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3894 chandransh 1 
#!/usr/bin/env python
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'''
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This daemon has been taken from the blog post of
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<a href="http://www.jejik.com/authors/sander_marechal/">Sander Marechal</a>
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at http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/
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Some of the references within the code comments are no longer available.
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'''
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import sys, os, time, atexit
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from signal import SIGTERM
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class Daemon:
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	"""
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	A generic daemon class.
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	Usage: subclass the Daemon class and override the run() method
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	"""
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	def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
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		self.stdin = stdin
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		self.stdout = stdout
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		self.stderr = stderr
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		self.pidfile = pidfile
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	def daemonize(self):
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		"""
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		do the UNIX double-fork magic, see Stevens' "Advanced
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		Programming in the UNIX Environment" for details (ISBN 0201563177)
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		http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
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		"""
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		try:
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			pid = os.fork()
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			if pid > 0:
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				# exit first parent
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				sys.exit(0)
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		except OSError, e:
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			sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
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			sys.exit(1)
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		# decouple from parent environment
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		os.chdir("/")
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		os.setsid()
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		os.umask(0)
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		# do second fork
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		try:
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			pid = os.fork()
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			if pid > 0:
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				# exit from second parent
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				sys.exit(0)
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		except OSError, e:
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			sys.stderr.write("fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
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			sys.exit(1)
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		# redirect standard file descriptors
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		sys.stdout.flush()
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		sys.stderr.flush()
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		si = file(self.stdin, 'r')
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		so = file(self.stdout, 'a+')
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		se = file(self.stderr, 'a+', 0)
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		os.dup2(si.fileno(), sys.stdin.fileno())
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		os.dup2(so.fileno(), sys.stdout.fileno())
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		os.dup2(se.fileno(), sys.stderr.fileno())
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		# write pidfile
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		atexit.register(self.delpid)
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		pid = str(os.getpid())
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		file(self.pidfile,'w+').write("%s\n" % pid)
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	def delpid(self):
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		os.remove(self.pidfile)
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	def start(self):
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		"""
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		Start the daemon
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		"""
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		# Check for a pidfile to see if the daemon already runs
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		try:
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			pf = file(self.pidfile,'r')
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			pid = int(pf.read().strip())
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			pf.close()
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		except IOError:
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			pid = None
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		if pid:
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			message = "pidfile %s already exist. Daemon already running?\n"
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			sys.stderr.write(message % self.pidfile)
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			sys.exit(1)
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		# Start the daemon
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		self.daemonize()
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		self.run()
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	def stop(self):
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		"""
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		Stop the daemon
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		"""
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		# Get the pid from the pidfile
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		try:
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			pf = file(self.pidfile,'r')
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			pid = int(pf.read().strip())
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			pf.close()
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		except IOError:
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			pid = None
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		if not pid:
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			message = "pidfile %s does not exist. Daemon not running?\n"
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			sys.stderr.write(message % self.pidfile)
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			return # not an error in a restart
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		# Try killing the daemon process
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		try:
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			while 1:
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				os.kill(pid, SIGTERM)
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				time.sleep(0.1)
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		except OSError, err:
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			err = str(err)
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			if err.find("No such process") > 0:
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				if os.path.exists(self.pidfile):
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					os.remove(self.pidfile)
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			else:
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				print str(err)
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				sys.exit(1)
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	def restart(self):
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		"""
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		Restart the daemon
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		"""
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		self.stop()
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		self.start()
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	def run(self):
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		"""
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		You should override this method when you subclass Daemon. It will be called after the process has been
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		daemonized by start() or restart().
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		"""
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		pass