How to fix not working brightness control keys

tags: linux, xorg, thinkpad, acpi, brightness

After installing i3 window manager, I startded to tune it up.

Shortly I revealed that brightness control keys do not work. After googling awhile I found this answer on the StackExchange.

On Debian/Ubuntu make sure you have acpitool installed:

apt-get install acpitool

Using acpi_listen I’ve found that Fn+F5(XF86MonBrightnessDown) and Fn+F6(XF86MonBrightnessUp) respond for these ACPI events on my laptop:

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

So I added following rules:

# /etc/acpi/events/thinkpad-backlight-down
event=video/brightnessdown BRTDN 00000087 00000000
action=/etc/acpi/thinkpad-display-brightness.sh down

# /etc/acpi/events/thinkpad-backlight-up
event=video/brightnessup BRTUP 00000086 00000000
action=/etc/acpi/thinkpad-display-brightness.sh up

and action script /etc/acpi/thinkpad-display-brightness.sh which will be called when approprite event happens:

#!/bin/sh
BASE_DIR=/sys/class/backlight/intel_backlight

test -d $BASE_DIR || exit 0

MIN=50
MAX=$(cat $BASE_DIR/max_brightness)
ACTUAL=$(cat $BASE_DIR/actual_brightness)

if [ "$1" = down ]; then
    ACTUAL=$((ACTUAL-100))
else
    ACTUAL=$((ACTUAL+100))
fi

if [ "$ACTUAL" -lt $MIN ]; then
    ACTUAL=$MIN
elif [ "$ACTUAL" -gt $MAX ]; then
    ACTUAL=$MAX
fi

echo $ACTUAL > $BASE_DIR/brightness

chmod +x /etc/acpi/thinkpad-display-brightness.sh

After restarting ACPI daemon, I’ve got properly working brightness control keys.

OS with systemd:

sudo systemctl restart acpid

Slackware:

/etc/rc.d/rc.acpid restart

Furthermore, it works in both Xorg session and in the TTY consoles.

Update 2019-11-15 Update 2022-05-21