jwmud/jwmudlib/daemon.py

# This file is part of jwmud, written by Helmut Pozimski in 2014.
#
#       jwmud is free software: you can redistribute it and/or modify
#       it under the terms of the GNU General Public License as published by
#       the Free Software Foundation, version 2 of the License.
#
#       jwmud is distributed in the hope that it will be useful,
#       but WITHOUT ANY WARRANTY; without even the implied warranty of
#       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#       GNU General Public License for more details.
#
#       You should have received a copy of the GNU General Public License
#       along with jwmud.  If not, see <http://www.gnu.org/licenses/>.

# -*- coding: utf8 -*-

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
        self.__pid = 0
        self.__pidfile = ""

    def Daemonize(self):
        """ Turns the calling process 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
        # noinspection PyArgumentList
        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
            # noinspection PyUnresolvedReferences
            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(str(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