How To Install and Use Docker on Ubuntu 22.04

Docker is an application that simplifies the process of managing application processes in containers. Containers let you run your applications in resource-isolated processes. They’re similar to virtual machines, but containers 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 containers and images, and push an image to a Docker Repository.

Prerequisites

To follow this tutorial, you will need the following:

• One Ubuntu 22.04 server set up by following the Ubuntu 22.04 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 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:

Next, install a few prerequisite packages which let apt use packages over HTTPS:

Then add the GPG key for the official Docker repository to your system:

Add the Docker repository to APT sources:

Update your existing list of packages again for the addition to be recognized:

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

You’ll see output like this, although the version number for Docker may be different:

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:

Docker should now be installed, the daemon started, and the process enabled to start on boot. Check that it’s running:

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 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.

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

By default, the docker 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:

docker: 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:

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

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:

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:

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.

Step 3 — Using the Docker Command

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

To view all available subcommands, type:

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

  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 containers
  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 containers
  port        List port mappings or a specific mapping for the container
  ps          List containers
  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 containers
  rm          Remove one or more containers
  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 containers
  stats       Display a live stream of container(s) resource usage statistics
  stop        Stop one or more running containers
  tag         Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE
  top         Display the running processes of a container
  unpause     Unpause all processes within one or more containers
  update      Update configuration of one or more containers
  version     Show the Docker version information
  wait        Block until one or more containers stop, then print their exit codes

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

To view system-wide information about Docker, use:

Let’s explore some of these commands. We’ll start by working with images.

Step 4 — Working with Docker Images

Docker containers 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:

The output will indicate that Docker in working correctly:

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 the search subcommand. For example, to search for the Ubuntu image, type:

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:

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 official ubuntu image to your computer:

You’ll see the following output:

Using default 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 run a container using the downloaded image with the run subcommand. As you saw with the hello-world example, if an image has not been downloaded when docker is executed with the run subcommand, the Docker client will first download the image, then run a container using it.

To see the images that have been downloaded to your computer, type:

The output will look similar to the following:

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 run containers 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 run containers in more detail.

Step 5 — Running a Docker Container

The hello-world container you ran in the previous step is an example of a container that runs and exits after emitting a test message. Containers can be much more useful than that, and they can be interactive. After all, they are similar to virtual machines, only more resource-friendly.

As an example, let’s run a container using the latest image of Ubuntu. The combination of the -i and -t switches gives you interactive shell access into the container:

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

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 run any 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:

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

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

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

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 containers on our system next.

Step 6 — Managing Docker Containers

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

You will see output similar to the following:

CONTAINER ID        IMAGE               COMMAND             CREATED

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

To view all containers — active and inactive, run docker ps with the -a switch:

You’ll see output similar to this:

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:

CONTAINER ID   IMAGE     COMMAND   CREATED         STATUS                     PORTS     NAMES
1c08a7a0d0e4   ubuntu    "bash"    3 minutes ago   Exited (0) 2 minutes 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 the ID of 1c08a7a0d0e4:

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

CONTAINER ID   IMAGE     COMMAND   CREATED         STATUS         PORTS     NAMES
1c08a7a0d0e4   ubuntu    "bash"    6 minutes ago   Up 8 seconds             dazzling_taussig

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

Once you’ve decided you no longer need a container anymore, remove it with the docker 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 the hello-world image and remove it.

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 run help command for more information on these options and others.

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

Step 7 — Committing Changes in a Container to a Docker Image

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 the docker rm command, the changes will be lost 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 commit the changes to a new Docker image instance using the following command.

The -m switch is for the commit message 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 the container ID of d9b100f2f636, the command would be:

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:

You’ll see output like this:

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 derived from the existing ubuntu 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 run a 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 containers from it.

Step 8 — Pushing Docker Images to a Docker Repository

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.

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

Then you may push your own image using:

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

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

The push refers 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 results in an error of this sort, then you likely did not log in:

The push refers 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 run a new container.

• 27/03/2023
• No Comments
• Docker

How to Get Started With Portainer, a Web UI for Docker

Portainer is a popular Docker UI that helps you visualise your containers, images, volumes and networks. Portainer helps you take control of the Docker resources on your machine, avoiding lengthy terminal commands.

Portainer recently reached version 2.0 which added support for Kubernetes clusters. The tool also supports Docker Swarm and Azure ACI environments. In this tutorial, we’ll be keeping it simple and using Portainer to manage a local Docker installation.

Two editions of the software are available, the free and open-source CE and commercial Business. The extra capabilities of Business are mostly focused on enhanced access, quota management, and administrator controls.

Install Portainer

Make sure you’ve got Docker installed and running before proceeding any further. Docker 19.01 is required for all Portainer features to be fully supported.

First of all, you’ll need to create a new Docker volume. Portainer will use this to store its persistent data. Ours is going to be called portainer_data.

docker volume create portainer_data

Next, use Docker to start a new Portainer container:

docker run -d -p 9000:9000 --name=portainer --restart=unless-stopped -v /var/run/docker.sock:/var/run/docker.sock -v portainer_data:/data portainer/portainer-ce

This command will pull the portainer/portainer-ce image and start a new container from it. The container will be detached and executing in the background (-d).

The volume created earlier is mounted to /data within the container, where Portainer stores all its application data. The host’s Docker socket is also mounted into the container, so that Portainer has access to your machine’s Docker instance. Finally, port 9000 on the host is bound to port 9000 within the container. This is the port Portainer exposes its web UI on.

First Run

You can now login to Portainer by visiting http://localhost:9000 in your browser. You’ll need to set a password for the admin user upon first use. You’ll then land on the Home screen.

Before beginning to use Portainer, it’s worth looking at the app’s own configuration options. Click the “Settings” link in the left navigation menu. Here, you can change Portainer security settings, set a custom application logo and opt out of anonymous usage statistics collection. Most of the settings should be fairly self-explanatory, with the majority focused on limiting the power afforded to non-administrator users.

The “Authentication” submenu in the navigation bar lets you configure how users login to Portainer. Portainer uses its own internal user management system by default but you can choose to use an existing LDAP server or OAuth provider. Select the method to use and then fill out the form fields to setup your preferred authentication system. When using the built-in users database, you can use the “Users” link in the sidemenu to create additional users and sort them into teams.

Endpoints

Portainer lets you manage multiple Docker endpoints. To begin with, you’ll see a single “local” endpoint, representing the Docker Engine running on your own machine.

To add an additional endpoint, click the “Endpoints” link in the sidebar. Next, click the blue “Add endpoint” button. Choose the type of endpoint you’ll be using and supply your connection details.

All being well, you’ll be able to add your endpoint. It’ll show up as a new selectable tile on the Portainer homescreen. Detailed guidance on adding additional endpoints is outside the scope of this introductory guide as success will require correct configuration of the host you’re connecting to.

Managing Containers

You’re now ready to begin using Portainer to interact with Docker. From the homescreen, click your “local” endpoint. It will become selected within Portainer, giving you access to the full management UI. You’ll arrive at a simple dashboard giving you an overview of your containers, images and volumes.

Click “Containers” on the dashboard or in the sidebar to open the container management screen. You’ll see a table displaying all your Docker containers.

To take an action against a container, click the checkbox next to its name. You can now use the button row at the top of the screen to start, stop, restart or remove the container. Containers which are currently running will show a green “running” state while stopped ones get a red “stopped”.

If you’re using a fresh Docker installation, your only container might be Portainer itself. Take care not to stop this container, as it’s serving the Portainer web UI you’re using!

Click the name of a container to view and change its details. This screen allows you to inspect the container’s properties, create a new Docker image from its current state and manage its network connections.

At the top of the screen, you’ll find five buttons under “Container status” that allow you to view the container’s logs (“Logs”), inspect its Docker manifest (“Inspect”), view resource usage statistics (“Stats”), access an interactive console (“Console”) or attach a console to the foreground process in the container (“Attach”).

Create a Container

To create a new container, return to the Containers screen and click the blue “Add container” button. You may also edit an existing container – effectively destroying it and replacing it with a new one with modified properties – by using the “Duplicate/Edit” button on the container details screen. Both operations display the same interface.

First, type a name for your new container. Next, specify the Docker image to use. For public images on Docker Hub, such as wordpress:latest, you can type an image name without providing any additional configuration.

To use images stored within a private registry, you’ll first need to add the registry’s details to Portainer. Click the “Registries” link under the Settings heading in the left sidebar. Press the blue “Add registry” button and define the URL, username and password of your registry. You’ll then be able to select it in the “Registry” dropdown on the container creation screen. You may also use the Registries screen to set credentials for Docker Hub connections, allowing you to pull private images and avoid the rate limits applied to unauthenticated users.

You’re now ready to deploy your container by pressing the “Deploy the container” button at the bottom of the form. Before proceeding, review the additional settings which are displayed above the button. You can configure port binding, force Portainer to pull the image before deploying and choose to remove the container automatically when it exits.

At the bottom of the screen, you’ll find an advanced settings UI that offers even more options – too many to cover exhaustively here. These replicate the entire functionality of the docker run CLI command, enabling you to set up the container’s command, entrypoint, volumes, network interfaces and environment variables. Much of this UI should feel intuitive if you’re already familiar with Docker’s capabilities.

Using Container Stacks

The container creation screen only permits you to spin up one container at a time. Portainer has built-in support for “stacks” which allow you to deploy linked containers. This functionality is based on docker-compose version 2.

Click the “Stacks” item in the navigation bar, then press the “Add stack” button. There’s no support for creating stacks graphically – you have to paste or upload a docker-compose.yml file. You may also choose to connect to a Git repository and use its docker-compose.yml directly.

Before deploying the stack, you’re able to set environment variables that will be made available to the containers. Choose which level of Portainer access control to apply and then click “Deploy the stack”. Portainer will pull all the images and create all the containers specified by the Compose file.

Select your stack from the Stacks screen to manage its containers collectively. You can stop all the containers in the stack, or delete the stack entirely, using the buttons at the top of the screen. There’s also controls to duplicate the stack or create a reusable template from its current state.

Templates can be accessed from the stack creation screen and allow you to quickly spin up new instances of frequently used services. Portainer also ships with a number of built-in templates, accessible from the “App Templates” link in the navigation bar.

RELATED: How to Install Docker and Docker Compose on Linux

Portainer’s Convenience

Portainer helps you quickly create, manage and monitor Docker containers. It provides a graphical interface to Docker CLI commands that can sometimes become long and unwieldy. It also makes Docker accessible to users who may be unfamiliar with command-line interfaces.

Besides its container management capabilities, Portainer also provides visibility into the other fundamental Docker resources. The Images screen allows you to view, pull, import, export and delete the images available on your endpoint. The Networks and Volumes screens act similarly, enumerating and providing control over their respective resources. Finally, the Events table offers a comprehensive listing of all the actions taken by the Docker engine. This can be useful when reviewing past actions and identifying when certain containers were created or destroyed.

• 24/01/2023
• No Comments
• Docker