python守护进程

#!/usr/bin/env python
import os
import syslog
import time
def showProcessInfo(msg):
    # ps -eo pid,ppid,pgid,pgrp,sess,tty,tpgid,cmd
    pid=os.getpid()
    ppid=os.getppid()
    pgid=os.getpgid(0)
    pgrp=os.getpgrp()
    sid=os.getsid(0)

    print "%s pid=%d ppid=%d pgid=%d pgrp=%d sid=%d" % \
          (msg, pid, ppid, pgid, pgrp, sid)

def lf_syslog_open():
    syslog.openlog("pydaemon", syslog.LOG_PID, syslog.LOG_DAEMON)

def daemonize():
    # fork1
    pid=os.fork()
    if pid<0:
        # error
        print "fork1 error"
        return -1
    elif pid>0:
        # parent.
        exit(0)
    else:
        # child.
        pass
    showProcessInfo("fork 1 ok")

    os.setsid()
    showProcessInfo("setsid ok")

    # fork2
    pid=os.fork()
    if pid<0:
        # error
        print "fork2 error"
        return -1
    elif pid>0:
        # parent.
        exit(0)
    else:
        # child.
        pass
    showProcessInfo("fork 2 ok")

    os.chroot("/")
    os.umask(022)
    os.close(0)
    os.close(1)
    os.close(2)
    fd=os.open('/dev/null', 2)
    os.dup(fd)
    os.dup(fd)

    showProcessInfo("daemonize ok (should not be printed)")
    syslog.syslog(syslog.LOG_INFO, "daemonize ok")

# main
if __name__ == "__main__":
    # invoke from shell
    print "hello"
    showProcessInfo("main start")
    lf_syslog_open()
    daemonize()

    # daemon process
    time.sleep(10)

    syslog.closelog()
    showProcessInfo("main end")