To cleanup unused/dnagling docker images: sudo docker image prune

To cleanup ununsed volumes: sudo docker volume prune

To list current docker images: sudo docker images

To remove docker image by image_id: sudo docker rmi <your_image_id1> <your_image_id2>

(sometimes, docker rmi command will throw up errors like:
Error response from daemon: conflict: unable to delete 78f7412b7923 (must be forced) - image is being used by stopped container ebfe07787e7c

This means there are some stopped docker containers using those images. Run this command to find and delete all stopped docker containers: sudo docker rm $(sudo docker ps -q -a)

Best Practice

First run sudo docker image prune. This command also frees up any used volumes automatically and tells you how much disk space got freed.

Then run sudo docker images . This will show current images. If you see something like this

(i)23:46 $ sudo docker images
REPOSITORY                                            TAG           IMAGE ID       CREATED         SIZE
registry.heroku.com/herokudeemo/web                   latest        01c19839a389   2 days ago      91.5MB
rust                                                  latest        9333a9f0c0a6   2 days ago      1.23GB
<none>                                                <none>        78f7412b7923   4 days ago      14.4GB
<none>                                                <none>        b763fba2a7c4   4 days ago      14.4GB
<none>                                                <none>        300133543a17   6 days ago      14.4GB
<none>                                                <none>        a87b7bff727b   7 days ago      14.4GB
<none>                                                <none>        59d8fb4c96c9   7 days ago      14.4GB
postgres                                              12            e782ad565d74   4 weeks ago     314MB
postgres                                              latest        26c8bcd8b719   4 weeks ago     314MB
debian                                                buster-slim   48e774d3c4f5   4 weeks ago     69.3MB
rust                                                  1.49          00150f445191   3 months ago    1.25GB
hello-world                                           latest        bf756fb1ae65   16 months ago   13.3kB

Here there are still some images with REPOSITORY: <none> and TAG:<none>. These images are supposed to be pruned but could not because there are some stopped docker containers still referring them. So first remove all stopped docker containers: sudo docker rm $(sudo docker ps -q -a)

Now run the prune command again to remove dangling images: sudo docker image prune

If you run docker images now, you should see all dangling images gone.