Common Minecraft Server Errors
Server won't start? Here are the most common reasons and how to fix them.
1. "You need to agree to the EULA"
Error: The server stops immediately after downloading files.
Fix: Open the eula.txt file and change eula=false to eula=true. Save and restart.
2. "Java version mismatch" / "Unsupported Class Version"
Error: Exception in thread "main" java.lang.UnsupportedClassVersionError
Cause: You are using an old version of Java for a modern Minecraft version.
Fix:
- Minecraft 1.21+ needs Java 21.
- Minecraft 1.18-1.20 needs Java 17.
- Minecraft 1.16 needs Java 8 or 11.
3. "Failed to bind to port"
Error: FAILED TO BIND TO PORT!
Cause: Another server is already running on port 25565, or you are trying to use a port that is already taken.
Fix:
- Check if a "ghost" server process is running in the background and kill it.
- Change the `server-port` in `server.properties` to something else (e.g., 25566).
4. "Watchdog" Crash
Error: The server has stopped responding! (Watchdog)
Cause: The server is frozen or lagging so badly it shut itself down.
Fix: Increase the max-tick-time in server.properties to -1 (to disable it) or 60000. Also, check your CPU/RAM usage.