I'm seeing a lot more Server Core deployments as 2012 adoption increases. Which I think is awesome - I love Server Core. But there are still a couple things that were completely trivial on a GUI edition of Windows that are a tad tricky on Core.
For instance, here I am on Server 2012 Core using the sconfig utility to set up Windows Automatic Updates:
This is just a lab environment, so I don't mind automatic updates and reboots. But I have two Active Directory domain controllers in this lab, and I don't want them rebooting at the same time. So how do I change the "every day at 3:00 AM" schedule so that I can stagger the patching and reboots? On a GUI install it would be trivial of course. Here, not as much.
The first thing I did was briefly look for a registry entry in HKLM:\Software\Microsoft\Windows\CurrentVersion\WindowsUpdate\, but I didn't see anything that looked like it would help me modify the Windows Update schedule like I wanted to.
These are domain members, so of course I could use Group Policy to do it, but I didn't want to create and link separate GPOs for each server that I wanted to have a different Windows Update schedule. Plus I wanted to figure out how to do it on non domain-joined machines as well.
Ah - Local Policies! To edit local policies on Core servers, we'll need to connect to them remotely from what I like to call "a tools machine." When you have a bunch of Server Core machines running out there, you should also keep one machine around that has a full GUI install. I personally like to install all my tools (like RSAT) on that one machine, and use it to centrally manage all of the Core machines remotely.
Here I am using mmc on my tools machine to add Group Policy Object Editor snapins for several of the Server Core computers:
Again, the name of the snapin is Group Policy Object Editor, and target the remote machine as you add the snapin. You'll of course need RPC over TCP connectivity to the remote machine, and you'll need to modify Windows Firewall on the remote machine to allow the incoming connection. (I like to use domain Group Policies for that, so all my machines have consistent firewall settings.)
All that's left to do now is navigate to Computer Configuration > Administrative Templates > Windows Components > Windows Update, and configure the "Configure Automatic Updates" setting for the server. It allows you to modify the hour and the day of the week that Windows Update will download and install updates on that machine.
As per Active Directory Group Policy application precedence, remember that any conflicting domain-based GPO will override settings you make to a machine's Local Policy.
Lastly - don't forget that automatic update option 4 - "Auto download and schedule the install" - is the only option here that applies to Server Core. The others won't work because Server Core can't "notify" the user of updates the way it could were the GUI installed.