Install Docker on CentOS 7

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Step 0 – Prerequisites

Docker requires a 64-bit OS and version 3.10 or higher of the Linux kernel. To check your OS architecture and kernel version:
$ uname -r
The output:
Docker engine
Run yum packages update
$ sudo yum update 


Step 1 – Add Docker repo

Create the docker.repo file
$ sudo touch /etc/yum.repos.d/docker.repo
Open docker.repo
$ sudo vi /etc/yum.repos.d/docker.repo
Add the following in docker.repo:
[dockerrepo]
name=Docker Repository
baseurl=https://yum.dockerproject.org/repo/main/centos/7/
enabled=1
gpgcheck=1
gpgkey=https://yum.dockerproject.org/gpg

Step 2 – Install docker-engine

$ sudo yum install docker-engine
The output:
docker install

Step 3 – Start and enable docker

$ sudo systemctl start docker
$ sudo systemctl enable docker

Step 4 – Add user to docker group

The docker engine, for communication uses Unix socket instead of a TCP port, the socket is owned by root user, other users can access it using sudo, otherwise you may get “Cannot connect to the Docker daemon. Is the docker daemon running on this host?”. To directly use docker command, create a docker group (will has read/write permission on the socket) and add your user to it.
Create the docker group
$ sudo groupadd docker
Add your user to docker group
$ sudo usermod -aG docker <your_username>
Log out and log back in

Step 5 – Verification

Verify if docker engine is installed properly and the added user works without sudo.
docker run hello-world 
The output:
docker test

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