daemon.py

   1 # This code seems to be in public domain
   2 # http://www.google.com/search?client=opera&rls=en&q=unix+daemon+double+fork&sourceid=opera&ie=utf-8&oe=utf-8
   3
   4 import sys, os
   5
   6 def daemonize():
   7
   8     # do the UNIX double-fork magic, see Stevens' "Advanced
   9     # Programming in the UNIX Environment" for details (ISBN 0201563177)
  10         try:
  11                 pid = os.fork()
  12                 if pid > 0:
  13                         # exit first parent
  14                         sys.exit(0)
  15         except OSError, e:
  16                 print >>sys.stderr, "fork #1 failed: %d (%s)" % (e.errno, e.strerror)
  17                 sys.exit(1)
  18
  19         # decouple from parent environment
  20         os.chdir("/")
  21         os.setsid()
  22         os.umask(0)
  23
  24         # do second fork
  25         try:
  26                 pid = os.fork()
  27                 if pid > 0:
  28                         # exit from second parent, print eventual PID before
  29                         print "Daemon PID %d" % pid
  30                         sys.exit(0)
  31         except OSError, e:
  32                 print >>sys.stderr, "fork #2 failed: %d (%s)" % (e.errno, e.strerror)
  33                 sys.exit(1)
  34
  35         #TODO - move standard output to log file/library
  36         #               -there should be more here - see comments on http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66012
  37         # Redirect standard file descriptors
  38         sys.stdin = open('/dev/null', 'r')
  39         sys.stdout = open('/dev/null', 'w')
  40         sys.stderr = open('/dev/null', 'w')