使用python创建守护进程

def ():
    try:
        if os.fork() > 0:
            os._exit(0)
    except OSError, error:
        print 'fork #1 failed: %d (%s)' % (error.errno, error.strerror)
        os._exit(1)
    os.chdir('/')
    os.setsid()
    os.umask(0)
    try:
        pid = os.fork()
        if pid > 0:
            print 'Daemon PID %d' % pid
            os._exit(0)
    except OSError, error:
        print 'fork #2 failed: %d (%s)' % (error.errno, error.strerror)
        os._exit(1)

lockfile = 'Server.pid'
fp = open(lockfile, 'w')
try:
    fcntl.lockf(fp, fcntl.LOCK_EX | fcntl.LOCK_NB)
except IOError:
    print 'Another instance is running'
    sys.exit(0)