Kubuntu 9.04 current as of 2009.02.20
Lenovo SL 400 laptop with Intel integrated x4500 graphics.
Symptoms:
-- Change the brightness of the LCD backlight to any value above the minimum value (using KDE's own controls or xbacklight, or even piping a number via sysfs it does not matter). The backlight will adjust, but several seconds later the backlight ALWAYS gets reset to 0, yielding a very dim screen.
What DOES work:
-- The backlight CAN be adjusted via the /sys/devices/virtual/backlight/acpi_video0/brightness interface manually, and the standard GUI tools from KDE 4.2 also DO work. This bug is NOT about the adjustment not working, it is about a rogue program that is incorrectly dimming the screen every several seconds.
What is Broken:
-- Some program, I do not know which one, is automatically setting the backlight brightness to 0 every several seconds.
-- Here is what I know the problem is NOT:
-- It is NOT in the HAL backlight modules, since I have turned off HAL temporarily and the problem persists
-- It is NOT in KDE's powerdevil, I turned that service off entirely and the problem persists
-- Turning off DPMS and using the NoPM flags in the Xserver itself do NOT fix the problem
-- It MIGHT be coming from events triggered by interaction with the Xserver. When I set the brightness from
a vterm it did not get reset until I switched back to the Xdesktop
What is the current work-around:
-- I was able to manually echo a desired brightness level into the /sys/devices/virtual/backlight/acpi_video0/brightness file, and then IMMEDIATELY revoke write permissions for EVERYONE (including root) from the file to prevent whatever program is resetting the brightness to 0 from being able to write:
example as root: echo 10 > brightness && chmod 000 brightness
Could you provide the output from "ps" this might help narrow down which application it could be.