Aspire 5742 function button is screwy on Linux

ColPanek

My son gave me this machine because it ran "upgraded" Windows 10 like a lame sloth. I've put Kubuntu and MX Linux on it and they both ran well, and we've used it to teach class over the internet. But I can't figure out how to adjust the screen brightness. There's a conflict between the brightness and screen ext/int functions; they both run at once. I've fooled with the keyboard settings endlessly, and fruitlessly. It's the blue "Fn" button that doesn't have the right driver, or something. Fn + any of the other F buttons doesn't work either.

Leostat

X Backlight may allow you to change it from the command line. If the below works, you could always re map the function keys to run the commands from the keybaord settings. Janky yes, but it may work!

sudo apt-get install xbacklight
xbacklight -inc 10
xbacklight -dec 10

ColPanek

Excellent suggestion ... except no, it didn't work on my machine. The screen brightness isn't adjustable for some reason. All the buttons and sliders move, but the screen ignores it.

Leostat

Ahk! Does xbacklight -get give you  any info on the backlight? And do you have anything if you  ls /sys/class/backlight/

ColPanek

Leostat said:

Ahk! Does xbacklight -get give you  any info on the backlight? And do you have anything if you  ls /sys/class/backlight/

$ xbacklight -get
44.444444
 
$ ls /sys/class/backlight/
acpi_video0  intel_backlight

More mysterious output:

$ xbacklight -steps 6
100.000000

$ xbacklight -steps 20
22.222222

$ xbacklight -get
22.222222

$ xbacklight -steps 3
33.333333

$ xbacklight -steps 100
44.44444

But.... nothing changes the actual screen brightness, although the onscreen indicator says it is when I hit the up or down brightness

Leostat

So from the ls what may be happening is xbacklight may be sending the brightness commands to the 'wrong' backlight as there is both an Intel and a Standard acpi device. My guess is the standard acpi is the graphics card, and the Intel is the igpu 

You can echo a number into a file within the above directories directly to check if the distro is physically able to chnage the brightness, arch wiki to the rescue
https://wiki.archlinux.org/index.php/backlight#ACPI

You need to be root / sudo when you do, hopefully this works!

Failing this, There is also a note where you may need to add a flag to the kernel to suppress the acpi device to be able to control the brightness