Lightdm refuses to work after installing kubuntu-desktop

[KnightStalker]

After installing kubuntu-desktop meta package I saw a prompt telling me that both sddm and lightdm are available and I am forced to choose one between them.so I chose lightdm.on the next reboot I was unable to use GUI.
After 2-3 weeks,I retried using sudo dpkg-reconfigure lightdm and selected lightdm.still fails to run GUI.
sddm works fine and is able to handle both Plasma and Unity.
Ubuntu 15.04 with lightdm 1.14.2-0ubuntu1

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: lightdm 1.14.2-0ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-22.22-generic 3.19.8-ckt1
Uname: Linux 3.19.0-22-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.17.2-0ubuntu1.1
Architecture: amd64
CurrentDesktop: KDE
Date: Thu Jul 9 21:15:22 2015
InstallationDate: Installed on 2015-06-09 (30 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[Robert Ancell (robert-ancell)]

Your lightdm,.log shows that you are failing to authenticate:
[+83.70s] DEBUG: Session pid=1546: Authentication complete with return value 7: Authentication failure

So it appears that something in PAM is failing (or you are typing the wrong password!)

[KnightStalker (knightstalker123)]

Robert Ancell,Perhaps apport didn't generate good quality logs.I indeed enter wrong passwords a lot when I try to login.
but that is NOT the problem.It doesn't even get to login prompt when it fails the way I mentioned.It freezes on a black screen.and it doesn't show anything.after a small time I'll see the regular detailed start up screen.(The one you can see when Kubuntu/Ubuntu is starting up and you press Esc button to see)and then it freezes up,this time forever.(or is very slow?but sddm works instantly)
I do not know how to create better quality logs.

[Robert Ancell (robert-ancell)]

The log file is /var/log/lightdm/lightdm.log. If you can reproduce the problem and then copy that file that would be useful in debugging.

[Launchpad Janitor (janitor)]

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

[Hibernator (psychotux)]

Bug hit me with Ubuntu 15.10 Beta 2 and now again on today released 15.10.

What I did:
I attempted to apt install kubuntu-desktop on freshly installed system.

What happened:
apt-get failed showing :
Errors were encountered while processing:
 /var/cache/apt/archives/kde-config-telepathy-accounts_4%3a15.08.2-0ubuntu1_amd64.deb
 /var/cache/apt/archives/kaccounts-providers_4%3a15.08.2-0ubuntu1_all.deb
kde-telepathy-minimal: Depends: telepathy-mission-control-5 (>= 1:5.12) but 1:5.16.3-1ubuntu4 is installed
Package system was _completely_ broken. No more software installations or removals possible. apt-get install -f had no effect.
See also thread on this German Ubuntu forum about the broken package system bug:
https://forum.ubuntuusers.de/topic/software-center-nach-installation-von-kde-auss/

At next reboot the system hung displaying only an Oxygen mouse cursor, no login manager appeared. System was completely trashed, not even virtual consoles worked. See also this successor bug: https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1473149

What I expected to happen:
A smooth installation of KDE.

What I suspect to be the error:
The KDE package apparently installed incompletely due the bad dependencies mentioned and left the system in a broken state.

What I expect to be done:
Hot Fix: Remove the offending package "kde-telepathy" from metapackage kubuntu-desktop_1.331_amd64.deb.

PATCH INCLUDED:
I made and uploaded a patched kubuntu-desktop_1.331_amd64.deb package file which does not contain kde-telepathy.
To install KDE without destroying your system, download the patched .deb and install it via dpkg -i

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "Patched kubuntu-desktop_1.331_amd64.deb without the offending subpackage kde-telepathy" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[JNH (jordannh)]

I was having the same issue. I discovered the issue when I found errors written to `/var/log/seat0-greeter.log`:

    Error writing X authority: Failed to open X authority /var/lib/lightdm/.Xauthority: No such file or directory

Indeed, I only had `/var/lib/lightdm-data`. Running the command

    mkdir /var/lib/lightdm

and rebooting fixed the issue for me.

[Chris Guiver (guiverc)]

Thank you for reporting this bug to Ubuntu.

Ubuntu 15.04 (vivid) reached end-of-life on February 4, 2016.

See this document for currently supported Ubuntu releases:
https://wiki.ubuntu.com/Releases

We appreciate that this bug may be old and you might not be interested in discussing it any more. But if you are then please upgrade to the latest Ubuntu version and re-test. If you then find the bug is still present in the newer Ubuntu version, please add a comment here telling us which new version it is in.

[Launchpad Janitor (janitor)]

[Expired for lightdm (Ubuntu) because there has been no activity for 60 days.]