Code for experimenting with session ID, process group ID, and signal handling

forker.py

import os
import signal


def sighup_handler(signum, frame):
    print 'SIGHUP handled by', os.getpid()

def sigtstp_handler(signum, frame):
    print 'SIGTSTP handled by', os.getpid()

def sigint_handler(signum, frame):
    print 'SIGINT handled by', os.getpid()

cpid = os.fork()

if cpid == 0:
    print 'In first child'
    print 'PGID: ', os.getpgrp(), 'SID: ', os.getsid(0), 'PPID: ', os.getppid(), 'PID: ', os.getpid()

    signal.signal(signal.SIGHUP, sighup_handler)
    signal.signal(signal.SIGTSTP, sigtstp_handler)
    signal.signal(signal.SIGINT, sigint_handler)

    cpid_2 = os.fork()
    if cpid_2 == 0:
        print 'In second child'
        print 'PGID: ', os.getpgrp(), 'SID: ', os.getsid(0), 'PPID: ', os.getppid(), 'PID: ', os.getpid()        
        signal.signal(signal.SIGHUP, sighup_handler)
        signal.signal(signal.SIGTSTP, sigtstp_handler)
        signal.signal(signal.SIGINT, sigint_handler)
        while True:
            pass
    else:
        while True:
            pass
else:
    print 'In parent'
    print 'PGID: ', os.getpgrp(), 'SID: ', os.getsid(0), 'PPID: ', os.getppid(), 'PID: ', os.getpid()
    signal.signal(signal.SIGHUP, sighup_handler)
    signal.signal(signal.SIGTSTP, sigtstp_handler)
    signal.signal(signal.SIGINT, sigint_handler)
    while True:
        pass