Quick install

This quick-install script works if you are running the docker registry image using docker-compose and the service in docker-compose.yml is called registry. I recommend to use our example on how to install the docker registry for Gitlab (not yet available).

Run this in the directory where docker-compose.yml  is located!

wget -qO- https://techoverflow.net/scripts/install-registry-autocleanup.sh | sudo bash

Need an explanation (or not using docker-compose)?

Docker registry instances will store every version of every image you push to them, so especially if you are in a continous integration environment you might want to do periodic cleanups that delete all images without a tag.

The command to do that is

registry garbage-collect /etc/docker/registry/config.yml -m

You can use a systemd service like

[Unit]
Description=registry-gc

[Service]
Type=oneshot
ExecStart=/usr/local/bin/docker-compose exec -T registry bin/registry garbage-collect /etc/docker/registry/config.yml -m
WorkingDirectory=/opt/my-registry

and a timer like

[Unit]
Description=registry-gc

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target

to run the command daily. You need to adjust both the WorkingDirectory and the exact docker-compose exec command to suit your needs.

Copy both files to /etc/systemd/system and enable the timer using

sudo systemctl enable registry-gc.timer

and you can run it manually at any time using

sudo systemctl start registry-gc.service

Problem:

In your Gitlab build jobs that use docker you see error messages like

Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.40/auth: dial unix /var/run/docker.sock: connect: permission denied

Solution:

usermod -a -G docker gitlab-runner

to give the user running the jobs permission to access docker resources then restart the server/VM on which the runner is installed !

Still doesn’t work? Check if you have installed docker correctly. We recommend to use our automated install script, see How to install docker and docker-compose on Ubuntu in 30 seconds.

Note: This will not only remove docker images without a tag but all docker images not associated to a running or stopped container. See our previous post How to automatically cleanup (prune) docker images daily in case this is not the desired behaviour.

docker image prune provides an easy way to remove “unused” docker images from a system and hence fixes or significantly delays docker eating up all your disk space on e.g. automated disk space.

I created a systemd-timer based daily image removal routine using TechOverflow’s Simple systemd timer generator.

Quick install using

wget -qO- https://techoverflow.net/scripts/install-cleanup-docker-all.sh | sudo bash

This is the script which automatically creates & installs both systemd config files.

#!/bin/sh
# This script installs automated docker cleanup.
# onto systemd-based systems.
# See https://techoverflow.net/2020/02/04/how-to-remove-all-docker-images-that-are-not-associated-to-a-container/
# for details on what images are removed.
# It requires that docker is installed properly

cat >/etc/systemd/system/PruneDockerAll.service <<EOF
[Unit]
Description=PruneDockerAll

[Service]
Type=oneshot
ExecStart=/bin/bash -c "docker image ls --format '{{.ID}}' | xargs docker image rm ; true"
WorkingDirectory=/tmp
EOF

cat >/etc/systemd/system/PruneDockerAll.timer <<EOF
[Unit]
Description=PruneDockerAll

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target
EOF

# Enable and start service
systemctl enable PruneDockerAll.timer && sudo systemctl start PruneDockerAll.timer

To view the logs, use

journalctl -xfu PruneDockerAll.service

To view the status, use

sudo systemctl status PruneDockerAll.timer

To immediately cleanup your docker images, use

sudo systemctl start PruneDockerAll.service

Removing all docker containers that are currently stopped is simple:

docker container prune

In case you want to skip the Are you sure you want to continue? [y/N] confirmation, use:

docker container prune -f

Also see our post on How to remove all docker images that are not associated to a container.

In our previous post we showed how to prune docker images to free up space on your hard drive. However, this approach will not remove images that have tags (i.e. names) associated with them.

Often you want to remove all images that are not required by one of the containers (both running and stopped containers).

This is pretty easy:

docker image ls --format '{{.ID}}' | xargs docker image rm

This command will list all image IDs using docker image ls --format '{{.ID}}' and run docker image rm for every image ID.

Since docker image rm will fail for images that are associated to either a running or a stopped container (hence that image won’t be deleted), this will only delete those images that are not associated to any container.

In case you get a lot of those error messages as output from the command:

Error response from daemon: conflict: unable to delete 1f9cfa8dc305 (cannot be forced) - image is being used by running container 22a27af7d595
Error response from daemon: conflict: unable to delete 9af515ad5c74 (must be forced) - image is being used by stopped container 2ebcbd936841

don’t worry, that’s fine, that just means one of your images is associated to a container and hence won’t be deleted.

Use --format  '{{.ID}}':

docker container ls --format '{{.ID}}'

Use --format  '{{.ID}}':

docker image ls --format '{{.ID}}'

Problem:

You are trying to run a docker bitnami/mariadb container but when you try to start it up, you see an error message like

mariadb_1   | mkdir: cannot create directory '/bitnami/mariadb': Permission denied

Solution:

bitnami containers mostly are non-root-containers, hence you need to adjust the permissions for the data directory mapped onto the host.

First, find out what directory your /bitnami is mapped to on the host. For example, for

services:
     mariadb:
         image: 'bitnami/mariadb:latest'
         environment:
             - ALLOW_EMPTY_PASSWORD=yes
         volumes:
             - '/var/lib/my_docker/mariadb_data:/bitnami'

it is mapped to /var/lib/my_docker/mariadb_data.

Now chown this directory to 1001:1001 since the image is using UID 1001 as the user running the command:

sudo chown -R 1001:1001 [directory]

for example

sudo chown -R 1001:1001 /var/lib/my_docker/mariadb_data