Python class that runs fully daemonized (with a double fork)

gistfile1.py

import sys, os, time, atexit
from signal import SIGTERM

class Daemon:

	'''
	Base Daemon class that takes care of the start, stop, and forking of the processes.
	Used to daemonize any Python script.
	'''

	def __init__(self, pidfile, worker_id, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
		self.pidfile = pidfile
		self.worker_id = worker_id
		self.stdin = stdin
		self.stdout = stdout
		self.stderr = stderr
		self.init_time = int(time.time())
		self.successful_job_count = 0
		self.failed_job_count = 0
		self.avg_job_time = 0

	def daemonize(self):
		'''
		Double-forks the process to daemonize the script.
		'''
		try:
			pid = os.fork()
			if pid > 0:
				# Exit from first parent
				sys.exit(0)
		except OSError, e:
			sys.stderr.write("Fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
			sys.exit(1)

		# Decouple from parent environment
		os.chdir("/")
		os.setsid()
		os.umask(0)

		# Second fork
		try:
			pid = os.fork()
			if pid > 0:
				# Exit from second parent
				sys.exit(0)
		except OSError, e:
			sys.stderr.write("Fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
			sys.exit(1)

		# Redirect standard file descriptors
		sys.stdout.flush()
		sys.stderr.flush()
		si = file(self.stdin, 'r')
		so = file(self.stdout, 'a+')
		se = file(self.stderr, 'a+', 0)
		os.dup2(si.fileno(), sys.stdin.fileno())
		os.dup2(so.fileno(), sys.stdout.fileno())
		os.dup2(se.fileno(), sys.stderr.fileno())

		# Write the PID file
		atexit.register(self.delpid)
		pid = str(os.getpid())
		file(self.pidfile, 'w+').write("%s\n" % pid)

	def delpid(self):
		# Removes the PID file
		os.remove(self.pidfile)

	def start(self):
		'''
		Start the daemon.
		'''
		# Check for a PID file to see if the Daemon is already running
		try:
			pf = file(self.pidfile, 'r')
			pid = int(pf.read().strip())
			pf.close()
		except IOError:
			pid = None

		if pid:
			message = "PID file %s already exist. Daemon already running?\n"
			sys.stderr.write(message % self.pidfile)
			sys.exit(1)

		# No PID file, start the daemon
		self.daemonize()
		self.run()

	def stop(self):
		'''
		Stop the daemon.
		'''
		# Get the PID from the PID file
		try:
			pf = file(self.pidfile, 'r')
			pid = int(pf.read().strip())
			pf.close()
		except IOError:
			pid = None

		if not pid:
			message = "PID file %s does not exist. Daemon not running?\n"
			sys.stderr.write(message % self.pidfile)
			return # not an error in a restart

		# Try to kill the daemon process
		try:
			while 1:
				os.kill(pid, SIGTERM)
				time.sleep(0.1)
		except OSError, err:
			err = str(err)
			if err.find("No such process") > 0:
				if os.path.exists(self.pidfile):
					os.remove(self.pidfile)
			else:
				print str(err)
				sys.exit(1)

	def restart(self):
		'''
		Restart the daemon.
		'''
		self.stop()
		self.start()

	def run(self):
		'''
		The script to execute by the daemon after it starts.
		'''
		pass