Podman Tutorial

A Podman Tutorial

Introduction This is an introduction for the podman tutorial.

Podman Installation Instructions

Please follow the installation process as per this link. Nice to use brew for the installtion process.

Running Podman

brew install podman

Next, create and start your first Podman machine:

podman machine init
podman machine start

You can then verify the installation information using:

podman info

Get Installed Podman version

podman -v

Pulling and Displaying Images

podman pull <Registry>/<user>/<image name>:<tag/version>
podman pull registry.redhat.io/rhel7/rhel:7.9

After the execution of the pull command, the image is stored locally in your system. You can list the images in your system by using the podman images command.

podman images

Container and Container Images

Running and Displaying Containers

The podman run command to create a new container that uses the image.

podman run registry.redhat.io/rhel7/rhel:7.9 echo 'Red Hat'

When the container finishes the execution of echo, the container is stopped because no other process keeps it running.

podman ps

However, stopping a container is not the same as removing a container. Although the container is stopped, Podman does not remove it. You can list all containers (running and stopped) by adding the --all flag to the podman ps command.

podman ps --all
podman ps --all --format=json

You can also automatically remove a container when it exits by adding the --rm option to the podman run command.

podman run --rm registry.redhat.io/rhel7/rhel:7.9 echo 'Red Hat'

You can assign a name to your containers by adding the --name flag to the podman run command.

podman run --name podman_rhel7 registry.redhat.io/rhel7/rhel:7.9 echo 'Red Hat'

Exposing Containers

podman run -p 8080:8080 registry.access.redhat.com/ubi8/httpd-24:latest

If you want the container to run in the background, to avoid the terminal being blocked, then you can use the -d option.

podman run -d -p 8080:8080 registry.access.redhat.com/ubi8/httpd-24:latest

Port Forwarding

A container's network namespace is isolated, which means that a networked application is only accessible within the container. Port forwarding maps a port from the host machine where the container runs to a port inside of a container.

The -p option of the podman run command forwards a port. The option accepts the form HOST_PORT:CONTAINER_PORT.

For example, the following command maps port 80 inside the container to port 8075 on the host machine.

podman run -p 8075:80 my-app

To publish a container to a specific host and to limit the networks it is accessible from, use the following form. Port 80 in the my-app container is available from port 8075 only from the host machine, which is accessible via the localhost 127.0.0.1 IP address.

podman run -p 127.0.0.1:8075:80 my-app

List Port Mappings

To list port mappings for a container, use the podman port command. For example, the following command reveals that port 8010 of the host machine is mapped to port 8008 within the container.

podman port my-app

The --all option lists port mappings for all containers.

podman port --all

Using Environment Variables

You can pass environment variables to a container by using the -e option.

podman run -d -e NAME='Red Hat' -p 8080:8080 registry.access.redhat.com/ubi8/httpd-24:latest

Podman Desktop

Podman Desktop is a graphical user interface, which is used to manage and interact with containers in local environments. It uses the Podman engine by default, and supports other container engines as well, such as Docker. You can download Podman Desktop

podman-desktop

Container Networking Basics

Managing Podman Networks

Podman network management is done via the podman network subcommand. This subcommand includes the following operations:

Creates a new Podman network

 podman network create
 podman network create example-net

This command accepts various options to configure properties of the network, including gateway address, subnet mask, and whether to use IPv4 or IPv6.

Lists existing networks

podman network ls

Lists existing networks and a brief summary of each. Options for this command include various filters and an output format to list other values for each network.

podman network inspect

Outputs a detailed JSON object containing configuration data for the network.

Removes a network

podman network rm

Removes any networks

Removes any networks that are not currently in use by any running containers.

podman network prune

Connects an already running container to or from an existing network. Alternatively, connect containers to a Podman network on container creation by using the --net option. The disconnect command disconnects a container from a network.

podman network connect

For example, the following command creates a new Podman network called example-net:

podman network create example-net

To connect a new container to this Podman network, use the --net option. The following example command creates a new container called my-container, which is connected to the example-net network.

podman run -d --name my-container --net example-net container-image:latest

When you create new containers, you can connect them to multiple networks by specifying network names in a comma-separated list. For example, the following command creates a new container called double-connector that connects to both the postgres-net and redis-net networks.

podman run -d --name double-connector --net postgres-net,redis-net container-image:latest

Alternatively, if the my-container container is already running, then run the following command to connect it to the example-net network:

podman network connect example-net my-container

Networking in Containers

Containers attached to Podman networks are assigned private IP addresses for each network. Other containers in the network can make requests to this IP address. For example, a container called my-app is attached to the apps network. The following command retrieves the private IP address of the container within the apps network.

podman inspect my-app -f '{{.NetworkSettings.Networks.apps.IPAddress}}'

Enabling Domain Name Resolution

When you use the default Podman network, the domain name system (DNS) for other containers in that network is disabled. To enable DNS resolution between containers, create a Podman network and connect your containers to that network.

