RimWorld multiplayer server: mods, desyncs and hosting

RimWorld ships with no multiplayer of any kind, and the two mods that add it work in completely different ways. The Multiplayer mod puts several players in one colony and keeps every machine running the same simulation in lockstep; it has no dedicated server and never has, so somebody's game is the server. RimWorld Together gives every player their own colony on a shared planet and does have a proper standalone server, which is the one hosting companies sell. Picking the wrong one is the mistake that wastes a weekend, so this guide starts there and then covers the server properly: install, config files, mod lists, commands, backups and the desyncs.

The two ways to play RimWorld with other people#

The question to ask your group is not which mod is better. It is whether you want to sit down and play the same colony together for three hours, or whether you want a world that is still there on a Tuesday afternoon when one person logs in. Those are different games, and they need different software.

If you want the first, the Multiplayer mod is excellent and you do not need a server at all. If you want the second - and this is the thing most people mean when they search for RimWorld server hosting - you want RimWorld Together.

Multiplayer: one colony, lockstep, no server#

The Multiplayer mod, originally by Zetrith and now maintained by the rwmt team, does not stream the game state to anybody. Every machine, host and clients alike, runs the identical RimWorld simulation. The host distributes commands - a draft order, a bill change, a designation - stamped with a tick number, and everyone applies them at the same tick and arrives at the same world.

That design has three consequences and you should know all of them before you start.

There is no dedicated server. The project's own answer to whether it supports one is a flat no. Hosting is done from inside the game: main menu, Multiplayer, host a new game or an existing save. The host's copy of RimWorld is the authority. When they close the game, the session ends and nothing advances until they open it again.

Every player needs an identical setup. Same RimWorld version, same DLCs where the mods need them, the same mods at the same versions, enabled in the same order, with the same mod settings. Anything that differs is a machine that will compute a different result. Recent versions of the mod synchronise most of this for you when you connect, but the underlying requirement has not changed.

Desyncs are the failure mode. When one machine's simulation diverges, the mod notices and tells you. The common causes are mismatched mod files or settings, a mod that uses randomness the mod cannot intercept, a config changed mid-game, and - frequently overlooked - the host's own machine struggling, because a host whose frame rate falls below the session's tick rate drags the whole game out of step. The mod writes a desync report automatically into an MpDesyncs folder, and that file is what a mod author needs to fix the cause.

For direct connections the mod listens on UDP 30502. Steam-based hosting routes through Steam's networking instead and needs no port opened at all, which is why most small groups never touch a router.

Can you host Multiplayer on a server?#

Not in the way you host a Minecraft server. There is no headless build, no console, no config file, no RCON. RimWorld is a Unity game with a user interface, and the Multiplayer mod's host mode is a menu you click.

Two workarounds exist and both are worse than they sound. You can run a full RimWorld install on a VDS under a virtual framebuffer and treat that machine as the permanent host - it works, it needs a game licence sitting idle on that box, it needs a desktop-sized machine because the host is running the full game with rendering, and every restart is a manual click. Or you can accept that one person is the host and everyone plays when they are online, which is what almost everyone does. Choosing between a VDS and a game panel is the honest version of that trade-off; for this specific case the panel cannot help you, because there is nothing server-shaped to run.

The mod also ships an arbiter: a second, headless-ish instance of the game launched alongside the host purely to cross-check the simulation and pinpoint who desynced. It is a debugging aid, not a server. It costs the host machine real CPU and memory and it does not keep the colony alive when they quit.

RimWorld Together: separate colonies, a real server#

RimWorld Together takes the opposite approach. The server does not simulate RimWorld at all. It is a small .NET console program that holds the planet, everybody's settlements, their saves, the market and the event queue, and relays actions between players. Each player runs their own colony at their own pace on their own machine, and the shared layer is the world map: caravans, raids on each other, trade, gifts, guilds and sites.

Because the server is not running the game, it is extremely light. The project's own description of the hardware requirement is that a modern e-toaster would do, and that is close to true: bandwidth and disk matter more than CPU.

An older mod called Open World did the same thing and is no longer maintained, so you will still see that name on hosting panels and in old guides. If you are starting a world now, start it on the maintained project, and check which RimWorld version the server release you are running targets - the mod tracks RimWorld's current major version and a mismatch there is the first thing to rule out when clients cannot connect.

Installing and running the server#

Download the server files from the project's releases and unpack them somewhere the operating system will not fight you over permissions. Then run the executable. There is no installer and no build step.

$ mkdir -p /opt/rwt && cd /opt/rwt$ unzip ~/Downloads/rimworld-together-server.zip$ ./RimworldTogether

There is also an official container image, which is the tidier way to run it on your own Linux box:

$ mkdir -p RWTData$ docker run -it --rm -v './RWTData:/Data' -p 25555:25555 \    ghcr.io/rimworld-together/rimworld-together:latest

On first start the server writes its whole directory structure and every config file with defaults, then stops waiting for input on the console. That first run is the point at which to stop it, edit the configs, and start it again.

/opt/rwt/  Configs/        ServerConfig.json and the rest  Configs/Actions/  per-action tuning, one file each  Assets/         Maps, Users, Saves, Settlements, Sites, Guilds, WorldObjects  Backups/        Servers and Users  Logs/           System and Chat

One port, and it is the same one in the config, the container mapping and the client's connect dialog. If players get a connection refused, the order to check is: is the process running, is the port allocated, is the client pointed at the right address. Game server ports explained covers why "the server is up" and "the port is reachable" are two separate claims.

