How to remove Docker images?

Docker is a great tool to for software development and delivery. It enables you to separate applications from your infrastructure and deliver them softly and quickly.

How to remove Docker images?

Sometimes when we keep creating Docker images on our machine, or even on some cloud running Docker Container it'll soon start to run out of space. In this short post I'd like to share how I get rid of unnecessary Docker images.

The first step is to check the present images on your machine with this command:

$ docker images

The output should be like this:

REPOSITORY              TAG                 IMAGE ID    
mysql                   5.7                 b598110d0fff
mysql                   latest              ed1ffcb5eff3
<none>                  <none>              e81ad38baa90
redis                   latest              dcf9ec9265e0
ruby                    2.6.5-alpine        3304101ccbe9
postgres                latest              f9b3d2f9a593
mongo                   latest              58477a771fb4
rabbitmq                latest              86a895bb41d6
redis                   5.0.3-alpine        3d2a373f46ae

The output shows us the repository, it's the name at Docker Hub repository for the image. The TAG is the version of the image and the Image ID is the ID generated by Docker when we pull an image for our machine.

Before remove the desired image, it's important to know that the image is possibly associated with one or more containers. To check what containers are associated with images use the command below:

$ docker ps -a

The output will show us the ID of the container in our machine, the ID of an image we pulled and the entry command - this is the command to run our dockerized application.

CONTAINER ID        IMAGE                   COMMAND               
b8b33f28e089        ffb1b540cc8f            "/bin/sh -c 'apt-get…"
e2c8159a0ee6        ffb1b540cc8f            "/bin/sh -c 'apt-get…"
8d0910845ea5        ec6c8a057b83            "/bin/sh -c 'apt-get…"
c977dd983867        ec6c8a057b83            "/bin/sh -c 'apt-get…"
94f9fc8e6186        929b84501e14            "/bin/sh -c 'bundle …"
8d5de5c2c7a3        61f362c8bfb9            "/bin/sh -c 'bundle …"
3e3972e6aa86        15cc0f691e7b            "/bin/sh -c 'bundle …"
f3175c20bad5        ed8edff8b2e2            "/bin/sh -c 'bundle …"
f76d4f777146        ed8edff8b2e2            "/bin/sh -c 'bundle …"
4eed76085da4        postgres                "docker-entrypoint.s…"
505fc40d64c0        e81ad38baa90            "/bin/sh -c 'bundle …"
1804e73a047a        redis                   "docker-entrypoint.s…"
3241275444f3        postgres                "docker-entrypoint.s…"
154e700f0e65        postgres                "docker-entrypoint.s…"
28bfc42fdac6        mongo:latest            "docker-entrypoint.s…"
2e15f116cbf2        postgres                "docker-entrypoint.s…"
6ca6f9bd1f1b        rabbitmq:latest         "docker-entrypoint.s…"

To remove the container and the image we will use two commands:

$ docker rm <container_id>
$ docker rmi <image_id>

We can use the -f option for both commands to force the removal of a resource.
Here are the commands I use to remove all images and containers when I need to clean up my laptop.

$ docker ps -aq | xargs docker rm -f
$ docker images -aq | xargs docker rmi -f

Let's break it down. The docker ps is the command to show the running containers, the option -a will show all containers (even not running ones) and the -q option will output only the CONTAINER ID.

The xargs command is to build and execute a command from standard input. In our case we are passing to xargs the container id from the docker ps -aq command and the image id from the docker images -aq command. So, the xargs will build the exact command we need to remove the docker containers and images for each given ID we've got.

Removing Dangling Images

Dangling image means that a new build of the image was created, but wasn't given a name (untaged image). So, the old image becomes dangling. They'll be displayed as when you run docker images

If we need to remove only the dangling images, the command bellow works very fine. Add the option -a to also remove unused images.

$ docker images prune

So, hope this might be useful for you as it is for me.

Thanks for reading.