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Pull and Run Containers

Brief Introduction into Podman

At the time of writing Docker is the most popular and most widely used container solution on the market. Due to licensing restrictions the use of Docker is often forbidden in a larger context if used without a proper license. In the following we are using Podman, an open-source alternative, instead of Docker, but most of the commands can be used with Podman and Docker alike. Please refer to the Setup section for Podman for installation instructions for your OS.

Verify the Podman installation

podman run hello-world

Output

Hello from Docker!
This message shows that your installation appears to be working correctly.

Basic Podman Commands

Now that everything is set up, it is time to issue the first podman commands. Let's pull our first image from Dockerhub. As a start we want to pull this Python image.

podman pull python

Output

Resolved "python" as an alias (/etc/containers/registries.conf.d/000-shortnames.conf)
Trying to pull docker.io/library/python:latest...
Getting image source signatures
Copying blob 9c94b131279a done
Copying blob c485c4ba3831 done
Copying blob d31b0195ec5f done
Copying blob 9b1fd34c30b7 done
Copying blob 4bc8eb4a36a3 done
Copying blob de4cac68b616 done
Copying blob 470924304c24 done
Copying blob 8999ec22cbc0 done
Copying config 28d8ca9ad9 done
Writing manifest to image destination
Storing signatures
28d8ca9ad96db542a2071ad13fa82533a14441b84d52e91ad395d663deb2ec82

The podman pull command fetches the python image from a registry and saves it locally to our system. Use the command podman images to see a list of all images on your system.

podman images

Output

REPOSITORY                   TAG         IMAGE ID          CREATED          SIZE
docker.io/library/python     latest      28d8ca9ad96d      11 days ago      1.03 GB

Let's now run a container based on the python image. To do that we use the command podman run:

podman run python

Nothing really seemed to happen this time. This is not a bug. Many things were going on behind the scenes: When you call the command podman run, the podman client finds the image, loads up the container and runs a command inside the container. We ran podman run python without providing a command, and thus it directly exited again without producing output. Let's try again by providing a command to podman run.

podman run python python3 --version

Output

Python 3.12.2

We now ran the command python3 --version in the container and, as expected, the python version number was printed out to the terminal. Again, once the command finished the container exits. The general pattern for running commands in a container is podman run [options] image-name [command] [arguments].

Hopefully, you noticed that all of this happened pretty quickly. Imagine you needed to boot up a virtual machine, run the command and destroy the VM. That's the speed difference mentioned in the introduction. The podman ps command shows you all containers that are currently running.

podman ps

Output

CONTAINER ID      IMAGE      COMMAND      CREATED        STATUS         PORTS        NAMES

As expected, since no containers are running, we see a blank line. Use podman ps -a to get a more complete output:

podman ps -a

Output

CONTAINER ID        IMAGE                                 COMMAND              CREATED             STATUS                      PORTS               NAMES
bf509388514d        docker.io/library/python:latest       "python3 --version"  7 seconds ago       Exited (0) 6 seconds ago                        hungry_blackwell
71e6eac3b31c        docker.io/library/python:latest       "python3"            12 seconds ago      Exited (0) 11 seconds ago                       flamboyant_hodgkin

You might be wondering now if there is a way to run more than one command in a container. Invoking the run command with the -it flag will give you an interactive tty session in the container. Then you can run as many commands in the container as you want to, like in a normal bash or Python interpreter.

podman run -it python python3

Output

Python 3.12.2 (main, Mar 12 2024, 11:02:14) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

podman run -it python bash

Output

root@43f5d561dcd3:/#

Interestingly, we also get an interactive Python interpreter by only running the command podman run -it python. Keep that in mind, we will see later why this works in that case.

So far, we have had no access to files from the local filesystem inside the container. But you probably want to have exactly that. With Podman, you can easily mount folders inside a container. Supply the -v option when running the podman run command and as an argument pass the absolute path on the local filesystem on the left side and on the right side the absolute path inside the container. Split both paths with a :. You can use -v multiple times in one podman run command. The command below mounts the directory test from the users home-directory to the path /opt/test inside the container.

podman run -v $HOME/test:/opt/test --rm -it alpine:latest sh

Output

Resolved "alpine" as an alias (/etc/containers/registries.conf.d/000-shortnames.conf)
Trying to pull docker.io/library/alpine:latest...
Getting image source signatures
Copying blob 7264a8db6415 done
Copying config 7e01a0d0a1 done
Writing manifest to image destination
Storing signatures
/ #

/ # cd /opt/test
/ # touch foo
/ # exit
$ cd $HOME/test
$ ls

Output

foo

Package Permissions within the Container

Because of permissions and user IDs, it might happen, that you cannot access the files, that were written by the application within Podman. Podman uses the root-user if not specified differently somewhere else, which means, for example, that files, directories, and packages that were written or installed within the container would have user and group root as the default. This may result in an access denied error message if you try to access those artifacts with a non-root user. To avoid that, you have to pass you local user ID to Podman:

