do the UNIX double-fork magic, see Stevens' "Advanced 
        Programming in the UNIX Environment" for details (ISBN 0201563177)
        http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16

def _daemonize(self):
        """
        do the UNIX double-fork magic, see Stevens' "Advanced 
        Programming in the UNIX Environment" for details (ISBN 0201563177)
        http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
        """
        try:
            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)

        os.setsid()
        os.chdir("/")
        os.umask(0)

        try:
            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()
        if self.stdin:
            si = file(self.stdin, 'r')
            os.dup2(si.fileno(), sys.stdin.fileno())
        if self.stdout:
            so = file(self.stdout, 'a+')
            os.dup2(so.fileno(), sys.stdout.fileno())
        if self.stderr:
            se = file(self.stderr, 'a+', 0)
            os.dup2(se.fileno(), sys.stderr.fileno())
        atexit.register(self.delpid)
        pid = str(os.getpid())
        file(self.pidfile, 'w+').write("%s\n" % pid)