My desktop was on the kernel 4.15.0-48-generic. Then in the middle of this May the system suggested to upgrade itself to the kernel 4.15.0-50-generic, and I said "OK".
The upgrade was unsuccessful, the desktop didn't boot after that. So I had to manually switch to the old 4.15.0-48-generic kernel, and purge the 4.15.0-50-generic kernel.
After that the system stopped to suggest upgrading its kernel, and I think there is a setting somewhere, which forces the system to stay on the old kernel.
How to roll the system back to its normal way of upgrading kernel?
history
(I also have date/times in my log files to aid finding things, but it's not the default for command history). I'd look forapt-mark
(hold)apt-mark showhold
returns nothing...dpkg -l | grep linux-image-generic
linux-image-<version>-generic
packagessudo apt install linux-image-generic
, That metapackage is how Ubuntu pushes kernel upgrades.