gsd-backlight-helper fails to change backlight

[Mahiar Mody]

In Saucy Salamander (Ubuntu 13.10), nothing happens when programmatically changing the backlight using the command:
pkexec /usr/lib/gnome-settings-daemon/gsd-backlight-helper --set-brightness 50

After issuing the above-mentioned command:

1. There is no difference in the screen brightness.
2. The slider in the "System Settings" -> "Brightness & Lock" remains unchanged.

However, the value specified with --set-brightness argument is correctly reflected in the file:
/sys/class/backlight/acpi_video0/actual_brightness
and
/sys/class/backlight/acpi_video0/actual_brightness

Additionally, I'm using the proprietary Video driver for the AMD graphics accelerators from fglrx-updates. (I can't use the X.org X Server open source driver, because I get a lot of visual artefacts / screen refresh problems when I use it).

Furthermore, adjusting the brightness directly from the GUI, using the slider in "System Settings" -> "Brightness & Lock" works correctly, changing the screen brightness, as is expected. This change in screen brightness can be confirmed by issuing the following commands:

pkexec /usr/lib/gnome-settings-daemon/gsd-backlight-helper --get-brightness
and
cat /sys/class/backlight/acpi_video0/actual_brightness
and
cat /sys/class/backlight/acpi_video0/actual_brightness

Ubuntu Release:
--------------------------
Description: Ubuntu 13.10
Release: 13.10

Package version:
-----------------------------
gnome-settings-daemon:
  Installed: 3.8.5-0ubuntu11.1
  Candidate: 3.8.5-0ubuntu11.1
  Version table:
 *** 3.8.5-0ubuntu11.1 0
        500 http://us.archive.ubuntu.com/ubuntu/ saucy-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     3.8.5-0ubuntu9 0
        500 http://us.archive.ubuntu.com/ubuntu/ saucy/main amd64 Packages

Expected Behavior:
-------------------------------
After issuing the command pkexec /usr/lib/gnome-settings-daemon/gsd-backlight-helper --set-brightness XX, the following should happen:

1. The screen brightness should increase or decrease as per the XX value specified.
2. The slider in the "System Settings" -> "Brightness & Lock" should change to reflect the new value.

What Happens Instead:
-----------------------------------
1. There is no difference in the screen brightness.
2. The slider in the "System Settings" -> "Brightness & Lock" remains unchanged.

[Mahiar Mody (mahiarmody)]

Any update on this? Do you need more info on this bug? Please let me know.

[Sebastien Bacher (seb128)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. The issue you are reporting is an upstream one and it would be nice if somebody having it could send the bug to the developers of the software by following the instructions at https://wiki.ubuntu.com/Bugs/Upstream/GNOME. If you have done so, please tell us the number of the upstream bug (or the link), so we can add a bugwatch that will inform us about its status. Thanks in advance.

[Sebastien Bacher (seb128)]

could be similar to bug #1153173

[Mahiar Mody (mahiarmody)]

I've reported the bug upstream as you've suggested. Here's the link:
https://bugzilla.gnome.org/show_bug.cgi?id=720370

Yes, this is similar to the bug ID you've provided, but I'm not sure if it's the same issue. I'm having the problem on my Desktop (All-in-one Desktop) machine and not a laptop.

Furthermore, this issue was not present when the very same machine had Ubuntu 13.04 installed. All worked fine then. Only after upgrading to Ubuntu 13.10 has this issue arrisen. I upgraded using the ISO, and did a full re-format and re-encryption of the full disk. So this seems to be an Ubuntu 13.10 problem, and not an Ubuntu 13.04 problem, as the other bug states.

[Mahiar Mody (mahiarmody)]

Hello Sebastien,

The gnome team came back with a "Not A Bug". Here's the reply (from Bastien Nocera [gnome-settings-daemon developer] ):

"The pkexec helper doesn't work but the brightness slider works. That means that
gnome-settings-daemon works, and that it's using XRandR and not the pkexec
helper to change the brightness.

You can double-check that with:
xrandr -q --verbose | grep -i backlight

Furthermore, the pkexec helper isn't public API. The public API is through
D-Bus."

Any idea on how to fix this? Or is there a better way to do it? I tried with DBus as shown below, but had questionable success:

dbus-send --session --print-reply --dest="org.gnome.SettingsDaemon" /org/gnome/SettingsDaemon/Power org.gnome.SettingsDaemon.Power.Screen.SetPercentage uint32:percentage

For Example: To set brightness to 30%

dbus-send --session --print-reply --dest="org.gnome.SettingsDaemon" /org/gnome/SettingsDaemon/Power org.gnome.SettingsDaemon.Power.Screen.SetPercentage uint32:30

When the above-mentioned dbus-send command is issued, the slider in the GUI is correctly positioned to reflect the percentage requested, but the brightness is not always altered to match.

Put another way, the dbus-send reliably only changes the slider position. However, the brightness is not always changed with the slider movement. The brightness changes sometimes, while sometimes remains unaltered. This happens randomly.

Any suggestions?

Any way to get pkexec to work?

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.