Problem
Simple yum update canceled at bad time messes up your system...
Solution
yum update stuck on systemd-sysv package... pstree -a doesn't show anything useful.
Ctrl+c helps, but breaks the system, as yum stopped in update phase.
yum doesn't work after that, rpm still does.
I've followed advice from here (http://forums.fedoraforum.org/showthread.php?t=296884):
# package-cleanup --dupes > duplicates.txt
Remove odd lines.
# awk 'NR%2==0' duplicates.txt > single-duplicates.txt
Replace new lines with spaces.
# awk '{ printf "%s ", $0 }' single-duplicates.txt > duplicates.txt
Copy-paste content of duplicates after command.
# rpm --nodeps --noscripts -e [paste here]
To fix rpm db. DB is fixed, but yum doesn't work, as rpm libs update failed, symlinks point to new file(lib) versions, but libs are still old version... Fix links manually with ln -sf, until yum stars working. Then you can reinstall packages using 'yum reinstall ...', which should fix symlinks for real (put new libs in place and fix symlinks).
It seems systemd is the culprit of all my problems, as all systemd operations (systemctl) hang, and the only way to continue them is to kill hanged process (check pstree -ap).
After update finishes, try to reboot...
reboot hangs, systemd starts consuming a lot of cpu (30-40%).
Providers managed reboot, which can be ordered through web interface and should complete in 5 minutes is running 11 minutes... CPU consumption still high.
Killing dbus helped to wake up systemd, then at last server rebooted. Before I tried sending signals to systemd, nothing helped.