I am using Toshiba L510 AND Ubuntu 12.04. I Cannot control brightness of my system using function keys. What could be the cause?
5 Answers
Open a terminal using Ctrl+Alt+t
and type sudo apt-get install xbacklight
. That will install xbacklight if it isn't already there (I can't remember whether it's a default package!).
Then type xbacklight -set x
replacing the x with a number between 1 and 99 to set the percentage brightness for your screen backlight. You can actually set to 0 (and I do because I hate bright screens) but I understand that can cause problems on some displays so I don't recommend trying it.

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I just wanted to add, you can then set a keyboard shortcut to something like xbacklight -inc 10
to increase the brightness by 10%.
Unfortunately, you can't use Fn + Another Key since like he said, Fn is reserved for the BIOS. It's weird because my Fn + F7 works in turning off/on the screen, and Fn + F2 works in turning off (but not on) my wifi, but F5 and F6 do not adjust brightness... Hope someone can find a real fix soon.
Try adding acpi_backlight=vendor
as a boot option. To do that, open a terminal window, and run
gksu gedit /etc/default/grub
Locate this line: GRUB_CMDLINE_LINUX="".
Edit it to look like this: GRUB_CMDLINE_LINUX="acpi_backlight=vendor"
Save the file, then, in a terminal, run sudo update-grub
.
Reboot, and check if the brightness keys work.
That worked for me!
Related link : Brightness function keys not working
I had the same problem on my Toshiba
I installed fnfxd
package search synaptics Package Manger for it or
sudo apt-get install fnfxd
It solved my problem

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I have a Satellite L55-b5338 running Zorin. This worked for my volume control and brightness, but not my wifi toggle or my touchpad enable/disable. I'll see if I can find commands to bind for those. – TecBrat Feb 09 '16 at 14:20
This has fixed it both on a Toshiba L510 and a P850.
1) Edit /etc/default/grub and change this variable:
GRUB_CMDLINE_LINUX="pcie_aspm=force acpi_osi=Linux acpi_backlight=legacy"
2) Edit /etc/modprobe.d/blacklist.conf and add this line at the end of the file:
blacklist toshiba_acpi
3) Update the grub config file:
sudo update-grub
4.) Reboot.

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ls /sys/class/backlight/
to the question. – mikewhatever Jun 27 '12 at 05:21toshset
maybe it's worth checking out. redshift was also recommended – Savvas Radevic Jun 27 '12 at 05:27