How to Use Podman Containers by Common Users on AlmaLinux

Containerization has revolutionized software development, making it easier to deploy, scale, and manage applications. Among container engines, Podman has emerged as a popular alternative to Docker, offering a daemonless, rootless, and secure way to manage containers. AlmaLinux, a community-driven Linux distribution with enterprise-grade reliability, is an excellent platform for running Podman containers.

This guide explains how common users can set up and use Podman on AlmaLinux, providing detailed instructions, examples, and best practices.

Why Choose Podman on AlmaLinux?

Before diving into the details, let’s explore why Podman and AlmaLinux are a perfect match for containerization:

• Podman’s Advantages:

  • No daemon required, which reduces system resource usage.
  • Rootless mode enhances security by allowing users to run containers without administrative privileges.
  • Compatibility with Docker CLI commands makes migration seamless.

• AlmaLinux’s Benefits:

  • Enterprise-grade stability and compatibility with Red Hat Enterprise Linux (RHEL).
  • A community-driven and open-source Linux distribution.

Setting Up Podman on AlmaLinux

Step 1: Install Podman

First, install Podman on your AlmaLinux system. Ensure your system is up to date:

sudo dnf update -y
sudo dnf install podman -y

Verify Installation

After installation, confirm the Podman version:

podman --version

Step 2: Rootless Podman Setup

One of Podman’s standout features is its rootless mode, allowing common users to manage containers without requiring elevated privileges.

Enable User Namespace

Rootless containers rely on Linux user namespaces. Ensure they are enabled:

sysctl user.max_user_namespaces

If the output is 0, enable it by adding the following line to /etc/sysctl.conf:

user.max_user_namespaces=28633

Apply the changes:

sudo sysctl --system

Test Rootless Mode

Log in as a non-root user and run a test container:

podman run --rm -it alpine sh

This command pulls the alpine image, runs it interactively, and deletes it after exiting.

Basic Podman Commands for Common Users

Here’s how to use Podman for common container operations:

1. Pulling Images

Download container images from registries like Docker Hub:

podman pull nginx

View Downloaded Images

List all downloaded images:

podman images

2. Running Containers

Start a container using the downloaded image:

podman run -d --name my-nginx -p 8080:80 nginx

Explanation:

• -d: Runs the container in detached mode.
• --name my-nginx: Assigns a name to the container.
• -p 8080:80: Maps port 8080 on the host to port 80 inside the container.

Visit http://localhost:8080 in your browser to see the Nginx welcome page.

3. Managing Containers

List Running Containers

To view all active containers:

podman ps

List All Containers (Including Stopped Ones)

podman ps -a

Stop a Container

podman stop my-nginx

Remove a Container

podman rm my-nginx

4. Inspecting Containers

For detailed information about a container:

podman inspect my-nginx

View Container Logs

To check the logs of a container:

podman logs my-nginx

5. Using Volumes for Persistent Data

Containers are ephemeral by design, meaning data is lost when the container stops. Volumes help persist data beyond the container lifecycle.

Create a Volume

podman volume create my-volume

Run a Container with a Volume

podman run -d --name my-nginx -p 8080:80 -v my-volume:/usr/share/nginx/html nginx

You can now store persistent data in the my-volume directory.

Working with Podman Networks

Containers often need to communicate with each other or the outside world. Podman’s networking capabilities make this seamless.

Create a Network

podman network create my-network

Connect a Container to a Network

Run a container and attach it to the created network:

podman run -d --name my-container --network my-network alpine

Inspect the Network

View details about the network:

podman network inspect my-network

Podman Compose for Multi-Container Applications

Podman supports Docker Compose files via Podman Compose, allowing users to orchestrate multiple containers easily.

Install Podman Compose

Install the Python-based Podman Compose tool:

pip3 install podman-compose

Create a docker-compose.yml File

Here’s an example for a web application:

version: '3.9'

services:
  web:
    image: nginx
    ports:
      - "8080:80"

  db:
    image: postgres
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: password

Run the Compose File

Navigate to the directory containing the file and run:

podman-compose up

Use podman-compose down to stop and remove the containers.

Rootless Security Best Practices

Running containers without root privileges enhances security, but additional measures can further safeguard your environment:

1. Use Non-Root Users Inside Containers
   Ensure containers don’t run as root by specifying a user in the Dockerfile or container configuration.

2. Limit Resources
   Prevent containers from consuming excessive resources by setting limits:

   podman run -d --memory 512m --cpus 1 nginx
   

3. Scan Images for Vulnerabilities
   Use tools like Skopeo or Trivy to analyze container images for security flaws.

Troubleshooting Common Issues

1. Container Fails to Start

Check the logs for errors:

podman logs <container-name>

2. Image Not Found

Ensure the image name and tag are correct. Pull the latest version if needed:

podman pull <image-name>

3. Podman Command Not Found

Ensure Podman is installed and accessible in your PATH. If not, re-install it using:

sudo dnf install podman -y

Best Practices for Common Users

1. Use Podman Aliases: Simplify commands with aliases, e.g., alias pps='podman ps'.

2. Clean Up Unused Resources: Remove dangling images and stopped containers:

   podman system prune
   

3. Keep Podman Updated: Regular updates ensure you have the latest features and security fixes.

4. Enable Logs for Debugging: Always review logs to understand container behavior.

Conclusion

Podman on AlmaLinux offers a secure, efficient, and user-friendly platform for running containers, even for non-root users. Its compatibility with Docker commands, rootless mode, and robust features make it an excellent choice for developers, sysadmins, and everyday users.

By following this guide, you now have the tools and knowledge to set up, run, and manage Podman containers on AlmaLinux. Experiment with different configurations, explore multi-container setups, and embrace the power of containerization in your workflows!