One of our family's laptops, an Asus G750JS, comes with both a keyboard backlight and a display backlight – a common feature of modern gaming laptops. In Windows OS, the brightness control of these backlights appears to work out-of-the-box, using the following Fn-key combinations:
Fn+F3 = dimmer
Fn+F4 = brighter
Fn+F5 = dimmer
Fn+F6 = brighter
In Linux, I've always had to edit the grub file (/etc/default/grub) by adding acpi_osi= to get these Fn-key combinations to work, using the following line of the grub file in many Ubuntu-based distros:
or in Manjaro17:
However, with Manjaro17-xfce that I’m using, the following edited entry...
...gave a repeated ACPI error, each time the laptop booted up. However, once booted, the machine seemed to behave normally, the above Fn-key combinations working for both backlights.
Understandably, it feels uncomfortable to have error messages on your computer. To fix the ACPI error, it seemed that all I had to do was add ‘Linux’ to make the previous line of code read…
On doing this the ACPI error no longer appeared during boot-up. However, the caveat is that though the Fn+F3/F4 for keyboard brightness will work, the Fn+F5/F6 keys for display brightness won’t. But, Fn+F5/F6 is not essential, as display brightness can instead be controlled by right-clicking on the Xfce Power Manager Settings icon (on the right-hand side of the panel, next to the clock time) and using the brightness-control slider button.
To open the grub file for editing, open terminal and type:
gksudo mousepad /etc/default/grub
Enter [login] password, then scroll down to the relevant line and add acpi_osi=Linux as indicated above. Remember to save the changes made to the grub file and then update grub, before rebooting, by typing:
sudo update-grub [You might need to open a second copy of the terminal to run this]
Hoping this tutorial clarifies a thread on this topic, found elsewhere on the forum at
Though I've found the above to solve the backlight issue for an Asus G750, it's possible that it will work for other gaming computers.