Docker is an open-source platform that simplifies the process of developing, shipping, and running applications inside containers. This guide will cover the installation of Docker on Ubuntu 20.04 and provide an overview of its basic usage.

Prerequisites

• A system running Ubuntu 20.04
• A user account with sudo privileges
• Internet access

Step 1: Update System Packages

Before installing Docker, update the package repository to ensure you have the latest software versions:

sudo apt update && sudo apt upgrade -y

Step 2: Install Required Dependencies

Docker requires certain dependencies to be installed. Run the following command to install them:

sudo apt install -y apt-transport-https ca-certificates curl software-properties-common

Step 3: Add Docker’s Official GPG Key

To verify the authenticity of the Docker package, add its GPG key:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | 
sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

Step 4: Add the Docker Repository

Add the official Docker repository to your system sources:

echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] 
https://download.docker.com/linux/ubuntu focal stable" | 
sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Step 5: Install Docker

Update the package list and install Docker Engine:

sudo apt update
sudo apt install -y docker-ce docker-ce-cli containerd.io

Step 6: Verify Docker Installation

Check if Docker is installed correctly by running:

docker --version

To ensure Docker is running:

sudo systemctl status docker

If it is not running, start it with:

sudo systemctl start docker

To enable Docker to start on boot:

sudo systemctl enable docker

Step 7: Run Docker Without Sudo (Optional)

By default, Docker requires sudo privileges. To run it as a non-root user, add your user to the docker group:

sudo usermod -aG docker $USER

Log out and log back in for the changes to take effect.

Step 8: Test Docker Installation

Run a test container to verify that Docker is working correctly:

docker run hello-world

If the installation is successful, you should see a message confirming that Docker is running properly.

Basic Docker Commands

Pull an Image

To download an image from Docker Hub:

docker pull ubuntu

List Installed Images

docker images

Run a Container

To start a container from an image:

docker run -it ubuntu bash

This command runs an Ubuntu container and opens an interactive shell.

List Running Containers

docker ps

To see all containers, including stopped ones:

docker ps -a

Stop a Container

To stop a running container:

docker stop <container_id>

Remove a Container

To remove a stopped container:

docker rm <container_id>

Remove an Image

To delete an image:

docker rmi <image_id>

Clean Up Unused Resources

Remove all stopped containers and unused images:

docker system prune -a

Conclusion

Docker is a powerful tool that simplifies application deployment and management. This guide covered the installation process and basic commands to help you get started with Docker on Ubuntu 20.04.