Hello,
I installed Kubuntu 19.04 on my Sony Laptop a week ago. Everything ran smoothly for a couple of days, until I did my daily software update (apt update/upgrade) the day before yesterday. Since then the system doesn't start completely anymore. In fact, kate DOES come up on top of a "black screen of death" and it works fine. However, none of my 4 work spaces initialize. Neither do I see the starter icon on the left bottom or the systems/application tray. From the kate terminal panel I can run software update/upgrade. Thist works as usual, but nothing Plasma-related has been updated so far as far as I can see. I wonder how I can fix the situation without completely installing everything from scratch...
Using the kate terminal extension I can see that /var/log/syslog contains the following message:
Aug 15 10:24:39 hslaptop dbus-daemon[1106]: [session uid=1000 pid=1106] Successfully activated service 'org.kde.kwalletd5'
Aug 15 10:24:43 hslaptop kernel: [ 159.758315] plasmashell[1623]: segfault at 0 ip 00007f0fd111bae8 sp 00007ffe2c512410 error 4 in libkcupslib.so[7f0fd10f3000+30000]
Aug 15 10:24:43 hslaptop kernel: [ 159.758326] Code: 4d fe ff 44 89 fe 48 89 df 31 d2 48 89 1c 24 41 89 c6 48 8d 9c 24 b0 00 00 00 e8 53 7f fd ff ba 03 01 00 00 48 89 df 49 89 c4 <48> 8b 00 4c 89 e6 ff 50 10 31 f6 48 89 df e8 35 85 fd ff 48 89 df
Aug 15 10:24:47 hslaptop kernel: [ 163.711916] perf: interrupt took too long (2505 > 2500), lowering kernel.perf_event_max_sample_rate to 79750
Researching the issue I find that uninstalling print-manager makes the system work again. But surely this cannot be THE solution...
Thanks for any help
H. Stoellinger

When you update, are you using full-upgrade, or just upgrade? Using full-upgrade is the correct usage in *buntu based distros. Using the upgrade option You may be missing some upgraded bits, or something that needs replacing/uninstalled for those updates may not be removed.
Try a full-upgrade and see if that fixes anything.

Thanks for your hint! I tried apt full-upgrade: it didn't seem to do anything with regard to plasma (just upgraded Firefox, eg.). I found a hint in one of the forums of KDE which suggested purging print-manager. I did so - and everything works again now.
Regards from Salzburg
H. Stoellinger