XF86MonBrightnessUp/XF86MonBrightnessDown special keys not working

Question

I'm trying to enable some multimedia keys, and the ones for volume do work. F5 and F6, the ones for increasing/decreasing do not work, I do not know why. When I run in the terminal:

xbacklight +10

I can see the working effect. When I try my binded special keys (which are set to ~/.config/i3/config):

# Sreen brightness controls
bindsym XF86MonBrightnessUp exec xbacklight -inc 20 # increase screen brightness
bindsym XF86MonBrightnessDown exec xbacklight -dec 20 # decrease screen brightness

Obviously, the media keys must be combined with the fn key. However, I don't see the effect. Any solutions?

Answer 1

This is an old question, but an answer may help out others. I ran into an issue upon a fresh installation of i3wm on my laptop where, for whatever reason, my XF86MonBrightnessUp/Down keys weren't being registered (I checked with xev). What I ended up doing is creating acpi actions and events which corresponded to the keys being pressed.

The following are the actions/events I defined in /etc/acpi/actions and /etc/acpi/events, respectively:

Actions

/etc/acpi/actions/bl-down.sh

#!/bin/sh

bl_device=/sys/class/backlight/acpi_video0/brightness
echo $(($(cat $bl_device)-1)) | sudo tee $bl_device

/etc/acpi/actions/bl-up.sh

#!/bin/sh

bl_device=/sys/class/backlight/acpi_video0/brightness
echo $(($(cat $bl_device)+1)) | sudo tee $bl_device

Events

/etc/acpi/events/bl-down

event=video/brightnessdown BRTDN 00000087 00000000
action=/etc/acpi/actions/bl-down.sh

/etc/acpi/events/bl-up

event=video/brightnessup BRTUP 00000086 00000000
action=/etc/acpi/actions/bl-up.sh

You can verify your brightnessup/down acpi event codes by using acpi_listen in your terminal and then pressing the relevant key combination (e.g., for me, it's Fn + Down Arrow for brightness down).

Finally, don't forget to restart acpid with sudo /etc/init.d/acpid reload

Note: Your backlight device may be defined in a different location than /sys/class/backlight/acpi_video0 - that's just where mine happened to be. Do some poking around.