在CentOS7上安装Docker，安装顺利，启动报错

在CentOs7上安装Docker步骤如下：
首先我们要检查版本，因为在linux上安装Docker内核必须是3.0以上版本

uname -r

1. 安装docker yum install docker
2. 安装过程当中有提示输入y回车继续
3. 安装之后可以查看一下docker的版本 docker -v
4. 启动docker命令 systemctl start docker 这里会报错，下面解决
5. 设置docker开机自启 systemctl enable docker
6. 重启docker systemctl restart docker
7. 停止docker systemctl stop docker

在启动的时候报错：

Job for docker.service failed because the control process exited with error code  . See "systemctl status docker.service" and "journalctl -xe" for details.

执行提示命令 systemctl status docker.service
内容如下：

● docker.service - Docker Application Container Engine
   Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Mon 2019-05-20 13:13:33 EDT; 28s ago
     Docs: http://docs.docker.com
  Process: 5379 ExecStart=/usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/do                                  cker/docker-runc-current --default-runtime=docker-runc --exec-opt native.cgroupdriver=system                                  d --userland-proxy-path=/usr/libexec/docker/docker-proxy-current --init-path=/usr/libexec/do                                  cker/docker-init-current --seccomp-profile=/etc/docker/seccomp.json $OPTIONS $DOCKER_STORAGE                                  _OPTIONS $DOCKER_NETWORK_OPTIONS $ADD_REGISTRY $BLOCK_REGISTRY $INSECURE_REGISTRY $REGISTRIE                                  S (code=exited, status=1/FAILURE)
 Main PID: 5379 (code=exited, status=1/FAILURE)

May 20 13:13:31 localhost.localdomain systemd[1]: Starting Docker Application Container.....
May 20 13:13:31 localhost.localdomain dockerd-current[5379]: time="2019-05-20T13:13:31.5..."
May 20 13:13:31 localhost.localdomain dockerd-current[5379]: time="2019-05-20T13:13:31.5..."
May 20 13:13:32 localhost.localdomain dockerd-current[5379]: time="2019-05-20T13:13:32.53...
May 20 13:13:33 localhost.localdomain dockerd-current[5379]: Error starting daemon: SELi...)
May 20 13:13:33 localhost.localdomain systemd[1]: docker.service: main process exited, ...RE
May 20 13:13:33 localhost.localdomain systemd[1]: Failed to start Docker Application Co...e.
May 20 13:13:33 localhost.localdomain systemd[1]: Unit docker.service entered failed state.
May 20 13:13:33 localhost.localdomain systemd[1]: docker.service failed.
Hint: Some lines were ellipsized, use -l to show in full.

解决办法：
打开docker的配置文件： vi /etc/sysconfig/docker
修改如下位置：

修改之后重启成功。