CentOS 7
Add this file:
/etc/yum.repos.d/docker.repo: [dockerrepo] name=Docker Repository baseurl=https://yum.dockerproject.org/repo/main/centos/7/ enabled=1 gpgcheck=0 #gpgkey=https://yum.dockerproject.org/gpg
Update and Install Docker
yum update yum install -y docker-engine
Give Users Permissions to Use Docker
usermod -a -G docker username