Verify that there are no docker images on the local system:
sudo docker images
Note that if we try to run the docker images command with out sudo we get a permissions error:
ubuntu@ubuntu:~$ docker images
Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get "http://%2Fvar%2Frun%2Fdocker.sock/v1.24/images/json": dial unix /var/run/docker.sock: connect: permission denied
We can fix that by adding the "ubuntu" user to the "docker" group:
sudo usermod -aG docker ubuntu
newgrp docker # Trick to load new group permissions
Now we can run docker images without being root
Next, run the Docker version of the classic 'hello world' test:
docker run hello-world
You should see output that looks like the following:
ubuntu@ubuntu:~$ docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
2db29710123e: Pull complete
Digest: sha256:9ade9cc2e26189a19c2e8854b9c8f1e14829b51c55a630ee675a5a9540ef6ccf
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
(amd64)
3. The Docker daemon created a new container from that image which runs the
executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it
to your terminal.
To try something more ambitious, you can run an Ubuntu container with:
$ docker run -it ubuntu bash
Share images, automate workflows, and more with a free Docker ID:
https://hub.docker.com/
For more examples and ideas, visit:
https://docs.docker.com/get-started/
Let's rerun the docker images and see what changed:
ubuntu@ubuntu:~$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-world latest feb5d9fea6a5 8 days ago 13.3kB
Ok, great. We don't need that image around anymore. So what command do we need to delete the image? Run docker help to see a list of all the possible docker commands.
It looks like it would be docker rmi, so let's try it:
ubuntu@ubuntu:~$ docker rmi hello-world
Error response from daemon: conflict: unable to remove repository reference "hello-world" (must force) - container 39c0bbdce667 is using its referenced image feb5d9fea6a5
Well, that didn't work. We can't remove the image while there is a container referencing it. Let's see what containers are running, using docker ps
ubuntu@ubuntu:~$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
Well, that didn't show us what we wanted to see, let's rerun it with the --all option:
ubuntu@ubuntu:~$ docker ps --all
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
39c0bbdce667 hello-world "/hello" About a minute ago Exited (0) About a minute ago nifty_turing
The --all option shows all containers, not just the running containers. (For more info see https://docs.docker.com/engine/reference/commandline/ps/)
Now that we know the container id that is referencing our hello-world image, we can delete it using the docker rm command, as follows:
docker rm 39c0bbdce667
Now if we rerun the docker ps --all command, we see that the container is gone:
ubuntu@ubuntu:~$ docker ps --all
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
Once the container is zapped, we can delete the image:
ubuntu@ubuntu:~$ docker rmi hello-world
Untagged: hello-world:latest
Untagged: hello-world@sha256:9ade9cc2e26189a19c2e8854b9c8f1e14829b51c55a630ee675a5a9540ef6ccf
Deleted: sha256:feb5d9fea6a5e9606aa995e879d862b825965ba48de054caab5ef356dc6b3412
Deleted: sha256:e07ee1baac5fae6a26f30cabfe54a36d3402f96afda318fe0a96cec4ca393359
And just to confirm that it is actually deleted:
ubuntu@ubuntu:~$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE