Programming Forums > Script Programming > Python

thinkgeek · Jul 2nd, 2005, 1:24 PM

I have written a script which wil fork a process and the main process gets free form the terminal. I want to make process run in background.
I am using the os.fork() method to fork a process but it is returning a non zero pid.Why?

Below is the code. I want to do double forking to make it independent of any terminal and independently in background. The code given below is not working.

Can anybody help it out or give me some interesting links for creating
daemons in Unix using python.
__________________________________________________

(Toggle Plain Text)

	def create_daemon(self):
		first_pid = os.fork()
		if (first_pid == 0):
			os.setsid()
			signal.signal(signal.SIGHUP,signal.SIG_IGN)
			second_pid = os.fork()
			if (second_pid == 0):
				os.chdir("/")
				os.umask(0)
			else:
				os._exit(0)
		else:
			os._exit(0)
		try:
			maxfd = os.sysconf("SC_OPEN_MAX")
		except (AttributeError, ValueError):
			maxfd = 256
		for fd in range(0, maxfd):
			try:
				os.close(fd)
			except OSError:
				pass
		os.open("/dev/null", os.O_RDONLY)	# standard input (0)
		os.open("/dev/null", os.O_RDWR)	   # standard output (1)
		os.open("/dev/null", os.O_RDWR)	   # standard error (2)

_________________________________________________

Cerulean · Jul 3rd, 2005, 8:21 AM

Which fork is returning non-zero?
I always use this lovely cookbook recipe whenever I need to fork. Never failed me so far.

thinkgeek · Jul 4th, 2005, 6:57 AM

I have tried that recipe but it is not working properly in my case.
Where exactly to place it in my code? I have experimented many
times with no return. It is failing to fork any process.

Cerulean · Jul 4th, 2005, 6:24 PM

Quote:

I have tried that recipe but it is not working properly in my case.
Where exactly to place it in my code? I have experimented many
times with no return. It is failing to fork any process

What is not working? Just copy that createDaemon function.. into your file and run the function when you want to fork into the background...
try running:

(Toggle Plain Text)

createDaemon()
time.sleep(10)

See if you have control of the terminal straight after you run it, or if the shell blocks for 10 seconds.
And answer the question I asked you

thinkgeek · Jul 4th, 2005, 10:52 PM

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if __name__ == "__main__":
																															 
   # Self-test.
																															 
   retCode = createDaemon()
																															 
   # If executed with superuser privilages, there should be a new file in the
   # "/" directory.  It should contain the function's return code, the daemon's
   # PID, PPID, and PGRP.  Its PID should not equal its PGRP, and its PPID
   # should equal 1.  If it's executed without superuser privilages, the file
   # won't be created and no errors will be reported.
   open("createDaemon.log", "w").write("rc: %s; pid: %d; ppid: %d; pgrp: %d" %\
	  (retCode, os.getpid(), os.getppid(), os.getpgrp()))
   time.sleep(10)
   sys.exit(0)

Above is my main program where I am calling the daemon program.
And to your question I am getting the control of the terminal straight after I run it.

Please explain?

Cerulean · Jul 5th, 2005, 11:46 AM

Well then, you have successfully forked. Congratulations.

Jul 2nd, 2005, 1:24 PM	#1
thinkgeek Newbie Join Date: Jul 2005 Posts: 10 Rep Power: 0	Forking process using python/Writing daemons I have written a script which wil fork a process and the main process gets free form the terminal. I want to make process run in background. I am using the os.fork() method to fork a process but it is returning a non zero pid.Why? Below is the code. I want to do double forking to make it independent of any terminal and independently in background. The code given below is not working. Can anybody help it out or give me some interesting links for creating daemons in Unix using python. __________________________________________________ (Toggle Plain Text) def create_daemon(self): first_pid = os.fork() if (first_pid == 0): os.setsid() signal.signal(signal.SIGHUP,signal.SIG_IGN) second_pid = os.fork() if (second_pid == 0): os.chdir("/") os.umask(0) else: os._exit(0) else: os._exit(0) try: maxfd = os.sysconf("SC_OPEN_MAX") except (AttributeError, ValueError): maxfd = 256 for fd in range(0, maxfd): try: os.close(fd) except OSError: pass os.open("/dev/null", os.O_RDONLY) # standard input (0) os.open("/dev/null", os.O_RDWR) # standard output (1) os.open("/dev/null", os.O_RDWR) # standard error (2) def create_daemon(self): first_pid = os.fork() if (first_pid == 0): os.setsid() signal.signal(signal.SIGHUP,signal.SIG_IGN) second_pid = os.fork() if (second_pid == 0): os.chdir("/") os.umask(0) else: os._exit(0) else: os._exit(0) try: maxfd = os.sysconf("SC_OPEN_MAX") except (AttributeError, ValueError): maxfd = 256 for fd in range(0, maxfd): try: os.close(fd) except OSError: pass os.open("/dev/null", os.O_RDONLY) # standard input (0) os.open("/dev/null", os.O_RDWR) # standard output (1) os.open("/dev/null", os.O_RDWR) # standard error (2) _________________________________________________

Jul 4th, 2005, 6:57 AM	#3
thinkgeek Newbie Join Date: Jul 2005 Posts: 10 Rep Power: 0	I tried that but ... I have tried that recipe but it is not working properly in my case. Where exactly to place it in my code? I have experimented many times with no return. It is failing to fork any process.

Jul 4th, 2005, 10:52 PM	#5
thinkgeek Newbie Join Date: Jul 2005 Posts: 10 Rep Power: 0	I tried it and here are the details (Toggle Plain Text) if __name__ == "__main__": # Self-test. retCode = createDaemon() # If executed with superuser privilages, there should be a new file in the # "/" directory. It should contain the function's return code, the daemon's # PID, PPID, and PGRP. Its PID should not equal its PGRP, and its PPID # should equal 1. If it's executed without superuser privilages, the file # won't be created and no errors will be reported. open("createDaemon.log", "w").write("rc: %s; pid: %d; ppid: %d; pgrp: %d" %\ (retCode, os.getpid(), os.getppid(), os.getpgrp())) time.sleep(10) sys.exit(0) if __name__ == "__main__": # Self-test. retCode = createDaemon() # If executed with superuser privilages, there should be a new file in the # "/" directory. It should contain the function's return code, the daemon's # PID, PPID, and PGRP. Its PID should not equal its PGRP, and its PPID # should equal 1. If it's executed without superuser privilages, the file # won't be created and no errors will be reported. open("createDaemon.log", "w").write("rc: %s; pid: %d; ppid: %d; pgrp: %d" %\ (retCode, os.getpid(), os.getppid(), os.getpgrp())) time.sleep(10) sys.exit(0) Above is my main program where I am calling the daemon program. And to your question I am getting the control of the terminal straight after I run it. Please explain?

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Jul 3rd, 2005, 8:21 AM	#2
Cerulean Professional Programmer Join Date: Apr 2005 Location: London, England Posts: 459 Rep Power: 4	Which fork is returning non-zero? I always use this lovely cookbook recipe whenever I need to fork. Never failed me so far.

Jul 5th, 2005, 11:46 AM	#6
Cerulean Professional Programmer Join Date: Apr 2005 Location: London, England Posts: 459 Rep Power: 4	Well then, you have successfully forked. Congratulations.

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Programming Forums > Script Programming > Python

Forking process using python/Writing daemons