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Failed to Bind to Port

The server quits during startup complaining that it cannot open its network port. Nothing is wrong with the world or mods, another program is already holding the port the server wants to use.

What does this error mean?
A Minecraft server listens on a TCP port (25565 by default). 'Address already in use' means that port is occupied, usually by a previous server instance that did not shut down cleanly, or by another service on the machine. 
Address already in use
Most Common Causes
  • A previous server instance is still running in the background.
  • A crashed Java process never released the port (a zombie process).
  • Two server instances are configured to use the same port.
  • Another application on the machine already uses that port.
  • A wrong server-port value combined with port forwarding or a Docker mapping.
How To Diagnose
  1. On Linux run 'ss -tulpn | grep 25565' (or 'netstat -tulpn') to see which process owns the port.
  2. On Windows run 'netstat -ano | findstr 25565' to get the PID using it.
  3. List running Java processes with 'jps -l' or 'ps aux | grep java'.
  4. Confirm the server-port value in server.properties matches what you expect.
Recommended Fixes
  • Stop the old process
    Kill the lingering Java process (Linux: 'kill <pid>'. Windows: 'taskkill /PID <pid> /F'), then start the server again.
  • Change the port
    Set a free port in server.properties (e.g. server-port=25566) if you intentionally run multiple servers.
  • Ensure a clean shutdown
    Always stop the server with the 'stop' command so it releases the port properly.
  • Free a reserved port
    If another service owns the port, move that service or pick a different Minecraft port.
Analyze My Log
Frequently Asked Questions

Use 'ss -tulpn' on Linux or 'netstat -ano' on Windows to map the port to a process ID.

Yes, give each one a unique server-port and forward both ports if needed.

25565 for Java Edition. You only need to set it explicitly when running multiple servers.