Update failure 1: login stuck in loop. In January 2019 the
Ubuntu software updater put me into a nasty endless login loop. The
recipe then is to hit CNTRL + ALT + F3 (or F1 or F2) to start a
terminal-like login screen; this worked, be it haphazardly needing
multiple reboots. When that screen appeared it was better to install
and switch to the lightdm display manager which opens this CNTRL + ALT
+ F3 screen reliably. The standard recipes are then to check the
ownership of .Xauthority, the permissions of /tmp, and to muck with
the nvidia driver, but in my case the culprit was the workspace grid
Gnome extension in
~/.local/share/gnome-shell/extensions. Its removal made Ubuntu
finally start up; renewal from the extension
revived my workspace layout.
This update failure cost me two days of frantic googling until I found
Update failure 2: CPU frequency lowered. In April 2019 the Ubuntu software updater again acted disastrously: after the mandatory restart my Portégé X30 became terribly slow. It took three weeks to find the cause and remedy given here while the culprit remains unidentified. I had already tried a complete Ubuntu 18.04 re-install; repeating all its fine tuning took another week. Thanks, Ubuntu!