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= Installing Docker on Linux =

This guide provides step-by-step instructions for installing Docker Community Edition (CE) on various Linux distributions and introduces fundamental Docker commands and concepts, including creating a simple Dockerfile. This is an essential skill for modern application deployment and management, especially when leveraging the power of dedicated servers from [https://powervps.net/?from=32 PowerVPS] for your containerized workloads.

== Prerequisites ==
Before you begin, ensure you have:
# A Linux server with root or sudo privileges. [[Dedicated Servers]] from PowerVPS offer excellent performance and full root access, ideal for running Docker.
# A stable internet connection to download packages.
# Basic familiarity with the Linux command line.
# For this guide, we will cover installation on Debian/Ubuntu and CentOS/RHEL-based systems.

== Installing Docker CE ==

Docker CE can be installed using the official repositories. This is the recommended method as it ensures you receive timely updates.

=== On Debian/Ubuntu ===
# '''Update package lists:'''
<pre>
sudo apt update
</pre>
# '''Install prerequisite packages:''' These allow apt to use a repository over HTTPS.
<pre>
sudo apt install apt-transport-https ca-certificates curl software-properties-common gnupg lsb-release
</pre>
# '''Add Docker's official GPG key:'''
<pre>
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
</pre>
# '''Set up the stable Docker repository:'''
<pre>
echo \
"deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \
$(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
</pre>
# '''Update package lists again to include the new repository:'''
<pre>
sudo apt update
</pre>
# '''Install Docker Engine, containerd, and Docker Compose:'''
<pre>
sudo apt install docker-ce docker-ce-cli containerd.io docker-compose-plugin
</pre>
# '''Verify the installation:'''
<pre>
sudo docker run hello-world
</pre>
You should see a message indicating that your installation appears to be working correctly.

=== On CentOS/RHEL/Fedora ===
# '''Uninstall older versions (if any):'''
<pre>
sudo yum remove docker docker-client docker-client-latest docker-common docker-latest docker-latest-logrotate docker-logrotate docker-engine podman runc
</pre>
# '''Install required packages:'''
<pre>
sudo yum install -y yum-utils device-mapper-persistent-data lvm2
</pre>
# '''Add Docker's stable repository:'''
<pre>
sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
</pre>
# '''Install Docker Engine, containerd, and Docker Compose:'''
<pre>
sudo yum install docker-ce docker-ce-cli containerd.io docker-compose-plugin
</pre>
# '''Start the Docker daemon:'''
<pre>
sudo systemctl start docker
</pre>
# '''Enable Docker to start on boot:'''
<pre>
sudo systemctl enable docker
</pre>
# '''Verify the installation:'''
<pre>
sudo docker run hello-world
</pre>
Similar to Debian/Ubuntu, you should see a confirmation message.

== Post-installation Steps ==

=== Manage Docker as a non-root user ===
To run Docker commands without `sudo`, add your user to the `docker` group.
# '''Add user to the docker group:'''
<pre>
sudo usermod -aG docker $USER
</pre>
# '''Apply the group changes:''' You will need to log out and log back in, or run:
<pre>
newgrp docker
</pre>
Now you can run Docker commands directly:
<pre>
docker run hello-world
</pre>

=== Basic Docker Commands ===
Here are some fundamental Docker commands to get you started:

* '''`docker --version`''': Displays the installed Docker version.
* '''`docker info`''': Provides detailed information about your Docker installation, including the number of containers, images, and storage driver.
* '''`docker pull <image_name>`''': Downloads a Docker image from a registry (like Docker Hub).
<pre>
docker pull ubuntu:latest
</pre>
* '''`docker images`''': Lists all Docker images available locally.
<pre>
docker images
</pre>
* '''`docker run <image_name>`''': Creates and starts a new container from an image.
<pre>
docker run -it ubuntu bash
</pre>
The `-it` flags allocate a pseudo-TTY and keep STDIN open, allowing you to interact with the container.
* '''`docker ps`''': Lists all running containers.
<pre>
docker ps
</pre>
* '''`docker ps -a`''': Lists all containers, including stopped ones.
<pre>
docker ps -a
</pre>
* '''`docker stop <container_id_or_name>`''': Stops a running container.
<pre>
docker stop my_running_container
</pre>
* '''`docker rm <container_id_or_name>`''': Removes a stopped container.
<pre>
docker rm my_stopped_container
</pre>
* '''`docker rmi <image_id_or_name>`''': Removes a Docker image.
<pre>
docker rmi ubuntu:latest
</pre>

== Creating a Dockerfile ==

A Dockerfile is a script that contains instructions for building a Docker image. It's the blueprint for your containerized application.

Let's create a simple Dockerfile for a basic Nginx web server.

# '''Create a directory for your project:'''
<pre>
mkdir my-nginx-app
cd my-nginx-app
</pre>
# '''Create a simple HTML file to serve:'''
<pre>
echo "<h1>Hello from my Dockerized Nginx!</h1>" > index.html
</pre>
# '''Create the Dockerfile:'''
<pre>
nano Dockerfile
</pre>
# '''Add the following content to the Dockerfile:'''
<pre>
# Use an official Nginx runtime as a parent image
FROM nginx:latest

# Copy the current directory contents into the container at /usr/share/nginx/html
COPY . /usr/share/nginx/html

# Expose port 80 to the outside world
EXPOSE 80

# Command to run when the container launches
CMD ["nginx", "-g", "daemon off;"]
</pre>
# '''Build the Docker image:'''
<pre>
docker build -t my-nginx-image .
</pre>
The `.` at the end specifies the build context (the current directory).
# '''Run a container from your new image:'''
<pre>
docker run -d -p 8080:80 my-nginx-image
</pre>
The `-d` flag runs the container in detached mode. `-p 8080:80` maps port 8080 on your host to port 80 inside the container.
# '''Verify by accessing your web server:''' Open a web browser and navigate to `http://your_server_ip:8080`. You should see "Hello from my Dockerized Nginx!".

== Troubleshooting ==

* '''Docker daemon not running:'''
* Check status: `sudo systemctl status docker`
* Start daemon: `sudo systemctl start docker`
* Enable on boot: `sudo systemctl enable docker`
* '''Permission denied when running Docker commands:'''
* Ensure your user is in the `docker` group: `sudo usermod -aG docker $USER`
* Log out and log back in, or use `newgrp docker`.
* '''`hello-world` container fails to run:'''
* Check network connectivity: Can you reach `https://registry-1.docker.io`?
* Ensure Docker is installed correctly and the daemon is running.
* '''Port conflicts:''' If you cannot map a host port (e.g., `-p 8080:80`), another service might be using that port. Try a different host port (e.g., `-p 8081:80`). You can check port usage with `sudo netstat -tulnp | grep :8080`.

== Further Reading ==
* [[Docker Compose Installation]]
* [[Kubernetes Basics]]
* [[Container Orchestration]]

[[Category:Containerization]]
[[Category:Docker]]
[[Category:System Administration]]

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