Ksplice, according to its developers, "enables running systems to stay secure without the disruption of re-booting. Specifically, Ksplice creates re-bootless updates that are based on traditional source code patches. These updates are as effective as traditional updates, but they can be applied seamlessly, with no downtime."
Guess what? It works.
I don't have a carrier-grade server in the house, but I do have an Ubuntu 9.04 desktop and the developers have just released a version of Ksplice Uptrack for it. So, I installed this Python-based update system on my Gateway 503GR. This PC has a 3GHz Pentium IV CPU, 2GBs of RAM, an ATI Radeon 250 graphics card, and a 300GB SATA (Serial Advanced Technology Attachment) hard drive.
Before installing Ksplice, though, I zapped my hard disk and reinstalled Ubuntu 9.04, aka Jaunty Jackalope, from a CD of its first release. You won't want to do that, but I wanted to give it as much of a workout as I could manage.
I had a bit of trouble installing it at first, although the installation routine itself is as easy as can be. My problem was that the Ksplice installation routine ran afoul of the automatic update system. I solved this by killing that system off, resetting the Debian package system.
After that, it was smooth sailing and I had replaced Ubuntu's default update system with Ksplice. A few minutes later I'd updated the entire system with Ksplice with all the latest patches, without even a hint that I might need to reboot for a security upgrade. Nice.
By default, Ksplice shows up in your system menu-bar so you can keep an eye on what's happening with your updates. While Ksplice itself is open-source software, and the service for individual users is free, you'll need to pay a service fee if you're a business using Ksplice to keep your servers up-to-date.
Since Ksplice doesn't require any changes to the Linux kernel I strongly suspect you'll soon be seeing its technology used with other Linux distributions. After all, as great as Linux is about letting you run for months on end without wasting time or money on a reboot, it will be even better when we can run Linux for years without rebooting.