Docker Beginners: 1

What is Docker?

Introduction

What is Docker?

An open-source project that automates the deployment of software applications inside containers by providing an additional layer of abstraction and automation of OS-level virtualization on Linux.

Install Docker Engine on Ubuntu

OS requirements

To install Docker Engine, you need the 64-bit version of one of these Ubuntu versions:

  • Ubuntu Lunar 23.04
  • Ubuntu Kinetic 22.10
  • Ubuntu Jammy 22.04 (LTS)
  • Ubuntu Focal 20.04 (LTS)

Docker Engine for Ubuntu is compatible with x86_64 (or amd64), armhf, arm64, s390x, and ppc64le (ppc64el) architectures.

Install using the apt repository

Before you install Docker Engine for the first time on a new host machine, you need to set up the Docker repository. Afterward, you can install and update Docker from the repository.

Set up the repository

  1. Update the apt package index and install packages to allow apt to use a repository over HTTPS:
sudo apt-get update
sudo apt-get install ca-certificates curl gnupg
  1. Add Docker’s official GPG key:
sudo install -m 0755 -d /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
sudo chmod a+r /etc/apt/keyrings/docker.gpg
  1. Use the following command to set up the repository:
echo \
"deb [arch="$(dpkg --print-architecture)" signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
"$(. /etc/os-release && echo "$VERSION_CODENAME")" stable" | \
sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Note

If you use an Ubuntu derivative distro, such as Linux Mint, you may need to use UBUNTU_CODENAME instead of VERSION_CODENAME.

  1. Update the apt package index:
sudo apt-get update

Install Docker Engine

  1. Install Docker Engine, containerd, and Docker Compose.

To install the latest version, run:

sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
  1. Verify that the Docker Engine installation is successful by running the hello-world image.
sudo docker run hello-world
  1. This command downloads a test image and runs it in a container. When the container runs, it prints a confirmation message and exits.

You have now successfully installed and started Docker Engine.

To install a specific version of Docker Engine, start by listing the available versions in the repository:

# List the available versions:
apt-cache madison docker-ce | awk '{ print $3 }'

5:24.0.0-1~ubuntu.22.04~jammy
5:23.0.6-1~ubuntu.22.04~jammy
<...>

Select the desired version and install:

VERSION_STRING=5:24.0.0-1~ubuntu.22.04~jammy
sudo apt-get install docker-ce=$VERSION_STRING docker-ce-cli=$VERSION_STRING containerd.io docker-buildx-plugin docker-compose-plugin
  1. Verify that the Docker Engine installation is successful by running the hello-world image.

sudo docker run hello-world

Tip

Receiving errors when trying to run without root?

The docker user group exists but contains no users, which is why you’re required to use sudo to run Docker commands. Continue to Linux postinstall to allow non-privileged users to run Docker commands and for other optional configuration steps.

Upgrade Docker Engine

If you can’t use Docker’s apt repository to install Docker Engine, you can download the deb file for your release and install it manually. You need to download a new file each time you want to upgrade Docker Engine.

  1. Go to https://download.docker.com/linux/ubuntu/dists/open_in_new.

  2. Select your Ubuntu version in the list.

  3. Go to pool/stable/ and select the applicable architecture (amd64, armhf, arm64, or s390x).

  4. Download the following deb files for the Docker Engine, CLI, containerd, and Docker Compose packages:

    • containerd.io_<version>_<arch>.deb
    • docker-ce_<version>_<arch>.deb
    • docker-ce-cli_<version>_<arch>.deb
    • docker-buildx-plugin_<version>_<arch>.deb
    • docker-compose-plugin_<version>_<arch>.deb
  5. Install the .deb packages. Update the paths in the following example to where you downloaded the Docker packages.

sudo dpkg -i ./containerd.io__.deb \
  ./docker-ce__.deb \
  ./docker-ce-cli__.deb \
  ./docker-buildx-plugin__.deb \
  ./docker-compose-plugin__.deb
The Docker daemon starts automatically.
 
  1. Verify that the Docker Engine installation is successful by running the hello-world image.

sudo service docker start
sudo docker run hello-world
This command downloads a test image and runs it in a container. When the container runs, it prints a confirmation message and exits.

You have now successfully installed and started Docker Engine.

Tip

Receiving errors when trying to run without root?

The docker user group exists but contains no users, which is why you’re required to use sudo to run Docker commands. Continue to Linux postinstall to allow non-privileged users to run Docker commands and for other optional configuration steps.

Upgrade Docker Engine

To upgrade Docker Engine, download the newer package files and repeat the installation procedure, pointing to the new files.

Install using the convenience script

Docker provides a convenience script at https://get.docker.com/open_in_new to install Docker into development environments non-interactively. The convenience script isn’t recommended for production environments, but it’s useful for creating a provisioning script tailored to your needs. Also refer to the install using the repository steps to learn about installation steps to install using the package repository. The source code for the script is open source, and you can find it in the docker-install repository on GitHubopen_in_new.

Always examine scripts downloaded from the internet before running them locally. Before installing, make yourself familiar with potential risks and limitations of the convenience script:

  • The script requires root or sudo privileges to run.
  • The script attempts to detect your Linux distribution and version and configure your package management system for you.
  • The script doesn’t allow you to customize most installation parameters.
  • The script installs dependencies and recommendations without asking for confirmation. This may install a large number of packages, depending on the current configuration of your host machine.
  • By default, the script installs the latest stable release of Docker, containerd, and runc. When using this script to provision a machine, this may result in unexpected major version upgrades of Docker. Always test upgrades in a test environment before deploying to your production systems.
  • The script isn’t designed to upgrade an existing Docker installation. When using the script to update an existing installation, dependencies may not be updated to the expected version, resulting in outdated versions.

Tip: preview script steps before running

You can run the script with the --dry-run option to learn what steps the script will run when invoked:

curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh ./get-docker.sh --dry-run

This example downloads the script from https://get.docker.com/open_in_new and runs it to install the latest stable release of Docker on Linux:

curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh
Executing docker install script, commit: 7cae5f8b0decc17d6571f9f52eb840fbc13b2737
<...>

Use Docker as a non-privileged user, or install in rootless mode?

The installation script requires root or sudo privileges to install and use Docker. If you want to grant non-root users access to Docker, refer to the post-installation steps for Linux. You can also install Docker without root privileges, or configured to run in rootless mode. For instructions on running Docker in rootless mode, refer to run the Docker daemon as a non-root user (rootless mode).

Install pre-releases

Docker also provides a convenience script at https://test.docker.com/open_in_new to install pre-releases of Docker on Linux. This script is equal to the script at get.docker.com, but configures your package manager to use the test channel of the Docker package repository. The test channel includes both stable and pre-releases (beta versions, release-candidates) of Docker. Use this script to get early access to new releases, and to evaluate them in a testing environment before they’re released as stable.

To install the latest version of Docker on Linux from the test channel, run:

curl -fsSL https://test.docker.com -o test-docker.sh
sudo sh test-docker.sh

Upgrade Docker after using the convenience script

If you installed Docker using the convenience script, you should upgrade Docker using your package manager directly. There’s no advantage to re-running the convenience script. Re-running it can cause issues if it attempts to re-install repositories which already exist on the host machine.

Uninstall Docker Engine

  1. Uninstall the Docker Engine, CLI, containerd, and Docker Compose packages:
sudo apt-get purge docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin docker-ce-rootless-extras
  1. Images, containers, volumes, or custom configuration files on your host aren’t automatically removed. To delete all images, containers, and volumes:
sudo rm -rf /var/lib/docker
sudo rm -rf /var/lib/containerd

You have to delete any edited configuration files manually.