How to know if rebooting the system is necessary after package upgrades?

If using a GUI, e.g. the default GNOME GUI on Ubuntu, after upgrading packages sometimes the information is displayed that rebooting the system is necessary.

When working on the command line e.g.
sudo apt-get update
sudo apt-get upgrade

or
sudo aptitude update
sudo aptitude safe-upgrade

usually no such information is offered.

How do I know? How do the GUI tools now?Start Free Trial