How do I know whether to reboot after upgrading packages in Ubuntu?

Question

I have a PC running Ubuntu server.

Sometimes when I ssh into it, I get a message that some packages need upgrading.

I upgrade the software by running (as root)

aptitude update && aptitude safe-upgrade

Sometimes that is enough. But sometimes I need to reboot as well, and I am not told this until I ssh in subsequently. How can I find out sooner?

Ideally I'd like to upgrade by running something like

aptitude update && aptitude safe-upgrade &&
if aptitude needs-reboot ; then shutdown -r now ; fi

but the aptitude needs-reboot command does not exist. What should I run instead?

---

Clarifications:

• Actually I have two PCs, one running 10.04 (lucid) and the other running 11.04 (natty). I'd hope it would be the same solution for both.
• Strictly command line solutions only please. One of these PCs doesn't have a display, and neither of them has a keyboard.

Answer 1

You only need to reboot if the kernel is upgraded.

Answer 2

How about this (run as root): apt-get update && apt-get dist-upgrade --dry-run | grep linux-; if [ $? -eq 0 ]; then yes | apt-get dist-upgrade && reboot; else yes | apt-get dist-upgrade; fi

If there is a kernel update grep linux- will return 0 and then you will reboot. The yes command could be replaced by apt-get dist-upgrade --assume-yes. There will be no reboot if no kernel update is found.