How to install Docker on CentOS

Copied from open source Docker Docs

Docker is supported on the following versions of CentOS:

CentOS 7.X

Installation on other binary compatible EL7 distributions such as Scientific Linux might succeed, but Docker does not test or support Docker on these distributions.

This page instructs you to install using Docker-managed release packages and installation mechanisms. Using these packages ensures you get the latest release of Docker. If you wish to install using CentOS-managed packages, consult your CentOS documentation.

Prerequisites

Docker requires a 64-bit installation regardless of your CentOS version. Also, your kernel must be 3.10 at minimum, which CentOS 7 runs.

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, is it recommended that you fully update your system. Please 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

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

Install with the script

Log into your machine as a user with sudo or root privileges.
Make sure your existing yum packages are up-to-date.
```
$ sudo yum update
```

Run the Docker installation script.

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

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

Start the Docker daemon.
```
$ sudo service docker start
```

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

$ sudo docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from hello-world
a8219747be10: Pull complete 
91c95931e552: Already exists 
hello-world:latest: The image you are pulling has been verified. Important: image verification is a tech preview feature and should not be relied on to provide security.
Digest: sha256:aa03e5d0d5553b4c3473e89c8619cf79df368babd1.7.1cf5daeb82aab55838d
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.
        (Assuming it was not already locally available.)
 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

For more examples and ideas, visit:
 http://docs.docker.com/userguide/

Install without the script

Log into your machine as a user with sudo or root privileges.
Make sure your existing yum packages are up-to-date.
```
$ sudo yum update
```

Add the yum repo yourself.

For CentOS 7 run:

$ cat >/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

Install the Docker package.
```
$ sudo yum install docker-engine
```
Start the Docker daemon.
```
$ sudo service docker start
```
Verify docker is installed correctly by running a test image in a container.
```
$ sudo docker run hello-world
```

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:

Log into Centos as a user with sudo privileges.
Create the docker group and add your user.

sudo usermod -aG docker your_username
Log out and log back in.

This ensures your user is running with the correct permissions.
Verify your work by running docker without sudo.
```
$ docker run hello-world
```

Start the docker daemon at boot

To ensure Docker starts when you boot your system, do the following:

  $ sudo chkconfig docker on

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.

Uninstall

You can uninstall the Docker software with yum.

List the package you have installed.

$ yum list installed | grep docker
yum list installed | grep docker
docker-engine.x86_64                1.7.1-1.el7
                                                                                                                                                         @/docker-engine-1.7.1-1.el7.x86_64.rpm

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.
To delete all images, containers, and volumes, run the following command:
```
$ rm -rf /var/lib/docker
```
Locate and delete any user-created configuration files.