Accidentally, my docker goes wrong, and cannot be started.

`docker ps`gives the following error

```
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

```

And `systemctl status docker.service` gives the following outputs:

```
● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
  Drop-In: /etc/systemd/system/docker.service.d
       └─override.conf
   Active: failed (Result: start-limit-hit) since Tue 2018-11-20 18:27:11 PST; 11s ago
 Docs: https://docs.docker.com
  Process: 16519 ExecStart=/usr/bin/dockerd --host=fd:// --add-runtime=nvidia=/usr/bin/nvidia-container-runtime (code=exited, status=1/FAILURE)
 Main PID: 16519 (code=exited, status=1/FAILURE)

Nov 20 18:27:09 loccalhost systemd[1]: Failed to start Docker Application Container Engine.
Nov 20 18:27:09 loccalhost systemd[1]: docker.service: Unit entered failed state.
Nov 20 18:27:09 loccalhost systemd[1]: docker.service: Failed with result 'exit-code'.
Nov 20 18:27:11 loccalhost systemd[1]: docker.service: Service hold-off time over, scheduling restart.
Nov 20 18:27:11 loccalhost systemd[1]: Stopped Docker Application Container Engine.
Nov 20 18:27:11 loccalhost systemd[1]: docker.service: Start request repeated too quickly.
Nov 20 18:27:11 loccalhost systemd[1]: Failed to start Docker Application Container Engine.
Nov 20 18:27:11 loccalhost systemd[1]: docker.service: Unit entered failed state.
Nov 20 18:27:11 loccalhost systemd[1]: docker.service: Failed with result 'start-limit-hit'.

```