monitor backlight won't turn off, wrote a daemon to force it on / off

Mark Greenwood fatgerman at ntlworld.com
Mon May 4 10:43:17 BST 2009


On Monday 04 May 2009 08:25:36 dave selby wrote:
> Hi All,
> 
> I have a system where the monitor will blank but absolutely will not turn off.
> 
> I have checked xorg.conf for DPMS, tweaked configs and googled etc and
> came to realize I am not alone.
> I came across http://www.shallowsky.com/linux/x-screen-blanking.html
> which shed some light but did not want to
> use the suggested workaround so I have written 'backlight_daemon.py'
> 
> It checks 'xset -q' every couple of seconds and if it finds that the
> monitor should be off, it 'vbetool dpms off''s to
> force the issue, reports what it is doing to syslog :)
> 
> It needs to be run as root, I start it by adding
> 
> @reboot /usr/local/bin/backlight_daemon.py
> 
> to my roots crontab. Its easier than setting up a /etc/init.d/...
> 
> Anyhow it solved my problem and I wanted to share it with you guys,
> 
> Cheers
> 
> Dave

It may not be that complicated. I had a similar problem and found that I simply needed to be a member of the 'video' group.

Mark

> 
> 
> 
> 
> 
> #!/usr/bin/env python
> 
> # Copyright 2008 David Selby dave6502<SPAM>@googlemail.com
> 
> # backlight_daemon is free software: you can redistribute it and/or modify
> # it under the terms of the GNU General Public License as published by
> # the Free Software Foundation, either version 3 of the License, or
> # (at your option) any later version.
> 
> # kmotion is distributed in the hope that it will be useful,
> # but WITHOUT ANY WARRANTY; without even the implied warranty of
> # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> # GNU General Public License for more details.
> 
> # You should have received a copy of the GNU General Public License
> # along with backlight_daemon. If not, see <http://www.gnu.org/licenses/>.
> 
> 
> import os, sys, pwd, time, syslog
> from subprocess import * # breaking habit of a lifetime !
> 
> 
> def main():
>     # the backlight daemon
>     log_it('Starting ...')
>     while True:
>         user = find_user()
>         check_change(user)
> 
> 
> def find_user():
>     # wait for a valid user who can 'xset -q -display:0.0', return that user
>     while True:
>         users = [i[0] for i in pwd.getpwall() if i[2] > 500 or i[2] == 0]
>         for user in users:
>             pipe = Popen(['sudo -u %s xset -q -display :0.0' % user],
> shell=True, stdout=PIPE, stderr=PIPE, close_fds=True)
>             if pipe.communicate()[1] == '':
>                 log_it('Selected user \'%s\'' % user)
>                 return user
>         time.sleep(10)
> 
> 
> def check_change(user):
>     # check 'xset -q' and execute 'vbetool dpms on|off'
>     monitor_on = False # system starting so monitor assumed to be off
>     while True:
>         pipe = Popen(['sudo -u %s xset -q -display :0.0' % user],
> shell=True, stdout=PIPE, stderr=PIPE, close_fds=True)
>         xset_q, xset_err = pipe.communicate()
>         if xset_err != '':
>             break # 'user' no longer valid
> 
>         if monitor_on and xset_q.find('Monitor is Off') != -1:
>             log_it('Forcing monitor backlight off')
>             # sudo to set env variables for root in this shell
>             Popen(['sudo vbetool dpms off'], shell=True, close_fds=True)
>             monitor_on = False
> 
>         if not monitor_on and xset_q.find('Monitor is On') != -1:
>             log_it('Forcing monitor backlight on')
>             # sudo to set env variables for root in this shell
>             Popen(['sudo vbetool dpms on'], shell=True, close_fds=True)
>             monitor_on = True
> 
>         time.sleep(2)
> 
> 
> def log_it(msg):
>     # log 'msg' to syslog
>     syslog.openlog('backlight_daemon', syslog.LOG_PID)
>     syslog.syslog(msg)
>     syslog.closelog()
> 
> 
> main()
> 
> 
> 
> 
> 



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