAINER_CACHEDIR). If it's unset, Apptainer will use $HOME/.apptainer/cache as default.

You can clear the cache manually by deleting the contents of the folder or using the following commands. Removing the cache will not cause issues in job scripts, other than requiring an image to be re-downloaded the next time it is pulled.