If your laptop’s brightness function keys don’t work after installing Ubuntu, try this quick and easy fix.
Open up the terminal with CTRL-ALT-T and edit your grub config with your favourite text editor. For the purpose of this example we’ll use nano.
sudo nano /etc/default/grub
While there, append the GRUB_CMDLINE_LINUX_DEFAULT line with acpi_osi=. The line should now read “quiet splash acpi_osi=”.
Save and exit, and then update your grub.
Now reboot and your backlight function keys should be working!