How to Add Podman Container Images on AlmaLinux

Podman is a containerization platform that allows developers and administrators to run and manage containers without needing a daemon process. Unlike Docker, Podman operates in a rootless manner by default, enhancing security and flexibility. AlmaLinux, a community-driven, free, and open-source Linux distribution, is highly compatible with enterprise use cases, making it an excellent choice for running Podman. This blog post will guide you step-by-step on adding Podman container images to AlmaLinux.

Introduction to Podman and AlmaLinux

What is Podman?

Podman is a powerful tool for managing OCI (Open Container Initiative) containers and images. It is widely regarded as a more secure alternative to Docker, thanks to its daemonless and rootless architecture. With Podman, you can build, run, and manage containers and even create Kubernetes YAML configurations.

Why AlmaLinux?

AlmaLinux, a successor to CentOS, is a robust and reliable platform suited for enterprise applications. Its stability and compatibility with Red Hat Enterprise Linux (RHEL) make it an ideal environment for running containers.

Combining Podman with AlmaLinux creates a powerful, secure, and efficient system for modern containerized workloads.

Prerequisites

Before you begin, ensure the following:

1. AlmaLinux System Ready: You have an up-to-date AlmaLinux system with sudo privileges.
2. Stable Internet Connection: Required to install Podman and fetch container images.
3. SELinux Considerations: SELinux should be in a permissive or enforcing state.
4. Basic Linux Knowledge: Familiarity with terminal commands and containerization concepts.

Installing Podman on AlmaLinux

Step 1: Update Your System

Begin by updating your AlmaLinux system to ensure you have the latest software and security patches:

sudo dnf update -y

Step 2: Install Podman

Podman is available in the default AlmaLinux repositories. Use the following command to install it:

sudo dnf install -y podman

Step 3: Verify Installation

After the installation, confirm that Podman is installed by checking its version:

podman --version

You should see output similar to:

podman version 4.x.x

Step 4: Enable Rootless Mode (Optional)

For added security, consider running Podman in rootless mode. Simply switch to a non-root user to leverage this feature.

sudo usermod -aG podman $USER
newgrp podman

Fetching Container Images with Podman

Podman allows you to pull container images from registries such as Docker Hub, Quay.io, or private registries.

Step 1: Search for Images

Use the podman search command to find images:

podman search httpd

This will display a list of available images related to the httpd web server.

Step 2: Pull Images

To pull an image, use the podman pull command:

podman pull docker.io/library/httpd:latest

The image will be downloaded and stored locally. You can specify versions (tags) using the :tag syntax.

Adding Podman Container Images

There are various ways to add images to Podman on AlmaLinux:

Option 1: Pulling from Public Registries

The most common method is to pull images from public registries like Docker Hub. This was demonstrated in the previous section.

podman pull docker.io/library/nginx:latest

Option 2: Importing from Local Files

If you have an image saved as a TAR file, you can import it using the podman load command:

podman load < /path/to/image.tar

The image will be added to your local Podman image repository.

Option 3: Building Images from Dockerfiles

You can create a custom image by building it from a Dockerfile. Here’s how:

1. Create a Dockerfile:

FROM alpine:latest
RUN apk add --no-cache nginx
CMD ["nginx", "-g", "daemon off;"]

2. Build the image:

podman build -t my-nginx .

This will create an image named my-nginx.

Option 4: Using Private Registries

If your organization uses a private registry, authenticate and pull images as follows:

1. Log in to the registry:

podman login myregistry.example.com

2. Pull an image:

podman pull myregistry.example.com/myimage:latest

Managing and Inspecting Images

Listing Images

To view all locally stored images, run:

podman images

The output will display the repository, tags, and size of each image.

Inspecting Image Metadata

For detailed information about an image, use:

podman inspect <image-id>

This command outputs JSON data containing configuration details.

Tagging Images

To tag an image for easier identification:

podman tag <image-id> mytaggedimage:v1

Removing Images

To delete unused images, use:

podman rmi <image-id>

Troubleshooting Common Issues

1. Network Issues While Pulling Images

• Ensure your firewall is not blocking access to container registries.
• Check DNS resolution and registry availability.

ping docker.io

2. SELinux Denials

If SELinux causes permission issues, review logs with:

sudo ausearch -m avc -ts recent

You can temporarily set SELinux to permissive mode for troubleshooting:

sudo setenforce 0

3. Rootless Mode Problems

Ensure your user is added to the podman group and restart your session.

sudo usermod -aG podman $USER
newgrp podman

Conclusion

Adding Podman container images on AlmaLinux is a straightforward process. By following the steps outlined in this guide, you can set up Podman, pull container images, and manage them efficiently. AlmaLinux and Podman together provide a secure and flexible environment for containerized workloads, whether for development, testing, or production.

If you’re new to containers or looking to transition from Docker, Podman offers a compelling alternative that integrates seamlessly with AlmaLinux. Take the first step towards mastering Podman today!

By following this guide, you’ll have a fully functional Podman setup on AlmaLinux, empowering you to take full advantage of containerization. Have questions or tips to share? Drop them in the comments below!