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MickeyKnox

Member

Registered: 2010-02-27

Posts: 169

Failed to start Load/Save Screen Backlight Brightness after upgrade

Yesterday i ran an upgrade on my Samsung N150 Netbook. Since then, the backlight brightness control doesn't work anymore. The screen is always at maximum brightness.

I also get this during boot:

[FAILED] Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0
See 'systemctl status systemd-backlight@backlight:acpi_video0.service' for details.

The output of said command is:

* systemd-backlight@backlight:acpi_video0.service - Load/Save Screen Backlight Brightness of backlight:acpi_video0
   Loaded: loaded (/usr/lib/systemd/system/systemd-backlight@.service; static)
   Active: failed (Result: exit-code) since Tue 2014-07-01 13:15:54 CEST; 1h 7min ago
     Docs: man:systemd-backlight@.service(8)
  Process: 448 ExecStart=/usr/lib/systemd/systemd-backlight load %i (code=exited, status=1/FAILURE)
 Main PID: 448 (code=exited, status=1/FAILURE)

Jul 01 13:15:54 kobold systemd-backlight[448]: Failed to get backlight or LED device 'backlight:acpi_video0': No such file or directory
Jul 01 13:15:54 kobold systemd[1]: Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0.

With tab i found there are some more backlight services (not sure if that's relevant):

systemd-backlight@backlight:acpi_video0.service
systemd-backlight@backlight:intel_backlight.service
systemd-backlight@backlight:samsung.service

EDIT: Ooops, i didn't meant to post just yet...

For brightness control i used the following perl script, which is bound to the brightness keys:

#!/usr/bin/perl

$current = `setpci -s 00:02.0 F4.B`;

$new = hex $current;
$new += $ARGV[0];

system (sprintf "setpci -s 00:02.0 F4.B=%x", $new);

printf "setting brightness to %x\n", $new;

I wrote this several years ago, and it has been working ever since.
Is there now a new, maybe less obscure way to control brightness?

Last edited by MickeyKnox (2014-07-01 13:35:06)

Pse

Member

Registered: 2008-03-15

Posts: 413

Re: Failed to start Load/Save Screen Backlight Brightness after upgrade

Intel user here. For brightness controls to work I had to add the following configuration for Xorg:

Section "Device"
	Identifier "Intel Graphics"
	Driver "intel"
	Option "AccelMethod" "sna"
	Option      "Backlight"  "intel_backlight"
EndSection

Then you should be able to control brightness through your desktop environment (Gnome, KDE, etc).

If you want to control brightness through the console, you can use the following:

cd /sys/class/backlight/intel_backlight
cat max_brightness #to check highest possible value
echo 500 | sudo tee brightness

Replace "500" with a reasonable value.

Last edited by Pse (2014-07-02 18:37:47)

MickeyKnox

Member

Registered: 2010-02-27

Posts: 169

Re: Failed to start Load/Save Screen Backlight Brightness after upgrade

Hi Pse, thanks, the command line controls work.

I found there is another directory /sys/class/backlight/samsung with the same contents, however, they don't work.

Actually, i don't use a desktop environment, but a window manager (xmonad to be precise). I think the Xorg configuration snippet won't help me.

I will probably just go ahead and fiddle your commands into my perl script, unless you know a better way?

jugg

Member

Registered: 2014-07-03

Posts: 14

Re: Failed to start Load/Save Screen Backlight Brightness after upgrade

I'm on a samsung with intel, and I bind XF86MonBrightness{Up,Down} keys to `xbacklight -{inc,dec} 10` respectively.  Backlight level restores itself to previous level on boot.  No custom tweaks/scripts required.  I'm on the LTS kernel 3.10.46 with Awesome WM.

If you read the referenced man page for systemd-backlight@.service, you'll find that it persists to /var/lib/systemd/backlight/  You can try cleaning that directory to see if it clears up the boot messages.

MickeyKnox

Member

Registered: 2010-02-27

Posts: 169

Re: Failed to start Load/Save Screen Backlight Brightness after upgrade

Thanks jugg, with the xorg configuration snippet above i got xbacklight to work and bound it to the XF86MonBrightness keys.

The aforementioned message is still there and the laptop boots with maximum brightness. Not initially, but as soon as these messages start, most of them prefixed with [ OK ], the monitor turns to maximum brightness.

In /var/lib/systemd/backlight there is a single file called platform-samsung:backlight:samsung with the content: 1
I tried both deleting that file as well as changing its content to 0, with no effect.

The man page you mentioned says i can configure backlight to not restore its value setting something to 0. I did not get where i actually would've to configure that.

oliparcol

Member

From: Paris

Registered: 2010-02-26

Posts: 38

Re: Failed to start Load/Save Screen Backlight Brightness after upgrade

Hello,

Thank you Pse, directly editing the sysfs brightness modify the brightness of my samsung n220.

I have the same issue since an unknown kernel or systemd update a long time ago. I found a fedora bug report about the brightness save and restore not working anymore. It seems that a patch was needed to make the service works.

On my laptop, the xbacklight command is also not working.

Thank you

EDIT
After adding the Xorg configuration, the xbacklight command works again !

Last edited by oliparcol (2014-07-16 13:19:25)