World Corruption
The server cannot load the world and reports level.dat as corrupted. This is the world's master file, the good news is Minecraft keeps a backup copy, so recovery is often quick.
What does this error mean?
level.dat stores core world data (seed, spawn, game rules, time). If it is damaged, usually from a crash or power loss mid-save, the world will not load. Minecraft keeps a previous copy named level.dat_old for exactly this situation.
level.dat corrupted
Most Common Causes
- A crash or kill during a world save.
- The disk filling up while writing the file.
- Sudden power loss or an unclean shutdown.
- Underlying disk or filesystem errors.
- Two processes writing the same world at once.
How To Diagnose
- Check the world folder for level.dat_old next to level.dat.
- Verify the disk has free space ('df -h' on Linux).
- Look for I/O errors in the system logs.
- Confirm only one server process is using the world.
Recommended Fixes
- Restore level.dat_old
Copy level.dat_old over level.dat (back up the broken one first) and restart. - Restore from backup
If both files are bad, roll the world back to your most recent good backup. - Free disk space
Clear space so saves can complete, then restart the server. - Repair with an NBT editor
As a last resort, open the file in an NBT tool to recover salvageable data.
Frequently Asked Questions
Usually not, level.dat_old or a backup typically restores everything but the last save.
Always stop with the 'stop' command, keep free disk space, and run scheduled backups.
It is the previous version of level.dat that Minecraft keeps automatically as a safety net.