If you’re running a server, always-on media box, or other system that’s powered by Ubuntu, you probably don’t love having to reboot just to install security updates. Ksplice, a semi-free service, eliminates the need for downtime. More here

Ksplice operates in way strikingly similar to Ubuntu’s built-in Update Manager, checking for the latest vulnerabilities and fixes posted by Linux system administrator and builders around the globe and pinging you when updates are available. The difference is that Ksplice makes the fixes without requiring you to reboot at all.

More here: Never reboot again with Linux and Ksplice