Hmm. D2GS is the program described in the first link that enables closed realm support. It is the Game Server. It depends on D2CS/D2DBS which are in the second link (Character Server and Database Servers respectively). All 3 need to be running for a fully functional realm. Unfortunately while D2CS and D2DBS are easy to set up on a linux box, and in all likelihood already is set up on henrietta, D2GS is a Windows-only program. However, I've set it up to run under Wine in Debian before for LoD 1.09, so it's still possible. That was a long time ago though, so I can't say for certain that current versions of Wine will run D2GS as flawlessly as before.