Linux as a Virtualization Guest Containers

Hello and welcome to our hands-on guide for Docker container management on Linux. In this tutorial, you’ll learn how to install Podman (a Docker-compatible runtime), pull and manage Docker images, and run containers in various modes. Let’s dive in!

Why Use Containers?

Containers package an application’s binaries, libraries, configuration, and data into a single, portable image.

• Manual setups scatter configuration files, data directories, and logs across the filesystem, making migrations tedious.
• A Docker image encapsulates everything. Copy it to a new host and “just work.”

Containers give you:

• Consistent environments across development, staging, and production
• Rapid provisioning and scaling
• Isolation without the overhead of full virtual machines

Installing Podman for Docker Compatibility

CentOS Stream 8 does not include Docker by default. Instead, install Podman with a Docker‐CLI wrapper:

sudo dnf install podman

This pulls in podman-docker, so you can use familiar docker commands backed by Podman.

Configure the Default Registry

To ensure unqualified pulls (e.g., docker pull nginx) only search Docker Hub:

sudo vim /etc/containers/registries.conf

Comment out the existing entries and replace with:

# unqualified-search-registries = ["registry.fedoraproject.org", "registry.access.redhat.com", "registry.centos.org", "docker.io"]
unqualified-search-registries = ["docker.io"]

Save and exit. Podman now defaults to Docker Hub for image pulls.

Suppress the Podman-Docker Warning

Podman prints a one-time notice when emulating Docker. Disable it:

sudo touch /etc/containers/no-docker

Searching for Docker Images

List all high-level Docker commands:

docker help

Search for the nginx image:

docker search nginx | head -n 10

Sample output:

NAME                               DESCRIPTION                                         STARS     OFFICIAL   AUTOMATED
nginx                              Official build of NGINX.                            19719     [OK]
rancher/nginx-conf                 Nginx configuration for Rancher                      12
bitnami/nginx                      Bitnami Docker Image for NGINX                      115
...

Choose the official [OK] image for stability and support.

Pulling Docker Images

Pull the latest NGINX image:

# Fully qualified
docker pull docker.io/library/nginx:latest

# Or shorthand
docker pull nginx

Expected output:

Trying to pull docker.io/library/nginx:latest...
Getting image source signatures
Copying blob c4ffe9532b5f done
Copying config 12766a6745 done
Writing manifest to image destination
Storing signatures
12766a6745eea133de...d4bc72b417c123b15619

Managing Docker Images

List all local images:

docker images

Example:

REPOSITORY          TAG       IMAGE ID       CREATED         SIZE
nginx               latest    12766a6745ee   2 days ago      146 MB

Pull, remove, and force-delete images:

# Pull a specific tag
docker pull nginx:1.20.2

# Remove by tag
docker rmi nginx:1.20.2

# Remove by image ID (prefix is fine if unambiguous)
docker rmi 8f34c303855f

# Force remove images and dependent containers
docker rmi --force nginx

Running Containers with Docker

Foreground Mode

Run NGINX in the foreground to view logs live:

docker run nginx

You’ll see:

/docker-entrypoint.sh: Configuration complete; ready for start up
2022/03/30 08:58:17 [notice] 1#1: start worker process 32
...

Press Ctrl+C to stop and exit (container stops as well).

Detached Mode

Run NGINX in the background:

docker run -d nginx

The command returns a long container ID:

7953475436b958ea43ee1553bd905ae722f8f69c874ad5854f0454ea4e62d0b

Listing Containers

# Only running
docker ps

# All containers (running & stopped)
docker ps --all
# or
docker container ls --all

Sample running container:

CONTAINER ID   IMAGE     COMMAND                  CREATED         STATUS         PORTS     NAMES
92a87f978de3   nginx     "nginx -g 'daemon of…"   30 seconds ago  Up 28 seconds             happy_morse

Stop and Remove

# Stop a running container
docker stop happy_morse

# Remove a stopped container
docker rm happy_morse

# Combine stop + remove
docker rm --force happy_morse

Naming, Port Mapping, and Networking

By default Docker assigns random names. Customize names and publish ports:

docker run -d \
  --name mywebserver \
  -p 8080:80 \
  nginx

• --name mywebserver: Assigns a friendly name
• -p 8080:80 : Maps host port 8080 to container port 80

Testing Connectivity

Use Netcat to verify HTTP access:

nc localhost 8080
GET /

Press Enter twice. You should see:

<html>
<head><title>Welcome to nginx!</title></head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and working.</p>
...
</body>
</html>

sudo docker run -d -p 80:80 --name mywebserver nginx

Common Docker Commands

Getting Help

Every Docker command supports --help. For example:

docker run --help
docker rm --help

Use the help flag to explore options, flags, and examples.

Links and References

• Docker Documentation
• Podman Project
• Docker Hub
• Kubernetes Basics