Somehow my X was chrashed (running at 100% CPU). That's why I issued "init 3".
Firstly I noticed that "init 3" took about 2 minutes to finish, which I find
odd.

After runlevel change X and kdm is still running. Another try gives me
$ rckdm stop
redirecting to systemctl stop rcxdm.service
Failed to issue method call: Unit rcxdm.service not loaded.

BTW what is the right systemctl command to stop kdm? Don't see any
rcxdm.service...

This is the log of "init 3"
2014-12-05T12:35:30.309597+01:00 bart systemd[1]: Stopping Daemon for power
management...
2014-12-05T12:35:30.310007+01:00 bart systemd[1]: Stopping Disk Manager...
2014-12-05T12:35:30.310316+01:00 bart systemd[1]: Stopping Authorization
Manager...
2014-12-05T12:35:30.310604+01:00 bart systemd[1]: Stopping User Manager for
1001...
2014-12-05T12:35:30.310891+01:00 bart systemd[1]: Stopping Execution Queue
Daemon...
2014-12-05T12:35:30.311222+01:00 bart systemd[1]: Stopping User Manager for
1102...
2014-12-05T12:35:30.311514+01:00 bart systemd[1]: Stopping user-1000.slice.
2014-12-05T12:35:30.311800+01:00 bart systemd[1]: Removed slice
user-1000.slice.
2014-12-05T12:35:30.314391+01:00 bart systemd[1]: Stopping user-1006.slice.
2014-12-05T12:35:30.314872+01:00 bart systemd[1]: Removed slice
user-1006.slice.
2014-12-05T12:35:30.315258+01:00 bart systemd[1]: Stopping user-0.slice.
2014-12-05T12:35:30.315648+01:00 bart systemd[1]: Removed slice user-0.slice.
2014-12-05T12:35:30.315993+01:00 bart systemd[1]: Stopping LVM2 metadata
daemon...
2014-12-05T12:35:30.316437+01:00 bart systemd[1]: Stopping Stop Read-Ahead Data
Collection 10s After Completed Startup.
2014-12-05T12:35:30.316795+01:00 bart systemd[1]: Stopped Stop Read-Ahead Data
Collection 10s After Completed Startup.
2014-12-05T12:35:30.317139+01:00 bart systemd[1]: Stopping Cleanup of Temporary
Directories...
2014-12-05T12:35:30.317513+01:00 bart systemd[1]: Stopping Graphical Interface.
2014-12-05T12:35:30.317850+01:00 bart systemd[1]: Stopped target Graphical
Interface.
2014-12-05T12:35:30.318206+01:00 bart systemd[1]: Stopping LSB: X Display
Manager...
2014-12-05T12:35:30.527111+01:00 bart systemd[1]: Started Purge old kernels.
2014-12-05T12:35:30.527509+01:00 bart systemd[1]: Started Manage Sound Card
State (restore and store).
2014-12-05T12:35:30.527847+01:00 bart systemd[1]: Starting Restore Sound Card
State...
2014-12-05T12:35:30.610220+01:00 bart systemd[1]: Starting Trigger Flushing of
Journal to Persistent Storage...
2014-12-05T12:35:30.610647+01:00 bart systemd[1]: Mounted Configuration File
System.
2014-12-05T12:35:30.610954+01:00 bart systemd[1]: Starting Show Plymouth Boot
Screen...
2014-12-05T12:35:30.611266+01:00 bart systemd[1]: Mounted FUSE Control File
System.
2014-12-05T12:35:30.611607+01:00 bart systemd[1]: Starting Tell Plymouth To
Write Out Runtime Data...
2014-12-05T12:35:31.879886+01:00 bart systemd[19793]: Stopping Default.
2014-12-05T12:35:32.124898+01:00 bart systemd[19793]: Stopped target Default.
2014-12-05T12:35:32.125265+01:00 bart systemd[19793]: Starting Shutdown.
2014-12-05T12:35:32.125617+01:00 bart systemd[19793]: Reached target Shutdown.
