报错详情：

 docker.service - Docker Application Container Engine
   Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled; vendor preset: disabled)
   Active: failed (Result: start-limit) since 一 2019-07-15 23:29:49 CST; 4min 59s ago
     Docs: https://docs.docker.com
  Process: 31870 ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock (code=exited, status=1/FAILURE)
 Main PID: 31870 (code=exited, status=1/FAILURE)

7月 15 23:29:47 iZ2zedg8xo32ri334fa5hdZ systemd[1]: Failed to start Docker Application Container Engine.
7月 15 23:29:47 iZ2zedg8xo32ri334fa5hdZ systemd[1]: Unit docker.service entered failed state.
7月 15 23:29:47 iZ2zedg8xo32ri334fa5hdZ systemd[1]: docker.service failed.
7月 15 23:29:49 iZ2zedg8xo32ri334fa5hdZ systemd[1]: docker.service holdoff time over, scheduling restart.
7月 15 23:29:49 iZ2zedg8xo32ri334fa5hdZ systemd[1]: Stopped Docker Application Container Engine.
7月 15 23:29:49 iZ2zedg8xo32ri334fa5hdZ systemd[1]: start request repeated too quickly for docker.service
7月 15 23:29:49 iZ2zedg8xo32ri334fa5hdZ systemd[1]: Failed to start Docker Application Container Engine.
7月 15 23:29:49 iZ2zedg8xo32ri334fa5hdZ systemd[1]: Unit docker.service entered failed state.
7月 15 23:29:49 iZ2zedg8xo32ri334fa5hdZ systemd[1]: docker.service failed.
[root@iZ2zedg8xo32ri334fa5hdZ docker]# systemctl start docker
[root@iZ2zedg8xo32ri334fa5hdZ docker]# systemctl status docker
● docker.service - Docker Application Container Engine
   Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled; vendor preset: disabled)
   Active: active (running) since 一 2019-07-15 23:34:56 CST; 5s ago
     Docs: https://docs.docker.com
 Main PID: 32149 (dockerd)
    Tasks: 10
   Memory: 29.9M
   CGroup: /system.slice/docker.service
           └─32149 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

解决：如果是配置了国内镜像，并且镜像文件为/etc/docker/daemon.json，则修改文件后缀为.conf即可正常启动docker 服务