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#1 2013-01-27 13:06:19

daGrevis
Member
From: Riga, Latvia
Registered: 2011-10-16
Posts: 81
Website

[SOLVED] Can't change the backlight

So I read through Wiki.

~ ⮀ $ ⮀xbacklight
No outputs have backlight property
~ ⮀ $ ⮀ls -a /sys/class/backlight 
.  ..

I'm kinda stuck now. What should I do?

I own Dell Inspiron 15R SE.

Last edited by daGrevis (2013-02-04 11:42:54)

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#2 2013-02-01 07:31:24

x-rix
Member
From: Berlin, Germany
Registered: 2012-08-08
Posts: 32

Re: [SOLVED] Can't change the backlight

This is normally the case when you are missing graphics drivers. Make sure you have everything you need (maybe re-install the driver for good measure?)

Also, try adding acpi_backlight=vendor or, if that doesn't work, acpi_backlight=legacy as kernel boot parameter and see if it changes anything.


Life's not fair, but the root password helps.
- The BOFH

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#3 2013-02-04 11:39:34

daGrevis
Member
From: Riga, Latvia
Registered: 2011-10-16
Posts: 81
Website

Re: [SOLVED] Can't change the backlight

I added `acpi_osi=Linux acpi_backlight=vendor` to my kernel boot params and woohoo, I have `/sys/class/backlight/dell_backlight/` dir!

There is only one problem. When I try to change the brightness:

~~~
~ ⮀ $ ⮀sudo echo 5 > /sys/class/backlight/dell_backlight/brightness
zsh: permission denied: /sys/class/backlight/dell_backlight/brightness
~~~

My wild guess is that I'm not in a correct group. Am I right?

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#4 2013-02-04 11:42:31

daGrevis
Member
From: Riga, Latvia
Registered: 2011-10-16
Posts: 81
Website

Re: [SOLVED] Can't change the backlight

Hmm, anyway `echo 5 | sudo tee /sys/class/backlight/dell_backlight/brightness` works w/o being a root. smile

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#5 2013-03-07 10:13:52

trescott2000
Member
Registered: 2013-03-07
Posts: 3

Re: [SOLVED] Can't change the backlight

FYI: echo seems to check for root authority differently then others. Another way to set the brightness to maximum without being root, is to us cp to copy the max_brightness file over the brightness file. This works fine with sudo.

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#6 2013-03-07 10:42:28

skanky
Member
From: WAIS
Registered: 2009-10-23
Posts: 1,838

Re: [SOLVED] Can't change the backlight

It's not echo, it's because the redirection is not covered by the sudo.
Think of it like (conceptually, if not accurately):

(sudo echo 5) > file

"...one cannot be angry when one looks at a penguin."  - John Ruskin
"Life in general is a bit shit, and so too is the internet. And that's all there is." - scepticisle

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