You no longer need to reboot a running Linux system to apply security patches to it.
Excuse me whilst I pick my jaw up from the sub-sub-sub-basement floor. If this checks out in the field, on multiple distros, then a lot of sysadmins are going to be able to get a lot more sleep at night. And the comment by one David Pottage:
This should be good for distro kernels.The mind reels a bit. Security patches are the most gotta-do-it-right-NOW things that come down the pipe for any system. Open-source systems that are widely audited, like Linux, tend to get patches a lot quicker than Windows (which had attacks in the wild with no fixes available for some 271 days in 2007), or even Mac OS X. Any closed system that depends on a single organization to secure it will always have slower reaction time than an open system with enough (mutually independent, distributed) resources to throw at it. As Eric S. Raymond wrote in The Cathedral and The Bazaar, "given enough eyeballs, all bugs are shallow". As long as there is some meritocratic control over the "official" patch-submission process - and there is - it's now easier than ever to keep critical systems up and secure, in ways and at speeds that simply can't be matched in the Microsoft world. Remember, even if your uptime is 99.999%, (the so-called "five nines gold standard"), you're still down five minutes and fifteen seconds every year. Murphy's Law says at least five minutes of that time will be when it was really, truly important that the system not be down.
Just think if you can prepare a special kernel module that will apply security patches to a running kernel, then so can your favorite distro. In future when there is a security update, instead of downloading a ~20Mb kernel package from security.debian.org or the like, and then waiting until a suitable time to install it and reboot the system, you can download a small package containing patching modules for the standard kernels from that distro, and install it immediately...
You can't repeal Murphy's Law, but I think it does give us a big step towards an insurance policy.