Docker is a great tool, and I can't imagine myself managing my servers without it anymore.
But if you are not careful, disk space can be a concern.
docker system df will show you how much disk space is used and with
-v flag (verbose), you can see the unique image size for each image.
# docker system df TYPE TOTAL ACTIVE SIZE RECLAIMABLE Images 17 16 3.583GB 582.8MB (16%) Containers 37 37 6.162MB 0B (0%) Local Volumes 16 16 33B 0B (0%) Build Cache 0B 0B
As you can see I have 17 images but only 16 are active, with a total of
docker image ls and I can see that it is an older version of my ghost blog, so a
docker system prune -a and problem solved.
One more thing,
docker system prune -a don't remove dangling volumes, for that you need to run
docker volume rm $(docker volume ls -q --filter dangling=true)