How to control backlight by terminal command

Question

I am try to make a program that control the bright of Linux OS, but I need to know how to control the monitor backlight just using terminal commands? I need to be able to increase, decrease. And also dim screen (and return undo dim) if it is possible too.

Answer 1

There are many possibilities. Just to name a few:

1.Bare echo

echo 8 > /sys/class/backlight/intel_backlight/brightness

For this to work, the user must be in the video group.

Look at /sys/class/backlight/intel_backlight/max_brightness to see what maximum brightness is supported.

2.The simplest to use

Install xbacklight package and then try

 xbacklight -inc 20     # increase backlight by 20%
 xbacklight -dec 30     # decrease by 30%
 xbacklight -set 80     # set to 80% of max value
 xbacklight -get        # get the current level

3.Over sophisticated

Run xrandr --verbose and look for a line with resolution like LVDS1 connected 1024x600+0+0. The name of your display (LVDS1 in this example) is needed here. Now you are ready to set brightness

xrandr --output LVDS1 --brightness 0.4

But this sets only software, not hardware brightness so you can exceed the limits (in both directons). Don't expect beautiful results but if you are brave enough to experiment a little bit then fasten your seatbelt and run

xrandr --output LVDS1 --brightness 1.7
xrandr --output LVDS1 --brightness -0.4  #yes, negative value is possible
xrandr --output LVDS1 --brightness 1

You can torture more your display with xrandr, but be ready to reboot your computer if something goes wrong. For example play with the following

xrandr --output LVDS1 --reflect x
xrandr --output LVDS1 --reflect xy
xrandr --output LVDS1 --reflect normal     # return to normal state
xrandr --output LVDS1 --rotate left
xrandr --output LVDS1 --rotate inverted
xrandr --output LVDS1 --rotate normal      # again, back to normal

Answer 2

An alternative to bare echo with XFCE4 Power Manager

On my DELL Inspiron 11 xbacklight doesn't work ("No outputs have backlight property"). The bare echo method as described by user362097 does work.

If you're using Xubuntu or some distribution using the XFCE4 Power Manager, you can use xfpm-power-backlight-helper:

pkexec xfpm-power-backlight-helper --get-max-brightness
# I get 6009
pkexec xfpm-power-backlight-helper --set-brightness 1000

Answer 3

For externally connected monitors there are Linux utilities that support DDC/MCCS, the VESA standard for controlling monitor settings from a PC. MCCS commands can be issued via i2c (kernel i2c-dev module) to DVI, DisplayPort, HDMI monitors, or USB for USB connected monitors. I've found the command line utility ddcutil to be a reliable DDC/MCCS tool. If you need a small system-tray front end to ddcutil, I've written vdu_controls (a python Qt script). I've written a brief intro to vdu_controls, ddcutil and DDC/MCCS in an OpenSUSE forum post.

% ddcutil --display 2 getvcp 10
VCP code 0x10 (Brightness): current value =    50, max value =   100

% ddcutil --display 2 setvcp 10 90

Answer 4

Why torture yourself? Wouldn't you rather a nice gui?

This simple script is written to work with the backlight system, mentioned in @user3620917's answer as "Bare Echo". But, once you figured out whatever command works on your system, you can adapt this slider to work with it.

It requires the small yad, which consumes little RAM, and leaves nothing running in the background when you close the slider. To understand the basic function, and to ensure you have yad, try this at a command-line:

yad --scale --print-partial

full script:

#!/bin/sh 
BrPath='/sys/class/backlight/intel_backlight/' 
BrCur=`cat ${BrPath}brightness` 
BrMax=`cat ${BrPath}max_brightness` 
BrMin=$(( (BrMax + (100 - 1)) / 100))   # 100th max-brightness, rounded up to nearest integer 
yad --scale --min-value $BrMin --max-value $BrMax --value $BrCur --print-partial --title 'Set brightnessradky's Dpup Stretch 7.5 (RC3)' --width 300 --fixed --sticky --mouse --on-top --escape-ok --button OK --hide-value | while read BrNew 
   do echo "$BrNew" > ${BrPath}brightness 
   done

