> ## 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.
# Manage and configure containers
> This guide covers managing and configuring containers using Docker and Podman, including installation, image handling, and container operations.
Welcome to this comprehensive guide on container management and configuration. In this article, we explore how containers simplify application deployment and migration by encapsulating everything—daemons, configuration files, logs, and databases—in a single, portable unit. Unlike traditional setups (e.g., a conventional MariaDB installation where components are scattered in various directories), containerized applications streamline the process of moving applications between different systems.
***
## Installing Podman to Emulate Docker
In some environments, such as CentOS Stream 8, Docker might not have official support. In these cases, you can install Podman, which offers a Docker-compatible command-line interface. To install Podman using the dnf package manager, execute the following command:
```bash theme={null}
sudo dnf install podman
```
After installation, Podman allows you to use familiar Docker commands as it seamlessly translates them under the hood. The installation output might resemble the following:
```bash theme={null}
# Sample installation output
Install 1 Package
Total download size: 67 k
Installed size: 230
Is this ok [y/N]: y
Downloading Packages:
podman-docker-4.0.2-1.module_el8.7.0+1106+45480 208 kB/s | 67 kB 00:00
----------------------------------------------------------
Total 94 kB/s | 67 kB 00:00
Running transaction check.
Transaction check succeeded.
Running transaction test.
Transaction test succeeded.
Running transaction
Preparing :
Installing : podman-docker-2:4.0.2-1.module_el8.7.0+1106+45480ee0 1/1
Verifying : podman-docker-2:4.0.2-1.module_el8.7.0+1106+45480ee0 1/1
Installed:
podman-docker-2:4.0.2-1.module_el8.7.0+1106+45480ee0.noarch
Complete!
[aaron@LFCS-CentOS ~]$
```
***
## Configuring Podman’s Default Registry
Podman’s configuration file is located at `/etc/containers/registries.conf`. Open it using your preferred text editor (for example, vim):
```bash theme={null}
sudo vim /etc/containers/registries.conf
```
Find the line that configures unqualified search registries:
```plaintext theme={null}
unqualified-search-registries = ["registry.fedoraproject.org", "registry.access.redhat.com", "registry.centos.org", "docker.io"]
```
Comment out the above line and add the following to set `docker.io` as the default registry:
```plaintext theme={null}
# unqualified-search-registries = ["registry.fedoraproject.org", "registry.access.redhat.com", "registry.centos.org", "docker.io"]
unqualified-search-registries = ["docker.io"]
```
If you receive a message about emulating the Docker CLI with Podman, you can disable this behavior by creating a specific file:
```bash theme={null}
sudo touch /etc/containers/no-docker
```
***
## Working with Images
### Searching for an Image
For this guide, we will use the popular Nginx web server as an example. To locate available Nginx images, run:
```bash theme={null}
docker search nginx
```
The output may include entries such as:
```plaintext theme={null}
docker.io/rancher/nginx
docker.io/vmware/nginx-photon
docker.io/ibmcom/nginx-ingress-controller-ppc64le Docker Image for IBM Cloud Private-CE (Community Edition) ppc64le ingress controller component
...
```
The official image, often referred to as `docker.io/library/nginx`, is well-supported and highly rated.
### Pulling an Image
To pull the official Nginx image, use its fully qualified name:
```bash theme={null}
docker pull docker.io/library/nginx
```
For convenience, you can also use the short form:
```bash theme={null}
docker pull nginx
```
To pull a specific version (for instance, version 1.20.2), run:
```bash theme={null}
docker pull nginx:1.20.2
```
After pulling an image, you can list the available images with:
```bash theme={null}
docker images
```
Example output:
```plaintext theme={null}
REPOSITORY TAG IMAGE ID CREATED SIZE
docker.io/library/nginx 1.20.2 8f34c303855f 17 hours ago 146 MB
docker.io/library/nginx latest 12766a6745ee 17 hours ago 146 MB
```
If you wish to remove a specific version, execute:
```bash theme={null}
docker rmi nginx:1.20.2
```
Images can also be referenced by their IMAGE ID, using just enough characters to uniquely identify them.
***
## Running and Managing Containers
### Creating and Attaching to a Container
To create and run a new container using the Nginx image, use:
```bash theme={null}
docker run nginx
```
This command creates a container and attaches your terminal to its output. If you find that the container’s logs (for example, startup messages from `/docker-entrypoint.sh`) continuously appear, press Ctrl+C to detach and terminate the container.
To run the container in detached mode, use the `-d` option:
```bash theme={null}
docker run -d nginx
```
This command returns a hexadecimal container ID and allows the container to run in the background.
### Listing, Stopping, and Removing Containers
To list active containers, run:
```bash theme={null}
docker ps
```
For a complete list of containers (including those that have exited), use:
```bash theme={null}
docker ps --all
```
To stop a container, specify its container ID or assigned name. For example, to stop a container named `interesting_mcclintock`:
```bash theme={null}
docker stop interesting_mcclintock
```
After stopping the container, remove it with:
```bash theme={null}
docker rm interesting_mcclintock
```
If the container is running and you wish to force its removal, use:
```bash theme={null}
docker rm --force interesting_mcclintock
```
### Removing Images
If you try to remove an image that is currently in use, Docker will produce an error:
```bash theme={null}
docker rmi nginx
```
Example error message:
```plaintext theme={null}
Error: image used by 92a87f978de328e0ec460a3775006b394459fa9f043da39179d6693416e976f2: image is in use by a container
```
To force the removal of an image (this will stop and remove any dependent containers), add the `--force` option:
```bash theme={null}
docker rmi --force nginx
```
***
## Advanced: Naming Containers and Port Mapping
For improved container management, you can assign custom names and set up port mapping between the host and container. To run Nginx in a container named `mywebserver` with host port 8080 mapped to container port 80, use:
```bash theme={null}
docker run -d -p 8080:80 --name mywebserver nginx
```
This configuration directs any connection to port 8080 on your machine to port 80 inside the container. To test the setup, you can use netcat:
```bash theme={null}
nc localhost 8080
```
After connecting, type the following command:
```HTTP theme={null}
GET /
```
Then press Enter. This simulates a browser request to Nginx, displaying the default HTML page. Press Ctrl+C to exit the netcat session.
Note: Mapping to privileged ports (ports below 1024) requires root privileges. For example, to map host port 80 to container port 80, use:
```bash theme={null}
sudo docker run -d -p 80:80 --name mywebserver nginx
```
***
## Getting Help
For detailed information about any Docker command, append the `--help` option. For example:
```bash theme={null}
docker container --help
```
Or to get help for a specific command like `docker rm`:
```bash theme={null}
docker rm --help
```
Below is an example of help output for Podman’s container removal command:
```plaintext 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
--cidfile stringArray Read the container ID from the file
--depend Remove container and all containers that depend on the selected container
-f, --force Force removal of a running or unusable container
-i, --ignore Ignore errors when a specified container is missing
-l, --latest Act on the latest container podman is aware of
-t, --time uint Not supported with the "--remote" flag
Seconds to wait for stop before killing the container
-v, --volumes Remove anonymous volumes associated with the container
```
***
## Conclusion
This guide demonstrated the key steps in managing and configuring containers on Linux using Docker and Podman. We covered installing Podman, configuring its default registry, working with images, running containers in both attached and detached modes, and advanced topics like port mapping and naming containers. Continue exploring these concepts to elevate your container management skills.
Happy containerizing!