docker 启动失败，报错 Failed to start Docker Application Container Engine.

[root@localhost ~]# docker images
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

[root@localhost ~]# service docker restart
Redirecting to /bin/systemctl restart docker.service
Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.


[root@localhost ~]# systemctl status docker.service
● docker.service - Docker Application Container Engine
   Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
   Active: failed (Result: start-limit) since Sun 2021-05-30 02:08:49 EDT; 48s ago
     Docs: https://docs.docker.com
  Process: 21471 ExecStart=/usr/bin/dockerd (code=exited, status=1/FAILURE)
 Main PID: 21471 (code=exited, status=1/FAILURE)

May 30 02:08:49 localhost.localdomain systemd[1]: docker.service failed.
May 30 02:08:49 localhost.localdomain systemd[1]: docker.service holdoff time over, scheduling restart.
May 30 02:08:49 localhost.localdomain systemd[1]: Stopped Docker Application Container Engine.
May 30 02:08:49 localhost.localdomain systemd[1]: start request repeated too quickly for docker.service
May 30 02:08:49 localhost.localdomain systemd[1]: Failed to start Docker Application Container Engine.
May 30 02:08:49 localhost.localdomain systemd[1]: Unit docker.service entered failed state.
May 30 02:08:49 localhost.localdomain systemd[1]: docker.service failed.
May 30 02:08:55 localhost.localdomain systemd[1]: start request repeated too quickly for docker.service
May 30 02:08:55 localhost.localdomain systemd[1]: Failed to start Docker Application Container Engine.
May 30 02:08:55 localhost.localdomain systemd[1]: docker.service failed.

重启系统后，可以正常启动了，why？？