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I'm a new Ubuntu user, installed Ubuntu 16.04 (on my MSI laptop) a couple of days ago, and I've loved it so far but there's something that's been bothering me... the screen brightness changes randomly.

It is really strange that it changes without doing anything, at any time and without pressing any button, but I also think that it can't come out of nothing, so there must be a cause.

I have no experience in Linux, but tried to do some little research to find out what is happening:

  1. Used the evtest command to scan all /dev/input/event*

This was the result:

  1. Enter device event number 5 (Video Bus)

  2. Then waited till the screen brightness changed randomly again to see the output about the event. This was the output (a sample):

Every time the brightness increases or decreases randomly, the information about the new event is displayed in the terminal (after a couple of hours the output is really long).

So it seems like some events happen, I just don't know why.

Sorry for the long post, just wanted to give as much information as possible.

I would really appreciate your help, thanks.

(Fun fact: brightness changed while writing this)

lans88
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  • I noticed that when on battery power some linuxes decrease brithness very soon after there is no activity. It happens in a matter of seconds. When I started to type or move the mouse the brightness increased again. Is it maybe linked to your activity? Are you on battery or plugged in? Take a look at power settings. – nobody Jul 02 '16 at 10:31
  • I kept the laptop plugged in and battery in 100% to see if it was that, but still the same, brightness changed without doing anything so It's hardly related to energy settings (the same happens when it's unplugged)...Could it be something about the Video bus? – lans88 Jul 03 '16 at 00:35

1 Answers1

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You can try this: Brightness randomly up and down on MSI laptop

You can add the following to /usr/share/X11/xorg.conf.d/10-quirks.conf:

  Section "InputClass"
  Identifier "Spooky Ghosts"
  MatchProduct "Video Bus"
  Option "Ignore" "on"
  EndSection

This basically ignores messages from the Video Bus, which seems to be sending pseudo fn+up fn+down messages randomly.

Also to add on, the brightness changing correlates to CPU voltage changes. MSI laptops seem to have a weird mobo setup, and Ubuntu may misinterpret some of the messages sent by the BIOS as brightness up/down messages

Note that this fix is not permanent, and some OS updates may overwrite 10-quirks.conf. as it is used to fix hardware bugs such as these. But if you see your screen brightness changing again, you can simply redo this step.

Community
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euwbah
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  • Welcome to Ask Ubuntu! We recommend that you include essential parts from the article in your answer as well as the link. – anonymous2 Aug 08 '16 at 18:08