Activating Server Core

Slmgr.vbs is the tool that designed to be used to activate Server Core.

Windows Software Licensing Management Tool
Usage: slmgr.vbs [MachineName User Password] <One of the Options>
MachineName: if machine name is not provided, slmgr.vbs runs on local machine (do not require User/Password)
Note, this management tool is only for Windows
Global Options:
-did                                 , Display product GUIDs and descriptions
-ilc <License File>                  , Install license
-ipk <Product Key>                   , Install product key
-upk <Product GUID>                  , Uninstall specified product key
-ato [Product GUID]                  , Activate specified product
, (activate all products if parameter not provided)
-atp <Product GUID> <Confirmation ID>, Activate specified product with user-provided confirmation ID
-dli [Product GUID]                  , Display license information for specified product
, (all licenses are displayed if parameter not provided)
Volume Licensing: Key Management Service (KMS) Options:
-dbi                                 , Display KMS and client license information
-skms <KMS Machine Name>             , Set name of KMS Computer to be used
-ckms                                , Clear name of KMS computer used
-sai <ActivationInterval>            , Set how often client connects to KMS computer (in minutes) before computer is activated
-sri <RenewalInterval>               , Set how often client connects to KMS computer (in minutes) after computer is activated
-bmc                                 , Immediately attempt to connect client to KMS computer
-ekms <Product Key>                  , Enable Key Management Service on this machine