A: The normal DCPROMO command with a graphical interface can't be run on Server Core. Instead, you must create an unattended answer file to perform the demotion.

The easiest way to create this file is to run DCPROMO on a DC running on a full install of Windows, walk through the demotion steps, then export the settings on the final dialog box, which will create the answer file.

Make sure you then click Cancel, so the server you're running the wizard on doesn't actually get demoted!

Below is a sample demotion file:

; DCPROMO unattend file (automatically generated by dcpromo)
; Usage:
; dcpromo.exe /unattend:L:\Temp\dcdemote.txt
;
; You may need to fill in password fields prior to using the unattend file.
;
[DCInstall]
; Demotion
RetainDcMetadata=No
IsLastDCInDomain=No
; Set AdministratorPassword to the correct value prior to using the unattend file
AdministratorPassword=Password
RemoveDNSDelegation=No 

You will need to edit the file and put in an actual AdministratorPassword as this is blanked out at creation and after each use for security reasons. To perform the demotion just run the command below:

dcpromo.exe /unattend:<unattend file location and name>

To see more FAQs for Windows, virtualization, SharePoint, System Center, and other issues you might have, click at John Savill's FAQs.