Tools / Project Zomboid / Fixes
Fix Project Zomboid Port Already in Use
The game server tried to bind a UDP/TCP port that another process is already using. Only one process can listen on the same IP and port.
When this is the problem
- The log contains java.net.BindException or Address already in use.
- A second server instance was started while the old one was still running.
- Changing mods does not affect the failure; startup stops at networking.
Repair steps
- Stop duplicate Project Zomboid server processes and wait a few seconds for the port to release.
- Check which process owns the port with ss -lunpt or your host panel's process view.
- If running multiple servers, give each server a unique DefaultPort and matching firewall rule.
- Restart after changing ports, then check the new log for a successful network bind.
Prevent it next time
- Use one process manager or host panel, not manual shell starts plus panel starts.
- Reserve a unique port range for every PZ server on the machine.
- Keep firewall and port-forwarding rules in sync with DefaultPort.
Check the fresh log
After changing the server, restart once and analyze the newest log tail. Do not keep debugging the old failed startup log after the config changes.