fork.py

#!/usr/bin/python

import os

def daemonize():
    # See http://www.faqs.org/faqs/unix-faq/programmer/faq/ - Section 1.7
    print('--- %s: daemonizing' % os.getpid())
    if os.fork():   # launch child and...
        print('--- %s: kill parent 1' % os.getpid())
        os._exit(0) # kill off parent
    print('--- %s: old sid: %r' % (os.getpid(), os.getsid(os.getpid())))
    os.setsid()
    print('--- %s: new sid: %r' % (os.getpid(), os.getsid(os.getpid())))
    if os.fork():   # launch child and...
        print('--- %s: kill parent 2' % os.getpid())
        os._exit(0) # kill off parent again.

    # File descriptor redirection intentionally left out so that we continue to see logging on stdout.
    # The failure case doesn't make it here anyway.

    print('--- %s: daemonizing done' % os.getpid())

if __name__ == "__main__":
    print 'starting as %d' % os.getpid()
    daemonize()
    print 'stopping as %s' % os.getpid()

gistfile2.txt

On Ubuntu 10.04 (Python 2.6.5) - the error case:

imac:~ ssh -t lucidbox "./fork.py"
starting as 22325
--- 22325: daemonizing
--- 22325: kill parent 1
Connection to lucidbox closed.



On Ubuntu 9.04 (Python 2.6.2):

imac:~ ssh -t jauntybox "./fork.py"
starting as 23203
--- 23203: daemonizing
--- 23227: old sid: 23203
--- 23227: new sid: 23227
--- 23228: daemonizing done
stopping as 23228
--- 23227: kill parent 2
--- 23203: kill parent 1
Connection to jauntybox closed.



Either machine without using pseudo terminal:

imac:~ ssh box "./fork.py"
starting as 22629
--- 22629: daemonizing
--- 22654: old sid: 22629
--- 22654: new sid: 22654
--- 22655: daemonizing done
stopping as 22655