Docker 'overlay' takes too much size - how to debug?

Question

running df -h I get:

overlay          79G   70G  5.8G  93% /var/lib/docker/overlay2/a7bcb73019b20505a640593453aee3578647e027ccf90a607ad1806a9b25edd4/merged

Any idea how I can check why it takes so much space?

Answer 1

An overlay filesystem, like a bind mount, doesn't use any disk space itself. What's reported is the disk space of the underlying filesystem. In this case, if you run df /var/lib/docker you'll see the same disk space allocated to that underlying filesystem, and you can review what is used on that mount.

If the issue is docker, then docker system prune would be a first step. If that doesn't help and you see significant usage from the /var/lib/docker folder you want to clean, see this answer for additional suggestions.