2014-12-05T12:35:32.125951+01:00 bart systemd[19793]: Starting Exit the
Session...
2014-12-05T12:35:32.126294+01:00 bart systemd[1]: Stopped LVM2 metadata daemon.
2014-12-05T12:35:32.126618+01:00 bart systemd[1]: Stopped Execution Queue
Daemon.
2014-12-05T12:35:32.126940+01:00 bart systemd[1]: Stopped Authorization
Manager.
2014-12-05T12:35:32.129139+01:00 bart systemd[1]: Stopped Disk Manager.
2014-12-05T12:35:32.129564+01:00 bart systemd[1]: Stopped Daemon for power
management.
2014-12-05T12:35:32.129951+01:00 bart systemd[1]: Started Tell Plymouth To
Write Out Runtime Data.
2014-12-05T12:35:32.130346+01:00 bart systemd[1]: Started Trigger Flushing of
Journal to Persistent Storage.
2014-12-05T12:35:32.697776+01:00 bart systemd[19575]: Stopping Default.
2014-12-05T12:35:32.698270+01:00 bart systemd[19575]: Stopped target Default.
2014-12-05T12:35:32.717529+01:00 bart systemd[19575]: Starting Shutdown.
2014-12-05T12:35:32.717997+01:00 bart systemd[19575]: Reached target Shutdown.
2014-12-05T12:35:32.718387+01:00 bart systemd[19575]: Starting Exit the
Session...
2014-12-05T12:35:35.062984+01:00 bart systemd[1]: Stopped User Manager for
1001.
2014-12-05T12:35:35.063411+01:00 bart systemd[1]: Stopping user-1001.slice.
2014-12-05T12:35:35.063717+01:00 bart systemd[1]: Removed slice
user-1001.slice.
2014-12-05T12:35:35.734627+01:00 bart systemd[1]: Stopped User Manager for
1102.
2014-12-05T12:35:35.735046+01:00 bart systemd[1]: Stopping user-1102.slice.
2014-12-05T12:35:35.735400+01:00 bart systemd[1]: Removed slice
user-1102.slice.
2014-12-05T12:35:43.478476+01:00 bart kdm: :0[17392]: pam_unix(xdm:session):
session closed for user wiesing
2014-12-05T12:35:47.420488+01:00 bart xdm[21427]: Shutting down service
kdm..done
2014-12-05T12:35:47.422104+01:00 bart systemd[1]: Stopped LSB: X Display
Manager.
2014-12-05T12:36:02.082804+01:00 bart /usr/sbin/cron[24007]:
pam_unix(crond:session): session opened for user freundt by (uid=0)
2014-12-05T12:36:06.015422+01:00 bart systemd[1]: Stopped Cleanup of Temporary
Directories.
2014-12-05T12:36:06.015851+01:00 bart systemd[1]: Stopping Replay Read-Ahead
Data...
2014-12-05T12:36:06.016165+01:00 bart systemd[1]: Stopped Replay Read-Ahead
Data.
2014-12-05T12:36:06.016456+01:00 bart systemd[1]: Starting File System Quota
Check...
2014-12-05T12:36:06.376098+01:00 bart systemd[1]: Started Set Up Additional
Binary Formats.
2014-12-05T12:36:06.376513+01:00 bart systemd[1]: Started File System Check on
Root Device.
2014-12-05T12:36:06.376828+01:00 bart systemd[1]: Started File System Quota
Check.
2014-12-05T12:36:06.379674+01:00 bart systemd[1]: Starting Enable File System
Quotas...
2014-12-05T12:36:06.854571+01:00 bart systemd[1]: Stopped User Manager for
1102.
2014-12-05T12:36:06.855940+01:00 bart systemd[1]: Removed slice
user-1102.slice.
2014-12-05T12:36:06.897699+01:00 bart systemd[1]: Started Restore Sound Card
State.
2014-12-05T12:36:06.902554+01:00 bart systemd[1]: Starting user-1006.slice.