-u $(id -u ${USER}):$(id -g ${USER})

podman run --rm -it \
       -u $(id -u ${USER}):$(id -g ${USER}) \
       -v $HOME/test:/opt/test \
       alpine:latest \
       sh

What about the --rm option though? You might have already noticed that we can still see leftover containers from previous runs that even exited by running podman ps -a. Throughout this lesson you will run podman run multiple times. This will leave containers which in turn will occupy disk space. It is necessary to regularly delete old containers from the disk. To do that you can run the podman rm command. Copy the container IDs from the output of podman ps -a and paste them alongside the command.

podman rm bf509388514d 71e6eac3b31c

Output

bf509388514d0d84f2def765a75677dcfd1624d0acf63756319423c087597e74
71e6eac3b31c37ff603e8eb7af4064db1cc0a95afde07d24e6fc0203399d6667

This can be a repetitive task. You can delete a bunch of containers in one go as shown in the following command:

podman container prune

This command deletes all containers that are not running.

One last useful thing: Combine the podman run command with the option --rm as was shown before. This will automatically delete the container once it exits from it. But be careful, this is only useful, if you want to run the container only once. It is definitely gone afterwards and will have to be re-created if you wish to run it again.

Volumes

We have already seen how to mount folders from the host to the container (these are called bind mounts). Volumes are the only way to have persistent data within a container and the reason why so many containers (like databases) use them. Because often it is not needed to access the files from the host system, we can let Podman manage this persistent storage.

podman volume ls

With this command we can list all existing volumes.

podman volume create test_volume

Here we created a volume called test_volume.

podman volume ls

Output

DRIVER    VOLUME NAME
local     test_volume

Volumes are particularly useful because they are OS independent and fully managed by Podman. Some additional advantages of volumes:

  • Volumes are easier to back up or migrate than bind mounts.
  • Volumes can be more safely shared among multiple containers.

In the end, volumes are names for folders on the host (like / or ~). We can see their location on the host, if we inspect a volume.

podman volume inspect test_volume

Output

[
    {
        "Name": "test_volume",
        "Driver": "local",
        "Mountpoint": "/home/username/.local/share/containers/storage/volumes/test_volume/_data",
        "CreatedAt": "2023-09-05T18:19:21.061104666+02:00",
        "Labels": {},
        "Scope": "local",
        "Options": {}
    }
]

We can mount a volume like a folder from a host system by using its name on the left side of the : in -v argument.

podman run -it \
       -v test_volume:/test \
       alpine:latest \
       touch /test/foo

After a volume is unmounted, we can use the following command to remove it.

podman volume rm test_volume

Note: All containers associated with a volume need to be removed beforehand.

Task: Run your own image

Task Description

Your goal in this exercise is to run a Jupyter notebook inside a container. You need to be able to open the Jupyter notebook in the browser of the host system and run Python commands inside. Delete the created container afterwards and make sure, that there are no leftover containers.

  1. Find the right image called docker.io/jupyterhub/singleuser (~300 MB) from Dockerhub and pull it.
  2. Create a folder called jupyter on your local system.
  3. Run a Jupyter container based on the image you just pulled. Bind the port 8888 to localhost. Mount the folder created locally into the container. Note the hints below.
  4. Open the Jupyter notebook in the browser of your host system by opening the link that appears in the terminal: http://127.0.0.1:8888/lab?token=...
  5. Run a simple calculation.
  6. Stop the container and delete the container image.

Hints: Use the option -p 127.0.0.1:8888:8888 to bind the Jupyter notebook port to your host system, while the option -v $(pwd):/home/jovyan mounts the current folder into the container. Please also read the section about user-related configurations and add the following options: --user root -e NB_USER="jovyan" -e CHOWN_HOME=yes -w "/home/jovyan"

Solution

We use the image jupyterhub/singleuser from Dockerhub. Start the container, using the podman run command.

