Minecraft Server Not Starting: Troubleshooting Guide (2026)

Minecraft Server Not Starting: Troubleshooting Guide (2026)

Your Minecraft server will not start. Here are the most common causes and how to fix each one.

1. EULA Not Accepted

Error: You need to agree to the EULA in order to run the server.

Fix:

1. Open eula.txt in the server folder
2. Change eula=false to eula=true
3. Save and start the server again

2. Wrong Java Version

Error: Unsupported class file major version or UnsupportedClassVersionError

| Minecraft Version | Required Java | |-------------------|---------------| | 1.17 | Java 16+ | | 1.18 to 1.20.4 | Java 17+ | | 1.20.5+ | Java 21+ |

Fix:

java -version

If wrong, install the correct version and update your start script.

3. Port Already in Use

Error: Failed to bind to port or Address already in use

Fix:

• Another process uses port 25565
• Check with netstat -tlnp | grep 25565 (Linux) or netstat -aon | findstr 25565 (Windows)
• Stop the conflicting process or change server-port in server.properties

4. Not Enough RAM

Error: OutOfMemoryError or server freezes during startup

Fix: Increase RAM in your start command:

java -Xms4G -Xmx4G -jar server.jar nogui

Minimum RAM by server type:

| Server Type | Minimum RAM | |-------------|-------------| | Vanilla (5 players) | 2 GB | | Paper (10 players) | 3 GB | | Forge/Fabric modded | 4 to 6 GB | | Heavy modpack | 8 GB+ |

5. Corrupted World

Symptoms: Server crashes immediately or after loading world

Fix:

1. Check logs/latest.log for chunk errors
2. Try a world backup if available
3. Delete the corrupted region file from world/region/
4. Region files are named r.X.Z.mca. The log tells you which one is corrupt

6. Mod or Plugin Conflict

Symptoms: Crash on startup after adding new mods/plugins

Fix:

1. Remove all mods/plugins
2. Start server (should work)
3. Add them back one at a time
4. The last one added before the crash is the problem
5. Check version compatibility

7. Missing Libraries

Error: ClassNotFoundException or NoClassDefFoundError

Fix:

• Re-download the server jar
• For Forge: re-run the installer with --installServer
• For Fabric: re-run the Fabric installer

8. File Permission Issues (Linux)

Error: Permission denied or Access denied

Fix:

chmod +x run.sh
chown -R mcuser:mcuser /path/to/server/

Reading Crash Logs

The most important file is logs/latest.log. Look for:

• Lines starting with ERROR or FATAL
• The first exception in a stack trace
• Caused by: lines (the real error is often here)

For modded servers, also check crash-reports/ folder.

Quick Checklist

1. EULA accepted?
2. Correct Java version?
3. Port 25565 available?
4. Enough RAM allocated?
5. World files intact?
6. All mods/plugins compatible?
7. Correct file permissions?
8. Firewall allows port 25565?

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