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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Update a Project Zomboid dedicated server by stopping it cleanly, backing up the world and configuration, running SteamCMD with app ID 380870, restarting on the intended branch, and then synchronizing clients and Workshop mods. The safe sequence is stop → back up → update → start → verify. A same-branch patch update is normally an in-place operation, but Build 41 and Build 42 saves are incompatible, and a mod revision mismatch can prevent players from joining.
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Before you update: identify the change you are making
Project Zomboid server files, the saved world, player data, client game builds, and Workshop downloads must be compatible. First decide whether you are applying a patch within the same major branch or moving between major branches.
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The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →| Situation | Recommended approach | Main risk |
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| Patch update on the same branch | Back up the server, run SteamCMD with app_update 380870 validate, restart, and test. |
A mod or patch can still alter save behavior. |
| Build 41 to Build 42 | Keep separate server folders and saves, and plan a new Build 42 world. | Build 41 savegames cannot be loaded by Build 42. |
| Pinned legacy branch | Keep the branch argument in the SteamCMD command and update only when that branch receives a compatible build. | Players on the default branch will not match the server. |
The Indie Stone’s official Build 42 Checklist states: “Build 41 savegames clearly will not be compatible with Build 42.” Treat that as a hard migration boundary, not a warning that can be solved by copying files. The current material describes Build 42 as the default branch, but branch names and patch numbers can change. Check the build displayed by Steam and by the server startup log at the time of the update instead of relying on an old article’s number.
What you need before taking the server offline
- Administrative access to the Windows machine or the Linux service account that owns the installation.
- A controlled install directory for SteamCMD, or access to the Steam client’s Library → Tools installation.
- Enough disk space for the updated server files and a dated backup.
- A maintenance window long enough to stop, copy the data, update, start, and test one client connection.
- A record of the current
ModsandWorkshopItemsvalues from the server configuration. - For Internet play, access to the host firewall and router settings for the UDP ports configured by the server.
Announce the downtime before stopping the process. Do not copy, edit, or restore save files while the server is still writing to them; a live copy can be incomplete and may corrupt the only usable world backup.
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Back up the data that cannot be redownloaded
SteamCMD can download fresh binaries, but it cannot recreate a lost world, player inventory, whitelist, or server configuration. Stop the server with the in-game console command quit, or use the service manager’s stop action and wait for the process to exit.
- Copy the complete
Zomboid/Server/directory to a dated backup location. This preserves server settings, spawn configuration, sandbox options, and the mod lists. - Copy
Zomboid/Saves/Multiplayer/<servername>, replacing<servername>with the actual save-directory name. - On Linux, preserve the player database when your setup uses one. Keep it with the matching server and save backup.
- Record the backup date, branch, server build shown before shutdown, and the exact
ModsandWorkshopItemsvalues. - Confirm that the copied directories contain files and that the backup is readable before beginning the update.
Keep more than one dated backup when the world matters. Store at least one copy outside the live server directory so a failed disk operation or an accidental cleanup cannot remove both copies.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteUpdate with SteamCMD
Standard current-branch command
Run SteamCMD with a dedicated install directory. Replace the path with the folder used by your server:
steamcmd +force_install_dir <server-folder> +login anonymous +app_update 380870 validate +quit380870 is the Project Zomboid dedicated-server app ID. force_install_dir prevents SteamCMD from updating an unintended installation, login anonymous uses the public dedicated-server depot when available, app_update downloads the server files, validate checks the downloaded files, and quit exits SteamCMD after completion.
Updating a pinned legacy branch
If the world is intentionally kept on a legacy branch, include that branch argument rather than allowing SteamCMD to move it to the default branch. For example, a Build 41 installation may use:
steamcmd +force_install_dir <server-folder> +login anonymous +app_update 380870 -beta legacy41 validate +quitUse the exact branch name documented for your server’s chosen version; legacy41 is an example, not a promise that every future installation will expose the same label. The branch on the server, the branch selected by every player, and the branch expected by the installed mods must agree.
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On a Windows machine with the full Steam client, the dedicated server appears under Steam Library → Tools. Install or update it there, then launch the server script from its installation folder. This is convenient for a graphical host, but it is less suitable for unattended or headless maintenance because updates and restarts depend on an interactive desktop session.
Headless Windows and Linux
Use SteamCMD with a controlled directory and run the server under the intended service account. Do not update as one user and start as another unless both accounts have deliberate permissions to the same files. A service account that cannot read the updated directory can look like a failed game update even when SteamCMD completed successfully.
Restart and verify the new build
- Start the server with
StartServer64.baton Windows, or use the Linux service/start script configured for your installation. - Watch the startup output until the server reports that it is ready. Do not invite players while Workshop downloads or world initialization is still running.
- Check the startup log for the expected branch and build. Compare it with the build shown by the Steam client or SteamCMD update output.
- Confirm that the expected server name, settings, map, and player database loaded.
- Join with a test client before announcing that the server is open.
A successful SteamCMD download only proves that files were obtained and validated. The startup log is the authoritative check that the executable, branch, configuration, and save loaded together.
Keep Workshop mods synchronized
At startup, the server checks every ID listed in WorkshopItems and downloads newer Workshop versions. The separate Mods value controls which installed mod identifiers are enabled. Record both values before changing anything; an update is easier to diagnose when you can distinguish a game-file change from a mod-list change.
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- Start with the existing
WorkshopItemsandModsvalues. - Allow the server to finish its Workshop checks and downloads.
