Garry's Mod or GMod is a modification for the first-person shooter Half-life 2. It is a physics sandbox game that allows the player to manipulate objects and experiment with physics, with the realism provided by the Source engine. The dedicated server component can be run as a Windows Service using FireDaemon. FireDaemon will allow you to have the dedicated server start automatically at boot prior to login, allow you to start multiple instances of the dedicated server and so forth. This HOWTO will show you how set it up. You can also use Trinity or PanelDaemon to manage FireDaemon and other Windows services via a web browser.

GMOD Dedicated Server Setup Under FireDaemon
1. First download and install the HLDS Update Tool. The download is small (< 2 MB). Install into the directory of your choice (eg. C:\GMOD).
2. Download the GMOD server files via Valve's content servers. First before downloading the files, go to the directory where you installed the HLDS Update Tool. Create a shortcut to "HldsUpdateTool.exe". Next edit the properties of the shortcut and in the target box, at the end of it (with a space before the following), put:
-command update -game garrysmod -dir .
The target box should now look something like:

Now click the shortcut you created and let it run (it might take a few hours to update everything). You should also run the shortcut every week or so to grab the latest server updates (stop your server first though).

Garry's Mod is also different than most other mods in that it uses HL2 episode 2 sdk, so you will find the game files in the subdirectory "orangebox" (Eg. "C:\GMOD\orangebox\garrysmod\")
3. Download and install FireDaemon Pro into the directory of your choice (typically C:\Program Files\FireDaemon). FireDaemon can be downloaded from here.
4. GMOD uses 1 configuration file to store it's settings. You can find it in "orangebox\garrysmod\cfg\server.cfg" in the directory where you installed the server.
5. Next start the FireDaemon GUI from the desktop shortcut. Click on the "Create a new service definition" button in the toolbar (or type Ctrl+N) and enter the information into the fields as you see below. Obviously adjust paths to suite your installation. Pay special attention to the Parameters list.

The most important field on the tab is the Parameters. The Parameters define the initial setup of your server.

Here's the full parameter list you should have:
-console -game garrysmod -secure +map gm_construct -autoupdate +log on +maxplayers 32 -port 27015 +ip 1.2.3.4 +exec server.cfg
"-console" enables text base server display. The server can only be automatically restarted in text based mode.
"-game" loads the mod.
"-secure" enables VAC protection of your server (valve anti cheat). You can remove this command if you do not want to use VAC.
"+map" loads a specified map on server startup. You can change "gm_construct" to whatever map you want. This command should never be removed.
"-autoupdate" Enables auto update of the server, valve has not implemented this in windows so you will have to manually update SRCDS/GMOD yourself. It's simply here for the sake of legacy support if valve ever decides to add it.
"+log on" Displays the output of information on the screen. You can turn optionally it off (+log off), but keeping it on makes it easier to debug any errors you might encounter.
"maxplayers 32" This controls the maximum of amount of players you want your server to run. You can only control the max players on server startup. This command should never be removed.
"-port 27015" This is the default server port for SRCDS. You can change it to anywhere from 27015 to 27020. Changing it is generally used when you host multiple servers (as each server has to use its own port when using the same IP). This command should never be removed.
"+ip" should be the IP of your computer (not 127.0.0.1, go here to get your IP). This command should never be removed.
"+exec server.cfg" This simply executes your server.cfg file on server startup. If you run multiple servers from the same installation, you can specify other config files (eg. server2.cfg)
6. Now click on the Settings tab. If you DON'T want to see your dedicated server running, uncheck the Interact with Desktop check box & select "Hidden" from the "Show Window" dropdown. Also uncheck Graceful Shutdown as SRCDS doesn't respond to it. You can optionally run SRCDS as the user you installed it as. In the Logon Account field type your username (eg. Administrator) and then enter the user's password twice in the Password and Confirm fields.

7. Now click on the Advanced tab. You can change the Process Priority to allocate more CPU time to the dedicated server or specify which CPU or core the dedicated server will run on (in the case of multi-processor, hyperthreaded or multi-core CPUs).

8. Now click on the Dependencies tab. Make sure the service depends on the lanmanworkstation (Workstation) service to ensure the TCP/IP and CIFS stacks are both up prior to starting SRCDS.

9. Now click on the Install button to install and start GMOD!

Below is an example server.cfg file: