After logging into KDE 4.7 kded4 uses 100% cpu. If I kill it and run kded4 I get the following error:

$ kded4
kded4: symbol lookup error: /nix/store/0m90pj734awzzwz2zflmziqnfdiv5mp9-ntrack-014/lib/ntrack/modules/ntrack-libnl3.so: undefined symbol: ntrack_list_insert_sorted
kded(29300): Communication problem with  "kded" , it probably crashed. 
Error message was:  "org.freedesktop.DBus.Error.NoReply" : " "Message did not receive a reply (timeout by message bus)" " `

If I restart it with kdeinit4_wrapper kded4 it runs at 100% again:

It seems to be related to: https://bugs.archlinux.org/task/23612 and their solution was to downgrade ntrack to 013. The upstream bug they point to is: https://bugs.launchpad.net/ntrack/+bug/750554 and I also get similar results:

$ objdump -p /nix/store/0m90pj734awzzwz2zflmziqnfdiv5mp9-ntrack-014/lib/ntrack/modules/ntrack-libnl3.so | grep NEEDED 
NEEDED               libnl.so.3
NEEDED               libnl-route.so.3
NEEDED               libc.so.6

I tried to downgrade to ntrack 013 locally but then kded4 dies immediately.

Submitted by Cillian de Róiste on 15 August 2011 at 16:07

Closing this issue: kded4 no longer uses 100% CPU on my system and can be started with kdeinit4_wrapper kded4
(nixpkgs r28857)