本文只介绍在centos中安装docker环境
    Centos上安装Docker如下:

    1. sudo su
    2. yum install -y yum-utils device-mapper-persistent-data lvm2
    3. yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
    4. yum install -y docker-ce 
    5. systemctl start docker
    6. systemctl enable docker

    安装完毕以后, 查看Docker版本:
    `sh docker version