Docker Cheat Sheet

April 15, 2020 - 5 min read

Cheat Sheet

To make it easier for me, I started some time ago to create a cheat sheet for Docker. Since I don’t want to keep this knowledge only for myself, I share some of the most important CLI commands I need in my daily do-ing.

When you start to deal with continuous integration tools, you quickly get to the point where you also use a private container registry.

Docker provides a very simple way to use a registry and log in with your credentials:

$ docker login registry.gitlab.com

To make the docker login command non-interactive, such as required for GitLab CI, you can set the --password-stdin flag to provide a password via STDIN.

Using STDIN prevents the password from ending up in the shell’s history or log files.

$ echo "${CI_REGISTRY_PASSWORD}" | docker login -u "${CI_REGISTRY_USER}" "${CI_REGISTRY}" --password-stdin

System health

In order to check the current Docker Disk Usage and thus the allocation of the system a simple command

$ docker system df

Purging all unused or dangling Images, Containers, Volumes, and Networks

Docker provides a single command that will clean up any resources — images, containers, volumes, and networks — that are dangling (not associated with a container):

$ docker system prune

To additionally remove any stopped containers and all unused images (not just dangling images), add the -a flag to the command:

$ docker system prune -a

Removing Docker Images

Removing dangling (untagged) Images

Docker images consist of multiple layers. Dangling images are layers that have no relationship to any tagged images. They no longer serve a purpose and consume disk space. They can be located by adding the filter flag, -f with a value of dangling=true to the docker images command. When you’re sure you want to delete them, you can use one of the following commands:

$ docker rmi $(docker images -f "dangling=true" -q)

$ docker image prune

NOTE: If you build an image without tagging it, the image will appear on the list of dangling images because it has no association with a tagged image.

Removing specific Images by Pattern

Sometimes it is necessary to search an image for a certain <<pattern>>. A combination of Docker CLI and grep can help.

$ docker images -a |  grep "<<pattern>>"

If you are comfortable with the search/filter, you can use ‘awk’ to pass the IDs to the Docker CLI:

$ docker image rm $(docker images -a | grep "<<pattern>>" | awk '{print $3}')

$ docker images -a | grep "<<pattern>>" | awk '{print $3}' | xargs docker image rm

NOTE: Instead of image rm you could use the shorter version with rmi

Removing all Images

Also the deletion of all images can be solved with the Docker CLI. To do this, you can simply append -a to the command. -q returns the Image ID, which can be used to pass it on to other commands.

$ docker image rm $(docker images -a -q)

$ docker image rm $(docker image ls -q)

Removing Docker Containers

Similar to the docker images command, you can also add the parameter -a to the docker ps command, which lists the running containers, so that all containers are shown, even those that are no longer running.

The displayed container ID or name can then be reused:

$ docker container rm <<container_id/name>>

It is also possible to display only the exited containers:

$ docker ps -a -f status=exited

Removing specific Containers by Pattern

And similar to the images it works with the containers.

$ docker container rm $(docker ps -a | grep "<<pattern>>" | awk '{print $1}')

$ docker ps -a | grep "<<pattern>>" | awk '{print $1}' | xargs docker container rm

NOTE: In this case {print $1} returns the ID of the container.

Removing all stopped Containers

With the knowledge we have just gained, we can now simply delete all the containers that have exited.

# Historical command
$ docker rm -f $(docker ps -aq -f status=exited)

$ docker container prune

NOTE: We again only pass the ID to the Docker CLI using -q.

Removing all Containers

If we need to remove all containers, the running ones and the stopped ones we can use the following command.

$ docker container rm -f $(docker container ls -aq)

Removing all Volumes

To remove the volumes not used any longer, we can use.

$ docker volume rm $(docker volume ls -q)

$ docker volume prune

Removing all Builder cache

To remove the build cache, we can use.

$ docker builder prune

Stats for all running Containers

The docker stats command is used to display a live stream of container resource usage statistics. This command can be extended to display the statistics of all containers simultaneously.

$ docker ps -q | xargs docker stats

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