If you admin Windows Server 2012 enough, and you keep auto updates on like you should, you'll eventually run into this.
While logged in, Server 2012 will give you a winupdate reboot countdown that isn't easily stopped.
This can happen at any time, and first few times I saw it, I freaked. Two things need to happen to cause this scenario:
- Have Windows Update configured to auto update. A Good Thing
- Log into the server (either local or RDP) and leave that session locked overnight during patch night. I'll resist getting on my high horse of the difference between disconnect and log out, or about using GPO to log out disconnected sessions. Still, there are legetimite times an admin needs to stay logged into a server while disconnected.
So the server will patch itself, but not reboot. It's set to not force a logout, so it'll wait till your next interactive session and blindly tell you it's gotta reboot, and start the countdown, reguardless of time of day.
The fix is a April 2013 Windows Update (KB2822241) that allows you to then set a registry value (KB2835627) to force the reboot when you told the server to update and reboot. Personally I find this whole situation silly... but now at least we can set a GPO to control it.
Update 12/2013: There's now a update rollup for Windows 2012/8 (KB2885694) that reverts some of this silly featureset to the way it was in Server 2008 R2/Win7.