Prune your Docker

A friendly reminder to run docker system prune regularly on production servers.

I was updating a Docker image when I got a ‘No space left on device’ error.

My /var/lib/docker was taking 95GB(!) of storage. So I checked docker it was indeed the problem:

$ docker system df
TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          48        17        76.17GB   71.32GB (93%)
Containers      23        21        164.1MB   0B (0%)
Local Volumes   11        10        3.478GB   0B (0%)
Build Cache     8         0         0B        0B

Docker image bloat happens because when I update containers, I use docker compose pull followed by docker compose up -d. This keeps both the old and new images on disk.

Solution: run docker system prune after upgrade operations, but since we don’t rely on good habits on production servers, add a Cron job to do this regularly.

crontab -e

Add this line to run pruning at midnight daily.

0 0 * * * /usr/bin/docker system prune -af