Rogue pid causes hub not to start

My jupyterhub database had a PID entry for a user notebook server that no longer existed. When the hub started up and tried to health check that PID, it hit the following exception and failed to start. The only workaround was to nuke the database or perform surgery on it to remove the offending state.

Traceback (most recent call last):
  File "/opt/jupyterhub/envs/jupyterhub/bin/sudospawner", line 4, in <module>
    mediator.main()
  File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/site-packages/sudospawner/mediator.py", line 148, in main
    kill(**kwargs)
  File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/site-packages/sudospawner/mediator.py", line 52, in kill
    os.kill(pid, signal)
PermissionError: [Errno 1] Operation not permitted
ESC[31m[E 2017-04-17 20:40:54.603 JupyterHub app:1527]ESC[0;10m
    Traceback (most recent call last):
      File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/site-packages/jupyterhub/app.py", line 1524, in launch_instance_async
        yield self.initialize(argv)
      File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/types.py", line 179, in throw
        return self.__wrapped.throw(tp, *rest)
      File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/site-packages/jupyterhub/app.py", line 1315, in initialize
        yield self.init_spawners()
      File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/site-packages/jupyterhub/app.py", line 1087, in init_spawners
        status = yield spawner.poll()
      File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/site-packages/jupyterhub/spawner.py", line 834, in poll
        alive = yield self._signal(0)
      File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/site-packages/sudospawner/spawner.py", line 90, in _signal
        reply = yield self.do('kill', pid=self.pid, signal=sig)
      File "/opt/jupyterhub/envs/jupyterhub/lib/python3.5/site-packages/sudospawner/spawner.py", line 69, in do
        data_str = data_str[data_str.index('{'):data_str.rindex('}')+1]
    ValueError: substring not found

I'm not sure how it got into the state that it did. Maybe the notebook server went away while the hub was restarting? Regardless, the hub should be robust against the situation and at least start.

jupyterhub / sudospawner

Rogue pid causes hub not to start #32