Removal of Containers and Images

Overview

Teaching: 5 min
Exercises: 5 min

Questions

• How do you cleanup old containers?

• How do you delete images?

Objectives

• Learn how to cleanup after Docker

You can cleanup/remove a container docker rm

docker rm <CONTAINER NAME>

Note: A container must be stopped in order for it to be removed.

Remove old containers

Start an instance of the tutorial container, exit it, and then remove it with docker rm

Solution

docker run sl:latest
docker ps -a
docker rm <CONTAINER NAME>
docker ps -a

CONTAINER ID        IMAGE         COMMAND             CREATED            STATUS                     PORTS               NAMES
<generated id>      <image:tag>   "/bin/bash"         n seconds ago      Exited (0) t seconds ago                       <name>

<generated id>

CONTAINER ID        IMAGE         COMMAND             CREATED            STATUS                     PORTS               NAMES

You can remove an image from your computer entirely with docker rmi

docker rmi <IMAGE ID>

Remove an image

Pull down the Python 2.7 image (2.7-slim tag) from Docker Hub and then delete it.

Solution

docker pull python:2.7-slim
docker images python
docker rmi <IMAGE ID>
docker images python

2.7: Pulling from library/python
<some numbers>: Pull complete
<some numbers>: Pull complete
<some numbers>: Pull complete
<some numbers>: Pull complete
Digest: sha256:<the relevant SHA hash>
Status: Downloaded newer image for python:2.7-slim
docker.io/library/python:2.7-slim

REPOSITORY   TAG        IMAGE ID       CREATED       SIZE
python       3.7-slim   <SHA>          2 weeks ago   <size>
python       2.7-slim   <SHA>          2 years ago   <size>

Untagged: python@sha256:<the relevant SHA hash>
Deleted: sha256:<layer SHA hash>
Deleted: sha256:<layer SHA hash>
Deleted: sha256:<layer SHA hash>
Deleted: sha256:<layer SHA hash>
Deleted: sha256:<layer SHA hash>

REPOSITORY   TAG        IMAGE ID       CREATED       SIZE
python       3.7-slim   <SHA>          2 weeks ago   <size>

Helpful cleanup commands

What is helpful is to have Docker detect and remove unwanted images and containers for you. This can be done with prune, which depending on the context will remove different things.

• docker container prune removes all stopped containers, which is helpful to clean up forgotten stopped containers.
• docker image prune removes all unused or dangling images (images that do not have a tag). This is helpful for cleaning up after builds. It is similar to the more explicit command docker rmi $(docker images -f "dangling=true" -q). Another useful command is docker image prune -a --filter "until=24h", which will remove all images older than 24 hours.
• docker system prune removes all stopped containers, dangling images, and dangling build caches. This is very helpful for cleaning up everything all at once.

Key Points

• Remove containers with docker rm

• Remove images with docker rmi

• Perform faster cleanup with docker container prune, docker image prune, and docker system prune