linux daemon 参数

import os
import sys
import time
import atexit
import signal

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

    def daemonize(self):
        try:
            pid = os.fork()
            if pid > 0:
                sys.exit(0)
        except OSError as err:
            sys.stderr.write(f'Fork #1 failed: {err}\n')
            sys.exit(1)

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

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

        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())

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

        if pid:
            message = f'pidfile {self.pidfile} already exists. Daemon already running?\n'
            sys.stderr.write(message)
            sys.exit(1)

        self.daemonize()
        self.run()

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

        if not pid:
            message = f'pidfile {self.pidfile} does not exist. Daemon not running?\n'
            sys.stderr.write(message)
            return

        try:
            while 1:
                os.kill(pid, signal.SIGTERM)
                time.sleep(0.1)
        except OSError as 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):
        while True:
            time.sleep(1)

if __name__ == '__main__':
    daemon = Daemon('/tmp/daemon-example.pid')
    if len(sys.argv) == 2:
        if 'start' == sys.argv[1]:
            daemon.start()
        elif 'stop' == sys.argv[1]:
            daemon.stop()
        elif 'restart' == sys.argv[1]:
            daemon.restart()
        else:
            print('Unknown command')
            sys.exit(2)
        sys.exit(0)
    else:
        print('Usage: {} start|stop|restart'.format(sys.argv[0]))
        sys.exit(2)