Install Docker on Ubuntu 18.04

Introduction

Docker is an application (docker Install Docker on Ubuntu that simplifies the process of processing the application process in containers. Names allow you to run applications in resource-intensive processes. They look like virtual machines, but the names are more portable, more resource-friendly, and depend on the host operating system.

In this tutorial, you’ll install and use Docker Community Edition (CE) on Ubuntu 18.04. You’ll install Docker itself, work with containers and images, and push an image to a Docker Repository.

Prerequisites

To follow this tutorial, you will need the following:

• One Ubuntu 18.04 server set up by following the Ubuntu 18.04 initial server setup guide, including a sudo non-root user and a firewall.
• An account on Docker Hub if you wish to create your own images and push them to Docker Hub, as shown in Steps 7 and 8.

Step 1 — Installing Docker

The Docker installation package is not the latest version available in the official Ubuntu repository. To get the latest version, we will install Docker from the official Docker repository. To do this, we will add a new package source, add the GPG key from Docker to make sure 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 bionic stable"

Add the Docker repository to APT sources:

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

Next, update the package database with the Docker packages from the newly added repo:

sudo apt update

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: 18.03.1~ce~3-0~ubuntu
Version table:
18.03.1~ce~3-0~ubuntu 500
500 https://download.docker.com/linux/ubuntu bionic/stable amd64 Packages

Notice that docker-ce is not installed, but the candidate for installation is from the Docker repository for Ubuntu 18.04 (bionic).

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:

Output● docker.service - Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2018-07-05 15:08:39 UTC; 2min 55s ago
Docs: https://docs.docker.com
Main PID: 10096 (dockerd)
Tasks: 16
CGroup: /system.slice/docker.service
├─10096 /usr/bin/dockerd -H fd://
└─10113 docker-containerd --config /var/run/docker/containerd/containerd.toml

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.

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

By default, the docker the 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:

Outputdocker: 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 for the new group membership, log out of the server and back in, or type the following:

su - ${USER}

You will be prompted to enter your user’s password to continue.

Confirm that your user is now added to the docker group by typing:

id -nG

Output:

sammy sudo docker

If you need to add a user to the docker  group that you’re not logged in as declare that username explicitly using:

sudo usermod -aG docker username

The rest of this article assumes you are running the docker command as a user in the docker group. If you choose not to, please prepend the commands with sudo.

Let’s explore the docker command next.