● docker.service - Docker Application Container Engine
Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
Active: failed (Result: exit-code) since 二 2017-11-07 16:58:48 CST; 8s ago
Docs: http://docs.docker.com
Process: 2317 ExecStart=/usr/bin/docker-current daemon --exec-opt native.cgroupdriver=systemd $OPTIONS $DOCKER_STORAGE_OPTIONS $DOCKER_NETWORK_OPTIONS $ADD_REGISTRY
$BLOCK_REGISTRY $INSECURE_REGISTRY (code=exited, status=1/FAILURE)
Main PID: 2317 (code=exited, status=1/FAILURE)
11月 07 16:58:47 VM_0_6_centos systemd[1]: Starting Docker Application Container Engine...
11月 07 16:58:48 VM_0_6_centos docker-current[2317]: time="2017-11-07T16:58:48.329486752+08:00" level=fatal msg="Error starting daemon: mkdir /var/lib/docker: file exists"
11月 07 16:58:48 VM_0_6_centos systemd[1]: docker.service: main process exited, code=exited, status=1/FAILURE
11月 07 16:58:48 VM_0_6_centos systemd[1]: Failed to start Docker Application Container Engine.
11月 07 16:58:48 VM_0_6_centos systemd[1]: Unit docker.service entered failed state.
11月 07 16:58:48 VM_0_6_centos systemd[1]: docker.service failed.
解決方案：
目前docker肯定是出於未啓動狀態，所以直接操作
rm -rf /var/lib/docker
systemctl start docker
即可。