daemon.py

#! /bin/env python
#
# Routine to daemonize a process on unix
#
#
DAEMON_HOME = '/'


class NullDevice(object):

    def write(self, s):
        pass


def daemonize(homeDir=DAEMON_HOME):
    import os
    import sys

    if os.fork() != 0:  # Parent
        os._exit(0)  # Kill parent


    os.chdir(homeDir)   # Detach from parent tty
    os.setsid()  # and start new session
    os.umask(0)

    sys.stdin.close()  # Close stdin, stdout
    sys.stdout.close()
    sys.stdin = NullDevice()
    sys.stdout = NullDevice()

    for n in range(3, 256):  # Close any remaining file
        try:  # descriptors
            os.close(n)
        except Exception:
            pass

    if os.fork() != 0:  # finally fork again
        os._exit(0)  # to fully daemonize



def spawn(cmd, args):
    import string
    import os
    import signal

    # Prevent zombie orphans by ignoring SIGCHLD signal
    signal.signal(signal.SIGCHLD, signal.SIG_IGN)

    args = string.split(args)
    if os.fork() != 0:  # Calling Parent
        return  # allow this parent to continue running

    os.chdir(DAEMON_HOME)  # Temp Parent
    os.setsid()  # Detach from calling parent
    os.umask(0)

    if os.fork() != 0:  # Kill temp parent
        os._exit(0)  # Run cmd in new child

    os.execvpe(cmd, [cmd] + args, os.environ)


def createPid(pidPath='/var/run'):
    '''Creates PID file for process'''

    import os
    import sys

    currentPid = os.getpid() # Gets PID number
    if not currentPid:
        print 'Could not find PID'
        sys.exit()

    scriptFilename, _ = os.path.splitext(os.path.basename(sys.argv[0]))

    pidFile = '%s.pid' % (scriptFilename) # Creates PIDfile  filename
    pidFilePath = os.path.join(pidPath, pidFile)

    with open(pidFilePath, 'w') as fileh: # Writes PIDfile name
        fileh.write(currentPid)


if __name__ == "__main__":
    while True:
        daemonize()
        print "hello world"