CentOS

Docker runs on CentOS 7.X. An installation on other binary compatible EL7 distributions such as Scientific Linux might succeed, but Docker does not test or support Docker on these distributions.

These instructions install Docker using release packages and installation mechanisms managed by Docker, to be sure that you get the latest version of Docker. If you wish to install using CentOS-managed packages, consult your CentOS release documentation.

Prerequisites

Docker requires a 64-bit OS and version 3.10 or higher of the Linux kernel.

To check your current kernel version, open a terminal and use uname -r to display your kernel version:

$ uname -r

3.10.0-229.el7.x86_64

Finally, it is recommended that you fully update your system. Keep in mind that your system should be fully patched to fix any potential kernel bugs. Any reported kernel bugs may have already been fixed on the latest kernel packages.

Install Docker Engine

There are two ways to install Docker Engine. You can install using the yum package manager. Or you can use curl with the get.docker.com site. This second method runs an installation script which also installs via the yum package manager.

Install with yum

1. Log into your machine as a user with sudo or root privileges.

2. Make sure your existing packages are up-to-date.

   $ sudo yum update
   

3. Add the yum repo.

   $ sudo tee /etc/yum.repos.d/docker.repo <<-'EOF'
   
   [dockerrepo]
   
   name=Docker Repository
   
   baseurl=https://yum.dockerproject.org/repo/main/centos/7/
   
   enabled=1
   
   gpgcheck=1
   
   gpgkey=https://yum.dockerproject.org/gpg
   
   EOF
   

4. Install the Docker package.

   $ sudo yum install docker-engine
   

5. Enable the service.

   $ sudo systemctl enable docker.service
   

6. Start the Docker daemon.

   $ sudo systemctl start docker
   

7. Verify docker is installed correctly by running a test image in a container.

    $ sudo docker run --rm hello-world
   
    Unable to find image 'hello-world:latest' locally
   
    latest: Pulling from library/hello-world
   
    c04b14da8d14: Pull complete
   
    Digest: sha256:0256e8a36e2070f7bf2d0b0763dbabdd67798512411de4cdcf9431a1feb60fd9
   
    Status: Downloaded newer image for hello-world:latest
   
    Hello from Docker!
   
    This message shows that your installation appears to be working correctly.
   
    To generate this message, Docker took the following steps:
   
     1. The Docker client contacted the Docker daemon.
   
     2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
   
     3. The Docker daemon created a new container from that image which runs the
   
        executable that produces the output you are currently reading.
   
     4. The Docker daemon streamed that output to the Docker client, which sent it
   
        to your terminal.
   
    To try something more ambitious, you can run an Ubuntu container with:
   
     $ docker run -it ubuntu bash
   
    Share images, automate workflows, and more with a free Docker Hub account:
   
     https://hub.docker.com
   
    For more examples and ideas, visit:
   
     https://docs.docker.com/engine/userguide/
   

If you need to add an HTTP Proxy, set a different directory or partition for the Docker runtime files, or make other customizations, read our Systemd article to learn how to customize your Systemd Docker daemon options.

Install with the script

1. Log into your machine as a user with sudo or root privileges.

2. Make sure your existing packages are up-to-date.

   $ sudo yum update
   

3. Run the Docker installation script.

   $ curl -fsSL https://get.docker.com/ | sh
   

   This script adds the docker.repo repository and installs Docker.

4. Enable the service.

   $ sudo systemctl enable docker.service
   

5. Start the Docker daemon.

   $ sudo systemctl start docker
   

6. Verify docker is installed correctly by running a test image in a container.

   $ sudo docker run hello-world
   

If you need to add an HTTP Proxy, set a different directory or partition for the Docker runtime files, or make other customizations, read our Systemd article to learn how to customize your Systemd Docker daemon options.

Create a docker group

The docker daemon binds to a Unix socket instead of a TCP port. By default that Unix socket is owned by the user root and other users can access it with sudo. For this reason, docker daemon always runs as the root user.

To avoid having to use sudo when you use the docker command, create a Unix group called docker and add users to it. When the docker daemon starts, it makes the ownership of the Unix socket read/writable by the docker group.

Warning: The docker group is equivalent to the root user; For details on how this impacts security in your system, see Docker Daemon Attack Surface for details.

To create the docker group and add your user:

1. Log into your machine as a user with sudo or root privileges.

2. Create the docker group.

   $ sudo groupadd docker
   

3. Add your user to docker group.

   $ sudo usermod -aG docker your_username`
   

4. Log out and log back in.

   This ensures your user is running with the correct permissions.

5. Verify that your user is in the docker group by running docker without sudo.

   $ docker run hello-world
   

Start the docker daemon at boot

Configure the Docker daemon to start automatically when the host starts:

$ sudo systemctl enable docker

Uninstall

You can uninstall the Docker software with yum.

1. List the installed Docker packages.

   $ yum list installed | grep docker
   
   docker-engine.x86_64     1.7.1-0.1.el7@/docker-engine-1.7.1-0.1.el7.x86_64
   

2. Remove the package.

   $ sudo yum -y remove docker-engine.x86_64
   

   This command does not remove images, containers, volumes, or user-created configuration files on your host.

3. To delete all images, containers, and volumes, run the following command:

   $ rm -rf /var/lib/docker
   

4. Locate and delete any user-created configuration files.