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Basic Setup and Use of Podman

Podman is a utility provided as part of the libpod library. It can be used to create and maintain containers. The following tutorial will teach you how to set up Podman and perform some basic commands with Podman.

NOTE: the code samples are intended to be run as a non-root user, and use sudo where root escalation is required.

Installing Podman

For installing or building Podman, please see the installation instructions.

Familiarizing yourself with Podman

Running a sample container

This sample container will run a very basic httpd server that serves only its index page.

podman run -dt -p 8080:8080/tcp -e HTTPD_VAR_RUN=/var/run/httpd -e HTTPD_MAIN_CONF_D_PATH=/etc/httpd/conf.d \
                  -e HTTPD_MAIN_CONF_PATH=/etc/httpd/conf \
                  -e HTTPD_CONTAINER_SCRIPTS_PATH=/usr/share/container-scripts/httpd/ \
                  registry.fedoraproject.org/f29/httpd /usr/bin/run-httpd

Because the container is being run in detached mode, represented by the -d in the podman run command, Podman will print the container ID after it has run. Note that we use port forwarding to be able to access the HTTP server. For successful running at least slirp4netns v0.3.0 is needed.

Listing running containers

The Podman ps command is used to list creating and running containers.

podman ps

Note: If you add -a to the ps command, Podman will show all containers.

Inspecting a running container

You can “inspect” a running container for metadata and details about itself. We can even use the inspect subcommand to see what IP address was assigned to the container. As the container is running in rootless mode, an IP address is not assigned and the value will be listed as “none” in the output from inspect.

$ podman inspect -l | grep IPAddress\":
            "SecondaryIPAddresses": null,
            "IPAddress": "",

Note: The -l is a convenience argument for latest container. You can also use the container’s ID instead of -l.

Testing the httpd server

Now that we have the IP address of the container, we can test the network communication between the host operating system and the container using curl. The following command should display the index page of our containerized httpd server.

curl http://<IP_address>:8080

Viewing the container’s logs

You can view the container’s logs with Podman as well:

$ sudo podman logs --latest - - [07/Feb/2018:15:22:11 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.55.1" "-" - - [07/Feb/2018:15:22:30 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.55.1" "-" - - [07/Feb/2018:15:22:30 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.55.1" "-" - - [07/Feb/2018:15:22:31 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.55.1" "-" - - [07/Feb/2018:15:22:31 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.55.1" "-"

Viewing the container’s pids

And you can observe the httpd pid in the container with top.

$ sudo podman top <container_id>
    0 31873 31863  0 09:21 ?        00:00:00 nginx: master process nginx -g daemon off;
  101 31889 31873  0 09:21 ?        00:00:00 nginx: worker process

Checkpointing the container

Checkpointing a container stops the container while writing the state of all processes in the container to disk. With this a container can later be restored and continue running at exactly the same point in time as the checkpoint. This capability requires CRIU 3.11 or later installed on the system. To checkpoint the container use:

sudo podman container checkpoint <container_id>

Restoring the container

Restoring a container is only possible for a previously checkpointed container. The restored container will continue to run at exactly the same point in time it was checkpointed. To restore the container use:

sudo podman container restore <container_id>

After being restored, the container will answer requests again as it did before checkpointing.

curl http://<IP_address>:8080

Migrate the container

To live migrate a container from one host to another the container is checkpointed on the source system of the migration, transferred to the destination system and then restored on the destination system. When transferring the checkpoint, it is possible to specify an output-file.

On the source system:

sudo podman container checkpoint <container_id> -e /tmp/checkpoint.tar.gz
scp /tmp/checkpoint.tar.gz <destination_system>:/tmp

On the destination system:

sudo podman container restore -i /tmp/checkpoint.tar.gz

After being restored, the container will answer requests again as it did before checkpointing. This time the container will continue to run on the destination system.

curl http://<IP_address>:8080

Stopping the container

To stop the httpd container:

sudo podman stop --latest

You can also check the status of one or more containers using the ps subcommand. In this case, we should use the -a argument to list all containers.

sudo podman ps -a

Removing the container

To remove the httpd container:

sudo podman rm --latest

You can verify the deletion of the container by running podman ps -a.

Integration Tests

For more information on how to setup and run the integration tests in your environment, checkout the Integration Tests README.md

More information

For more information on Podman and its subcommands, checkout the asciiart demos on the README.md page.