daemonize a process class of python script

daemonize_class.py

import os
import sys
import time
import atexit


class Daemon(object):
    
    def __init__(self, pidfile="/dev/null", stdin="/dev/null", stdout="/dev/null", stderr="/dev/null"):

        self.stdin = stdin
        self.stdout = stdout
        self.stderr = stderr
        self.pidfile = pidfile

    def _daemonize(self):
        
        try:
            # the first fork to leave the parent process
            pid = os.fork()
            if pid > 0:
                sys.exit(0)
        except OSError, e:
            sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
            sys.exit(1)

        # leave the term
        os.setsid()
        os.chdir("/")
        # set file permission
        os.umask(0)

        try:
            # the second fork to forbid opening the term
            pid = os.fork()
            if pid > 0:
                sys.exit(0)
        except OSError, e:
            sys.stderr.write("fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
            sys.exit(1)

        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())

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

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

    def start(self):
        try:
            pf = file(self.pidfile,'r')
            pid = int(pf.read().strip())
            pf.close()
        except IOError:
            pid = None

        if pid:
            message = "pidfile %s already exist. Daemon already running?\n"
            sys.stderr.write(message % self.pidfile)
            sys.exit(1)

        try:
            self._daemonize()
            self._run()
        except Exception, e:
            print e

    def stop(self):
        try:
            pf = file(self.pidfile,'r')
            pid = int(pf.read().strip())
            pf.close()
        except IOError:
            pid = None

        if not pid:
            message = "pidfile %s does not exist. Daemon not running?\n"
            sys.stderr.write(message % self.pidfile)
            return

        try:
            while True:
                os.kill(pid, signal.SIGTERM)
                time.sleep(1)
        except OSError, err:
            err = str(err)
            if err.find("No such process") > 0:
                if os.path.exists(self.pidfile):
                    os.remove(self.pidfile)
            else:
                print str(err)
                sys.exit(1)

    def restart(self):
        self.stop()
        self.start()

    def _run(self):
        """
        you must inherit to implement this function
        """
        print "I'm Daemon Parent Class!"


class TestDaemon(Daemon):

    def _run(self):
        while True:
            test_file = file("/tmp/test_file.log",'a+')
            test_file.write("Test Daemon ok!  time:" + str(time.time()) + " Pid:" + str(os.getpid()) + "\n")
            test_file.close()
            time.sleep(1)


if __name__ == "__main__":

    daemon = TestDaemon("/tmp/test.pid")

    daemon.start()
    time.sleep(10)
    daemon.stop()
    daemon.restart()