A Linux ACPI brightness control script
Brightness icon in featured image by Elegant Themes
When I started using i3 window manager, I knew I’d basically have to re-engineer a number of desktop environment features myself around the bare window manager. One of these features is easy brightness control on my laptop.
The Arch Wiki has a *great* and in-depth page on this as it can be a very complex matter with a bunch of different ways to manage it on different hardware. Here! But after that, and if the ACPI method works for you, here is the script I came up with to manage it on Ubuntu!
ACPI brightness controls
So if you see something listed like this then you probably have a backlight you can interact with
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$ ls -l /sys/class/backlight/** /sys/class/backlight/some_backlight/: total 0 -r--r--r-- 1 root root actual_brightness -rw-r--r-- 1 root root bl_power -rw-r--r-- 1 root root brightness lrwxrwxrwx 1 root root device -> ../../card0-someSCREEN -r--r--r-- 1 root root max_brightness drwxr-xr-x 2 root root power lrwxrwxrwx 1 root root subsystem -> ../../../../../../../class/backlight -r--r--r-- 1 root root type -rw-r--r-- 1 root root uevent |
The files we’re interested in are brightness and max_brightness. Writing a value into brightness will… change the brightness! But one must be root to do this.
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$ echo /sys/class/backlight/some_backlight/max_brightness 900 # Maybe make it sane eh $ sudo bash -c 'echo 500 > brightness' |
My script
So I made a script to do it! (Here is the current version of the script in my dotfiles, which may differ since the writing of this post)
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#!/usr/bin/env bash set -e # Question: Under what circumstances could there be two backlight listings? # If I had this, I would set it up to adjust each in turn maybe. But I don't. # Usage if [ "$#" -eq 0 ]; then cat <<-EOF Usage: $0 [command] Increase or decrease screen brightness at hardware level by steps of 10% of max, as determined by the values under /sys/class/backlight/**. Limit values to the range of 0 to max_brightness. up | Increase brightness by 10% down | Decrease brightness by 10% current | Report current brightness This script needs root access - sudo is an option, but you may also consider allowing your user to run the script without a password prompt e.g.: # Append to /etc/sudoers Cmnd_Alias BRIGHT_CMDS=/bin/path/bright up, /bin/path/bright down username ALL=(root) NOPASSWD: BRIGHT_CMDS EOF exit 1 fi # Gather information backlight_dir='/sys/class/backlight' device_dir=$(ls "${backlight_dir}" | head -n 1) if [ -z "$device_dir" ]; then echo 'No backlight hardware is listed in /sys/class/backlight! Quitting.' exit 1 fi device_dir="${backlight_dir}/${device_dir}" brightness_file="${device_dir}/brightness" curr_brightness=$(cat "${brightness_file}") max_brightness=$(cat "${device_dir}/max_brightness") if [ "$1" == 'current' ]; then echo $( echo "(${curr_brightness} / ${max_brightness}) * 100" | bc -l) \ | cut -d'.' -f 1 else direction=$1 # Calculate step=$(( $max_brightness / 10 )) if [ $direction == 'up' ]; then new_brightness=$(( $curr_brightness + $step )) elif [ $direction == 'down' ]; then new_brightness=$(( $curr_brightness - $step )) else echo 'Argument $1 must be either "up" or "down". Quitting.' exit 1 fi # Limit range if [ "$new_brightness" -gt "$max_brightness" ]; then new_brightness="$max_brightness" fi if [ "$new_brightness" -lt 0 ]; then new_brightness=0 fi # "Do it" - the emperor echo $new_brightness > "${brightness_file}" fi |
Usage
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# Brightness up $ sudo bright up # Brightness down $ sudo bright down # Report current brightness level $ bright current |
If you’re going to bind this to some key combo, you may want to allow this to sudo without a password (as securely as possible).
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# `sudo visudo` and add these lines to your sudoers Cmnd_Alias BRIGHT_CMDS=/path/to/this/script/bright up, /path/to/this/script/bright down your_user ALL=(root) NOPASSWD: BRIGHT_CMDS |
Here is my binding for i3wm
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# Brightness controls bindsym XF86MonBrightnessUp exec sudo /path/to/this/script/bright up; exec notify-send -t 1 "Brightness: $(/path/to/this/script/bright current)%" bindsym XF86MonBrightnessDown exec sudo /path/to/this/script/bright down; exec notify-send -t 1 "Brightness: $(/path/to/this/script/bright current)%" |
So there you go!