RE:NODE's RimWorld line is exactly this shape of server - a persistent multiplayer colony with mods included - and every plan comes with one port allocation, which is all this needs. The configs and mod list are edited in the browser file manager or over SFTP; SFTP and the file manager has the connection details.

ServerConfig.json and the Configs folder#

The main file is Configs/ServerConfig.json. These are the defaults the server writes:

{  "Name": "RimWorld Together Server",  "Description": "",  "DiscordURL": "",  "SteamWorkshopURL": "",  "IP": "0.0.0.0",  "Port": 25555,  "MaxPlayers": 100,  "Verbosity": 0,  "DisplayChatInConsole": false,  "UseUPnP": false,  "UseClientSave": true,  "EnableServerBrowser": true,  "EnableServerTelemetry": true}

The rest of the folder splits by concern, and every file is written with defaults so you can read the shape before you change anything: ModConfig.json for the mod list, DifficultyConfig.json, StorytellerConfig.json and ScenarioConfig.json for what a new colony starts with, ChatConfig.json, PasswordConfig.json, WhitelistConfig.json, BackupConfig.json, and a Configs/Actions directory with one file per interaction - raids, caravans, trades, sites, events, the market, guilds - so you can price or disable each of them individually.

Backups get their own file and sensible defaults:

{  "AutomaticBackups": true,  "IntervalHours": 1,  "AutomaticDeletion": true,  "Amount": 6}

Hourly, six kept, oldest pruned. That is a good rotation and it is still not a backup, because it sits on the same disk as the thing it protects. Copy the whole server directory somewhere else on a schedule as well - backups that actually restore is the argument, and on RE:NODE the backup slots included with every plan are stored off the machine and restored with a button.

Mods: the list everyone shares#

Configs/ModConfig.json is where the server states its mod policy, in three lists: required mods, optional mods and forbidden mods. A joining client is checked against them. Required mods must be present, forbidden mods bar the connection, and optional mods are allowed either way - which is the important difference from the Multiplayer mod, where there is no such thing as an optional mod.

Practical rules for a shared mod list, on either mod:

1. Agree the list before day one. Adding a content mod to a world that already has colonies means every player re-syncs and some of them lose things. Removing one is worse.
2. Use a Steam collection. Publish one collection, put its link in SteamWorkshopURL, and tell people to subscribe to that and nothing else. A collection is the only mod list that stays in step by itself.
3. Pin the load order. RimWorld is exceptionally sensitive to order. Export your working mod list from the game and send the file rather than a screenshot.
4. Avoid mods that generate the world differently unless everyone has them, and treat performance mods as part of the list rather than personal choices.
5. Do not update mid-week. A workshop mod that updates under one player and not another is the most common cause of a Monday evening spent debugging. What to do when a mod update breaks has the recovery drill.

Server commands, admins and backups#

The server reads commands from its console, which on a panel is the console box. There is no separate remote protocol; the console is the admin interface.

Because the admin interface is the console, who has console access is a real security question rather than a formality. On RE:NODE that is what subusers and roles are for: a role can be console only, or files only, with no billing, and every action is recorded in the per-server activity log. Subusers and least privilege covers how to split it up sensibly.

Requirements and troubleshooting#

Note the third row. If somebody quotes you a price for a "RimWorld Multiplayer dedicated server" running the Zetrith mod, ask what it actually runs, because a machine capable of hosting that session is a desktop-class box with a graphical environment, not a $5 game plan.

Clients cannot connect. Check the version of the mod against the version of the server; they are released together and mismatches are refused. Then check the port, then the password.

A player joins and immediately drops. Usually the mod check: something required is missing or something forbidden is installed. The server log names it.

Desyncs in the Multiplayer mod. Compare mod versions, settings and load order across everyone, confirm the RimWorld build matches, and look at the host's performance. Send the file from the MpDesyncs folder to the mod's maintainers rather than guessing.

The world is huge on disk. Player saves and hourly backups accumulate. Lower Amount in BackupConfig.json, or move old backups off the server.

The server stops when you close the terminal. Run it as a service, or in a panel where the process supervision is somebody else's problem. A crash loop that is actually the memory limit rather than a config error is covered in why your game server keeps restarting.

FAQ#

Does RimWorld have official multiplayer?

No. Ludeon has never shipped multiplayer, and both options are community mods with different designs. Anything advertising official RimWorld multiplayer is describing one of those mods.

Can I run the Multiplayer mod on a hosting plan?

No. It has no dedicated server build, no headless mode and no console; hosting is a button inside the game. The only way to keep it running unattended is a full RimWorld install on a machine you control, with a graphical environment, which is a different purchase entirely.

How many people can play on one RimWorld Together server?

MaxPlayers defaults to 100 and the server is light enough that the number is rarely the limit. Twenty active players on a shared planet is a busy world. The practical constraints are how much moderation you want to do and how much disk the saves take.

Do all players need the same mods?

On the Multiplayer mod, yes, exactly, including settings and load order. On RimWorld Together the server states required, optional and forbidden mods, so optional ones can differ per player - which is the main reason larger groups end up there.

Why do we desync every time a raid happens?

Combat involves the most randomness, so it is where a divergence shows first rather than where it starts. The cause is almost always a mod difference or the host's machine falling behind. Compare the lists first, then watch the host's frame rate during the next fight.

Can I move a single-player colony onto a server?

Not directly on the Multiplayer mod, which starts from a save that the host loads and everyone joins. On RimWorld Together each player brings their own colony into the shared world, so a personal save can carry over as long as its mods satisfy the server's list.