Edit: You must have
acpi installed on your machine for these to work :)
Edit 2: This code increments/decrements the brightness values by 1, but some models will have values that range in the thousands, so modify the change accordingly.
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
echo $(($(cat $bl_device)-1)) | sudo tee $bl_device
echo $(($(cat $bl_device)+1)) | sudo tee $bl_device
event=video/brightnessdown BRTDN 00000087 00000000
event=video/brightnessup BRTUP 00000086 00000000
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
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.