Cant remove <none> images and do they need extra disk space?

Hello together.

First time in this Forum. Hope this is the right category.

So I tried to build my custom image from the official Redash Image (version 8.0.0.b32245) and the Dockerfile in place. For that I used the command docker build . --no-cache -t redash/oracle:v9.

Everything worked as expected. But when I list all images with docker images -a there are a lot of none images. According to this ressource this are the “good ones” and don’t use any disk space.

As you can see in the screenshot, they seem to use a lot of disk space.

My question is, does each image use the size in the right column? And is there a way to delete them? If I try it with the docker rmi <imageID> command, there is a Error:

Error response from daemon: conflict: unable to delete d1cc2eb53be3 (cannot be forced) - image has dependent child images

Thanks a lot.

OS Version/build: Debian Buster (x86_64 GNU/Linux)

App version: Docker 19.03.4

No, the size you see in the list is the sum of all layers in the image. The layers can be shared between images, so this number never reflects the actual size on your disk.

You should first find the images that are not related to others with

docker image ls -f 'dangling=true'

These are the images you can delete. To delete them all at once (if you are really sure about that) run

docker image rm $(docker image ls -f 'dangling=true' -q)