View Full Version : [kubuntu] Backlight switching off when logging into KDE Plasma Desktop

January 2nd, 2012, 12:09 PM
Hi everyone,

Happy New Year! I've got a problem with using KDE with Ubuntu 11.10 on an Acer 5336. There is a general problem with Acer laptops anyway when using Ubuntu in that, at boot, the backlight is switched off but there are solutions for that which means that I can get it switched on again and the login screen shows up fine.

If I log in to standard Ubuntu (Unity) there is no problem and the backlight stays on, but I wanted to try KDE, and when I try to login to the KDE Plasma Workspace, the backlight switches off again! It's a bit annoying, to be honest. To get the backlight working again requires running the command:

setpci -s 00:02.0 F4.b=00

I wrote a script for this and tried to get KDE Autostart to run it, but it won't because it needs to be run as root - result: my screen stays black!

Is there a way I can get KDE to run this script as root, or is there another way to run the command so that I can get my backlight on again? I can't see to input the command into a terminal, which would be the other way to do it, but it's a pain!

Any help would be appreciated.

March 22nd, 2012, 05:34 PM
For anyone else who is having this problem, here is an answer I found here:


Open a terminal and type in the terminal:

gedit ./etc/rc.local

This will open rc.local file. Now at the bottom make sure it looks like below and save.

sudo setpci -s 00:02.0 F4.B=00
exit 0

You should be fine, reboot and check it out.;)

My system's backlight comes back on fine during boot up with this modification. There's also a really helpful script for switching the backlight back on when you 'wake up' from suspend or hibernate

Good luck!