Symptom:

• Drive space used up even when little space is used by user (e.g. 1TB almost full when user uses <100G).

Diagnosis:

• /var/lib/docker/overlay2 had >773G of data (even when /var/lib/docker/container had little in it)

Solution:

1. Prune space taken up by docker containers using docker prune -a -f. This prunes away all container data.
2. Check that containers have been pruned using docker ps -a.
3. Re-run the container(s) of interest.

References:

• https://forums.docker.com/t/some-way-to-clean-up-identify-contents-of-var-lib-docker-overlay/30604