daemon.py

#  Daemon Module - basic facilities for becoming a daemon process
#
#  Combines ideas from Steinar Knutsens daemonize.py and
#  Jeff Kunces demonize.py

# Originally posted to python-list; an archive of the post is available
# here: http://aspn.activestate.com/ASPN/Mail/Message/python-list/504777
# Assumed is that the author intended for the (fairly trivial body of) code
# to be freely usable by any developer.

"""Facilities for Creating Python Daemons"""

import os
import time
import sys


class NullDevice:
  def write(self, s):
    pass


def daemonize():
  """
  daemonize:
    Purpose:
      Detach from stdin/stdout/stderr, return control of the term to the user.

    Returns:
      Nothing.

  """

  if os.name == "nt" or os.name == "ce":
    # No way to fork or daemonize on windows. Just do nothing for now?
    return

  if not os.fork():
    # get our own session and fixup std[in,out,err]
    os.setsid()
    sys.stdin.close()
    sys.stdout = NullDevice()
    sys.stderr = NullDevice()
    if not os.fork():
      # hang around till adopted by init
      ppid = os.getppid()
      while ppid != 1:
        time.sleep(0.5)
        ppid = os.getppid()
    else:
      # time for child to die
      os._exit(0)
  else:
    # wait for child to die and then bail
    os.wait()
    sys.exit()