Garry's Mod Gamemodes and How to Run Them on a Server
A fresh Garry's Mod dedicated server contains exactly three gamemodes. Look in garrysmod/gamemodes/ and you get base, sandbox and terrortown. That last one is Trouble in Terrorist Town, already installed and playable, and most operators never notice it. DarkRP, Prop Hunt, Murder, Deathrun and every nextbot chase mode are community content you install yourself. All follow the same folder contract, documented by Facepunch on its Gamemode Creation page.
Last verified: September 17, 2026. The September 2026 update went live on September 16 and brought 64-bit binaries to Windows, including the dedicated server. Pure Lua gamemodes do not care about bitness; a gamemode that depends on a compiled binary module does. See the September 2026 update guide.
What ships, and what you install
| Directory | What it is | Run it directly? |
|---|---|---|
gamemodes/base | The skeleton other gamemodes derive from. | No. It is a parent, not a product. |
gamemodes/sandbox | Toolgun, spawn menu, physics and building. What most players mean by Garry's Mod. | Yes. This is the default. |
gamemodes/terrortown | Trouble in Terrorist Town. Social deduction with hidden traitors. | Yes, with a map built for it. |
Everything else arrives as an addon or a manual copy into garrysmod/gamemodes/. The shape is always the same: a directory named after the gamemode, containing a gamemode/ subdirectory with the Lua inside. That directory name is the value you pass to the server, not the title in the server browser, not the Workshop item name, not the zip filename.
Selecting and switching the gamemode
The gamemode is a startup argument. Pass it with +gamemode alongside an explicit +map:
# Sandbox on a shipped map, the safe first boot.
./srcds_run -game garrysmod +gamemode sandbox +map gm_construct +maxplayers 24
# Trouble in Terrorist Town, already installed.
./srcds_run -game garrysmod +gamemode terrortown +map ttt_yourmap +maxplayers 24To switch a running server, set the gamemode convar, then load a suitable map with changelevel or host_map. The change lands with the map load, not with the convar. gamemode_reload also exists in the shipped build for reloading the active gamemode in place, but that is a development tool, not a way to move a live lobby between modes. Keep the mode you want in the startup line so a crash restart returns to it.
The map pairing rule
This is the most common reason an operator reports that the gamemode loaded but nothing works. A gamemode is Lua; a map is geometry plus entities, and most gamemodes need entities the map provides, starting with spawn points. Boot TTT on gm_construct and the round logic runs fine against a map with none of the placement it expects.
| Prefix | Built for | What that means for you |
|---|---|---|
gm_ | Sandbox | Only gm_construct and gm_flatgrass ship. Everything else is a download. |
rp_ | Roleplay, DarkRP and its relatives | Large persistent maps with districts, shops and buildable interiors. |
ttt_ | Trouble in Terrorist Town | Carries the spawn and weapon placement TTT rounds depend on. |
ph_ | Prop Hunt | Enclosed rooms stuffed with small props worth hiding as. |
de_ and cs_ | Counter-Strike heritage | Models and materials only resolve if CS:S is mounted and delivered to clients. |
The prefixes are a convention, not an enforced rule, so read a map's description before it goes into rotation. Note also that srcds_run defaults to DEFAULT_GAME="garrysmod" and DEFAULT_MAP="gm_construct": start without +map and it lands on sandbox's map whichever gamemode you asked for. More in the maps guide.
Comparing the main gamemode families
| Gamemode | What it is | Ships | Structure | Typical slots | What it costs a server |
|---|---|---|---|---|---|
| Sandbox | Toolgun, physics and building, no win condition | Yes | Persistent | 12 to 32 | Entity count follows whatever players build. Physics CPU and RAM climb together. |
| Trouble in Terrorist Town | Social deduction with hidden traitors | Yes, as terrortown | Round based | 16 to 32 | Quiet mid round, CPU spike at every reset. Slots matter more than memory. |
| DarkRP | Roleplay with jobs, an economy and player-built bases | No | Persistent | 32 and up | The heaviest of the five. Entities accumulate for the life of the map and RAM rises with them. |
| Prop Hunt | One team hides as map props, the other hunts | No | Round based | 12 to 24 | Light. Small maps, short rounds, modest slot counts. |
| Nextbot chase | Player-hunting bots on purpose-built maps | No | Usually round based | 8 to 16 | Pathfinding is server CPU per bot. Few players, high per-tick cost, large downloads. |
Round based versus persistent
That structure column decides how you size the machine, and it predicts load better than the gamemode's name does.
- Round based modes reset world state every few minutes, so entities are cleaned up and memory stays roughly flat across an evening. They consume CPU at the reset boundary and slots, because the experience scales with how many people are in the round. A 24 slot TTT server and a 24 slot sandbox server are not the same purchase, since TTT actually fills those slots.
- Persistent modes never reset until the map changes. Every prop, printer and base wall a player leaves behind stays in the entity list, so memory is the binding constraint and it only moves one way.
The failure mode for a persistent server is not a crash at peak player count. It is slow degradation eight hours in, once the entity list outgrows what the tick budget can walk. Plan a map rotation or a scheduled restart, and size RAM for the end of a session, not the start. Numbers in server requirements, costs in server cost and sizing.
Every installed gamemode brings content
This is the part operators underestimate. The gamemode's Lua only has to reach the server. Its maps, models, materials and sounds have to reach every player.
host_workshop_collectioninstalls a collection on the server at startup, which is not the same as delivering it to clients.sv_downloadurlwithsv_allowdownloadpoints clients at a FastDL mirror. The mirror's folder layout has to match exactly.sv_loadingurlreplaces the loading screen, which is where players sit while that transfer runs.sv_puregoverns how strictly clients must match the server's files, and a gamemode built around custom content can fail against a strict setting.
If players join and see purple checkerboards or ERROR signs, the gamemode is fine and the delivery is not. Start at missing textures and ERROR models, then content packs for mounting and the delivery paths.
Common problems
| Symptom | Cause | What to do |
|---|---|---|
| Server cannot find the gamemode at boot | The folder is nested one level too deep, usually from an archive that extracted as gamemodes/darkrp/darkrp/ | The directory immediately under gamemodes/ must itself contain the gamemode/ subdirectory. Move it up one level and restart. |
| Gamemode loads but nothing happens | Wrong map for the gamemode, no usable spawn or gameplay entities | Match the prefix, confirm the map was built for that mode, restart with an explicit +map. |
| Players stuck on the loading screen | The client is pulling gamemode content over a slow or broken path | Check the FastDL host is reachable and correctly laid out, prefer the Workshop collection where the addon supports it, and test from a clean client. |
| Addon gamemode broke after a game update | The gamemode, or a module it depends on, was not rebuilt for the new build | Read the addon's update notes, then boot sandbox on gm_construct to prove the server itself is healthy. |
Related Garry's Mod guides
- Trouble in Terrorist Town server, the gamemode you already have
- DarkRP server, the heaviest persistent mode
- Prop Hunt server
- Nextbots and chase gamemodes
- Maps, prefixes and rotations
- Dedicated-server setup
- Startup flags and server.cfg
- Workshop collections and addons
- Workshop download troubleshooting
- Lua scripting and admin commands
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