This is a pure copy paste incase the resource is someday removed from internet archives
You can find the original here https://web.archive.org/web/20191019114659/http://www.hells-reach.com/dedicatedserver/

The Haunted: Hell’s Reach uses the steam service to host and join multiplayer games. To launch a dedicated server you need to have the steam client running and the dedicated server tools installed.

The server needs to have internet ports open to ensure it gets listed on the steam server list. If the server is behind a NAT router or a firewall those ports must be forwarded and opened correctly.
The default ports are 7777/27016. 7777 is the default game port and 27016 is the port used for the steam service. If one wants to use 7778 as game port then 27017 will automatically be used as steam service port. The couples are: 7777/27016, 7778/27017, 7779/27018, 2780/27019, 2781/27020, 2782/27021… and so on.

The game port is easy to change with a command line parameter or by using the bat files that come with the game.

The dedicated server tools are installed from the library/tools menu in the steam client.

Game type, map name, admin password and game port are changed with command line parameters. The launch parameters are changed from properties/launch options (right click The Haunted Hells Reach Dedicated Server) to show the properties dialog.

In the above example, the full command line is:
TH-Temple?game=HauntedGame.TH_Game_coop?AdminPassword=f7yeQHdM.

Launching the server will start an inferno game on the temple map with f7yeQHdM as the administrator password.

There are also 12 bat files located in the Binaries/Win32 folder. The name of the bat files starts with Haunted DedicatedServer and can be used to quickly setup a server or to be used as a base for your own bat file. To run multiple instances on one server all that needs to be done is to open the ports and then launch the different bat files. We advise you to change the AdminPassword when using them.

Note that you still need to be logged in on the Steam network and have the Steam client running even if you use the bat files. The account does not have to own a copy of The Haunted: Hells Reach, though. It is enough just to be logged in.

list of available command line parameters
TH-Canyon, TH-Excavation, TH-Mine, TH-Museum, TH-SteelTown, TH-Stronghold, TH-Temple,
TH-WildWest
game=HauntedGame.TH_Game_coop (Inferno)
game=HauntedGame.TH_Game_TDM (Battle)
game=HauntedGame.TH_Game_survival (Survival)
game=HauntedGame.TH_Game_Conversion (Demonizer)
AdminPassword=f7yeQHdM, where f7yeQHdM is the desired password.
Port=7777 where 7777 is the default game port

admin commands
AdminLogin is to log in as an adminstrator. Example: AdminLogin f7yeQHdM
AdminChangeMap changes the map. Example AdminChangeMap TH-WildWest
AdminChangeGameType changes the gametype.
AdminChangeGameType Inferno
AdminChangeGameType Survival
AdminChangeGameType Battle
AdminChangeGameType Demonizer
AdminChangeDifficulty changes the difficulty.
AdminChangeDifficulty 1 (Easy)
AdminChangeDifficulty 2 (Normal)
AdminChangeDifficulty 3 (Hard)

Credits to whom ever the good person is that wrote the original HTML guide.

It may also be possible to install a headless dedicated server using steam cmd, i will experiment with that someday. If someone else wishes to create a headless dedicated server guide by all means do it. Unsure about Linux support at this time.