System Administrator: June 2017

Step 1 — Installing Docker

The Docker installation package available in the official Ubuntu 16.04 repository may not be the latest version. To get the latest and greatest version, install Docker from the official Docker repository. This section shows you how to do just that.

But first, let's update the package database:

sudo apt-get update

Now let's install Docker. Add the GPG key for the official Docker repository to the system:

sudo apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D

Add the Docker repository to APT sources:

sudo apt-add-repository 'deb https://apt.dockerproject.org/repo ubuntu-xenial main'

Update the package database with the Docker packages from the newly added repo:

sudo apt-get update

Make sure you are about to install from the Docker repo instead of the default Ubuntu 16.04 repo:

apt-cache policy docker-engine

You should see output similar to the follow:

Output of apt-cache policy docker-engine

docker-engine:    Installed: (none)    Candidate: 1.11.1-0~xenial    Version table:       1.11.1-0~xenial 500          500 https://apt.dockerproject.org/repo ubuntu-xenial/main amd64 Packages       1.11.0-0~xenial 500          500 https://apt.dockerproject.org/repo ubuntu-xenial/main amd64 Packages

Notice that docker-engine is not installed, but the candidate for installation is from the Docker repository for Ubuntu 16.04. The docker-engine version number might be different.

Finally, install Docker:

sudo apt-get install -y docker-engine

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:

Output
● docker.service - Docker Application Container Engine     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)     Active: active (running) since Sun 2016-05-01 06:53:52 CDT; 1 weeks 3 days ago       Docs: https://docs.docker.com   Main PID: 749 (docker)

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.