Plasma desktop shell closes unexpectedly after login

[pwabrahams]

I'm running Kubuntu 12.04, recently updated. Since that recent update, I'm not able to get the graphic interface at all. After I log in, I get the message "Plasma Desktop Shell closed unexpectedly". The problem is probably independent of any per-user files, since (from a terminal shell) I created a new user and logged in as that user. I got the same message.

I checked various logfiles, and the only one containing anything that might be relevant was apport.log. It had these messages (copied by hand since no other way to record them):

/var/crash/_usr_bin_nepomukservicestub.1000.crash already exists
executable: /usr/bin/plasma-desktop (command-line "/usr/bin/plasma-desktop --nocrashhandler")

So I guess that nepomuk is involved somehow.

I've also seen log messages like this:

No DBUS session-bus found.
kdenit4: Communication error with launcher. Exiting.

Lacking the graphic interface, I'm limited to actions that I can perform from a terminal.

[Snowhog]

When on the KDM login screen, press Alt+F1 and log in to the command line. Then try this:

sudo service kdm stop
rm /var/tmp/kdecache-<username>
rm /tmp/kde-<username>
sudo service kdm start

[pwabrahams]

restarting kdm didn't help

I tried stopping kdm, removing those two files, and restarting kdm. Alas, it did not help. But I did have another look at the system log and discovered two possibly revealing entries near the end: a segfault from plasma-desktop with the notation "error 6 in libc-2.15.so" followed a few lines later by a segfault in nepomuk-services.

[Snowhog]

I'm running Kubuntu 12.04, recently updated.

How did you update, and specifically, did you do a dist-upgrade, or just an update? If the latter, then in a CLI login (from KDM), run:

sudo apt-get update && sudo apt-get dist-upgrade

Then exit, reboot, and log in again.

[pwabrahams]

Could it be my sources.list file?

I just did an update (from Synaptic) before the trouble started. Since then, I've tried from the terminal window:
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
sudo apt-get autoremove
and even
sudo apt-get check

Nothing makes a difference.

But an idea just occurred to me. Why should I be having problems that other people don't, especially on a fully-updated system. Perhaps there's something wrong with my sources.list file, so I'm bringing in some bad software when I update. Here it is:

################################################## ###########
################### OFFICIAL UBUNTU REPOS ###################
################################################## ###########

###### Ubuntu Main Repos
deb http://us.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse

###### Ubuntu Update Repos
deb http://us.archive.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted universe multiverse
deb http://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse

###### Ubuntu Partner Repo
deb http://archive.canonical.com/ubuntu precise partner
deb-src http://archive.canonical.com/ubuntu precise partner

###### Ubuntu Extras Repo
deb http://extras.ubuntu.com/ubuntu precise main
deb-src http://extras.ubuntu.com/ubuntu precise main

################################################## ############
##################### UNOFFICIAL REPOS ######################
################################################## ############

###### 3rd Party Binary Repos

#### Audacity - http://audacity.sourceforge.net/
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys BB901940
deb http://ppa.launchpad.net/audacity-team/daily/ubuntu precise main

#### DeaDBeeF - http://deadbeef.sourceforge.net/
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3C8E2A7F
deb http://ppa.launchpad.net/alexey-smirnov/deadbeef/ubuntu precise main

#### GetDeb - http://www.getdeb.net
## Run this command: wget -q -O- http://archive.getdeb.net/getdeb-archive.key | sudo apt-key add -
deb http://archive.getdeb.net/ubuntu precise-getdeb apps

#### Gimp - https://launchpad.net/~otto-kesselgulasch/+archive/gimp
## Run this command: sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 614C4B38
deb http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu precise main

#### Google Chrome Browser - http://www.google.com/linuxrepositories/
## Run this command: wget -q https://dl-ssl.google.com/linux/linux_signing_key.pub -O- | sudo apt-key add -
deb http://dl.google.com/linux/chrome/deb/ stable main

#### Google Earth - http://www.google.com/linuxrepositories/
## Run this command: wget -q https://dl-ssl.google.com/linux/linux_signing_key.pub -O- | sudo apt-key add -
deb http://dl.google.com/linux/earth/deb/ stable main

#### Google Linux Software Repositories - http://www.google.com/linuxrepositories/
## Run this command: wget -q https://dl-ssl.google.com/linux/linux_signing_key.pub -O- | sudo apt-key add -
# deb http://dl.google.com/linux/deb/ stable non-free

#### Google Linux Software Repositories (Testing) - http://www.google.com/linuxrepositories/
## Run this command: wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add -
# deb http://dl.google.com/linux/deb/ testing non-free

#### Kubuntu Backports - https://edge.launchpad.net/~kubuntu-...hive/backports
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8AC93F7A
deb http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu precise main

#### Kubuntu Beta Backports - https://launchpad.net/~kubuntu-ppa/+archive/beta
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8AC93F7A
deb http://ppa.launchpad.net/kubuntu-ppa/beta/ubuntu precise main

#### Kubuntu Updates - https://edge.launchpad.net/~kubuntu-ppa/+archive/ppa
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8AC93F7A
deb http://ppa.launchpad.net/kubuntu-ppa/ppa/ubuntu precise main

#### Medibuntu - http://www.medibuntu.org/
## Run this command: sudo apt-get --quiet update && sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring && sudo apt-get --quiet update
deb http://packages.medibuntu.org/ precise free non-free

#### PlayDeb - http://www.playdeb.net/
## Run this command: wget -O- http://archive.getdeb.net/getdeb-archive.key | sudo apt-key add -
deb http://archive.getdeb.net/ubuntu precise-getdeb games

#### Ubuntu Tweak - http://ubuntu-tweak.com/
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 0624A220
deb http://ppa.launchpad.net/tualatrix/ubuntu precise main


####### 3rd Party Source Repos

#### Kubuntu Backports (Source) - https://edge.launchpad.net/~kubuntu-...hive/backports
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8AC93F7A
deb-src http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu precise main

#### Kubuntu Beta Backports (Source) - https://launchpad.net/~kubuntu-ppa/+archive/beta
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8AC93F7A
deb-src http://ppa.launchpad.net/kubuntu-ppa/beta/ubuntu precise main

#### Kubuntu Updates (Source) - https://edge.launchpad.net/~kubuntu-ppa/+archive/ppa
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8AC93F7A
deb-src http://ppa.launchpad.net/kubuntu-ppa/ppa/ubuntu precise main

#### Medibuntu (Source) - http://www.medibuntu.org/
## Run this command: sudo apt-get --quiet update && sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring && sudo apt-get --quiet update
deb-src http://packages.medibuntu.org/ precise free non-free

#### Ubuntu Tweak (Source) - http://ubuntu-tweak.com/
## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 0624A220
deb-src http://ppa.launchpad.net/tualatrix/ubuntu precise main


How can I check out possible problems with this list?

[Snowhog]

Given your list, I'd say "yes!" I'd comment this entry for starters:

deb http://ppa.launchpad.net/kubuntu-ppa/beta/ubuntu precise main

Then redo the sudo apt-get update and sudo apt-get dist-upgrade and see how things fare.

[pwabrahams]

Removing the beta repositories didn't help either

I commented out the beta repositories as you suggested and redid the upgrade/update, but that didn't help either. It may be that the beta packages are now embedded in a way that makes them difficult to remove. I tried removing libc, since the segfault diagnostic suggested that it might be involved, but there were far too many dependencies.

As a last resort I can just reinstall the entire system (saving my home directory), but I'd like to avoid that if possible.