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
