I have a Dell Studio 1558. When I originally installed 13.04 on it, I had to modify my
/etc/default/grub with the following:
GRUB_CMDLINE_LINUX_DEFAULT="acpi_backlight=vendor dell_laptop.backlight=0 quiet splash"
Doing that made everything work, the keyboard brightness buttons, the OSD in the top right corner, and the brightness slider in System Settings. However, upon upgrading to 13.10, I once again am unable to adjust the backlight. This is also the case if I use either of the following:
GRUB_CMDLINE_LINUX_DEFAULT="acpi_backlight=vendor quiet splash" GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
The backlight is stuck at a single brightness level, at a guess I think it's somewhere around 50%. The OSD still comes up if I push the keyboard buttons, but the bar only goes down one division from 100% and resets back to 100%, if I press decrease again. The slider in 'System Settings' does nothing.
Any help is greatly appreciated!
Doing both of the steps mentioned here fixed this issue with a Dell Studio 1558 and Ubuntu 13.10: http://ubuntuforums.org/showthread.php?t=2181534
I used "sudo vim /etc/default/grub" but use whatever editor you're comfortable with but you will need to use sudo to edit it as the root user.
I used "sudo vim /usr/share/X11/xorg.conf.d/20-intel.conf" and then ran
:set pasteand hit
ifor insert and pasted in the contents.
Then reboot and login again and your function key with the brightness up/down should work again.