How to host a Garry’s Mod server

Base Garry’s Mod is undemanding; a server running a large gamemode with a hundred addons is a different question entirely. The addons are the requirement, not the game.

How to install it

1. Install Steam’s command-line tool, then the Garry’s Mod dedicated server using an anonymous login.
2. Start it plain, on a default gamemode, and join it yourself before adding anything. This is your known-good baseline.
3. Build a Workshop collection in Steam and point the server at its ID. Managing addons individually stops working almost immediately.
4. Mount any other Source game content you rely on, or accept that players who do not own those games will see missing textures.
5. Add addons in batches, restarting between batches, so you can identify what broke.

steamcmd \
  +force_install_dir /home/gmod/server \
  +login anonymous \
  +app_update 4020 validate \
  +quit

# Counter-Strike: Source content is a SEPARATE install.
# Without it, huge numbers of addons show missing textures.
steamcmd \
  +force_install_dir /home/gmod/css \
  +login anonymous \
  +app_update 232330 validate \
  +quit

./srcds_run -game garrysmod \
  +gamemode sandbox +map gm_construct \
  +host_workshop_collection YOUR_COLLECTION_ID

How to configure it

// Point at the content you installed separately.
// This is what fixes the purple-and-black checkerboard.
"mountcfg"
{
    "cstrike"   "/home/gmod/css/cstrike"
}

• Gamemode and map are launch arguments, not config settings. Your gamemode largely determines which addons make sense.
• The workshop collection is the whole addon story. One ID, managed in Steam’s interface rather than on the server.
• Download size is part of the player experience. A server that takes five minutes to join loses people before they arrive.
• Set a password while you are still testing, then clear it when you open up.

Written from experience running these servers. If something here no longer matches what you are seeing, tell us and we will recheck it.