There is a difference between docker images and docker containers. Check this SO Question.
In short, a container is a runnable instance of an image. which is why you cannot delete an image if there is a running container from that image. You just need to delete the container first.
docker ps -a # Lists containers (and tells you which images they are spun from)
docker images # Lists images
docker rm <container_id> # Removes a stopped container
docker rm -f <container_id> # Forces the removal of a running container (uses SIGKILL)
docker rmi <image_id> # Removes an image
# Will fail if there is a running instance of that image i.e. container
docker rmi -f <image_id> # Forces removal of image even if it is referenced in multiple repositories,
# i.e. same image id given multiple names/tags
# Will still fail if there is a docker container referencing image
Update for Docker 1.13+ [Since Jan 2017]
In Docker 1.13, we regrouped every command to sit under the logical object it’s interacting with
Basically, above commands could also be rewritten, more clearly, as:
docker container ls -a
docker image ls
docker container rm <container_id>
docker image rm <image_id>
Also, if you want to remove EVERYTHING you could use:
docker system prune -a
WARNING! This will remove:
- all stopped containers
- all networks not used by at least one container
- all unused images
- all build cache