Brightness fn key shortcut doesn't work on ASUS laptop

In the terminal:

1. sudo nano /etc/default/grub

   Change

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
   

   to

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi="
   

   Then, save the file.

2. sudo update-grub

3. Restart computer.

---

The function keys (Fn+F5/F6) should now be active.

I found out that the grub file got modified after an upgrade of the system and had to do it again.

Disclaimer: I struggled with this on Mint/Mate-18 with my Asus 305CA, and got it to work, I do not know if it works on Ubuntu as well, but try... I did this:

Get Fn F5/F6 working:

sudo emacs /etc/default/grub

Change the following: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi="

sudo update-grub

reboot the system... Now the splash screen should show up.

Verify acpi commands with acpi_listen:

acpi_listen.

press Fn F5/F6. I got this:

video/brightnessdown BRTDN 00000087 00000000 K
video/brightnessup BRTUP 00000086 00000000 K

Add the event codes to acpi event:

sudo emacs /etc/acpi/events/asus-keyboard-backlight-down 

event=video/brightnessdown BRTDN 00000087

sudo emacs /etc/acpi/events/asus-keyboard-backlight-up

event=video/brightnessup BRTUP 00000086

Confirm you can change backlight by (where xx is an integer):

echo xx | sudo tee /sys/class/backlight/intel_backlight/brightness

Create a script:

sudo emacs /etc/acpi/asus-keyboard-backlight.sh 

Add the variable to the file:

KEYS_DIR=/sys/class/backlight/intel_backlight

I also set value to 10 instead of 1, as it was just too slow:

if [ "$1" = down ]; then
    VAL=$((VAL-10))
else
    VAL=$((VAL+10))
fi

The actual display brightness does not follow the bar in the splash. When it is full up/down, you can still continue to press Fn F5/F6 to change brightness.

You'll need to restart acpid for it to take effect:

sudo service acpid restart

this solution worked for me:

open terminal and type these commands:

sudo touch /usr/share/X11/xorg.conf.d/20-intel.conf

sudo nano /usr/share/X11/xorg.conf.d/20-intel.conf

Add the following lines to this file:

Section "Device"
        Identifier  "card0"
        Driver      "intel"
        Option      "Backlight"  "intel_backlight"
        BusID       "PCI:0:2:0"
EndSection

close file after saving then back to terminal and type these commands:

sudo nano /etc/default/grub

find this line

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

and replace it by

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi= acpi_backlight=intel"

then in terminal

sudo update-grub

restart your laptop and it will work probably.