2014-12-05T12:36:06.902936+01:00 bart systemd[1]: Created slice
user-1006.slice.
2014-12-05T12:36:06.903247+01:00 bart systemd[1]: Starting Session 121762 of
user freundt.
2014-12-05T12:36:06.903550+01:00 bart systemd[1]: Started Session 121762 of
user freundt.
2014-12-05T12:36:07.610356+01:00 bart /USR/SBIN/CRON[24007]:
pam_unix(crond:session): session closed for user freundt
2014-12-05T12:36:18.354363+01:00 bart quotaon[24562]: quotaon: using
/mnt/tmpdirs/aquota.group on /dev/mapper/vg0-tmpdirs [/mnt/tmpdirs]: Device or
resource busy
2014-12-05T12:36:22.120689+01:00 bart quotaon[24562]: quotaon: using
/mnt/tmpdirs/aquota.user on /dev/mapper/vg0-tmpdirs [/mnt/tmpdirs]: Device or
resource busy
2014-12-05T12:36:22.121061+01:00 bart systemd[1]: quotaon.service: main process
exited, code=exited, status=2/INVALIDARGUMENT
2014-12-05T12:36:22.121439+01:00 bart systemd[1]: Failed to start Enable File
System Quotas.
2014-12-05T12:36:22.121792+01:00 bart systemd[1]: Unit quotaon.service entered
failed state.
2014-12-05T12:36:36.446772+01:00 bart sudo:     rudi : TTY=pts/17 ;
PWD=/home/rudi ; USER=root ; COMMAND=/usr/bin/su
2014-12-05T12:36:36.447238+01:00 bart sudo: pam_unix(sudo:session): session
opened for user root by rudi(uid=0)
2014-12-05T12:36:36.447977+01:00 bart sudo: pam_systemd(sudo:session):
pam_putenv: delete non-existent entry; XDG_RUNTIME_DIR
2014-12-05T12:36:36.491023+01:00 bart su: (to root) rudi on none
2014-12-05T12:36:36.494087+01:00 bart su: pam_unix(su:session): session opened
for user root by rudi(uid=0)
2014-12-05T12:36:36.494459+01:00 bart su: pam_systemd(su:session): pam_putenv:
delete non-existent entry; XDG_RUNTIME_DIR
2014-12-05T12:37:01.618555+01:00 bart /usr/sbin/cron[29439]:
pam_unix(crond:session): session opened for user freundt by (uid=0)
2014-12-05T12:37:01.623809+01:00 bart systemd[1]: Starting Session 121763 of
user freundt.
2014-12-05T12:37:01.624823+01:00 bart systemd[1]: Started Session 121763 of
user freundt.
2014-12-05T12:37:02.092316+01:00 bart /USR/SBIN/CRON[29439]:
pam_unix(crond:session): session closed for user freundt
2014-12-05T12:37:06.818431+01:00 bart systemd[1]: Started Show Plymouth Boot
Screen.
2014-12-05T12:37:06.819204+01:00 bart systemd[1]: Started Dispatch Password
Requests to Console Directory Watch.
2014-12-05T12:37:06.821258+01:00 bart systemd[1]: Starting Wait for Plymouth
Boot Screen to Quit...
2014-12-05T12:37:06.821596+01:00 bart systemd[1]: Starting Terminate Plymouth
Boot Screen...
2014-12-05T12:37:06.847800+01:00 bart systemd[1]: Started Wait for Plymouth
Boot Screen to Quit.
2014-12-05T12:37:06.848209+01:00 bart systemd[1]: Started Terminate Plymouth
Boot Screen.
2014-12-05T12:37:06.848528+01:00 bart systemd[1]: Reached target Multi-User
System.
2014-12-05T12:37:06.848831+01:00 bart systemd[1]: Starting Update UTMP about
System Runlevel Changes...
2014-12-05T12:37:07.330171+01:00 bart systemd[1]: Started Update UTMP about
System Runlevel Changes.