pid file prevents starting the docker snap

[Stephen Buergler]

docker seems to not be able to start because of a pid file that was left behind.
This only happened on one of my hosts and hasn't happened again after fixing it.
I get these logs over and over again:

2020-04-30T06:47:38Z systemd[1]: Started Service for snap application docker.dockerd.
2020-04-30T06:47:49Z docker.dockerd[1127]: Error starting daemon: pid file found, ensure docker is not running or delete /var/snap/docker/423/run/docker.pid
2020-04-30T06:47:49Z systemd[1]: snap.docker.dockerd.service: Main process exited, code=exited, status=1/FAILURE
2020-04-30T06:47:49Z systemd[1]: snap.docker.dockerd.service: Failed with result 'exit-code'.
2020-04-30T06:47:50Z systemd[1]: snap.docker.dockerd.service: Service RestartSec=100ms expired, scheduling restart.
2020-04-30T06:47:50Z systemd[1]: snap.docker.dockerd.service: Scheduled restart job, restart counter is at 1.
2020-04-30T06:47:50Z systemd[1]: Stopped Service for snap application docker.dockerd.
2020-04-30T06:47:50Z systemd[1]: Started Service for snap application docker.dockerd.
2020-04-30T06:47:50Z docker.dockerd[1325]: Error starting daemon: pid file found, ensure docker is not running or delete /var/snap/docker/423/run/docker.pid
2020-04-30T06:47:50Z systemd[1]: snap.docker.dockerd.service: Main process exited, code=exited, status=1/FAILURE
2020-04-30T06:47:50Z systemd[1]: snap.docker.dockerd.service: Failed with result 'exit-code'.
2020-04-30T06:47:50Z systemd[1]: snap.docker.dockerd.service: Service RestartSec=100ms expired, scheduling restart.
2020-04-30T06:47:50Z systemd[1]: snap.docker.dockerd.service: Scheduled restart job, restart counter is at 2.
2020-04-30T06:47:50Z systemd[1]: Stopped Service for snap application docker.dockerd.
2020-04-30T06:47:50Z systemd[1]: Started Service for snap application docker.dockerd.
2020-04-30T06:47:50Z docker.dockerd[1390]: Error starting daemon: pid file found, ensure docker is not running or delete /var/snap/docker/423/run/docker.pid
2020-04-30T06:47:50Z systemd[1]: snap.docker.dockerd.service: Main process exited, code=exited, status=1/FAILURE
2020-04-30T06:47:50Z systemd[1]: snap.docker.dockerd.service: Failed with result 'exit-code'.
2020-04-30T06:47:51Z systemd[1]: snap.docker.dockerd.service: Service RestartSec=100ms expired, scheduling restart.
2020-04-30T06:47:51Z systemd[1]: snap.docker.dockerd.service: Scheduled restart job, restart counter is at 3.
2020-04-30T06:47:51Z systemd[1]: Stopped Service for snap application docker.dockerd.
2020-04-30T06:47:51Z systemd[1]: Started Service for snap application docker.dockerd.
2020-04-30T06:47:51Z docker.dockerd[1452]: Error starting daemon: pid file found, ensure docker is not running or delete /var/snap/docker/423/run/docker.pid
2020-04-30T06:47:51Z systemd[1]: snap.docker.dockerd.service: Main process exited, code=exited, status=1/FAILURE
2020-04-30T06:47:51Z systemd[1]: snap.docker.dockerd.service: Failed with result 'exit-code'.
2020-04-30T06:47:51Z systemd[1]: snap.docker.dockerd.service: Service RestartSec=100ms expired, scheduling restart.
2020-04-30T06:47:51Z systemd[1]: snap.docker.dockerd.service: Scheduled restart job, restart counter is at 4.
2020-04-30T06:47:51Z systemd[1]: Stopped Service for snap application docker.dockerd.
2020-04-30T06:47:51Z systemd[1]: Started Service for snap application docker.dockerd.
2020-04-30T06:47:51Z docker.dockerd[1511]: Error starting daemon: pid file found, ensure docker is not running or delete /var/snap/docker/423/run/docker.pid
2020-04-30T06:47:51Z systemd[1]: snap.docker.dockerd.service: Main process exited, code=exited, status=1/FAILURE
2020-04-30T06:47:51Z systemd[1]: snap.docker.dockerd.service: Failed with result 'exit-code'.
2020-04-30T06:47:52Z systemd[1]: snap.docker.dockerd.service: Service RestartSec=100ms expired, scheduling restart.
2020-04-30T06:47:52Z systemd[1]: snap.docker.dockerd.service: Scheduled restart job, restart counter is at 5.
2020-04-30T06:47:52Z systemd[1]: Stopped Service for snap application docker.dockerd.
2020-04-30T06:47:52Z systemd[1]: Started Service for snap application docker.dockerd.
2020-04-30T06:47:52Z docker.dockerd[1573]: Error starting daemon: pid file found, ensure docker is not running or delete /var/snap/docker/423/run/docker.pid
2020-04-30T06:47:52Z systemd[1]: snap.docker.dockerd.service: Main process exited, code=exited, status=1/FAILURE
2020-04-30T06:47:52Z systemd[1]: snap.docker.dockerd.service: Failed with result 'exit-code'.
2020-04-30T06:47:52Z systemd[1]: snap.docker.dockerd.service: Service RestartSec=100ms expired, scheduling restart.
2020-04-30T06:47:52Z systemd[1]: snap.docker.dockerd.service: Scheduled restart job, restart counter is at 6.
2020-04-30T06:47:52Z systemd[1]: Stopped Service for snap application docker.dockerd.
2020-04-30T06:47:52Z systemd[1]: snap.docker.dockerd.service: Start request repeated too quickly.
2020-04-30T06:47:52Z systemd[1]: snap.docker.dockerd.service: Failed with result 'exit-code'.
2020-04-30T06:47:52Z systemd[1]: Failed to start Service for snap application docker.dockerd.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Guillermo Bisheimer (gbisheimer)]

It happens every time that my machine is turned off improperly (i.e. power failure or system crash). A file named docker.pid is left in folder /var/snap/docker/current/run/ and this prevents the snap package to startup successfully. I have to manually remove the file to be able to start docker engine again.

tested with snap version
docker 19.03.11