Get Docker for CentOS

Estimated reading time: 7 minutes

To get started with Docker on CentOS, make sure you meet the prerequisites, then install Docker.

Prerequisites

OS requirements

To install Docker, you need the 64-bit version of CentOS 7.

Remove unofficial Docker packages

Red Hat’s operating system repositories contain an older version of Docker, with the package name docker instead of docker-engine. If you installed this version of Docker, remove it using the following command:

$ sudo yum -y remove docker

You may also have to remove the package docker-selinux which conflicts with the official docker-engine package. Remove it with the following command:

$ sudo yum -y remove docker-selinux

The contents of /var/lib/docker are not removed, so any images, containers, or volumes you created using the older version of Docker are preserved.

Install Docker

You can install Docker 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.
Some users cannot use third-party repositories, and must rely on the version of Docker in the CentOS repositories. This version of Docker may be out of date. Those users should consult the CentOS documentation and not follow these procedures.

Install using the repository

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

Set up the repository

Install yum-utils, which provides the yum-config-manager utility:
```
$ sudo yum install -y yum-utils
```

Use the following command to set up the stable repository:

$ sudo yum-config-manager \
    --add-repo \
    https://docs.docker.com/engine/installation/linux/repo_files/centos/docker.repo

Optional: Enable the testing repository. This repository is included in the docker.repo file above but is disabled by default. You can enable it alongside the stable repository. Do not use unstable repositories on on production systems or for non-testing workloads.

Warning: If you have both stable and unstable repositories enabled, installing or updating without specifying a version in the yum install or yum update command will always install the highest possible version, which will almost certainly be an unstable one.
```
$ sudo yum-config-manager --enable docker-testing
```
You can disable the testing repository by running the yum-config-manager command with the --disable flag. To re-enable it, use the --enable flag. The following command disables the testing repository.
```
$ sudo yum-config-manager --disable docker-testing
```

Install Docker

Update the yum package index.
```
$ sudo yum makecache fast
```
If this is the first time you have refreshed the package index since adding the Docker repositories, you will be prompted to accept the GPG key, and the key’s fingerprint will be shown. Verify that the fingerprint matches 58118E89F3A912897C070ADBF76221572C52609D and if so, accept the key.
Install the latest version of Docker, or go to the next step to install a specific version.
```
$ sudo yum -y install docker-engine
```
Warning: If you have both stable and unstable repositories enabled, installing or updating Docker without specifying a version in the yum install or yum upgrade command will always install the highest available version, which will almost certainly be an unstable one.
On production systems, you should install a specific version of Docker instead of always using the latest. List the available versions. This example uses the sort -r command to sort the results by version number, highest to lowest, and is truncated.

Note: This yum list command only shows binary packages. To show source packages as well, omit the .x86_64 from the package name.
```
$ yum list docker-engine.x86_64  --showduplicates |sort -r

docker-engine.x86_64  1.13.0-1.el7                               docker-main
docker-engine.x86_64  1.12.5-1.el7                               docker-main   
docker-engine.x86_64  1.12.4-1.el7                               docker-main   
docker-engine.x86_64  1.12.3-1.el7                               docker-main   
```
The contents of the list depend upon which repositories are enabled, and will be specific to your version of CentOS (indicated by the .el7 suffix on the version, in this example). Choose a specific version to install. The second column is the version string. The third column is the repository name, which indicates which repository the package is from and by extension its stability level. To install a specific version, append the version string to the package name and separate them by a hyphen (-):
```
$ sudo yum -y install docker-engine-<VERSION_STRING>
```
Start Docker.
```
$ sudo systemctl start docker
```
Verify that docker 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 an informational message and exits.

Docker is installed and running. You need 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

To upgrade Docker, first run sudo yum makecache fast, then follow the installation instructions, choosing the new version you want to install.

Install from a package

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

Go to https://yum.dockerproject.org/repo/main/centos/ and choose the subdirectory for your CentOS version. Download the .rpm file for the Docker version you want to install.

Note: To install a testing version, change the word stable in the URL to testing. Do not use unstable versions of Docker in production or for non-testing workloads.
Install Docker, changing the path below to the path where you downloaded the Docker package.
```
$ sudo yum -y install /path/to/package.rpm
```
Start Docker.
```
$ sudo systemctl start docker
```
Verify that docker 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 an informational message and exits.

Docker is installed and running. You need to 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.

Upgrade Docker

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

Uninstall Docker

Uninstall the Docker package:
```
$ sudo yum -y remove docker-engine
```
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
```

You must delete any edited configuration files manually.

Next steps

Continue to Post-installation steps for Linux
Continue with the User Guide.

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