When to reboot after aptitude safe-upgrade?

[Dan <ganchya@gmail.com>]

Hi,
I would like to know when I have to reboot my server after doing
safe-upgrade with aptitude. I googled it and I didn't find a clear
answer. In my desktop there is a package called update-notifier-common
which has some scripts that write a file called
/var/run/reboot-required when a reboot is required.

I do not have that package in my server so that I can not check that
file to know if I have to reboot the system. I do not want to install
that package because I prefer to keep the server as clean as possible.
In the server there is no X-server, gnome, etc...

Then, when do I have to reboot? Only when I update the kernel?

Thanks,
Dan