Docker Installation Steps

Step 1 — Installing Docker
The Docker installation package available in the official Ubuntu repository may not be the latest version. To ensure we get the latest version, we’ll install Docker from the official Docker repository. To do that, we’ll add a new package source, add the GPG key from Docker to ensure the downloads are valid, and then install the package.

First, update your existing list of packages:

$ sudo apt update

Next, install a few prerequisite packages which let apt use packages over HTTPS:

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

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

$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

Add the Docker repository to APT sources:

$ sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu focal stable"

This will also update our package database with the Docker packages from the newly added repo.

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:

Notice that docker-ce is not installed, but the candidate for installation is from the Docker repository for Ubuntu 20.04 (focal).

Finally, install Docker:

$ sudo apt install docker-ce

Docker should now be installed, the daemon started, and the process enabled to start on boot. Check that it’s running:

$ sudo systemctl status docker

The output should be similar to the following, showing that the service is active and running:

 docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2020-05-19 17:00:41 UTC; 17s ago
TriggeredBy: ● docker.socket
       Docs: https://docs.docker.com
   Main PID: 24321 (dockerd)
      Tasks: 8
     Memory: 46.4M
     CGroup: /system.slice/docker.service
             └─24321 /usr/bin/dockerd -H fd:// --

containerd=/run/containerd/containerd.sock

Installing Docker now gives you not just the Docker service (daemon) but also the docker command line utility, or the Docker client. We’ll explore how to use the docker command later in this tutorial.