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I am reading this Python book that shows a couple of scripts to create my own daemon. When I run the code it does absolutely nothing however. 

#! /usr/bin/env python

import sys, os

def daemonize(stdin='/dev/null', stdout='/dev/null',    stderr='/dev/null'):

#perform first fork 
   try:
       pid = os.fork()
       if pid > 0:
           sys.exit(0) #Exit first parent
   except OSError, e:
       sys.stderr.write("fork #1 failed: (%d) %s\n" % (e.errno,  e.strerror))
       sys.exit(1)

   #Decouple from the parent environment
   os.chdir("/")
   os.umask(0)
   os.setsid()
   #Perform second fork 
   try:
       pid = os.fork()
       if pid > 0:
           sys.exit(0) #Exit second parent
   except OSError, e:
       sys.stderr.write("fork #2 failed: (%d) %s\n" % (e.errno, e.strerror))
       sys.exit(1)
   #The process is now daemonized, redirect standard file descriptors. 
   for f in sys.stdout, sys.stderr:f.flush()

   si = file(stdin, 'r')
   so = file(stdout, 'a+')
   se = file(stderr, 'a+', 0)
   os.dup2(si.fileno(), sys.stdin.fileno())
   os.dup2(si.fileno(), sys.stdout.fileno())
   os.dup2(si.fileno(), sys.stderr.fileno())

The code above uses this daemonize() function. The daemonize() function is in a module called demon_process. Next, please check-out the code that uses this home-made daemon. 

from demon_process import daemonize 
import time
import sys

def mod_5_watcher():
    start_time = time.time()
    end_time = start_time + 20
    while time.time() < end_time:
        now = time.time()
        if int(now) % 5 == 0:
             sys.stderr.write('Mod 5 at %s\n' % now)
        else:
            sys.stdout.write('No mod 5 at %s\n' % now)
        time.sleep(1)


if __name__ == "__main__":
    daemonize(stdout='/Users/Los3r/Documents/pyMeBaby/demons/stdout.log', stderr='/Users/Los3r/Documents/pyMeBaby/demons/stderr.log')
    mod_5_watcher()

According to the book I am reading the script above should print statements to the files specified in the stdout and stderr variables overridden in the daemonize() function as called in main(). However, when I call this script, even using the sudo command, nothing happens. :/

I even try changing the directory the stdout and stderr write to as specified in the daemonize() function to /tmp/stdout.log and /tmp/stderr.log but the script still does not work.

What am I missing?

Thanks for reading this player. :D

Regards,

user_loser

user_loser
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  • Just for your information - you might be better off using supervisor to manage your process in daemon-like manner instead of writing your own daemonizing logic: http://supervisord.org/ – Mikko Ohtamaa Feb 06 '15 at 10:09
  • Thanks for responding with the helpful infos. I think the `screen` command also handles processes really well. – user_loser Feb 07 '15 at 01:47
  • The cool thing with supervisor is that it comes with reliable start/stop command and can also restart the process in the case of a abnormal termination. Here is my recent supervisor scripts for an app process: https://github.com/miohtama/LibertyMusicStore/blob/master/conf/supervisor.conf Alternatively if you target certain Linux distributions only you get away with systemd scripts, no external dependencies needed. – Mikko Ohtamaa Feb 07 '15 at 05:36

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