Explanation of all options: https://www.mankier.com/1/yad

To install:

• Confirm the simple echo command works on your machine. Try various values and see if your brightness changes.

  echo 10000000 > /sys/class/backlight/intel_backlight/brightness

• Confirm yad works:

  yad --scale --print-partial

• save the script in a file called set-brightness

• if needed, edit the BrPath= line to match your backlight path.
• put the script into /usr/local/bin
• create a launcher on your panel or desktop, which runs the command set-brightness. Since it's in /usr/local/bin, your OS should find it-- no need to enter entire path.

Causes of failure:

• Your backlight path might not be intel. Figure out which backlight path is correct for your machine https://askubuntu.com/questions/437983/how-to-find-backlight-is-managed-by-which-card
• You might have an old yad installed, or not installed at all. http://archive.ubuntu.com/ubuntu/pool/universe/y/yad/

• If you're not running as root, you may need to give your user (or all users) write-permissions on the brightness file

  chmod 666 /sys/class/backlight/intel_backlight/brightness

• You might have characters in your yad 'title' parameter that some versions of yad might not like, such as parens. (parens work for me, ymmv).

Answer 5

Hey guys here I will tell you easiest one to control your screen's brightness.

Here parameters range is 100-999 depending on your requirement adjust number in command line below

echo 200 | sudo tee /sys/class/backlight/intel_backlight/brightness

Hope it will be helpful to you.

Answer 6

I was looking for a command to adjust the backlight of a laptop's LCD panel running Fedora 30 XFCE.

For some reason xbacklight didn't work I also suppose that even if xbacklight worked in a graphical environment, like under X server, it wouldn't work in runlevel 3, in a virtual console So I found brightlight which works great for now, it works both under XFCE and in runlevel 3. Install with

sudo dnf install brightlight

for info running the command type:

brightlight -h

Answer 7

If you want to change it at the hardware level then it depends on which graphics card you have. I have radeon card + intel integrated card. So I change brightness by the following scripts for the 3 tasks you mentioned.

1. Increase brightness

cb=$(cat /sys/class/backlight/intel_backlight/brightness)   
nb=$(($cb + 50))     
echo $nb > /sys/class/backlight/intel_backlight/brightness     
notify-send -t 1 -a "My Brightness controller" $nb

2. Decrease brightness

cb=$(cat /sys/class/backlight/intel_backlight/brightness)    
nb=$(($cb - 50))    
echo $nb > /sys/class/backlight/intel_backlight/brightness     
notify-send -t 1 -a "My Brightness controller" $nb

3. Dim screen

cb=$(cat /sys/class/backlight/intel_backlight/brightness)    
if [ $cb -ne 0 ]    
then    
    nb=0    
    echo $cb > /home/prem/Documents/sys_files/old_bright    
else    
    nb=$(cat /home/prem/Documents/sys_files/old_bright)    
fi    
echo $nb > /sys/class/backlight/intel_backlight/brightness

In your case you may need to change the folder name from Intel, depending on your GPU.

Answer 8

step1: open terminal ctrl+alt+t

step2:xrandr | grep " connected" | cut -f1 -d " "

step3:xrandr --output [monitor-name] --brightness [brightness-level]

 example: xrandr --output LVDS-1 --brightness 0.75

The brightness level should be set between 0.5 to 1 for better visibility.

Answer 9

Here is the simple command to control brightness in any linux based system

First you have to know the monitoring screen connected to your computer.

To know this, run this command

xrandr -q

It will give useful information about screen

Here my screen connected to eDP

It might be different for you system

After knowing that run the below command

xrandr --output eDP --brightness [0-10]

Replace eDP by your connected screen from above output and you can have normal brighness values from 0.1 to 1.0