Warning: read the full article before typing commands you may regret.
If you are a docker user (may it be in production or on your development
machine), you may have accumulated quite a bit of now useless data. There are
some existing tools to clean your daemon of unused images and containers (like
docker-gc), but since the docker API 1.25 docker has an easy to
prune command that could me good enough for you.
Basic usage is pretty simple:
$ sudo docker system prune WARNING! This will remove: - all stopped containers - all networks not used by at least one container - all dangling images - all build cache Are you sure you want to continue? [y/N] y Deleted Containers: deleted: sha256:ea43728b2d10e7b0fe24036f9531caac96bd02f779b95a6620110f00ccd3b002 deleted: sha256:022db612b3070971ce7d51778806a1f995a9c3aa1a741a6c0be0bca603787387 ... approximately 2 gajillion hashes later... Total reclaimed space: 5.64GB
That’s nice, but it does not clean everything unused. For that you should add
--all option to remove every image and not only the dangling ones:
WARNING! This will remove: - all stopped containers - all networks not used by at least one container - all images without at least one container associated to them - all build cache Are you sure you want to continue? [y/N] y ... moar hashes... Total reclaimed space: 26.78GB
Of course that may not be ideal. Having caches is pretty useful after all. And
there is just the option for that:
--filter (only available starting at API
1.28). At the time of my writing there are only two filters:
label. In my case I only use the
until one which allows you to clean
everything older than a specified timestamp.
Of course I don’t put a timestamp in the command, I use
date to generate a
timestamp based on a human readable date:
$ sudo docker system prune --all --filter until=$(date -d "1 month ago" +%s)
This command uses a substitution via
$( command ), this allows you to get the
result of a command and inject it in another one as a string. The date command
itself is decomposed as:
date -d <time description> <time format>, where
+%s is the format to get a timestamp. You can check
man date for more info.
And voilà I rarely need the cache to be older than a month on my laptop (and one month is already pretty conservative, but that’s because I rarely have a good internet so I cache as much as I can).
Finally, if you feel adventurous enough you can add the
--force option so
that the command will not ask for confirmation. I use the following in a
cronjob on my continuous integration server:
$ sudo docker system prune --force --all --filter until=$(date -d "1 week ago" +%s)
A note about
sudo: on my dev machine (which is a GNU/Linux system) I only
use docker via
sudo because not doing so mean that your user has the same
power as root all the time. This is due to the fact that the docker daemon is a
privileged process running as root. See the official Docker