Ubuntu – Command to change brightness level in Ubuntu 17.10

Why not make one command that will increase by one or decrease by one based on the options you pass to it ? That's the basic idea behind the script you will see bellow. We store current value in CURRENT variable, then use bash's arithmetic expansion $(( numberA + numberB )) to increase or decrease by one. As for decision making, we call the script with single command line argument + to increase , or - for decrease.

Per muru's suggestion in the comments , I also made a small edit to the code, which now allows you to call brightness.sh with an integer parameter less than or equals to the max brightness

#!/bin/bash

###########
# Variables
###########
FILE="/sys/class/backlight/acpi_video0/brightness"
MAX="$(cat /sys/class/backlight/acpi_video0/max_brightness)"
MIN=0
CURRENT="$( cat  $FILE )"

###########
# functions
###########

function printUsage
{
  echo "Usage:"
  echo "sudo brightness.sh [ + | - | INTEGER ]"
}

######
# Main
######


if [ $# -eq 0  ];
then
   printUsage
   exit 0
fi


if [ "$1" == "+" ];
then
   NEW=$(( $CURRENT+1  ))
   # are we trying to go past maximum value ? If yes, quit
   if [ $NEW -ge $MAX  ]
   then 
       echo ">>> ERROR: Current value already the maximum; "
       echo ">>> Exiting"
       exit 1
   fi
   # if not, then proceed
   echo "$NEW" > "$FILE"

elif [ "$1" == "-"  ];
then
   NEW=$(( $CURRENT-1  ))
   # Is NEW value going past 0 ? If yes, quit
   if [ $NEW -le $MIN ]; 
   then
       echo ">>> Error: already at minimum. "
       echo ">>> Exiting."
       exit 1
    fi
    # If not, then continue
    echo "$NEW" >  "$FILE"

# Note: new test w/ regex; for portability
# probably better idea to use awk
elif [[ "$1" =~ ^[0-9]+$ ]] && [ $1 -le $MAX   ];
then
    echo "$1" > "$FILE"

else
    echo "<<< ERROR: wrong parameter "
    printUsage
    exit 1
fi

The issue is related to the Renoir graphics in AMD 4000 series processors. Here is a Phoronix article that gives a short description of it. Starting from Linux kernel 5.5, Renoir support was marked as no longer experimental. Kernel 5.7 is the newest kernel, so updating to that provides support for your processor.

I have a laptop with a 4500U. Upgrading to 5.7 helped fix every issue besides the brightness control.

The following steps to install the kernel comes from this answer which is a general version of an ubuntuforums.org post from user lykwydchykyn. The following steps contain some additions that I found useful when installing the kernel:

1. Go here (sorted by most recent build): https://kernel.ubuntu.com/~kernel-ppa/mainline/?C=N;O=D

2. Select the build you want, then navigate to the amd64/ directory.

3. Download 3 (maybe 4) debs to a folder somewhere:

    linux-headers-VERSION-NUMBER_all.deb
    linux-headers-VERSION-NUMBER_amd64.deb
    linux-image-VERSION-NUMBER_amd64.deb
    linux-image-extra-VERSION-NUMBER_amd64.deb    # if available
   

4. Install the debs with whatever package manager front-end you use, or use these commands:

    cd /path/to/folder/where/you/put/the/debs
    sudo dpkg -i *.deb
   

An additional resource is the Ubuntu wiki which explains how to install an upstream kernel with generic instructions. This is good for learning that you choose either the generic kernel or the lowlatency kernel and don't download all of them (like I did at first): https://wiki.ubuntu.com/Kernel/MainlineBuilds