# Install Docker Engine on CentOS

By

Charl Cronje

Update 2022-01-22 Your might find that you need have container communicate with each other, have a look at: Docker Networks

To install Docker Engine, you need a maintained version of CentOS 7 or 8. Archived versions aren’t supported or tested.

The centos-extras repository must be enabled. This repository is enabled by default, but if you have disabled it, you need to re-enable it.

The overlay2 storage driver is recommended.

Older versions of Docker were called docker or docker-engine. If these are installed, uninstall them, along with associated dependencies.

 sudo yum remove docker \
    docker-client \
    docker-client-latest \
    docker-common \
    docker-latest \
    docker-latest-logrotate \
    docker-logrotate \
    docker-engine

It’s OK if yum reports that none of these packages are installed.

The contents of /var/lib/docker/, including images, containers, volumes, and networks, are preserved. The Docker Engine package is now called docker-ce.

You can install Docker Engine in different ways, depending on your needs:

• Most users set up Docker’s repositories and install from them, for ease of installation and upgrade tasks. This is the recommended approach.
• Some users download the RPM package and install it manually and manage upgrades completely manually. This is useful in situations such as installing Docker on air-gapped systems with no access to the internet.
• In testing and development environments, some users choose to use automated convenience scripts to install Docker.

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.

Install the yum-utils package (which provides the yum-config-manager utility) and set up the stable repository.

 sudo yum install -y yum-utils
 sudo yum-config-manager \
    --add-repo \
    https://download.docker.com/linux/centos/docker-ce.repo

Install the latest version of Docker Engine and containerd, or go to the next step to install a specific version:

sudo yum install docker-ce docker-ce-cli containerd.io If prompted to accept the GPG key, verify that the fingerprint matches 060A 61C5 1B55 8A7F 742B 77AA C52F EB6B 621E 9F35, and if so, accept it.

Got multiple Docker repositories?

If you have multiple Docker repositories enabled, installing or updating without specifying a version in the yum install or yum update command always installs the highest possible version, which may not be appropriate for your stability needs.

 yum list docker-ce --showduplicates | sort -r

docker-ce.x86_64  3:18.09.1-3.el7                     docker-ce-stable
docker-ce.x86_64  3:18.09.0-3.el7                     docker-ce-stable
docker-ce.x86_64  18.06.1.ce-3.el7                    docker-ce-stable
docker-ce.x86_64  18.06.0.ce-3.el7                    docker-ce-stable

The list returned depends on which repositories are enabled, and is specific to your version of CentOS (indicated by the .el7 suffix in this example).

2. Install a specific version by its fully qualified package name, which is the package name (docker-ce) plus the version string (2nd column) starting at the first colon (:), up to the first hyphen, separated by a hyphen (-). For example, docker-ce-18.09.1.

sudo yum install docker-ce-<VERSION_STRING> docker-ce-cli-<VERSION_STRING> containerd.io

This command installs Docker, but it doesn’t start Docker. It also creates a docker group, however, it doesn’t add any users to the group by default.

sudo systemctl start docker

Verify that Docker Engine is installed correctly by running the hello-world image.

sudo docker run hello-world

This command downloads a test image and runs it in a container. When the container runs, it prints a message and exits.

This installs and runs Docker Engine. 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.

To upgrade Docker Engine, follow the installation instructions, choosing the new version you want to install.

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

Go to https://download.docker.com/linux/centos/ and choose your version of CentOS. Then browse to x86_64/stable/Packages/ and download the .rpm file for the Docker version you want to install.

To install a nightly or test (pre-release) package, change the word stable in the above URL to nightly or test. Learn about nightly and test channels.

Install Docker Engine, changing the path below to the path where you downloaded the Docker package.

sudo yum install /path/to/package.rpm

Docker is installed but not started. The docker group is created, but no users are added to the group.

sudo systemctl start docker

Verify that Docker Engine is installed correctly by running the hello-world image.

sudo docker run hello-world

This command downloads a test image and runs it in a container. When the container runs, it prints a message and exits.

This installs and runs Docker Engine. Use sudo to run Docker commands. Continue to Post-installation steps for Linux to allow non-privileged users to run Docker commands and for other optional configuration steps.

To upgrade Docker Engine, download the newer package file and repeat the installation procedure, using yum -y upgrade instead of yum -y install, and point to the new file.

• Docker provides a convenience script at get.docker.com to install Docker into development environments quickly and non-interactively. The convenience script is not recommended for production environments, but can be used as an example to create a provisioning script that is 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 can be found in the docker-install repository on GitHub.
• 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, and does not 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 (major) upgrades in a test environment before deploying to your production systems.
• The script is not 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, causing outdated versions to be used.

You can run the script with the DRY_RUN=1 option to learn what steps the script will execute during installation:

 curl -fsSL https://get.docker.com -o get-docker.sh
 DRY_RUN=1 sh ./get-docker.sh

This example downloads the script from get.docker.com 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

• Docker is installed. The docker service starts automatically on Debian based distributions. On RPM based distributions, such as CentOS, Fedora, RHEL or SLES, you need to start it manually using the appropriate systemctl or service command. As the message indicates, non-root users cannot run Docker commands by default.
• 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. Docker can also be installed 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).

Docker also provides a convenience script at test.docker.com to install pre-releases of Docker on Linux. This script is equivalent to the script at get.docker.com, but configures your package manager to enable the “test” channel from our package repository, which 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 are 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 is no advantage to re-running the convenience script, and it can cause issues if it attempts to re-add repositories which have already been added to the host machine.

Uninstall the Docker Engine, CLI, and Containerd packages:

 sudo yum remove docker-ce docker-ce-cli containerd.io

Images, containers, volumes, or customized configuration files on your host are not automatically removed. To delete all images, containers, and volumes:

 sudo rm -rf /var/lib/docker
 sudo rm -rf /var/lib/containerd

You must delete any edited configuration files manually