When using a network with DNS enabled, a container's hostname is the name assigned to the container. For example, if a container is started with the following command, then the other containers on the test-net network can make requests to the first container by using the basic-container hostname. The basic-container hostname resolves to the current IP address of the basic-container container.

podman run --net test-net --name basic-container example-image

Start Processes in Containers

Use the podman exec command to start a new process in a running container. The command uses the following syntax:

podman exec [options] container [command ...]
podman exec httpd cat /etc/httpd/conf/httpd.conf

Additionally, podman exec provides a number of options, such as:

• Use --env or -e to specify environment variables.
• Use --interactive or -i to instruct the container to accept input.
• Use --tty or -t to allocate a pseudo terminal.
• Use --latest or -l to execute the command in the last created container.

The following command sets the ENVIRONMENT variable and then executes the env command to print all environment variables. In this example, the container name is not necessary because the -l option is used

podman exec -e ENVIRONMENT=dev -l env

Open an Interactive Session in Containers

If you open a shell program with the --interactive option, the podman exec executes the shell program and receives your input, but the input is not captured by a terminal:

podman exec -il /bin/bash
pwd 1
ls

BTW: The podman exec -il command is identical to podman exec -i -l.

to open an interactive shell in a running container, combine the --interactive and --tty options:

podman exec -til /bin/bash
pwd
    /opt/app-root/src
exit
    $

Copy Files In and Out of Containers

Use the podman cp command to copy files to and from a running container. The command uses the following syntax:

podman cp [options] [container:]source_path [container:]destination_path

Use the following command to copy the /tmp/logs file from a container with ID a3bd6c81092e to the current directory:

podman cp a3bd6c81092e:/tmp/logs .

Use the following command to copy the nginx.conf file to the /etc/nginx/ directory in a container called nginx:

podman cp nginx.conf nginx:/etc/nginx

Use the following command to copy the nginx.conf file from the nginx-test container to the nginx-proxy container:

podman cp nginx-test:/etc/nginx/nginx.conf nginx-proxy:/etc/nginx

Managing the Container Lifecycle

Listing Containers

You can list running containers with the podman ps command.

podman ps

You can include stopped containers in the output by adding the --all or -a flag to the podman ps command.

podman ps --all

Inspecting Containers

podman inspect 7763097d11ab

In the following command, the Status field of the State object is retrieved for a container called redhat.

podman inspect --format='{{.State.Status}}' redhat

Stopping Containers Gracefully

The following command stops a container with a container ID 1b982aeb75dd.

podman stop 1b982aeb75dd

ou can stop all the running containers by using the --all or -a flag.

podman stop --all

If a container does not respond to the SIGTERM signal, then Podman sends a SIGKILL signal to forcefully stop the container. Podman waits 10 seconds by default before sending the SIGKILL signal. You can change the default behavior by using the --time flag.

podman stop --time=100

Stopping Containers Forcefully

You can send the SIGKILL signal to the container by using the podman kill command. In the following example, a container called httpd is stopped forcefully.

podman kill httpd

Pausing Containers

Both podman stop and podman kill commands eventually send a SIGKILL signal to the container. The podman pause command suspends all processes in the container by sending the SIGSTOP signal.

podman pause 4f2038c05b8c

The podman unpause command resumes a paused container.

podman unpause 4f2038c05b8c

Restarting Containers

Execute the podman restart command to restart a running container. You can also use the command to start stopped containers. The following command restarts a container called nginx.

podman restart nginx

Removing Containers

Use the podman rm command to remove a stopped container. The following command removes a stopped container with the container ID c58cfd4b90df.

podman rm c58cfd4b90df

You can add the --force (or -f) flag to remove the container forcefully.

podman rm c58cfd4b90df --force

You can also add the --all (or -a) flag to remove all stopped containers. This flag fails to remove running containers. The following command removes two containers.

podman rm --all