Installing Docker on Ubuntu 22.04

1. Updating package database:

   sudo apt update

2. Installing useful packages for the subsequent installation steps (may already be present):

   sudo apt-get install ca-certificates curl gnupg lsb-release

3. Adding Docker's GPG key to the repository:

   sudo mkdir -p /etc/apt/keyrings

   And :

   curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
   echo \
     "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
     $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

4. New package database update (to take into account the added repository):

   sudo apt update

5. Installing Docker packages:

   sudo apt-get install docker-ce docker-ce-cli containerd.io docker-compose-plugin

6. Verifying the installed Docker version:

   sudo docker version

   It will display something like this:

   Client: Docker Engine - Community
    Version:           20.10.17
    API version:       1.41
    Go version:        go1.17.11
    Git commit:        100c701
    Built:             Mon Jun  6 23:02:46 2022
    OS/Arch:           linux/amd64
    Context:           default
    Experimental:      true
   
   Server: Docker Engine - Community
    Engine:
     Version:          20.10.17
     API version:      1.41 (minimum version 1.12)
     Go version:       go1.17.11
     Git commit:       a89b842
     Built:            Mon Jun  6 23:00:51 2022
     OS/Arch:          linux/amd64
     Experimental:     false
   ...
   ...
   

7. Verifying the status of the Docker service:

   sudo systemctl status docker

   It will display something like this:

   ● docker.service - Docker Application Container Engine
      Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
      Active: active (running) since Fri 2022-07-04 17:55:53 CEST; 6min ago
   TriggeredBy: ● docker.socket
        Docs: https://docs.docker.com
      Main PID: 12804 (dockerd)
       Tasks: 17
      Memory: 39.0M
       CPU: 1.145s
      CGroup: /system.slice/docker.service
          └─12804 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
   

8. Now we can try the traditional "Hello, World !" example using the following command:

   sudo docker run hello-world

   It will display:

   Unable to find image 'hello-world:latest' locally
   latest: Pulling from library/hello-world
   2db29710123e: Pull complete
   Digest: sha256:7d246653d0511db2a6b2e0436cfd0e52ac8c066000264b3ce63331ac66dca625
   Status: Downloaded newer image for hello-world:latest
   
   Hello from Docker!
   This message shows that your installation appears to be working correctly.
   ...
   ...
   

9. To avoid having to enter sudo before the docker command, you can give permissions for Docker to the current user with:

   sudo groupadd docker

   Followed by:

   sudo usermod -aG docker $USER

   Then, log out and log back in for the new rights to take effect. And now we can execute the "Hello World" without sudo:

   docker run hello-world

   However, beware of security holes, see Docker daemon attack surface.