Ubuntu – Unable to change the screen brightness

I created a temporally bash script to adjust brightness level. Then I create 2 sortcuts at keyboard mapping settings to set up CTRL + Brightness UP or CTRL + Brightness Down with this script:

#!/bin/bash

# Step brightness value
STEP=2
# Max brightness value (defult 100)
MAX=100
# Min brightness value (defult 0)
MIN=0

COMMAND=$(xrandr --verbose | grep -i brightness | cut -f2 -d':' | tr -d "[:space:]")
ACTUAL=$(bc -l <<< $COMMAND*100 | cut -f1 -d'.')

while getopts ": u d" input
do
    case $input in
    u)  if [ $ACTUAL -lt $MAX ];then
                TOTAL=$(bc -l <<< $(($ACTUAL+$STEP))/100)
                $(xrandr --output DP-0 --brightness $TOTAL)
        fi;;
    d)  if [ $ACTUAL -gt $MIN ];then
                TOTAL=$(bc -l <<< $(($ACTUAL-$STEP))/100)
                $(xrandr --output DP-0 --brightness $TOTAL)
        fi;;
    ?)  printf "Usage: brightness [OPTION]\n"
        printf "Increase or decrease birghtness on Ubuntu Xorg.\n" 
        printf "WAYLAND MUST BE DISABLED\n\n"
        printf "  -u\t Increases brightness\n"
        printf "  -d\t Decreases brightness\n"
        exit 2;;
    esac
done

And in set custom shortcut I added this

I have an Asus GL502VM with Nvidia 1060 and a gsync display. I faced the same issue, haven't found a permanent fix but the workaround from here worked for me. In order to use it you need to install the nvidia driver instead of xorg one and modify the DP-0 value according to your setup, in my case according to xrandr --verbose my display is connected to DP-2 port. Also night light option will change the brightness level so I disabled it.

Brightness seems to be working in unity on 18.04 though.

The bug is reported https://bugs.launchpad.net/ubuntu/+bug/1767001