Found magic multi purpose Fn Key on my laptop!

Hey guys,

I’m new to the linux world (more or less).
I bought my laptop a new SSD and installed Ubuntu mate 15.05 64bit.
So here is the real problem.
My Acer 5742G Laptop has Function Keys for controlling the Brightness.
What should i say the Key combination (FN+Left)is working (so the sun appears) but at first, but the brightness does not change and there are happening additional things.
By pressing the button the first time the Screen resolution changes, pressing the combination the second time brings the original resolution back, doing it a third time turns the screen black, and last but not least pressing it a fourth time then crashes the GUI and I have to login again.
Now at first i started to use google about my Problem, and found something about changing the grub file by editing a line to
GRUB_CMDLINE_LINUX_DEFAULT=“quiet splash acpi_osi=”
but this just totally deactivated the “magic key”.

Then I found something about acpi_listen, where I can see if the buttons are recognized.
so I tried and got the following output when pressing the combination fn+left arrow.

video/brightnessdown BRTDN 00000087 00000000
video/switchmode VMOD 00000080 00000000 K
PNP0C14:01 000000bc 00000000

But i don’t have any idea what i have to do with this information.
That’s my problem that far and of course, if I press the button for brightness, the brightness doesn’t change.
Just found out that my FN+F5 key combination is not working, seems to be the one thats on FN+Left
any other key seem to work (start, stop, next, sleep mode, backgroundlight off, toggle wifi, deactivate mousepad, mut, vol up and vol down)

Hope some of you may can help me

Best regards from germany


Hello Mr P :slight_smile:

I had a look around

And to me, this looks like the way to go.

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Read through the bug reports here as there are also a few suggestions!:

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Hey guys thanks for your answer,
I tried different parameters for the grub config in different combinations, but it didn’t do what i expect:


So I was totally on the wrong way the problem.
After reading some other threads I found out that the backlight is controlled by the Graphics Driver
and i found a german thread where someone had screen freezes and crashes while using the brightness down button but he had the same Laptop specifications.

  • Acer Aspire 5742G
  • Nvidia GT540M
  • Intel i5-480M

Here is the Link:
Solution bringing thread
there i red about bumblebee and nvidia-prime, so I installed that bumblebee tool(never before heard of that) and now everything works (except FN+F5 but maybe that is just because there is no second monitor connected)
So the solution was easy in the end

sudo apt-get bumblebee bumblebee-nvidia

Thanks for your help guys :wink:
Cya next time I have a problem

Positive Side Effect, my Laptop is now cooling perfectly, yesterday he got a bit hot


Nice find :slight_smile: I have not used bumblebee