Prevent Windows Server 2012 from forcing a reboot after updates

Solution 1:

There is a Local Group Policies you can set to disable the automatic restarts. This should only be done on Windows Servers assuming a sysadmin is going to RDP into the server on a regular schedule and install updates and restart the server (see Patch Tuesday).

1. Press Windows Key+R to open the run prompt.
2. Type "gpedit.msc" and press enter.
3. In the "Local Group Policy Editor", navigate to Computer Configuration > Administrative Templates > Windows Components > Windows Update.
4. Enable the "Configure Automatic Updates" policy and set it to "2".
5. Enable the "No auto-restart with logged on users for scheduled automatic updates installations" policy.

Solution 2:

Finally Microsoft has produced a FIX for this behavior in an update rollup!

An update is available that lets you control how the Automatic Updates client applies updates in Windows 8 and Windows Server 2012. After you install this update, the "Configure Automatic Updates" policy setting will work again as it used to in previous Windows operating systems. Instead of installing updates during the daily maintenance cycle, Windows updates will be installed at the time and day that are scheduled in the "Configure automatic updates" policy setting.

Solution 3:

Disable the Windows Update service. Not in Service Manager - just stop it. The countdown is from the service, not Windows itself.

If you stop it - no more updates UNTIL the machine is manually restarted.

http://www.techspot.com/guides/230-prevent-automatic-windows-update-restarts/

Same works with Server 2012. net stop and then stop the service.