stdd/stddlib/daemon.py

# -*- coding: utf-8-*-
#
# This file is part of stdd, the simple time display daemon,
# written by Helmut Pozimski <helmut@pozimski.eu>,
# licensed under the 3-clause BSD license

import os
import sys


class Daemon(object):
	""" Tries to implement a well behaving unix daemon in a generic way,
	so the code could be used in different projects.

	"""

	def __init__(self, pfile_path, pfile_name):
		""" Initializes the object. """
		self.__pfile_path = pfile_path
		self.__pfile_name = pfile_name
		self.__daemon = False

	def Daemonize(self):
		""" Turns the calling prozess into a daemon running on it's own """

		try:
			# Fork for the first time
			self.__pid = os.fork()
		except OSError:
			sys.exit(os.EX_OSERR)
		else:
			if self.__pid > 0:
				sys.exit(os.EX_OK)
		# Become session and group leader
		os.setsid()
		try:
			#Fork for the second time
			self.__pid = os.fork()
		except OSError:
			sys.exit(os.EX_OSERR)
		else:
			if self.__pid > 0:
				sys.exit(os.EX_OK)
		# Change cwd to / to avoid interfering with other mounted file systems
		os.chdir("/")
		# Reset the umask
		os.umask(0)

		# Close possibly open file descriptors
		os.close(0)
		os.close(1)
		os.close(2)

		# And redirect them to /dev/null
		os.open("/dev/null", 0)
		os.open("/dev/null", 1)
		os.open("/dev/null", 2)

		self.__daemon = True

	def DropPriv(self, uid, gid):
		""" If the daemon is running as root user, drop privileges and continue
		running as the defined unprivileged user """
		if os.getuid() == 0:
			os.setgid(gid)
			os.setuid(uid)

	def SetName(self, name, cmdline):
		""" Sets the name of the process shown visible in ps and top,
		this allows to make your daemon look more like a standalone
		program instead of a python script.

		"""
		try:
			# First check if prctl is available, otherwise this function does nothing
			import prctl
		except ImportError:
			return False
		else:
			prctl.set_name(name)
			prctl.set_proctitle(cmdline)
			return True

	def Start(self):
		""" Performs the operations needed to "start" the daemon """
		if self.__daemon is True:
			if os.access(self.__pfile_path, os.F_OK & os.W_OK):
				self.__pidfile = open(os.path.join(self.__pfile_path, self.__pfile_name),
						"w")
				self.__pidfile.write(unicode(os.getpid()) + "\n")
				self.__pidfile.close()
				return True
			else:
				return False
		else:
			return False

	def Stop(self):
		""" Performs the operations needed to stop the daemon """
		if self.__daemon is True:
			try:
				os.remove(os.path.join(self.__pfile_path, self.__pfile_name))
			except OSError:
				return False
			else:
				return True
		else:
			return True