Ubuntu – How to get brightness controls working on a Sony VAIO Fit 15E

Brightness could be controlled by ACPI or by graphic driver. I suppose the one that controls your brightness is intel_backlight. However, you could easy find it out adding to your /etc/rc.local (before exit 0):

echo 5 > /sys/class/backlight/acpi_video0/brightness

or, alternatively:

echo 5 > /sys/class/backlight/intel_backlight/brightness

It seems that Fn-Keys do change the value of acpi_video0, the problem is that the controlling item is intel_backlight.

If the system starts with the kernel parameter acpi_backlight=vendor, the item acpi_video0 is replaced by the item intel, but then the Fn-Keys can not change the value of this item.

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