My plasma desktop environment worked very well before I installed kdm display manager.But after I installed the kdm and reboot my laptop, Gentoo booted into a black screen with a white checkbox, which was saying

  Could not start kdeinit5, Check your installation.

Then I clicked the okay button. It dropped down into the tty with some error messages.

  xauth: file /root/.serverauth.8002 does not exist

  X.Org X Server 1.18.4
  Release Date: 2016-7-19
  X Protocol Version 11: Revision 0
  Build Operatin System: Linux 4.4.39-gentoo #1 SMP Fri Jan 13 20:24:54 CST 2017 x86_64
  Kernel command line: BOOT_IMAGE=/boot/kernel-genkernel-x86_64-4.4.39-gentoo root=/dev/sda2 rootfstype=ext4 
  Build Date: 13 January 2017 11:03:46PM

  Current version of pixman: 0.34.0
  Before reporting problems., check http://wiki.x.org
  to make sure that you have the latest version.

  (==) Log File: "/var/log/Xorg.0.log", Time: Sat Jan 20 21:12:01 2017 
  (==) Using config directory "/etc/X11/xorg.conf.d"
  (==) Using system config directory "/usr/share/X11/xorg.conf.d"
  The application failed to start because it could not find not find or load the Qt platform plugin "xcd" in ""

  Available platform plugins are: wayland-org.kde.kwin.qpa, minimal, offscreen, wayland, xcb.
  Reinstalling the application may finx this problem.
  startkde: Starting up...
  /usr/bin/kdeinit5: relocation error: /usr/lib64/libQt5Gui.so.5: symbol _Z10qAllocMoreii, version Qt_5 not defined in file libQt5Core.so.5 with link time reference.
  startkde: Could not start kdeinit5. Check your installation.
  xinit: connection to X server lost.
  waiting for X server to shut down (II) Server terminated successfully (0). Closing log file.

However, it works pretty well before I installed kdm. I don't know why it crashed after I had installed kdm.

I also had found some advice from the Internet and tried. But those all didn't work. Can anyone give some solutions or some clues? My environment is:

  • plasma version is: plasma-5.26.0

  • kdm version is: kde-plasma/kdm-4.11.22

  • kernel version is 4.4.39

  • Looks like some kind of Qt version mismatch. Did kdm install another version of Qt? – StefanR Feb 1 '17 at 10:09
  • @StefanR I don't know exactly. how to check it out? – ResRelentelss Feb 1 '17 at 10:31
  • @StefanR Maybe it is, because I have noticed that there two versions of qt in my /usr/lib64 directory, one is qt4 , another is qt5 , but can you tell me how to resolve this problem and make my kde work again? thanks a lot. – ResRelentelss Feb 1 '17 at 13:27
  • It's really long time since I have used gentoo.. But the Qt version 5 is the one you want to be using here. So you should check that did you install correct version of KDM. How did you install it, what command did you use? I would remove that, because it is probably older than rest of the KDE you have installed. – StefanR Feb 1 '17 at 13:43
  • But the newest version of kdm in my portage is 4.11.22, how can I get the newer one? And I have tried to uninstall the kdm and use the sddm and xdm, this error still be there. – ResRelentelss Feb 2 '17 at 3:11

  First, thanks to @StefanR for saving my lots of time!
  Just as methioned by @StefanR above, this problem is caused by Qt version mismatched. After I removed the kdm by emerge -C kdm and updated some stuff referred qt by emerge -av @qt5-essentials @qt5-addons, my kde desktop environment works again as a charm.

Must be mentioned

  if you portage claimed that There are no sets to satisfy 'qt5-essentials' or There are no sets to satisfy '@qt5-addons', you maybe lack some layers in your system, solved by using following command:

  emerge layman
  layman -S
  layman -a qt
  layman -a gentoo 
  emerge --ask @qt5-essentials @qt5-addons

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