What is Docker?

Docker is an application that simplifies the process of managing application processes in containers. Containers let you run your applications in resource-isolated processes. They’re similar to virtual machines, but containers are more portable, more resource-friendly, and more dependent on the host operating system.

Step 1 - Installing Docker

Prerequisites

To follow this tutorial, you will need the following:

• One Ubuntu 22.04 server/VM, including a sudo non-root user and a firewall.

First, update your existing list of packages

sudo apt update -y

install a few prerequisite packages which let apt use packages over HTTPS

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

add the GPG key for the official Docker repository to your system

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

Add the Docker repository to APT sources

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

Do a sudo apt update -y to update your existing list of packages again for the addition to be recognized.

Make sure you are about to install from the Docker repo instead of the default Ubuntu repo

apt-cache policy docker-ce

You’ll see output like this, although the version number for Docker may be different

docker-ce:
  Installed: (none)
  Candidate: 5:20.10.14~3-0~ubuntu-jammy
  Version table:
     5:20.10.14~3-0~ubuntu-jammy 500
        500 https://download.docker.com/linux/ubuntu jammy/stable amd64 Packages
     5:20.10.13~3-0~ubuntu-jammy 500
        500 https://download.docker.com/linux/ubuntu jammy/stable amd64 Packages

Now lets install Docker

sudo apt install docker-ce

Check the status

sudo systemctl status docker

Step 2 — Executing the Docker Command Without sudo (Optional)

By default, the docker command can only be run the root user or by a user in the docker group, which is automatically created during Docker’s installation process. If you attempt to run the docker command without prefixing it with sudo or without being in the docker group, you’ll get an output like this

Output

docker: Cannot connect to the Docker daemon. Is the docker daemon running on this host?. See 'docker run --help'.

If you want to avoid typing sudo whenever you run the docker command, add your username to the docker group

sudo usermod -aG docker ${USER}

To apply the new group membership, log out of the server and back in. Confirm that your user is now added to the docker group by typing

id ${USER}

You should see docker in groups. Now you can use docker command without sudo