I'm using xubuntu 13.10. When I installed the system the fn keys for brightness worked, but somehow they aren't now. They stopped working with no reason.
The problem is that the keys are not even recognized. When I start showkey --scancodes in virtual terminal and try the brightness combination FN+left/right arrow the scancodes wont show, but for the volume (for example) it shows the scancodes right.
Anybody has any idea how to fix this.
I was googling for several days now and I can tell you that nothing solved my issue so far. Answer like setting acpi_backlight=vendor, or acpi_osi to something didn't work so don't post that. I also wanted to map those key to a script that would change ma brightness (I already made that script and it works) but I just can not get the keys to be recognized.