Comment 27 for bug 573984

I just got somewhere with this mess.

Did the following:

"cat /proc/acpi/video/GFX0/DD02/brightness" (Your brightness may be located in a different folder)

and it outputted (despite my screen being blindingly bright)

levels: 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
current: 0

So then I tried this

"sudo echo 50 > /proc/acpi/video/GFX0/DD02/brightness"

and got this output

bash: /proc/acpi/video/GFX0/DD02/brightness: Permission denied

So then I tried this

"sudo su
echo 50 > /proc/acpi/video/GFX0/DD02/brightness"

And viola, my brightness level changed.

So then I tried
"echo 0 > /proc/acpi/video/GFX0/DD02/brightness"

And presto, my screen went black.

I don't know too much about what's going on, but it looks like whatever triggers the above referenced file, doesn't have proper permissions. Only true root can actually change the value of the file, not sudo.