> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Linux as a Virtualization Guest Containers
> Hands-on guide to container management using Podman and Docker compatible CLI commands covering installation, pulling images, running and naming containers, port mapping, stopping and cleaning images.
Hello — this lesson demonstrates practical container management and configuration using Docker-compatible tooling (Podman on RHEL-based systems). We'll cover why containers are useful, how to install and configure Podman, and basic workflows: pulling images, running containers, mapping ports, stopping/removing containers, and cleaning up images.
Why use containers?
* Containers package an application and everything it needs (binaries, libraries, configuration, logs, and data) together. This eliminates fragmented configurations across /etc, /var/lib, /var/log, etc., and makes migration or replication to other hosts predictable and repeatable.
* Example: A MariaDB server inside a container keeps the daemon, configuration files, databases, and logs together. Copy or pull that container on another host and it behaves the same way.
Installing Docker-compatible tooling
* On modern RHEL-based distributions (CentOS Stream, RHEL) Docker packages may not be available; Podman is the recommended replacement. Podman is daemonless, OCI-compliant, and provides Docker-compatible CLI behavior via the podman-docker wrapper.
Install Podman with dnf:
```bash theme={null}
sudo dnf install podman
```
The podman-docker package provides docker CLI compatibility so many existing Docker commands (docker pull, docker run, docker ps, etc.) work unchanged.
Podman includes a Docker-CLI compatibility wrapper (podman-docker). You can use `docker ...` commands, or call `podman` directly. Podman is daemonless and integrates with systemd and rootless workflows.
Configuring default registries (optional)
* Container tools consult /etc/containers/registries.conf to determine search registries for unqualified image names. To prefer docker.io only, set the unqualified-search-registries array to \["docker.io"].
Example excerpt from /etc/containers/registries.conf:
```toml theme={null}
# An array of host[:port] registries to try when pulling an unqualified image, in order.
unqualified-search-registries = ["docker.io"]
```
* Suppress the informational docker wrapper message by creating the marker file:
```bash theme={null}
sudo touch /etc/containers/no-docker
```
Working with images and containers (nginx walkthrough)
Below is a practical workflow for finding, pulling, running, testing, and cleaning up an nginx container using the Docker-compatible CLI. Replace `docker` with `podman` if you prefer explicit Podman commands.
Search for nginx images in the registry:
```bash theme={null}
docker search nginx
```
Pull the official nginx image (long and short forms both work):
```bash theme={null}
docker pull docker.io/library/nginx
# or
docker pull nginx
```
Example pull output (truncated):
```text theme={null}
Trying to pull docker.io/library/nginx:latest...
Getting image source signatures
Copying blob c4ffe9532b5f done
Copying blob 2215908dc0a2 done
Copying config 12766a6745 done
Writing manifest to image destination
Storing signatures
12766a6745eea133de9fdcd03ff720fa971fdaf2
[aaron@LFCS-CentOS ~]$
```
List images available locally:
```bash theme={null}
docker images
```
Example:
```text theme={null}
REPOSITORY TAG IMAGE ID CREATED SIZE
docker.io/library/nginx latest 12766a6745ee 17 hours ago 146 MB
docker.io/library/nginx 1.20.2 8f34c303855f 17 hours ago 146 MB
```
Remove an older image tag:
```bash theme={null}
docker rmi nginx:1.20.2
```
Example output:
```text theme={null}
Untagged: docker.io/library/nginx:1.20.2
Deleted: 8f34c303855f0e55ca018386ff45cf47b1d7da554ab746b1c60049ebcf12d42c
[aaron@LFCS-CentOS ~]$
```
Creating and running containers
* By default, running without -d attaches your terminal to the container's stdout/stderr. Use Ctrl+C to stop.
Run in the foreground (attached):
```bash theme={null}
docker run nginx
```
Run detached (background):
```bash theme={null}
docker run -d nginx
# outputs container ID, e.g.:
# 92a87f978de3...
```
List running containers:
```bash theme={null}
docker ps
```
List all containers (running and stopped):
```bash theme={null}
docker ps --all
```
Stop and remove containers:
```bash theme={null}
docker stop
docker rm
```
Notes on safe image removal:
* docker rmi fails if an image is in use by any container. Preferred safe removal sequence:
1. Stop containers: docker stop \
2. Remove containers: docker rm \
3. Remove image: docker rmi \
Naming containers and exposing ports
* Assign a name and publish ports with --name and -p HOST:CONTAINER. Example: run nginx named mywebserver with host port 8080 mapped to container port 80:
```bash theme={null}
docker run -d -p 8080:80 --name mywebserver nginx
# Example returned container ID:
# 7953475436b9...
```
Testing the web server with netcat
* Use netcat (nc) to query the server. Pass host and port as separate arguments (no colon):
```bash theme={null}
nc localhost 8080
GET /
```
You should receive the nginx default index.html content:
```html theme={null}
Welcome to nginx!
...
```
Press Ctrl+C to exit nc.
Ports below 1024 are privileged. To bind host port 80 to a container, run the command with elevated privileges (sudo) or map a non-privileged host port (>=1024).
Binding to privileged port 80 (example):
```bash theme={null}
sudo docker run -d -p 80:80 --name mywebserver nginx
```
Getting help and Podman-specific options
* Get detailed help for any command with --help:
```bash theme={null}
docker run --help
docker rm --help
# or
podman run --help
```
Podman rm options (example excerpt):
```text theme={null}
podman rm [options] CONTAINER [CONTAINER...]
Examples:
podman rm imageID
podman rm mywebserver myflaskserver 860a4b23
podman rm --force --all
podman rm -f c684f0d469f2
Options:
-a, --all Remove all containers
-f, --force Force removal of a running or unusable container
-v, --volumes Remove anonymous volumes associated with the container
-t, --time uint Seconds to wait for stop before killing the container (default 10)
...
```
Quick reference: common Docker/Podman commands
| Action | Command |
| -------------------------- | ------------------------------------------------------------- |
| Search registry | `docker search ` |
| Pull image | `docker pull \` |
| List local images | `docker images` |
| Run container (foreground) | `docker run \` |
| Run detached | `docker run -d -p :\ --name \` |
| List running containers | `docker ps` |
| List all containers | `docker ps --all` |
| Stop container | `docker stop \` |
| Remove container | `docker rm \` |
| Remove image | `docker rmi \` |
Links and references
* [Podman documentation](https://podman.io/)
* [Containers configuration (containers.conf / registries.conf)](https://github.com/containers/image/blob/main/docs/containers-registries.5.md)
* [Docker CLI reference](https://docs.docker.com/engine/reference/commandline/cli/)
This concludes the short hands-on introduction to pulling images, running containers, mapping ports, and cleaning up images. Practice these commands in a lab environment to build confidence and reinforce container lifecycle management.