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Task03.md

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Task 3 - The Ubuntu Image

Great, now let's pull down a different image. Let's pull down the official Ubuntu container image from Docker hub:

docker pull ubuntu

You should see:

ubuntu@ubuntu:~$ docker pull ubuntu
Using default tag: latest
latest: Pulling from library/ubuntu
f3ef4ff62e0d: Pull complete
Digest: sha256:44ab2c3b26363823dcb965498ab06abf74a1e6af20a732902250743df0d4172d
Status: Downloaded newer image for ubuntu:latest
docker.io/library/ubuntu:latest

We can see that it was downloaded:

ubuntu@ubuntu:~$ docker images
REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
ubuntu       latest    597ce1600cf4   46 hours ago   72.8MB

Next, let's run the container in an interactive mode so that we execute various commands from the bash shell within the container. To do that, we need two options:

  • -i --> Interactive, Keep STDIN open even if not attached
  • -t --> Allocate a pseudo-TTY

While we are at it, we will assign a name to the container with the --name option.

So our command becomes:

docker run --name test -it ubuntu bash

And then we see our prompt change. Now we can run some commands that are executed inside the container:

ubuntu@ubuntu:~$ docker run --name test -it ubuntu bash
root@a843c11e5313:/# whoami
root
root@a843c11e5313:/# hostname
a843c11e5313
root@a843c11e5313:/# pwd
/
root@a843c11e5313:/# ls /
bin  boot  dev  etc  home  lib  lib32  lib64  libx32  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@a843c11e5313:/# ls /home
root@a843c11e5313:/# exit
exit
ubuntu@ubuntu:~$

The exit command kills the container executing in the foreground and returns us to our original prompt.

List the container:

ubuntu@ubuntu:~$ docker ps --all
CONTAINER ID   IMAGE     COMMAND   CREATED         STATUS                     PORTS     NAMES
a843c11e5313   ubuntu    "bash"    4 minutes ago   Exited (0) 3 minutes ago             test

We can run the container again by using the docker start command, remembering to pass in the interactive option:

ubuntu@ubuntu:~$ docker start -i test
root@a843c11e5313:/#
root@a843c11e5313:/# exit
exit
ubuntu@ubuntu:~$

If we use the --rm option with the run command, it cleans up the container when the command passed into the container exits:

docker run --name test2 -it --rm ubuntu ls

In this case, the ls command runs in the container, and then the container exits:

ubuntu@ubuntu:~$ docker run --name test2 -it --rm ubuntu ls
bin   dev  home  lib32  libx32  mnt  proc  run   srv  tmp  var
boot  etc  lib   lib64  media   opt  root  sbin  sys  usr
ubuntu@ubuntu:~$

Note that we named the container "test2" but when we run docker ps --all we do not see it listed, because of the --rm switch.


ubuntu@ubuntu:~$ docker ps --all
CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS                         PORTS     NAMES
a843c11e5313   ubuntu    "bash"                   2 hours ago      Exited (0) About an hour ago             test