Screen brightness keys don't function in KDE desktop

[Erno Kuusela]

My laptop's brightness adjustment keys (fn+arrows) don't work in Kubuntu session, they worked in Unity.

xev shows the keys send correct sounding keysyms (XF86MonBrightnessDown / Up), but they neither show the OSD effect of brightness adjustment nor do they have any effect on brightness.

Other fn key combinations work, eg. volume adjustment, mute, trackpad disable, suspend.

I can use the xbacklight command to change the brightness, and then OSD appears showing the new brightness setting.

I can use the brightness slider in the power saving settings and the brightness changes when I click apply.

In the global keyboard shortcuts settings, the key binding shows correctly: Under KDE Daemon, it shows "Increase Screen Brightness" is associated with the "Monitor Brightness Up" key.

Ubuntu version info:

Description: Ubuntu 14.04 LTS
Release: 14.04

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: kubuntu-desktop 1.308.1
ProcVersionSignature: Ubuntu 3.13.0-29.53-generic 3.13.11.2
Uname: Linux 3.13.0-29-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.2
Architecture: amd64
CurrentDesktop: KDE
Date: Sun Jun 22 14:04:01 2014
InstallationDate: Installed on 2013-10-02 (262 days ago)
InstallationMedia: Ubuntu 12.04.3 LTS "Precise Pangolin" - Release amd64 (20130820.1)
SourcePackage: kubuntu-meta
UpgradeStatus: Upgraded to trusty on 2014-06-19 (2 days ago)

[Erno Kuusela (erno-iki)]

The keys actually do work - they just do the changes in very small increments and you don't get the OSD feedback. Doing many keypresses in same direction or holding down the key works.

Same problem is described at https://forum.kde.org/viewtopic.php?f=225&t=120570