Minecraft Server Not Starting? Here's How to Fix It

Read the Logs First

When your Minecraft server refuses to start, the answer is almost always in the logs. Check logs/latest.log, the last 20-50 lines before the process exits contain the error. If the log file is empty or missing, the problem is pre-JVM (wrong Java path, missing jar, permissions). Here is a systematic minecraft server not starting fix for every common scenario.

Cause 1: Wrong Java Version

Minecraft 1.21+ requires Java 21. If you see errors like UnsupportedClassVersionError or class file version 65.0, your Java is too old.

• Check your version: java -version
• Install Java 21: sudo apt install temurin-21-jre (Debian/Ubuntu) or download from Adoptium.
• If multiple Java versions are installed, use sudo update-alternatives --config java to select the right one, or use the full path in your start script.

For more details, see our Java version errors guide.

Cause 2: EULA Not Accepted

The server generates eula.txt on first run and will not proceed until you change eula=false to eula=true. The log will clearly say You need to agree to the EULA.

Cause 3: Port Already in Use

If another process (or a previous server instance) is using port 25565, the server will fail with Address already in use. Find what is using the port:

sudo lsof -i :25565
# or
sudo ss -tlnp | grep 25565

Kill the conflicting process or change your server's port in server.properties.

Cause 4: Corrupted Server Jar

An incomplete download or a file system error can corrupt the jar. Re-download the server jar from papermc.io (or the relevant source) and replace the existing file. Verify the SHA256 hash if available.

Cause 5: Plugin Crashes the Server on Load

If the server started fine before you added a plugin, the plugin is likely the cause. Check the log for plugin-related stack traces. Quick fix: move the suspect plugin out of the plugins/ folder and restart. See plugin compatibility issues for in-depth troubleshooting.

Cause 6: Insufficient Permissions

On Linux, the user running the server must have read/write access to the server directory. If you see Permission denied in the logs:

ls -la /path/to/server/
# Fix ownership:
sudo chown -R mcuser:mcuser /path/to/server/

Cause 7: Not Enough RAM

If -Xmx requests more RAM than the system has available, the JVM cannot start at all. You will see Could not reserve enough space for object heap. Lower -Xmx to fit within available system RAM (leave at least 1-2 GB for the OS).

Cause 8: Corrupted World Data

If level.dat is corrupted, the server fails during world loading. Restore from backup or rename the world folder and let the server generate a fresh world to confirm this is the issue. See world corruption recovery for repair steps.

Quick Diagnostic Steps

1. Run java -version and confirm it matches server requirements.
2. Open eula.txt and confirm eula=true.
3. Check logs/latest.log for the specific error.
4. Try starting with zero plugins, move the plugins/ folder temporarily.
5. Try a fresh server jar and config in a clean directory.

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