Introduction
Docker is an application that makes it simple and easy to run application processes in a container, which are like virtual machines, only more portable, more resource-friendly, and more dependent on the host operating system.
In this tutorial, you’ll learn how to install and use it on an existing installation of Ubuntu 21.10.
Note: Docker requires a 64-bit version of Ubuntu as well as a kernel version equal to or greater than 3.10. The default 64-bit Ubuntu 21.10 server meets these requirements.
Installing Docker
Note: All the commands in this tutorial should be run as a non-root user. If root access is required for the command, it will be preceded by sudo.
The Docker installation package available in the official Ubuntu 21.10 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.
First, add the GPG key for the official Docker repository to the system:
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
Add the Docker repository to APT sources:
sudo bash -c 'echo "deb [arch=$(dpkg --print-architecture)] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" > /etc/apt/sources.list.d/docker-ce.list'
Next, 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 21.10 repo:
apt-cache policy docker-ce
You should see output similar to the follow:
docker-ce:
Installed: (none)
Candidate: 5:20.10.12~3-0~ubuntu-impish
Version table:
5:20.10.12~3-0~ubuntu-impish 500
500 https://download.docker.com/linux/ubuntu impish/stable amd64 Packages
5:20.10.11~3-0~ubuntu-impish 500
500 https://download.docker.com/linux/ubuntu impish/stable amd64 Packages
5:20.10.10~3-0~ubuntu-impish 500
500 https://download.docker.com/linux/ubuntu impish/stable amd64 Packages
Notice that docker-ce is not installed, but the candidate for installation is from the Docker repository for Ubuntu 21.10. The docker-ce version number might be different.
Finally, install Docker:
sudo apt-get install -y 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 Mon 2022-02-28 06:54:43 UTC; 8s ago
TriggeredBy: ● docker.socket
Docs: https://docs.docker.com
Main PID: 2398 (dockerd)
Tasks: 8
Memory: 29.9M
CPU: 375ms
CGroup: /system.slice/docker.service
└─2398 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.547798752Z" level=info msg="scheme \"unix\" not registered, fallback to default scheme" module=grpc
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.547839103Z" level=info msg="ccResolverWrapper: sending update to cc: {[{unix:///run/containerd/conta>
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.547857684Z" level=info msg="ClientConn switching balancer to \"pick_first\"" module=grpc
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.601928785Z" level=info msg="Loading containers: start."
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.803682067Z" level=info msg="Default bridge (docker0) is assigned with an IP address 172.17.0.0/16. D>
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.912000602Z" level=info msg="Loading containers: done."
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.935127854Z" level=info msg="Docker daemon" commit=459d0df graphdriver(s)=overlay2 version=20.10.12
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.935361734Z" level=info msg="Daemon has completed initialization"
Feb 28 06:54:43 ubuntu systemd[1]: Started Docker Application Container Engine.
Feb 28 06:54:43 ubuntu dockerd[2398]: time="2022-02-28T06:54:43.978811872Z" level=info msg="API listen on /run/docker.sock"
Installing Docker now gives you not just the Docker service (daemon) but also the docker command line utility, or the Docker client. Have fun!
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