Managing Containers Effectively with Podman (with examples)

Podman is a versatile and convenient command-line tool used for managing pods, containers, and container images. It provides a Docker-like command-line interface that facilitates easy transition for users familiar with Docker. Offering a rootless mode, Podman allows users to run containers without requiring root privileges, enhancing security. Here, we explore various use cases of Podman, with examples and detailed explanations to help you understand the command better.

List all containers (both running and stopped)

Code:

podman ps --all

Motivation:

Listing all containers, including those that are not currently running, is crucial for administrators who need an overview of all container instances on the system. It helps in managing resources, auditing container usage, and troubleshooting potential issues.

Explanation:

• podman ps: This command lists all active containers by default.
• --all: The --all flag extends the output to include containers that are not currently running. Without this flag, only active containers are displayed.

Example output:

CONTAINER ID  IMAGE        COMMAND     CREATED          STATUS                       NAMES
a1b2c3d4e5f6  alpine       top         10 minutes ago   Exited (0) 5 minutes ago     my_container
x9y8z7w6v5u4  nginx        nginx       30 minutes ago   Up 25 minutes                web_server

Create a container from an image, with a custom name

Code:

podman run --name container_name image

Motivation:

Creating a container with a custom name is useful for identification and organization, especially in environments where multiple containers might be running that have different roles or purposes.

Explanation:

• podman run: This command initializes and runs a new container from a specified image.
• --name container_name: This option allows you to assign a custom name to the container for easier identification.
• image: This specifies the container image from which the new container will be created.

Example output:

c7d8e9f1a2b3  container_name

Start or stop an existing container

Code:

podman start|stop container_name

Motivation:

Starting or stopping containers is a fundamental aspect of container management, allowing administrators to control the lifecycle of containers as needed for maintenance, updates, or resource optimization.

Explanation:

• podman start: This command starts a container that has been created but is not currently running.
• podman stop: This command halts a running container.
• container_name: The specific name or ID of the container to start or stop.

Example output:

container_name

Pull an image from a registry (defaults to Docker Hub)

Code:

podman pull image

Motivation:

Pulling images from a registry allows users to download container images onto their local systems to use as templates for creating containers. This is often the first step in deploying a containerized application.

Explanation:

• podman pull: Specifies that an image is to be downloaded from a repository.
• image: The name of the container image to be retrieved. By default, Podman uses Docker Hub, but other repositories can be specified.

Example output:

Trying to pull image from docker.io/library/image... 
Downloaded: sha256:123abc456def789ghi012jkl345mno678pqrs...

Display the list of already downloaded images

Code:

podman images

Motivation:

Viewing the list of locally stored images helps manage storage, assess available resources, and identify the basis for creating new containers.

Explanation:

• podman images: This command outputs the list of container images already present on the local system.

Example output:

REPOSITORY         TAG          IMAGE ID       CREATED        SIZE
nginx              latest       aef12345       2 weeks ago    133MB
alpine             latest       7865bcd        1 week ago     5.6MB

Open a shell inside an already running container

Code:

podman exec --interactive --tty container_name sh

Motivation:

Gaining shell access to a running container is essential for debugging, configuration, or real-time monitoring tasks. It allows administrators to interact directly with the container’s operating environment.

Explanation:

• podman exec: This command executes a command inside a running container.
• --interactive: Keeps STDIN open even if not attached.
• --tty: Allocates a pseudo-TTY.
• container_name: Specifies the running container to access.
• sh: The shell command to run within the container.

Example output:

/ # 

Remove a stopped container

Code:

podman rm container_name

Motivation:

Removing containers that are no longer needed helps prevent resource waste, freeing up space for new tasks and reducing system clutter.

Explanation:

• podman rm: Deletes a container from the system.
• container_name: The name or ID of the container to be removed.

Example output:

container_name

Display the logs of one or more containers and follow log output

Code:

podman logs --follow container_name

Motivation:

Viewing container logs is crucial for debugging and monitoring the performances of applications running inside containers, providing insights into application behavior.

Explanation:

• podman logs: Retrieves logs generated by a container.
• --follow: Continuously outputs new log entries (similar to tail -f).
• container_name: The specific container from which logs should be retrieved.

Example output:

2023-10-30T12:45:07.123 INFO Starting service
2023-10-30T12:45:12.456 WARN No data received
...

Conclusion:

Podman offers powerful and straightforward commands for managing containers and their lifecycle. Through the provided use cases, users can efficiently handle various aspects, from creating containers to extracting logs, thereby ensuring that systems run smoothly and resources are wisely managed. With Podman, users can enjoy a flexible, rootless experience akin to Docker, making it a robust tool in any container orchestration toolkit.