Introduction
Most Project Zomboid servers run themselves once they're set up. When something does go sideways, it's usually one of a handful of things: a bad mod update, a stale Workshop cache, or the JVM running out of headroom. This is the list I reach for when a ticket lands.
New to PZ hosting? Start with the Getting Started Guide. For settings questions, see the Server Configuration Guide.
Connection Issues
Players can't connect
Nine times out of ten the server is still booting. First boots (and post-update boots) can take a few minutes while PZ rebuilds caches. Open Web Console in the sidebar and wait until you see the "server is listening" lines before you panic.
If it's already up and still refusing connections, check the obvious stuff:
- Open the LOW.MS panel and confirm the service shows as running in Current Activity & Stats.
- Confirm players are using the IP and port from your service page. PZ uses UDP 16261 AND 16262 — both are required, both are game/connection ports, neither is a "Steam query" port despite what a lot of old guides claim. Source: pzwiki.
- If you set a password in
servertest.ini(via Configuration Files), double-check it. Case sensitive. - Everyone needs to be on the same game build. If you flipped the server to B42 unstable, every client has to opt in on Steam too.
Players get kicked mid-session
Usually desync, and usually RAM. PZ is a Java app and it leaks slowly. Open Current Activity & Stats, watch RAM and CPU for a few minutes under load, and if you're pegged near the top you've outgrown your tier. Zombie count is the next biggest lever — dropping from Insane to Normal is a huge win. While you're in Configuration Files, set SaveWorldEveryMinutes to 10 or 15; anything under 5 causes visible stutters on larger worlds.
Server not showing in the browser
Public listing can take several minutes to propagate after a restart. In the meantime, direct connect by IP works fine and is what I'd tell your players to do. Make sure Open=true and Public=true are both set in servertest.ini, and that both UDP 16261 and 16262 are reachable.
Server Crashes
Crashes on startup
First place I look is Log Viewer — it tails ~/Zomboid/console.txt in the browser, which is faster than SFTP. Rotated logs live in ~/Zomboid/Logs/ if you need history.
The three usual culprits: a mod that didn't survive the latest game patch, a corrupt save, or the JVM running out of heap during world load. Clear WorkshopItems and Mods in servertest.ini, restart, and see if it boots clean. If it does, it's a mod. If it doesn't, it's the save or memory.
Crashes after hours or days
Classic slow leak. Schedule a daily restart via Scheduled Tasks and the problem tends to vanish. If you see java.lang.OutOfMemoryError: Java heap space in console.txt, that's your RAM tier — it's not coming back without either a plan upgrade or a lighter world.
A few real perf levers you can pull before throwing money at it: raise ZombieUpdateDelta (lowers zombie update frequency), drop the zombie population a notch, or switch to shamblers-only. BloodSplatLifespanDays gets recommended a lot but it only controls visual decals — the RAM impact is negligible, so don't bother tuning it for performance.
Out of memory
When console.txt shows java.lang.OutOfMemoryError: Java heap space, the JVM has hit its ceiling. On LOW.MS, RAM is tied to the plan tier — you don't hand-edit ProjectZomboid64.json Xmx/Xms values the way a self-hoster would, you upgrade the plan. See Project Zomboid hosting plans for the current tiers.
Mod Issues
Mods won't load
Both WorkshopItems (the numeric IDs) and Mods (the folder names) have to be set in servertest.ini, semicolon-separated, no spaces. Miss either one and nothing loads. The Mods value is the internal folder name, not the Workshop title — File Manager and a look inside steamapps/workshop/content/108600/<id>/mods/ is the fastest way to find it.
Mod changes need a full restart. Soft reloads don't pick them up.
"Mods are out of sync. Please update your mods."
This is the single most common PZ mod error and the fix is almost always a stale Workshop cache on the server side. Self-serve path:
- Stop the server.
- Click Steam Update in the sidebar.
- Start it back up.
If that doesn't clear it, go to File Manager, delete steamapps/workshop/content/108600/ entirely, then hit Steam Update and restart. Steam will re-download everything from scratch. Tell your players to unsubscribe and resubscribe on their end too — both sides need matching file hashes.
Mod conflicts
Binary search beats guessing. Disable half your mods in Configuration Files, restart, see if the crash goes. Keep halving. Dependency mods like tsarslib need to load before the mods that use them — if you're getting null errors on startup, that's usually the cause. DoLuaChecksum=true is great for security but it'll boot players the instant a mod updates on only one side; flip it to false while you're debugging.
Performance Issues
Lag and low TPS
Open Current Activity & Stats and look at CPU first. PZ is heavily single-thread-bound, so the per-core speed matters more than core count. If you're running a high-player server on an older box, the Latest CPU Performance tier (Ryzen 7950X/9950X) is worth a look — it's the biggest tick-rate improvement available. Details on the plan page.
Past that, the biggest dials are zombie population and player count. Urban-focused distribution is cheaper than uniform, and pulling ZombieCount down one notch is essentially free performance.
Slow world loading
Fresh chunks are expensive. If players get stutter when they cross into new territory, a daily restart via Scheduled Tasks clears cached state and helps more than you'd think. Very large explored worlds eventually just need more RAM — there's no clever config knob that fixes that.
World and Save Issues
Corrupted world save
Stop the server, open Cloud Restore in the sidebar, pick the most recent snapshot from before the problem, restore. Cloud Backup and Cloud Restore are separate sidebar items — Backup is the one you run on a schedule, Restore is the one you reach for when things are on fire. If you've been running long enough to have PZ's own BackupsCount/BackupsPeriod snapshots, those live under Zomboid/Saves/ and you can pull them via File Manager.
Fresh start
Stop the server, use File Manager to delete or rename Zomboid/Saves/Multiplayer/servertest/, start it again. It'll generate a new world on boot. Take a Cloud Backup first — this wipes everything.
"My character got reset"
Player data lives in players.db, a single SQLite file at Zomboid/Saves/Multiplayer/servertest/players.db. It's not one file per player, so "check if their file exists" isn't a thing — the whole database either loaded or it didn't. If characters have gone missing across the board, something's wrong with that file and a Cloud Restore is your fastest path back. Individual missing characters are almost always a SteamID change or a B41→B42 save that didn't migrate cleanly.
Build 42
B42 is still on the unstable branch. Multiplayer landed in December 2025 and Indie Stone themselves recommend keeping it to 20 players or fewer for now. I wouldn't run it on a production community server yet unless your players know what they signed up for.
On LOW.MS, branch switching is done with Switch to Latest Experimental in the sidebar — that's a TCAdmin button, not a -beta flag. Clicking it points SteamCMD at the unstable branch and pulls the B42 build next time Steam Update runs.
Plan for more headroom than B41. B42 adds animals, expanded crafting, and basements, all of which are noticeably heavier. I don't have a hard floor to quote — Indie Stone haven't published one — but if you were comfortable on your current tier with B41, expect to want the next tier up on B42.
If B42 won't start at all, it's almost always a B41 save that isn't forward-compatible. Rename the save folder via File Manager and let it generate fresh.