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[Launchpad Bug Tracker <1399900@xxxxxxxxxxxxxxxxxx>]

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The screen brightness does not reliably respond to adjustments anymore since 14.10 release. 
Previously in 14.04 it was adjustable via a slider in Ubuntu Control Center and via the keyboard buttons (so there is driver and keyboard support for this laptop). 
Now the keyboard buttons as well as the slider have no effect and the brightness defaults to 100% which is on this device about five times brighter than the comfortable level, and strains the battery.

However about 1 in 20 bootups/logins, the brightness is adjustable, but
when I logout/login again in the user session, it might again become
locked to 100%. I have the suspicion that it depends on the loading of
desktop configs or the time I wait before typing my password to login.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: unity 7.3.1+14.10.20141016-0ubuntu1
ProcVersionSignature: Ubuntu 3.16.0-25.33-generic 3.16.7
Uname: Linux 3.16.0-25-generic x86_64
.tmp.unity.support.test.0:
 
ApportVersion: 2.14.7-0ubuntu8
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Sat Dec  6 12:20:50 2014
DistUpgraded: 2014-11-04 18:35:56,188 DEBUG enabling apt cron job
DistroCodename: utopic
DistroVariant: ubuntu
DkmsStatus:
 virtualbox, 4.3.18, 3.16.0-24-generic, x86_64: installed
 virtualbox, 4.3.18, 3.16.0-25-generic, x86_64: installed
EcryptfsInUse: Yes
GraphicsCard:
 Intel Corporation Haswell-ULT Integrated Graphics Controller [8086:0a16] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Lenovo Device [17aa:3978]
InstallationDate: Installed on 2014-02-02 (306 days ago)
InstallationMedia: Ubuntu-GNOME 14.04 "Trusty Tahr" - Alpha amd64 (20140201)
MachineType: LENOVO 20266
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.16.0-25-generic.efi.signed root=UUID=4bfb3686-b9f7-487d-81f6-eceb41097ad9 ro quiet splash acpi_backlight=vendor vt.handoff=7
SourcePackage: unity
UpgradeStatus: Upgraded to utopic on 2014-11-04 (31 days ago)
XorgConf:
 
dmi.bios.date: 10/31/2013
dmi.bios.vendor: LENOVO
dmi.bios.version: 76CN31WW
dmi.board.asset.tag: No Asset Tag
dmi.board.name: Yoga2
dmi.board.vendor: LENOVO
dmi.board.version: 31900058STD
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Lenovo Yoga 2 Pro
dmi.modalias: dmi:bvnLENOVO:bvr76CN31WW:bd10/31/2013:svnLENOVO:pn20266:pvrLenovoYoga2Pro:rvnLENOVO:rnYoga2:rvr31900058STD:cvnLENOVO:ct10:cvrLenovoYoga2Pro:
dmi.product.name: 20266
dmi.product.version: Lenovo Yoga 2 Pro
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.12+14.10.20140918-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.56-1
version.libgl1-mesa-dri: libgl1-mesa-dri 10.3.0-0ubuntu3
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.3.0-0ubuntu3
version.xserver-xorg-core: xserver-xorg-core 2:1.16.0-1ubuntu1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.9.0-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.4.0-2ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.914-1~exp1ubuntu4.1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.11-1ubuntu2
xserver.bootTime: Sat Dec  6 12:19:59 2014
xserver.configfile: /etc/X11/xorg.conf
xserver.errors:
 
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id                               16970 
 vendor                                     SDC
xserver.version: 2:1.16.0-1ubuntu1

** Affects: linux (Ubuntu)
     Importance: Low
         Status: Incomplete


** Tags: amd64 apport-bug compiz-0.9 third-party-packages ubuntu utopic
-- 
screen brightness cannot be changed anymore
https://bugs.launchpad.net/bugs/1399900
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