How to check what display-manager your using?

The default answer is to do:
$cat /etc/X11/default-display-manager
but that doesn't work on Gentoo.
Also

echo $DESKTOP_SESSION

returns "default" which obviously is not very useful.

So what worked for me is either:
$cat /etc/systemd/system/display-manager.service
or
$systemctl status display-manager
In my case, it's lightdm and  lightdm.service.

How to change the screen brightness konsole

Simple, do:
$echo 500 | sudo tee /sys/class/backlight/intel_backlight/brightness

Where one can check the max brightness with:
$cat /sys/class/backlight/intel_backlight/max_brightness
and the actual one with:
$cat /sys/class/backlight/intel_backlight/actual_brightness
or
$cat /sys/class/backlight/intel_backlight/brightness
(the controls for the keyboard should be in

/sys/class/leds/*kbd_backlighbut they are not)

A good scrpit that might help if the controls were available. 

More ideas can be found here (like using xrandr or $ sudo setpci -s 00:02.0 F4.B=80
)