I am running Ubuntu 13.04 64-bit on an Asus UX31A. To control the default screen and keyboard brightness after the start, I wrote this to the rc.local:
echo 0 > /sys/class/backlight/acpi_video0/brightness #echo 0 > /sys/devices/platform/asus-nb-wmi/leds/asus::kbd_backlight/brightness exit 0
The screen brightness is perfectly adjusted after every restart, but the keyboard backlight won't work. It's always at 100% and if I uncomment the second line the screen brightness won't work, too. Seems like the permission is denied or the script can't access the file, because the path is totally correct.