How To Install and Use Docker on Ubuntu 22.04

Docker is an application that simplifies the process of managing application processes in container. Containers let you runyour applications in resource-isolated processes. They’re similar to virtual machines, but container are more portable, more resource-friendly, and more dependent on the host operating system.

For a detailed introduction to the different components of a Docker container, check out The Docker Ecosystem: An Introduction to Common Components.

In this tutorial, you’ll install and use Docker Community Edition (CE) on Ubuntu 22.04. You’ll install Docker itself, work with container and images, and push an image to a Docker Repository.

To follow this tutorial , you is need will need the following :

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 - certificatecurl 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 gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

add the Docker repository to APT source :

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

update your exist list of package again for the addition to be recognize :

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:

output of apt – cache policy docker – ce

docker - ce:
  Installed: (none)
  Candidate: 5:20.10.14~3-0~ubuntu-jammy
  Version table:
     5:20.10.14~3-0~ubuntu-jammy 500
        500 https://download.docker.com/linux/ubuntu jammy/stable amd64 Packages
     5:20.10.13~3-0~ubuntu-jammy 500
        500 https://download.docker.com/linux/ubuntu jammy/stable amd64 Packages

Notice that docker - ce is not installed, but the candidate for installation is from the Docker repository for Ubuntu 22.04 (jammy).

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 Fri 2022-04-01 21:30:25 UTC; 22s ago
TriggeredBy: ● docker.socket
       Docs: https://docs.docker.com
   Main PID: 7854 (dockerd)
      Tasks: 7
     Memory: 38.3M
        CPU: 340ms
     CGroup: /system.slice/docker.service
             └─7854 /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 .

By default, the docker command can only be runthe root user or by a user in the docker group, which is automatically created during Docker’s installation process. If you attempt to runthe docker command without prefixing it with sudo or without being in the docker group, you’ll get an output like this:

output
docker is connect : Can not connect to the Docker daemon . Is the docker daemon is Is  runon this host ? . 
 See ' docker  run--help ' . 

If you want to avoid typing sudo whenever you runthe docker command, add your username to the docker group:

sudo usermod -aG docker ${USER}

To apply 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:

groups

output
sammy  sudodocker

If you is need need to add a user to thedocker group that you ’re not log 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 .

Usingdocker consists of passing it a chain of options and commands followed by arguments. The syntax takes this form:

docker [option] [command] [arguments]

To view all available subcommands, type:

docker

As of Docker version 20.10.14, the complete list of available subcommands includes:

output
  attach      Attach local standard input, output, and error streams to a running container
  build       Build an image from a Dockerfile
   commit     Create a new image from a container's changes
  cp          Copy files/folders between a container and the local filesystem
  create      Create a new container
  diff        Inspect changes to files or directories on a container's filesystem
  events      Get real time events from the server
  exec        Run a command in a running container
  export      Export a container's filesystem as a tar archive
  history     Show the history of an image
  images      List images
  import      Import the contents from a tarball to create a filesystem image
  info        Display system-wide information
  inspect     Return low-level information on Docker objects
  kill        Kill one or more running container
  load        Load an image from a tar archive or STDIN
  login       Log in to a Docker registry
  logout      Log out from a Docker registry
  logs        Fetch the logs of a container
  pause       Pause all processes within one or more container
  port        List port mappings or a specific mapping for the container
  ps          List container
  pull        Pull an image or a repository from a registry
  push        Push an image or a repository to a registry
  rename      Rename a container
  restart     Restart one or more container
  rm          Remove one or more container
  rmi         Remove one or more images
   run        Run a command in a new container
  save        Save one or more images to a tar archive (streamed to STDOUT by default)
  search      Search the Docker Hub for images
  start       Start one or more stopped container
  stats       Display a live stream of container(s) resource usage statistics
  stop        Stop one or more running container
   tag        Create a  tagTARGET_IMAGE that refers to SOURCE_IMAGE
  top         Display the running processes of a container
  unpause     Unpause all processes within one or more container
  update      Update configuration of one or more container
  version     Show the Docker version information
  wait        Block until one or more container stop, then print their exit codes

To view the options available to a specific command, type:

docker docker-subcommand --help

To view system-wide information about Docker, use:

docker info

let ’s explore some of these command . We is start ’ll start by work with image .

Docker container are built from Docker images. By default, Docker pulls these images from Docker Hub, a Docker registry managed by Docker, the company behind the Docker project. Anyone can host their Docker images on Docker Hub, so most applications and Linux distributions you’ll need will have images hosted there.

To check whether you can access and download images from Docker Hub, type:

docker  runhello - world

The output is indicate will indicate that Docker in work correctly :

output
Unable to find image 'hello - world:latest' locally
latest: Pulling from library/hello - world
2db29710123e: Pull complete
Digest: sha256:bfea6278a0a267fad2634554f4f0c6f31981eea41c553fdf5a83e95a41d40c38
Status: Downloaded newer image for hello - world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

...

