docker 安装

参考官网
https://docs.docker.com/engine/install/centos/

systemctl status firewalld
systemctl stop firewalld
systemctl disable firewalld
cat /etc/selinux/config
sed -i 's/=enforcing/=disable/' /etc/selinux/config
cat /etc/selinux/config
getenforce
setenforce 0
getenforce
yum remove docker 
                  docker-client 
                  docker-client-latest 
                  docker-common 
                  docker-latest 
                  docker-latest-logrotate 
                  docker-logrotate 
                  docker-engine
cat /etc/yum.repos.d/CentOS-Base.repo
yum install -y yum-utils
yum-config-manager --add-repo http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo
yum makecache #这个步骤很重要，否则下载依赖包会很慢或者失败。

安装指定版本如下：
yum list docker-ce --showduplicates | sort -r
yum list docker-ce-cli --showduplicates |sort -r
yum list containerd.io --showduplicates |sort -r
yum install docker-ce-18.09.9 docker-ce-cli-18.09.9 containerd.io-1.2.6