为什么此Python脚本不能在Ubuntu 12.04中作为启动应用程序运行？

Question

I've written this watchdog script to monitor VLC player and kill it when playback has stopped because VLC continues to inhibit the power management daemon after playback. The script works. I can run it from the command line or through IDLE and it kills VLC when playback stops. I've added many variations of the command to start the script to my startup applications as described here but when I reboot, if it is running at all, it stops as soon as VLC starts. Restarting it from a terminal cause it to stay running and do what it is supposed to do. I don't know if this is a problem with the script or something peculiar about Ubuntu Startup Applications (although I'm leaning towards Ubuntu). Maybe something to do with permissions? (Although I did chmod +x ) Should I be executing some other commands to make sure DBus is up before I launch the script? Part of me thinks that something isn't fully loaded when the script starts so I tried sleeping before launching using the *nix sleep command, the X-GNOME-Autostart-Delay , and time.sleep(n) in the python code. The pythonic way seems to have the best chance of success. The *nix ways seem to only make startup take longer and at the end of it I find that the process isn't even running. I'm using the python-setproctitle module to name the process so I can quickly see if it is running with a ps -e from terminal. I'm out of ideas and about ready to just manually run the script whenever I reboot (although in principle I think that the machine should do it for me because I told it to). Some variations of Startup Application command lines that I've tried are:

/path/to/script/vlc_watchdog.py
"/path/to/script/vlc_watchdog.py"
/path/to/script/vlc_watchdog.py &
"/path/to/script/vlc_watchdog.py &"
python /path/to/script/vlc_watchdog.py
python /path/to/script/vlc_watchdog.py &
"python /path/to/script/vlc_watchdog.py"
"python /path/to/script/vlc_watchdog.py &"
bash -c "/path/to/script/vlc_watchdog.py"
sleep 30 ; /path/to/script/vlc_watchdog.py
sleep 30 && /path/to/script/vlc_watchdog.py
etc...

Full script:

#!/usr/bin/env python
import time
time.sleep(30)
import dbus
import os
import subprocess
from subprocess import Popen, PIPE
import daemon
import setproctitle

setproctitle.setproctitle('VLC-Watchdog')
sleeptime = 5

def vlc_killer():
    bus = dbus.SessionBus()
    vlc_media_player_obj = bus.get_object("org.mpris.MediaPlayer2.vlc", "/org/mpris/MediaPlayer2")
    props_iface = dbus.Interface(vlc_media_player_obj, 'org.freedesktop.DBus.Properties')
    pb_stat = props_iface.Get('org.mpris.MediaPlayer2.Player', 'PlaybackStatus')
    if pb_stat == 'Stopped':
        os.system("kill -9 $(pidof vlc)")
    else:
        time.sleep(sleeptime)

def vlc_is_running():
    ps = subprocess.Popen(['ps', '-e'], stdout = PIPE)
    out, err = ps.communicate()
    for line in out.splitlines():
        if 'vlc' in line:
            return True
    return False

def run():
    while True:
        if vlc_is_running():
            vlc_killer()
        else:
            time.sleep(sleeptime)

with daemon.DaemonContext():
    run()

Answer 1

In the shell script that starts your Python code (the one in the Ubuntu startup/initialization process), use something like:

#!/bin/sh

set -x
exec > /tmp/errors.out 2>&1
/path/to/script/vlc_watchdog.py

Then after things go awry again (that is, after another reboot), inspect /tmp/errors.out to see the error messages related to whatever happened. There should be a Python traceback in there, or at least a shell error.