Free Docker Disk Space

If you are running out of disk space on your docker host, you can free up some space by removing unused docker images, containers, and volumes. I am running docker-compose and always watch the logs, since the service is not high scale yet, so the log files fill up. This means from time to time I need to free some disk space.

TL;DR Here are some commands to free up disk space:

# remove all stopped containers
docker container prune

# remove all unused images
docker image prune

# remove all unused volumes
docker volume prune

# remove all unused networks
docker network prune

The Log Files?

The log files are those that eat up space on my disk, I think. So I also remove them from time to time:

# remove all logs
sudo rm /var/lib/docker/containers/*/*-json.log

To show a sum of all the disk space docker uses:

> docker system df
TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          14        7         10.25GB   7.906GB (77%)
Containers      7         6         2.005MB   0B (0%)
Local Volumes   63        3         247.5MB   0B (0%)
Build Cache     167       0         632.9kB   632.9kB

They are not the ones eating up the space. So Moving on, to find it out.

It's Something Else

Now I need some linux skills, I guess it's a dummy move, but I am going down to the root cd / and run du -h -d1 . which shows me a readable list of all dirs under / and the disk space they occupy.

I see that /var is the one that eats up the most space, so I go there and run du -h -d1 . again.

In the end it's 11G that are in the overlay2 dir, see here:

> du -h -d1 .
24M	  ./image
4.0K  ./containers
4.0K  ./swarm
84K	  ./network
225M  ./volumes
16K	  ./plugins
16M	  ./buildkit
11G	  ./overlay2
4.0K  ./runtimes
4.0K  ./tmp
11G	.

After reading around a bit, it seems docker builder prune will clean up the build cache, let me try this. The worst that can happen is that the next docker build will take forever, but I can live with that.

> du -h -d1 .
9.5M    ./image
4.0K	./containers
4.0K	./swarm
84K	    ./network
225M	./volumes
16K	    ./plugins
16M	    ./buildkit
3.9G	./overlay2
4.0K	./runtimes
4.0K	./tmp
4.1G	.

Oh wow, I won 7G of disk space back. That's nice.