docker rmi

Learn to remove images with docker rmi.

docker rmi

docker rmi (docker image rm) deletes an image from the local store. If a container (running or stopped) uses the image, removal is refused; the container must be removed first:

$ docker rmi nginx:alpine
Error response from daemon: conflict: unable to remove repository reference "nginx:alpine" (must force) - container 7c2f4a9e1b3d is using its referenced image
$ docker rm web && docker rmi nginx:alpine
Untagged: nginx:alpine
Deleted: sha256:a5b6c7d8…

Bulk cleanup

Instead of deleting one by one, prune commands are used:

docker image prune          # only dangling images
docker image prune -a       # all images no container uses
docker image prune -a --filter "until=168h"   # those older than a week
docker rmi $(docker images -q -f dangling=true)

-a should be used carefully; images you use often are deleted too and need to be pulled again.

Exercise Image cleanup

Write three commands: force-remove the web container; delete the nginx:alpine image; then clean up the dangling images without asking for confirmation.

Show example solution

docker rm -f web
docker rmi nginx:alpine
docker image prune -f

Test yourself

For an image with several tags, what does docker rmi api:1.0 do?
- It deletes the containers
- It removes only that tag; the image stays with the other tags
- It deletes all tags and the image
- It errors
Show answer

It removes only that tag; the image stays with the other tags — When the last tag goes, the image is deleted too ("Untagged" and "Deleted").

Delete all unused images.

docker image prune ____ -f

Show answer

docker image prune -a -f

Match.

docker rmi

Deletes an image
Untagged

Tag removed
image prune

Cleans dangling ones
prune -a

All unused

Next lesson: docker pull

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