How to Update a Project Zomboid Server and Its Mods (B42)

To update a Project Zomboid server, back up Zomboid/Saves/Multiplayer/<servername> and Zomboid/Server/, stop the server with quit, update the game files with SteamCMD (app 380870, plus -beta legacy41 for Build 41), and start it. Workshop mods update on that same start: the server checks every ID in WorkshopItems and downloads new versions. The server must stay on the same build branch as the world, and every player must be on that branch too.

What you can change on an existing world vs what needs a new world

What is the current Project Zomboid version?

As of October 2026, the stable branch is Build 42.21, released to stable on 28 September 2026 after five days on Unstable (Steam announcement). Build 41 lives on the legacy41 branch, last patched with the 41.78.21 security hotfix. The Indie Stone now sends every update to Unstable first, then to stable. Our Project Zomboid 42.21 update guide covers what changed.

What goes where

The Zomboid folder is ~/Zomboid on Linux and C:\Users\<you>\Zomboid on Windows, unless the server starts with -cachedir.

Step 1: Back up first

Run save, then quit, so the world is written to disk. Copy Saves/Multiplayer/<servername> and the Server folder. With a big mod list, one Workshop update can break a save as easily as a game patch can.

Step 2: Check the build branch

Look at which branch the server installs. No branch means the current stable build (Build 42). legacy41 means Build 41. Never point a Build 41 world at the default branch to "update" it: Build 41 saves do not load in Build 42. If your group wants Build 42, start a new world and keep the old one on legacy41. See Build 41 vs Build 42 multiplayer.

Step 3: Update the game files

On a self hosted server, with it stopped:

steamcmd +force_install_dir /path/to/pzserver +login anonymous +app_update 380870 validate +quit

For Build 41, add -beta legacy41 after 380870. Running it without the beta flag on a Build 41 server switches it to Build 42.

Step 4: Start and let the mods update

Start the server and watch the log. It goes through every ID in WorkshopItems and downloads anything newer before the world loads. Big mod lists make this start slower. Wait for the line saying the server started before anyone joins.

Step 5: Check again with checkModsNeedUpdate

Mods keep updating while the server runs. Run checkModsNeedUpdate in the console now and then. It writes to the log whether any Workshop mod has a newer version. If one does, warn players with servermsg, then quit and start again.

Step 6: Tell players to match

Steam updates players' games and mods automatically. Players who opted into the Unstable beta in Steam must switch back to the default branch to join a stable server, and Build 41 players pick legacy41 under Properties > Game Versions and Betas.

The gotcha: mods update only when the server starts

Steam updates a mod on every player's PC within minutes of the author publishing it. A dedicated server only checks when it starts. So when one of your 40 mods updates at 3 PM, every player who joins after that gets:

Workshop item version is different than server's

and a kick, while the server happily keeps running the old version. Nothing is broken. The server is behind, and a restart fixes it. If a restart does not, stop the server, delete appworkshop_108600.acf in steamapps/workshop and start again, so the server checks every mod from scratch. Our workshop item version fix goes through every case.

Common problems

• "Workshop item version is different than server's": a mod updated after the last start. Restart the server.
• Players get a version mismatch after a patch: the server did not update yet, or a player is on Unstable. Since 42.21, players see a clear version mismatch message.
• Server will not start after an update: a mod is not compatible with the new patch. Remove the newest suspect from Mods, restart, and check the mod page.
• World gone after updating a Build 41 server: the server was updated without -beta legacy41 and now runs Build 42, which cannot load the save. Switch the branch back.
• Mod list edits disappear: the host writes WorkshopItems and Mods from its own settings on start. Change them there.

Updating on GamezServers

A Project Zomboid server from GamezServers checks Steam for a new game version every time it starts, and downloads Workshop updates on the same start. Press Backup, then Restart, and use the Check mod updates button afterwards. The server type picks the branch: Build 42 for the stable build, Build 41 (legacy) for legacy41. One thing to know: Workshop IDs and Mod IDs in Settings are written into the ini on every start, with the Build 42 backslash added for you, so edit mods there, not in the ini.

FAQ

How do I update mods on a Project Zomboid server?

Restart the server. It checks every Workshop ID on start and downloads new versions before the world loads.

Does updating Project Zomboid reset my world?

No, not within the same build. Back up first anyway, and never move a Build 41 world onto Build 42.

Why do players get kicked after a mod update?

Their game downloaded the new mod version and the server still has the old one. Restart the server.

How often should I restart a modded Project Zomboid server?

Daily at a quiet hour works well for big mod lists, plus a restart whenever checkModsNeedUpdate reports an update.