- Read the startup log for download failures, missing items, or changed revisions.
- Restart only when the server’s configuration or the mod instructions require it, and wait for the ready message again.
- Have every player update the game to the same branch and let their Steam client download the same Workshop revisions.
- Test a join with a client that has no stale duplicate mod folder or manually installed copy.
The error “workshop item version is different than the server” means the server and client have downloaded different revisions of the same item. Do not solve it by randomly deleting the world. Compare the item IDs and revisions, let both sides complete their downloads, and remove or update a deliberately changed mod only after preserving the original list and backup.
Build 41 and Build 42 save planning
Build 41 and Build 42 require separate branch and save planning. A Build 41 multiplayer save cannot be opened by Build 42, so keep the original Build 41 server and its backup intact if you want to continue that world. Create a separate Build 42 installation and save path rather than pointing a new branch at the old multiplayer directory.
Within one major branch, a patch update is generally intended to preserve the world in place. That does not guarantee that every mod is save-neutral: a mod author can change data structures, remove items, or require a migration step. Read the mod’s release notes and test the backed-up copy first when a mod update is known to affect saves.
Network checks after an update
A server can start correctly while outside players still cannot connect. LAN-only play normally does not require router forwarding. Internet players need the host firewall and router to allow the UDP ports configured by the server. A common Linux setup uses UDP 16261 for the main port and 16262 for the first additional player port, but these are defaults from a particular guide, not universal requirements. Verify the values in your server configuration and forward the complete configured range when necessary.
- Check that the server is listening on the expected UDP ports.
- Allow those ports through the operating system firewall.
- Forward the same ports from the router to the host’s local address for Internet play.
- Make sure the host’s local address has not changed after a reboot.
- Test from outside the LAN; a connection from the host itself does not prove that router forwarding works.
Why players cannot join after the update
The server and client use different branches
Check the branch selected in each player’s Steam properties and the branch reported in the server startup log. A Build 41 client cannot join a Build 42 server, and a client on the default branch will not match a server intentionally pinned to a legacy branch. Select one compatible branch for the group, or maintain separate installations.
The Workshop revision differs
Use the exact item-version error as a clue. Confirm that the server finished downloading each WorkshopItems entry and that every client has finished its corresponding Steam download. Compare the saved Mods and WorkshopItems lists before adding or removing anything.
The server is not ready yet
Large worlds and mod collections can take time to initialize. Wait for the ready message and inspect the log for a failed Workshop download, a missing dependency, or a startup exception before troubleshooting the network.
The save or configuration was changed
Stop the server and compare the live Zomboid/Server/ and multiplayer save directories with the dated backup. Restore only after stopping the process. If the failure began immediately after a mod or branch change, return to the matching branch and restore the pre-change files before testing one change at a time.
Internet connectivity is blocked
For remote players, verify UDP firewall rules, router forwarding, the configured port numbers, and the host’s current local address. A successful LAN connection narrows the problem to those external network controls.
Rollback when an update breaks the world
- Stop the server cleanly and prevent an automatic restart while you work.
- Keep the failed installation and its logs for diagnosis; do not overwrite your only evidence.
- Restore the dated
Zomboid/Server/directory, multiplayer save, and applicable player database. - Use SteamCMD to return the server files to the branch that matches that backup. A legacy branch requires its branch argument.
- Start the server and verify the old build, configuration, mods, and save before allowing players back in.
- Investigate the update on a copied test installation, not on the restored production world.
Redownloading binaries is straightforward; recovering an overwritten save is not. Keep the backup until the new build and its mod set have survived a complete test session.
Choosing an update method and hosting arrangement
| Approach | Advantages | Trade-offs |
|---|---|---|
| Steam client Tools install | Graphical installation and familiar library controls on Windows. | Less convenient for unattended updates, scheduled restarts, and headless hosts. |
| SteamCMD | Repeatable command, controlled install directory, and easy integration with service scripts. | Requires command-line setup, permissions management, and your own backup procedure. |
| Self-hosted | Direct control over files, branch selection, mods, backups, and network settings. | You administer updates, uptime, firewall rules, router forwarding, and recovery. |
| Managed hosting | The provider may handle updates, restarts, backups, and network administration. | Less control over maintenance timing, filesystem access, branch choices, and recovery procedures. |
Whichever arrangement you use, the operational requirements remain the same: identify the branch, stop before copying data, preserve the world and configuration, update the dedicated-server files, verify startup, and align every client and mod revision.
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A repeatable maintenance checklist
- Announce downtime and record the current branch and build.
- Stop with
quitor the service manager and wait for a clean exit. - Back up
Zomboid/Server/,Zomboid/Saves/Multiplayer/<servername>, and the Linux player database when used. - Save the current
ModsandWorkshopItemsvalues. - Run SteamCMD with
+app_update 380870 validate, adding the exact legacy branch argument when required. - Start with
StartServer64.bator the Linux start/service script. - Read the startup log for branch, build, save, and Workshop errors.
- Confirm the configured UDP ports and external firewall/router access if remote players connect.
- Test one client before reopening the server.
- Retain the dated backup until the updated world and mod set have been proven stable.
Key facts to keep with your server documentation
The dedicated-server app ID is 380870. Build numbers, branch labels, Workshop behavior, and default ports are volatile, so record what Steam and the startup log show during each maintenance window. The durable rule is compatibility: the server, world, clients, and mods must agree. Build 41 saves cannot be loaded by Build 42, while a same-branch patch is normally updated in place only after a verified backup.
Quick Recap
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