Cooked version of Python daemon base script.

daemon.py

#!/usr/bin/env python

# Origin: http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/
# Cooked up a bit by @jmhobbs

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

class Daemon:
	"""
	A generic daemon class.

	Usage: subclass the Daemon class and override the run() method
	"""
	def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
		self.stdin = stdin
		self.stdout = stdout
		self.stderr = stderr
		self.pidfile = pidfile

	def daemonize(self):
		"""
		do the UNIX double-fork magic, see Stevens' "Advanced
		Programming in the UNIX Environment" for details (ISBN 0201563177)
		http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
		"""
		try:
			pid = os.fork()
			if pid > 0:
				# exit 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)

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

	def delpid(self):
		os.remove(self.pidfile)

	def start(self):
		"""
		Start the daemon
		"""
		if self._status():
			sys.stderr.write("Daemon already running?\n")
			sys.exit(1)

		print "Daemon starting."
		# Start the daemon
		self.daemonize()
		self.run()

	def stop(self):
		"""
		Stop the daemon
		"""
		pid = None
		try:
			pid = self._status()
			if not pid:
				sys.stderr.write("Daemon not running?\n")
				return # not an error in a restart
		except Exception, e:
			print "Error:", e
			sys.exit(1)

		# Try killing 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:
				print "Daemon stopped."
				if os.path.exists(self.pidfile):
					os.remove(self.pidfile)
			else:
				print str(err)
				sys.exit(1)

	def status(self):
		if not self._status():
			status = "not running"
		else:
			status = "running"
		print "The daemon is %s." % status

	def _status(self):
		"""
		Check if the daemon is running
		"""

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

		if not pid:
			return None

		# See if it is alive
		try:
		    os.kill(pid, 0)
		except OSError, err:
		    if err.errno == errno.ESRCH:
				return None
		    elif err.errno == errno.EPERM:
				raise Exception( "Could not signal process with pid %d" % pid )
		    else:
		        raise Exception( "Unknown error" )
		else:
			return pid

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

	def run(self):
		"""
		You should override this method when you subclass Daemon. It will be called after the process has been
		daemonized by start() or restart().
		"""