Server stuck in a restart loop or will not start after an update

The server keeps crashing on startup since I updated.

Something in the update does not match: a plugin or mod for the old version, a Java version problem, or a config error. The console shows which.

Before you start: A backup (Backups) from before the update if you have one.

Step by step

1. Stop the server so it does not loop.
2. Start it once and read the console from the top until it stops: note the first ERROR.
3. If a plugin/mod is named, update it to a build for the new version, or remove it temporarily.
4. If it mentions "class file version" or Java, see the Java version guide.
5. If it mentions a config file and a line, fix that line (see the YAML guide).
6. If you cannot fix it now, restore the backup from before the update, or reinstall the previous version in Versions.
7. Next time, update on a test copy first, or take a backup right before updating.

Check it worked: The server reaches "Done" and stays running.

Why it happens: Updating Minecraft changes internals that old plugins and mods depend on.

If it loops with no clear error, send support the last 100 console lines.

More guides on Crashes, startup failures, and errors:

• Find and read crash reports and logs
• Java version errors
• Failed to bind to port or unable to access jarfile
• Crash or error caused by a plugin
• Crash caused by a mod
• Server freezes or watchdog kills it