podman run --name jupyter \
    -p 127.0.0.1:8888:8888 \
    -v $(pwd):/home/jovyan \
    --user root \
    -e NB_USER="jovyan" \
    -e CHOWN_HOME=yes \
    -w "/home/jovyan" \
    docker.io/jupyterhub/singleuser:latest
Output 
Trying to pull docker.io/jupyterhub/singleuser:latest...
Getting image source signatures
Copying blob 4f4fb700ef54 done  
Copying blob e307c92eb1bc done  
Copying blob 431ed4043ea7 done  
Copying blob 8258cbb4459c done  
Copying blob 23828d760c7b done  
Copying blob a2ad9d5d9baa done  
Copying blob 4f4fb700ef54 skipped: already exists  
Copying blob d1d25bb03eee done  
Copying blob 86bde7993e17 done  
Copying blob b208a6dc0909 done  
Copying blob 7d056bde2e15 done  
Copying blob 4f4fb700ef54 skipped: already exists  
Copying blob 4f4fb700ef54 skipped: already exists  
Copying blob 3ca42b5c562e done  
Copying blob a14c0913756f done  
Copying blob cbabeb5f45d4 done  
Copying blob 5bf4acbd1377 done  
Copying blob 7b78486634e4 done  
Copying blob 45b9b68cc5f1 done  
Copying blob 4f4fb700ef54 skipped: already exists  
Copying blob a30d8e248e6d done  
Copying blob f82b27d7762b done  
Copying blob 343abc863995 done  
Copying config ac0a460c5e done  
Writing manifest to image destination
Storing signatures
Entered start.sh with args: start-notebook.py
Running hooks in: /usr/local/bin/start-notebook.d as uid: 0 gid: 0
Done running hooks in: /usr/local/bin/start-notebook.d
Ensuring /home/jovyan is owned by 1000:100 
Running hooks in: /usr/local/bin/before-notebook.d as uid: 0 gid: 0
Sourcing shell script: /usr/local/bin/before-notebook.d/10activate-conda-env.sh
Done running hooks in: /usr/local/bin/before-notebook.d
Running as jovyan: start-notebook.py
[I 2024-04-01 14:31:02.170 ServerApp] jupyter_lsp | extension was successfully linked.
[I 2024-04-01 14:31:02.173 ServerApp] jupyter_server_terminals | extension was successfully linked.
[I 2024-04-01 14:31:02.175 ServerApp] jupyterlab | extension was successfully linked.
[I 2024-04-01 14:31:02.178 ServerApp] nbclassic | extension was successfully linked.
[I 2024-04-01 14:31:02.180 ServerApp] notebook | extension was successfully linked.
[I 2024-04-01 14:31:02.355 ServerApp] notebook_shim | extension was successfully linked.
[I 2024-04-01 14:31:02.368 ServerApp] notebook_shim | extension was successfully loaded.
[I 2024-04-01 14:31:02.370 ServerApp] jupyter_lsp | extension was successfully loaded.
[I 2024-04-01 14:31:02.371 ServerApp] jupyter_server_terminals | extension was successfully loaded.
[I 2024-04-01 14:31:02.371 LabApp] JupyterLab extension loaded from /opt/conda/lib/python3.11/site-packages/jupyterlab
[I 2024-04-01 14:31:02.372 LabApp] JupyterLab application directory is /opt/conda/share/jupyter/lab
[I 2024-04-01 14:31:02.372 LabApp] Extension Manager is 'pypi'.
[I 2024-04-01 14:31:02.382 ServerApp] jupyterlab | extension was successfully loaded.
[I 2024-04-01 14:31:02.384 ServerApp] nbclassic | extension was successfully loaded.
[I 2024-04-01 14:31:02.386 ServerApp] notebook | extension was successfully loaded.
[I 2024-04-01 14:31:02.386 ServerApp] Serving notebooks from local directory: /home/jovyan
[I 2024-04-01 14:31:02.386 ServerApp] Jupyter Server 2.13.0 is running at:
[I 2024-04-01 14:31:02.386 ServerApp] http://cf77c48ef980:8888/lab?token=b24f3f9e6d5aed33c7877fb75386bdd2e4de46ab6ba42e0a
[I 2024-04-01 14:31:02.386 ServerApp]     http://127.0.0.1:8888/lab?token=b24f3f9e6d5aed33c7877fb75386bdd2e4de46ab6ba42e0a
[I 2024-04-01 14:31:02.386 ServerApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[C 2024-04-01 14:31:02.388 ServerApp] 

    To access the server, open this file in a browser:
        file:///home/jovyan/.local/share/jupyter/runtime/jpserver-21-open.html
    Or copy and paste one of these URLs:
        http://cf77c48ef980:8888/lab?token=b24f3f9e6d5aed33c7877fb75386bdd2e4de46ab6ba42e0a
        http://127.0.0.1:8888/lab?token=b24f3f9e6d5aed33c7877fb75386bdd2e4de46ab6ba42e0a
[I 2024-04-01 14:31:02.713 ServerApp] Skipped non-installed server(s): bash-language-server, dockerfile-language-server-nodejs, javascript-typescript-langserver, jedi-language-server, julia-language-server, pyright, python-language-server, python-lsp-server, r-languageserver, sql-language-server, texlab, typescript-language-server, unified-language-server, vscode-css-languageserver-bin, vscode-html-languageserver-bin, vscode-json-languageserver-bin, yaml-language-server

When your container is running you can open your browser at http://126.0.0.1:8888/lab?token=.... After you closed the session you can remove it, using podman rm [name].

podman rm jupyter

Output

jupyter

podman ps -a

Output

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES