Thanks, that explains everything. The code I was using to test was copied from Twisted's daemonizing function: http://github.com/powdahound/twisted/blob/master/twisted/scripts/_twistd_unix.py#L155-169
It should probably be updated before more users upgrade to the new kernel and run into this issue. Ticket #823 ( http://twistedmatrix.com/trac/ticket/823) seems very related to this. On Thu, Sep 30, 2010 at 8:52 AM, Žiga Seilnacht <ziga.seilna...@gmail.com>wrote: > Hello, > > Garret Heaton wrote: > > I've simplified this issue down and am able to reproduce it without > > Twisted: http://gist.github.com/603154 > > > > Still not sure what the cause is, so if anyone has any ideas I'd love to > > hear them. Thanks! > > > > The behavior that you are seeing seems to be related to the change in > the 2.6.32 kernel, where they changed the child-runs-first scheduler > parameter to false. Setting that parameter to 1 with: > > $ sudo sysctl -w kernel.sched_child_runs_first=1 > > and rebooting the computer restores the behavior that you saw on the > old kernel for me. See http://lwn.net/Articles/352863/ for more details. > > Parent (which is the controlling process when ran with -t) exiting before > the child starts causes the child to receive SIGHUP signal immediately as > it starts running, before it has time to disassociate itself from the > parent's process group. It seems to me that this might be an actual bug > in twistd, it should block the SIGHUP signal across the fork() calls. > > Your test program has an additional assumption that the child will run > before the parent; the child in your program tries to write to stdout, > i.e. the controlling terminal, which gets closed once the parent exits. > > The modified test program below works for me regardless of the setting > of the kernel.sched_child_runs_first parameter. > > Hope this helps, > Ziga > > > > import os > import signal > > f = open("test_fork.out", "w") > > def daemonize(): > # See http://www.faqs.org/faqs/unix-faq/programmer/faq/ - Section 1.7 > print >> f, '--- %s: daemonizing' % os.getpid() > > signal.signal(signal.SIGHUP, signal.SIG_IGN) > if os.fork(): # launch child and... > print >> f, '--- %s: kill parent 1' % os.getpid() > os._exit(0) # kill off parent > print >> f, '--- %s: old sid: %r' % (os.getpid(), > os.getsid(os.getpid())) > os.setsid() > print >> f, '--- %s: new sid: %r' % (os.getpid(), > os.getsid(os.getpid())) > if os.fork(): # launch child and... > print >> f, '--- %s: kill parent 2' % os.getpid() > os._exit(0) # kill off parent again. > > signal.signal(signal.SIGHUP, signal.SIG_DFL) > print >> f, '--- %s: daemonizing done' % os.getpid() > > if __name__ == "__main__": > print >> f, 'starting as %d' % os.getpid() > daemonize() > print >> f, 'stopping as %s' % os.getpid() > > > > > _______________________________________________ > Twisted-Python mailing list > Twisted-Python@twistedmatrix.com > http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python >
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