[nmglug] screen brightness?

[Akkana Peck]

a writes:
> After inadvertently hitting some random keyboard letter key the screen went
> considerably dim. I then went to bios adjusted brigtness individually for
> both battery and non battery operation. The brightness holds up part way
> into computer loading at startup,then dims.Is there a non bios control of
> which I am unaware.I welcome an analysis.

Unfortunately it varies by manufacturer, but have a look into
/sys/class/backlight. On both of my current (Intel graphics) machines,
the file is /sys/class/backlight/intel_backlight/brightness
so you can do things like

cat /sys/class/backlight/intel_backlight/brightness

or

echo 3000 > /sys/class/backlight/intel_backlight/brightness
(from a root shell).

On my Asus the maximum is 4800 but I suspect that varies with make
and model.

Debian used to give me automagic controls on Fn-F6 and F7, but that
stopped working when I upgraded to 64-bit stretch so I had to set up
my own key bindings that used the /sys/class method. And yes, there
is something during the boot sequence that restores the brightness
from some saved value, but I don't know where that code lives.
I have the impression that it's restoring from whatever
/sys/class/backlight/intel_backlight/brightness was when the machine
last shut down, so if you use that method to set the brightness to
what you want, hopefully that will fix your problem.

        ...Akkana