Controlling brightness, the easy way

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I report here a simple procedure to set the brightness of your screen under GNU/Linux that does not rely on GUI applications, and does not rely on X11/Wayland being available on your system.

The proposed solution is based on using two keys of your choice (in the following we will use Fn+F5 and Fn+F6) to decrease/increase the current brightness of your screen. This is achieved by binding those keys through acpid to a shell script that does the dirty job.

Pre-requisites

I assume that you are able to:

Run simple commands from a terminal or a terminal emulator (xterm, urxvt, etc.)
Edit a file using a text editor (ed, vim, emacs, nano, joe, or whatever you like)
Install packages on your system (via apt-get, apt, synaptic, yum, pacman, or whatever you use/prefer)

Preliminary checks

The solution is based on setting brightness values through the /sys/class/backlight/* interface. So the first thing to check is that you actually have something there. In my system I have only the folder "intel_backlight":

    $ ls -l /sys/class/backlight/
    intel_backlight
    $

which in turns contains:

    $ ls /sys/class/backlight/intel_backlight
    actual_brightness  bl_power  brightness  device  
    max_brightness     power     subsystem   type    uevent
    $

Now, the exact pool of files you have in that folder depends on your hardware. The baseline is that there should be a file called brightness and another file called max_brightness. We don't need much more than that. So let's get started.

Install required stuff

You need to install acpid&friends. If you are root, just run:

    # apt-get install acpid acpi-support

in a terminal. If you are a luser with sudo privileges, run instead:

    $ sudo apt-get install acpid acpi-support

Before you continue, check that acpid is running:

    $ ps ax | grep /usr/sbin/acpid
     2084 ?        Ss     5:50 /usr/sbin/acpid
    $

You should also have some stuff in the folder /etc/acpi:

    $ ls /etc/acpi
    always-mute.sh              ejectbtn.sh       lenovo-bright.sh  
    asus-keyboard-backlight.sh  events            lid.sh           
    asus-wireless.sh            ibm-wireless.sh   mutebtn.sh        
    powerbtn-acpi-support.sh    sleep_suspend.sh  undock.sh
    power.sh                    sonybright.sh     voldownbtn.sh
    sleep_suspendbtn.sh         tosh-wireless.sh  volupbtn.sh
    $

This comes with acpi_support, usually.

Put the script in place

The script reported below, named set-bright.sh, is responsible for increasing (decreasing) the brightness when called with the parameter up (down). Just copy-paste the script in the following in the file /etc/acpi/set-bright.sh:

#!/bin/sh


if [ ! $# -le 1 ]; then 
        echo "Usage: $0 {up|down}"
        exit 1;
fi

INCR=80
BRIGHT_FILE=/sys/class/backlight/intel_backlight/brightness

min_br=0
max_br=`cat /sys/class/backlight/intel_backlight/max_brightness`
act_br=`cat /sys/class/backlight/intel_backlight/actual_brightness`


case $1 in 
        up)
        if [ ${act_br} -le ${max_br} ]; then 
                new_br=$((${act_br} + $INCR));
                if [ ${new_br} -gt ${max_br} ]; then 
                        new_br=${max_br};
                fi
                echo ${new_br} >> ${BRIGHT_FILE}
        fi 
        ;;
        down)
        if [ ${act_br} -gt ${min_br} ]; then 
                new_br=$((${act_br} - $INCR));
                if [ ${new_br} -lt ${min_br} ]; then 
                        new_br=${min_br};
                fi
                echo ${new_br} >> ${BRIGHT_FILE}
        fi 
        ;;
        *)
        echo "Usage: $0 {up|down}"
        exit 1;
esac

IMPORTANT Make sure that the file /etc/acpi/set-bright.sh is executable:

    # chmod 755 /etc/acpi/set-bright.sh

N.B.: you might need to edit the variables BRIGHT_FILE, INCR, max_br, and act_br to reflect your hardware configuration and/or your personal preferences.

Choose which buttons to use

We assume that you want to use the buttons Fn+F5 (press-function-and-F5-together) and Fn+F6 to decrease and increase the brightness, respectively. When those buttons are pressed, they trigger an acpi event. We need to know the name of such events. So we run:

    $ acpi_listen

This command prints on output the name of the acpi event associated to each button you press, until you hit Ctrl+C to terminate it. For instance, if I type Fn+F5 followed by Fn+F6 in my system I see:

    $ acpi_listen
    video/brightnessdown BRTDN 00000087 00000000
    video/brightnessup BRTUP 00000086 00000000

Note down the names of the events associated to Fn+F5 and Fn+F6 (you'll need them in a moment) and hit Ctrl+C to terminate acpi_listen.

Now as user root open the file /etc/acpi/events/brightup:

    # editor /etc/acpi/events/brightup

and be sure that it contains (at least) something like:

event=video[ /]brightnessup
action=/etc/acpi/set-bright.sh up

Notice that the first line (event=video...) is referring to the event video/brightnessup, that is the event generated by Fn+F6. The associated action is to call the script /etc/acpi/lenovo-bright.sh up

Now repeat the process described above and make sure that the file /etc/acpi/events/brightdown contains something like:

event=video[ /]brightnessdown
action=/etc/acpi/set-bright.sh down

After having saved those two files, just restart acpid:

    # /etc/init.d/acpid restart

and adjust your brightness as you like.

HTH

KatolaZ

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Last update: 2018-02-02