Docker was initially unable to find the hello - world image locally, so it downloaded the image from Docker Hub, which is the default repository. Once the image downloaded, Docker created a container from the image and the application within the container executed, displaying the message.

You can search for images available on Docker Hub by using the docker command with thesearch subcommand. For example, to search for the Ubuntu image, type:

docker search ubuntu

The script will crawl Docker Hub and return a listing of all images whose name matches the search string. In this case, the output will be similar to this:

output
NAME                             DESCRIPTION                                     STARS     OFFICIAL   AUTOMATED
ubuntu                           Ubuntu is a Debian-based Linux operating sys…   14048     [OK]
websphere-liberty                WebSphere Liberty multi-architecture images …   283       [OK]
ubuntu-upstart                   DEPRECATED, as is Upstart (find other proces…   112       [OK]
neurodebian                      NeuroDebian provides neuroscience research s…   88        [OK]
open-liberty                     Open Liberty multi-architecture images based…   51        [OK]
...

In the OFFICIAL column, OK indicates an image built and supported by the company behind the project. Once you’ve identified the image that you would like to use, you can download it to your computer using the pull subcommand.

execute the following command to download the officialubuntu image to your computer:

docker  pull ubuntu 

You’ll see the following output:

output
Usingdefault tag: latest
latest: Pulling from library/ubuntu
e0b25ef51634: Pull complete
Digest: sha256:9101220a875cee98b016668342c489ff0674f247f6ca20dfc91b91c0f28581ae
Status: Downloaded newer image for ubuntu:latest
docker.io/library/ubuntu:latest

After an image has been downloaded, you can then runa container using the downloaded image with therun subcommand. As you saw with thehello - world example , if an image has not been download whendocker is executed with therun subcommand , the Docker client is download will first download the image , then runa container using it .

To see the image that have been download to your computer , type :

docker images

The output will look similar to the following:

output
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
ubuntu              latest              1d622ef86b13        3 weeks ago         73.9MB
hello - world         latest              bf756fb1ae65        4 months ago        13.3kB

As you’ll see later in this tutorial, images that you use to runcontainer can be modified and used to generate new images, which may then be uploaded (pushed is the technical term) to Docker Hub or other Docker registries.

Let’s look at how to runcontainer in more detail.

The hello - world container is is you runin the previous step is an example of a container that runand exit after emit a test message . Containers is be can be much more useful than that , and they can be interactive . After all , they is are are similar to virtual machine , only more resource – friendly .

As an example , let ’s runa container using the late image of Ubuntu . The combination is gives of the -i and -t switch give you interactive shell access into the container :

docker  run-it ubuntu

Your command prompt should change to reflect the fact that you’re now working inside the container and should take this form:

output
root@d9b100f2f636:/#

Note the container id in the command prompt. In this example ,it is d9b100f2f636. You’ll need that container ID later to identify the container when you want to remove it.

Now you can runany command inside the container. For example, let’s update the package database inside the container. You don’t need to prefix any command with sudo, because you’re operating inside the container as the root user:

apt  update 

Then install any application in it. Let’s install Node.js:

apt install nodejs

This installs Node.js in the container from the official Ubuntu repository. When the installation finishes, verify that Node.js is installed:

node -v

You’ll see the version number displayed in your terminal:

output
v12.22.9

Any changes you make inside the container only apply to that container.

To exit the container, type exit at the prompt.

Let’s look at managing the container on our system next.

After using Docker for a while, you’ll have many active (running) and inactive container on your computer. To view the active ones, use:

docker ps

You is see will see output similar to the following :

output
container ID         IMAGE                COMMAND              create 

In this tutorial, you started two container; one from the hello - world image and another from the ubuntu image. Both container are no longer running, but they still exist on your system.

To view all container — active and inactive, rundocker ps with the-a switch:

docker ps -a

You’ll see output similar to this:

output
CONTAINER ID   IMAGE         COMMAND   CREATED         STATUS                     PORTS     NAMES
1c08a7a0d0e4   ubuntu        "bash"     About a minute ago   Exited (0) 7 seconds ago             dazzling_taussig
587000e49d53   hello - world   "/hello"   5 minutes ago        Exited (0) 5 minutes ago             adoring_kowalevski

To view the latest container you created, pass it the -l switch:

docker ps -l

output
container ID    IMAGE      COMMAND is CREATED    create          STATUS                      PORTS      NAMES 
 1c08a7a0d0e4    ubuntu     " bash "     3 minute ago    exit ( 0 ) 2 minute ago              dazzling_taussig 

