Error message on ray init when run inside Jupyter: setpgrp failed, processes may not be cleaned up properly

What is the problem?

Ray version and other system information (Python version, TensorFlow version, OS):

Ray 0.8.0 Python 3.6 Ubuntu 18.04

Does the problem occur on the latest wheels?

Yes, with ray-0.9.0.dev0.

Reproduction

Please provide a script that can be run to reproduce the issue. The script should have no external library dependencies (i.e., use fake or mock data / environments):

If we cannot run your script, we cannot fix your issue.

I am running juypyterlab 1.2.4 within docker, using an 18.04 base image. To reproduce, simply import ray and call ray.init.

import ray
ray.init()

And the error message will be generated.

2020-01-06 17:54:50,339	WARNING services.py:595 -- setpgrp failed, processes may not be cleaned up properly: [Errno 1] Operation not permitted.

PID, PGID, PPID, and SID all have the same value in this case. Outside of Jupyter, this error does not occur.

[edoakes]

ray stop is a bash command and will stop all ray processes running on the machine (started by ray.init() in python or ray start on the command line.

ray.shutdown() will stop all ray processes started by a previous ray.init() call in the current python process.

[edoakes]

Thanks for reporting this @mc-allen. After looking into this a bit, I was only able to reproduce in jupyterlab and unfortunately am not able to find a workaround.

This shouldn’t cause any significant problems, it just means that if the python process that called ray.init() (the jupyter notebook in this case) is terminated via SIGKILL, there may be some background processes left up. If this does happen for some reason, you can always clean these processes up manually using ray stop.