daemon.py

"""Generic linux daemon base class for python 3.x.
Source: https://web.archive.org/web/20131017130434/http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/"""

import atexit
import os
import signal
import sys
import time

from enums import *


class Daemon:
    """A generic daemon class.

    Usage: subclass the daemon class and override the run() method."""

    def __init__(self, pidfile):
        self.pidfile = pidfile

    def daemonize(self):
        """Deamonize class. UNIX double fork mechanism."""

        try:
            pid = os.fork()
            if pid > 0:
                # exit first parent
                sys.exit(0)
        except OSError as err:
            sys.stderr.write('fork #1 failed: {0}\n'.format(err))
            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 as err:
            sys.stderr.write('fork #2 failed: {0}\n'.format(err))
            sys.exit(1)

        # redirect standard file descriptors
        sys.stdout.flush()
        sys.stderr.flush()
        si = open(os.devnull, 'r')
        so = open(os.devnull, 'a+')
        se = open(os.devnull, 'a+')

        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())
        with open(self.pidfile, 'w+') as f:
            f.write(pid + '\n')

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

    def force_start(self):
        """Start the daemon even if it is already running. The pidfile will be overwritten. Only do this, if you intend
        to terminate a potentially still running daemon by some other means."""

        # delete pidfile if it exists
        if os.path.exists(self.pidfile):
            os.remove(self.pidfile)

        # start daemon
        self.start()

    def start(self):
        """Start the daemon."""

        # Check for a pidfile to see if the daemon already runs
        try:
            with open(self.pidfile, 'r') as pf:

                pid = int(pf.read().strip())
        except IOError:
            pid = None

        if pid:
            message = "pidfile {0} already exist. " + \
                      "Daemon already running?\n"
            sys.stderr.write(message.format(self.pidfile))
            sys.exit(1)

        # Start the daemon
        self.daemonize()
        self.run()

    def stop(self):
        """Stop the daemon."""

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

        if not pid:
            message = "pidfile {0} does not exist. " + \
                      "Daemon not running?\n"
            sys.stderr.write(message.format(self.pidfile))
            return  # not an error in a restart

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

    def __get_status(self):
        try:
            pf = open(self.pidfile, 'r')
            pid = int(pf.read().strip())
            pf.close()
        except IOError:
            return ServerStatus.stopped

        try:
            procfile = open("/proc/%d/status" % pid, 'r')
            procfile.close()
        except IOError:
            return ServerStatus.stale
        except TypeError:
            return ServerStatus.unknown

        return ServerStatus.running

    def status(self):
        if self.__get_status() == ServerStatus.stopped:
            print("PyDirectord is stopped")
            sys.exit(3)
        elif self.__get_status() == ServerStatus.running:
            print("PyDirectord is running")
            sys.exit(0)
        elif self.__get_status() == ServerStatus.stale:
            print("PyDirectord: PID file '" + self.pidfile + "' is stale")
            sys.exit(1)
        elif self.__get_status() == ServerStatus.unknown:
            print("PyDirectord status unknown")
            sys.exit(4)

    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()."""