spontaneous update requring system reboot

[mahesh]

I run my system 24/7. Occasionally, once maybe up to three times per year, I sit down at my machine to discover the System Notification Helper in the system tray signifying the system requires a reboot. How does this occur when I have not carried out a system update? There was no indication in the previous 8 hours of a system update available and I have not carried out a sudo command to update or install a package.

It is as though an update has been pushed onto the system without my sudo permission.