os.setsid operation not permitted

Question

Alright bear with me there seems to be some answers on google about that but I simply cannot get it.

I'm running it after two forks in a Django Celery environment. I don't know if these could have changed something but I assume they did not.

There is not much code to leave as a mighty

if __name__ == '__main__':
    os.setsid()

grants me the beautiful Operation not permitted

I'm running the latest stable Django, Debian, Celery and Python version.

Your example doesn't work because "setsid() fails if the calling process is already a process group leader" (from the description of "Operation not permitted" from the man page setsid(2)). That doesn't answer your question though, because after fork(2)ing you're no longer a process group leader. — Phillip, Dec 11 '14 at 08:25

arielf · Accepted Answer · 2016-02-17T01:19:21.137

Python's os.setsid() probably calls the underlying library call setsid(3).

The full ERRORS section in man 3 setsid is:

ERRORS
   EPERM  The  process group ID of any process equals the PID of the call-
          ing process.  Thus, in particular, setsid() fails if the calling
          process is already a process group leader.

IOW: the only cause for a setsid() failure, is when the calling process is already a process group leader. Ergo: you may ignore the failure. To verify that this is the case, compare what you get back from getpid() and getpgid() when os.setsid() fails:

#!/usr/bin/env python

import os
import errno

if __name__ == '__main__':
    try:
        os.setsid()
    except OSError, (err_no, err_message):
        print "os.setsid failed: errno=%d: %s" % (err_no, err_message)
        print "pid=%d  pgid=%d" % (os.getpid(), os.getpgid(0))

When I run the above I get:

os.setsid failed: errno=1: Operation not permitted
pid=17025  pgid=17025

Note that the process-id (pid) is equal to the process-group-id (pgid), meaning that this process is indeed already a process group leader.

P.S: Yes, it is a baffling feature of python to raise exceptions where a simple error return code would suffice to distinguish success from failure (just like the familiar Un*x libc APIs behave). This is unfortunately how the python system call interface is implemented, so you need to wrap many system calls with try: except ...: constructs to prevent python from aborting your code.

os.setsid operation not permitted

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