gui disappeared, tty7 visible, session continued

[Peter Nerlich]

While I was surfing text-orientated sites in chromium the session didn't crash, but disappeared, because i could hear the music in another tab playing, also as I had logged in in tty2

music stopped and login screen appeared after some minutes (after I loaded this up, right as I typed the line above on my mobile phone)

System:
Ubuntu 15.10

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: unity 7.3.2+15.10.20151016-0ubuntu1
ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3
Uname: Linux 4.2.0-16-generic x86_64
ApportVersion: 2.19.1-0ubuntu4
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
Date: Wed Nov 11 15:34:32 2015
DistUpgraded: Fresh install
DistroCodename: wily
DistroVariant: ubuntu
DkmsStatus:
 virtualbox, 5.0.4, 4.2.0-16-generic, x86_64: installed
 virtualbox, 5.0.4, 4.2.0-18-generic, x86_64: installed
GraphicsCard:
 Intel Corporation 3rd Gen Core processor Graphics Controller [8086:0166] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Fujitsu Limited. Device [10cf:16c2]
InstallationDate: Installed on 2015-10-25 (16 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
MachineType: FUJITSU LIFEBOOK A532
ProcEnviron:
 TERM=linux
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.2.0-16-generic root=UUID=95986feb-dd6d-429f-a43b-4644770cf004 ro quiet splash vt.handoff=7
SourcePackage: unity
UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/13/2012
dmi.bios.vendor: FUJITSU // Phoenix Technologies Ltd.
dmi.bios.version: Version 1.08
dmi.board.name: FJNBB1C
dmi.board.vendor: FUJITSU
dmi.chassis.type: 10
dmi.chassis.vendor: FUJITSU
dmi.modalias: dmi:bvnFUJITSU//PhoenixTechnologiesLtd.:bvrVersion1.08:bd04/13/2012:svnFUJITSU:pnLIFEBOOKA532:pvr:rvnFUJITSU:rnFJNBB1C:rvr:cvnFUJITSU:ct10:cvr:
dmi.product.name: LIFEBOOK A532
dmi.sys.vendor: FUJITSU
version.compiz: compiz 1:0.9.12.2+15.10.20151015-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.64-1
version.libgl1-mesa-dri: libgl1-mesa-dri 11.0.2-1ubuntu4
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 11.0.2-1ubuntu4
version.xserver-xorg-core: xserver-xorg-core 2:1.17.2-1ubuntu9
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.9.2-1ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.5.0+git20150819-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20150808-0ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.11-1ubuntu3
xserver.bootTime: Sun Nov 8 19:41:39 2015
xserver.configfile: default
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 13890
 vendor SEC
xserver.version: 2:1.17.2-1ubuntu9