Project Zomboid builds and common errors

All the files below are in Files, .cache, Server in the panel . The settings file is named after your server, servertest.ini by default. Stop the server before editing it.

Build 41 or Build 42

Build 42 is the current version and what new servers run. Build 41 is still available on Steam as the legacy41 branch.

Your situation	Run
New server or new world	Build 42
Keeping an old Build 41 world	Build 41
Mods that only support Build 41	Build 41

Server and every player must be on the same build. Players switch in Steam: right-click Project Zomboid, Properties, Betas.
Build 41 and Build 42 worlds are not compatible. Back up before switching.
To run Build 41, set the Steam beta branch to legacy41 on the Startup tab if your server shows that field, then press Reinstall Server under Settings. If there is no such field, open a ticket and we will set it.

Make the server private

Password: set Password= in the settings file. Players type it in the server password box when they add the server.
Whitelist: set Open=false. Only players with an account on the server can join. Add them from the Console:

Command	What it does
`adduser <username> <password>`	Creates an account for a player
`addusertowhitelist <username>`	Whitelists a player who is online now
`addalltowhitelist`	Whitelists everyone online
`removeuserfromwhitelist <username>`	Removes a player

Other related settings: AutoCreateUserInWhiteList=true adds new joiners automatically, DropOffWhiteListAfterDeath=true removes players when they die, and Public=false hides the server from the public list.

“Workshop version mismatch” when joining

The server has an older copy of a mod than the player, or the reverse.

Stop the server.
In Files, open steamapps/workshop and delete appworkshop_108600.acf.
Start the server. It checks every Workshop mod for updates, which can take a few minutes with many mods.

If one player still gets the error, they unsubscribe from all Project Zomboid Workshop items in Steam and join again; the game downloads the right versions.

“No space left on device” on startup

If the Console shows java.io.IOException: No space left on device right after Start making backup, the startup backup is opening too many files at once (big saves have tens of thousands of files). It is usually not your disk.

Stop the server and open the settings file.
Change BackupsOnStart=true to BackupsOnStart=false.
Save and start the server.

Keep regular backups with the panel’s Backups tab instead. If your disk really is full, see disk full.

“Port Closed” warning

This warning means the player is connected through Steam Relay instead of directly. The server still works, but play can be laggier.

Join from Multiplayer, Favorites with the IP and port from the panel, with Use Steam Relay unticked. Joining from a Steam invite always uses the relay.
If you uploaded your own .ini, its DefaultPort= and UDPPort= must match the ports your server has in the panel, not the game’s defaults of 16261 and 16262. Fix them and restart.

There is no router setup to do on our side; your server’s ports are already open.