Getting backlight to turn off on Dell Inspiron 8100 with Xubuntu 8.04 Hardy

All I wanted was to get the backlight to turn off when my laptop(Dell Inspiron 8100 laptop running Xubuntu 8.04 Hardy) was idle for a few minutes. Is that so wrong? Why did it take over 3 hours of googling and trying various things without really understanding what I was doing?

I did a whole lot of things, and I have no idea which ones were truly necessary or not, so I will start at the end, with the final change that actually got it to work, and work backwards from there.

I had everything configured properly but still the screensaver and turning off the monitor would not work. Then I found a Ubuntu Forums post that said that the gnome-screensaver module is turned off by default in Xubuntu 8.04 even though there is a place in the Settings Manager for configuring the screensaver! That would explain that all the changes I made to the screensaver configuration had no apparent effect! To make matters worse, apparently the gnome-power-manager settings for what to do when the computer is idle depend on the gnome-screensaver module to be activated, so power management is hobbled by default also. In any event, the fix is:

  • Settings -> Settings Manager -> Autostarted apps
  • Then click on Add to create a new entry
  • Then enter gnome-screensaver as the command (and any name and description you want)
  • Then exit out and restart the desktop (Ctrl-Alt-Backspace) to restart with the screensaver running.
So that was what finally got my gnome-power-manager settings to come to life.

Working backwards, here is how I configured the screensaver settings:
  • Settings -> Settings Manager -> Screensaver
  • Select a screensaver theme.
  • Set the slider for "Regard the computer as idle after"
  • Check the box for "Activate screensaver when idle."
  • Click on the Power Management button
  • On both the On AC Power and On Batter Power tabs set the slider for "Put display to sleep when inactive for:"
This will result in the screen saver kicking on after the time you set, and then the backlight turning off after the time you set Power Management screen. I couldn't find a way on these screens to go straight to turning off the backlight without going through the screensaver first.

However, after much fiddling around I was able to get the backlight to turn off without going through the screensaver first (at least not for long) by doing the following:
  • Set the screensaver to "Blank" on the screensaver settings page.
  • Start up gconf-editor from a terminal, then navigate to Apps -> Gnome-Power-Manager -> Timeout and set the values for sleep_display_ac and sleep_display_battery to both be 1.
This seemed to work to make the backlight turn off at the time set for the screensaver to turn on. Your mileage may vary.

Another thing I did was use gconf-editor to set the settings for Apps -> Gnome-Power-Manager -> Backlight -> dpms_method_ac and dpms_method_battery to "off". I think this may have been necessary to ensure that the backlight was told to turn off when the idle time setting was reached.

Other things I did earlier, but which I am not sure were necessary or not, were to install libsmbios-bin (sudo aptitude install libsmbios-bin) and then add dcdbas to /etc/modules (sudo nano etc/modules/ and then just put dcdbas on a line by itself). I read some posts that suggested these were necessary in order to allow Ubuntu to control the backlight on a Dell laptop, but who knows.

I learned that you can set more options of gnome-power-manager by installing gconf-editor (sudo aptitude install gconf-editor) then starting it by entering gconf-editor in a terminal, and then going

1 comment:

Nick said...

Thank you! I can confirm that this fix still works in 12.04, Precise Pangolin, only now the first step is:

Settings -> Settings Manager -> Session and Startup -> Application Autostart