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

sudo snap logs docker -f
2020-11-07T05:44:46Z systemd[1]: Stopped Service for snap application docker.dockerd.
2020-11-07T05:44:46Z systemd[1]: Started Service for snap application docker.dockerd.
2020-11-07T05:44:46Z docker.dockerd[6238]: failed to start daemon: pid file found, ensure docker is not running or delete /var/snap/docker/471/run/docker.pid
2020-11-07T05:44:46Z systemd[1]: snap.docker.dockerd.service: Main process exited, code=exited, status=1/FAILURE
2020-11-07T05:44:46Z systemd[1]: snap.docker.dockerd.service: Failed with result ‘exit-code’.
2020-11-07T05:44:47Z systemd[1]: snap.docker.dockerd.service: Scheduled restart job, restart counter is at 5.
2020-11-07T05:44:47Z systemd[1]: Stopped Service for snap application docker.dockerd.
2020-11-07T05:44:47Z systemd[1]: snap.docker.dockerd.service: Start request repeated too quickly.
2020-11-07T05:44:47Z systemd[1]: snap.docker.dockerd.service: Failed with result ‘exit-code’.
2020-11-07T05:44:47Z systemd[1]: Failed to start Service for snap application docker.dockerd.

删除pid

sudo rm -f /var/snap/docker/471/run/docker.pid

重启docker

sudo snap start docker