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Old 07-16-2013, 10:29 PM   #1
Registered: Nov 2011
Distribution: Slackware
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Contents of /sys/class/backlight vanished due to appended kernel param. ?

I have a Zenbook UX21A with Slackware-current 64 on it. The screen brightness keys did not work out of the box, so for a while I have just been adjusting it manually with the files in /sys/class/backlight. In my case, I usually have

The brightness file in intel_brightness was the one that controlled my screen brightness. I have been meaning to try to learn what the other one was for.

I was going to write a couple of scripts and attach them to the brightness keys, but yesterday, based on something I read in the Arch wiki, I attempted to add functionality to the keys by adding acpi_osi=\"!Windows 2012\" as a boot parameter in lilo.conf.

This did in fact give brightness control to the hotkeys, but the increments are too wide and inconveniently spaced. It basically gives me pitch black, too dim, too bright, and blinding. So I thought I would go back to /sys/class/backlight and see if I could use it in conjunction with the keys. But the directory is now completely empty.

So now I'm wondering whether or not that was supposed to happen, and if so, why? I didn't really know what I was doing with that kernel parameter, and I haven't been able to find any clues about what occurred.

Thanks for any help.

Last edited by Kallaste; 07-16-2013 at 10:32 PM.
Old 07-17-2013, 01:14 PM   #2
Didier Spaier
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Accoding to /usr/src/linux-3.2.45/Documentation/kernel-parameters.txt, this command has the effect of removing "Windows 2012" as built-in OS interface string.

But you could try other parameters.

If you didn't look at it yet, output of
grep /usr/src/linux/Documentation/kernel-parameters.txt
could give you some clues.

See also /usr/src/linux/Documentation/ABI/stable/sysfs-class-backlight.
Old 07-17-2013, 01:31 PM   #3
Registered: Oct 2010
Location: Pittsburgh, PA
Distribution: Slackware
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Hmm... I'm on slack64-current.. but my backlight is here:


maybe it just moved on you with the new kernel?
Old 07-19-2013, 11:19 PM   #4
Registered: Nov 2011
Distribution: Slackware
Posts: 363

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Not the Kernel Parameter


I am sorry for the delay. Thank you for the documentation. I read all of it and was at a loss for quite some time before I figured out my problem had nothing to do with the kernel parameter, but that in fact something else had happened. I still don't know what it was, but somehow a lot of my file structure got corrupted, including my personal files and other random things. It even broke my wireless driver. If I had checked to see if anything else was off before delving into researching the innocent kernel parameter, I would have noticed the damage a lot sooner.

Anyway, once I saw the damage and spent several hours trying to make heads or tails of it, I finally reinstalled. I would have liked to figure out the mystery, but unfortunately I had a project deadline and needed my laptop to work. So far everything is running smoothly again, but since I cannot think of anything else that could have happened, I am worried about a bad disk. This is my first SSD and I'm not well versed in the mechanics of checking them (smartmontools? manufacturer's tool?), but I will be looking into that soon.

Thanks again.

P.S. @ WhiteWolf1776: Sorry, /sys/class/backlight/intel_backlight/brightness is actually what I meant. Since the backlight directory was empty, I was typing it from memory and got it wrong.

Last edited by Kallaste; 07-19-2013 at 11:22 PM.


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