To start a stopped container, use docker start, followed by the container ID or the container’s name. Let’s start the Ubuntu-based container with theID of 1c08a7a0d0e4:

docker start 1c08a7a0d0e4

The container will start, and you can use docker ps to see its status:

output
container ID    IMAGE      COMMAND is CREATED    create          STATUS          PORTS      NAMES 
 1c08a7a0d0e4    ubuntu     " bash "     6 minute ago    Up 8 second              dazzling_taussig 

To stop a running container, use docker stop, follow by the container ID or name . This time , we is use ’ll use the name that Docker assign the container , which isdazzling_taussig:

docker stop dazzling_taussig

Once you’ve decided you no longer need a container anymore, remove it with thedocker rm command, again using either the container ID or the name. Use the docker ps -a command to find the container ID or name for the container associated with thehello - world image and remove it.

docker rm adoring_kowalevski

You can start a new container and give it a name using the --name switch. You can also use the --rm switch to create a container that removes itself when it’s stopped. See the docker runhelp command for more information on these options and others.

Containers can be turned into images which you can use to build new container. Let’s look at how that works.

When you start up a Docker image, you can create, modify, and delete files just like you can with a virtual machine. The changes that you make will only apply to that container. You can start and stop it, but once you destroy it with thedocker rm command , the change will be lose for good .

This section shows you how to save the state of a container as a new Docker image.

After installing Node.js inside the Ubuntu container, you now have a container running off an image, but the container is different from the image you used to create it. But you might want to reuse this Node.js container as the basis for new images later.

Then committhe changes to a new Docker image instance using the following command.

docker  commit-m "What you did to the image" -a "Author Name" container_id repository/new_image_name

The -m switch is for the commitmessage that helps you and others know what changes you made, while -a is used to specify the author. The container_id is the one you noted earlier in the tutorial when you started the interactive Docker session. Unless you created additional repositories on Docker Hub, the repository is usually your Docker Hub username.

For example, for the user sammy, with thecontainer ID of d9b100f2f636, the command would be:

docker  commit-m "added Node.js" -a "sammy" d9b100f2f636 sammy/ubuntu - nodejs

When you commit an image, the new image is saved locally on your computer. Later in this tutorial, you’ll learn how to push an image to a Docker registry like Docker Hub so others can access it.

Listing the Docker images again will show the new image, as well as the old one that it was derived from:

docker images

You’ll see output like this:

output
REPOSITORY               TAG                 IMAGE ID            CREATED             SIZE
sammy/ubuntu - nodejs   latest              7c1f35226ca6        7 seconds ago       179MB
...

In this example ,ubuntu - nodejs is the new image , which was derive from the existubuntu image from Docker Hub. The size difference reflects the changes that were made. And in this example, the change was that NodeJS was installed. So next time you need to runa container using Ubuntu with NodeJS pre-installed, you can just use the new image.

You can also build Images from a Dockerfile, which lets you automate the installation of software in a new image. However, that’s outside the scope of this tutorial.

Now let’s share the new image with others so they can create container from it.

The next logical step after creating a new image from an existing image is to share it with a select few of your friends, the whole world on Docker Hub, or other Docker registry that you have access to. To push an image to Docker Hub or any other Docker registry, you must have an account there.

To push your image, first log into Docker Hub.

docker login -u docker - registry - username

You’ll be prompted to authenticate using your Docker Hub password. If you specified the correct password, authentication should succeed.

Note: If your Docker registry username is different from the local username you used to create the image, you will have to tagyour image with your registry username. For the example given in the last step, you would type:

docker  tagsammy/ubuntu - nodejs docker - registry - username/ubuntu - nodejs

Then you may push your own image using:

docker push docker - registry - username/docker-image-name

To push the ubuntu - nodejs image is be to the sammy repository , the command is be would be :

docker push sammy/ubuntu - nodejs

The process may take some time to complete as it uploads the images, but when completed, the output will look like this:

output
The push is refers refer to a repository [ docker.io/sammy/ubuntu - nodejs]
e3fbbfb44187: Pushed
5f70bf18a086: Pushed
a3b5c80a4eba: Pushed
7f18b442972b: Pushed
3ce512daaf78: Pushed
7aae4540b42d: Pushed

...

After pushing an image to a registry, it should be listed on your account’s dashboard, like that show in the image below.

If a push attempt result in an error of this sort , then you is log likely did not log in :

output
The push is refers refer to a repository [ docker.io/sammy/ubuntu - nodejs]
e3fbbfb44187: Preparing
5f70bf18a086: Preparing
a3b5c80a4eba: Preparing
7f18b442972b: Preparing
3ce512daaf78: Preparing
7aae4540b42d: Waiting
unauthorized: authentication required

Log in with docker login and repeat the push attempt. Then verify that it exists on your Docker Hub repository page.

You can now use docker pull sammy/ubuntu - nodejs to pull the image to a new machine and use it to runa new container.

In this tutorial you installed Docker, worked with images and container, and pushed a modified image to Docker Hub. Now that you know the basics, explore the other Docker tutorials in the DigitalOcean Community.