criticalCrash ReportsAffects: 1.13+
How to Fix DataFixer / DFU Crash
Fix DataFixer crashes by increasing RAM, upgrading worlds in version steps, and removing interfering mods.
Quick Fix
Increase RAM allocation to at least 4GB. DFU (DataFixerUpper) needs extra memory when upgrading old worlds.
Error Message
Error during DataFixer initialization / DFU failedHow to Fix
1
Increase RAM: -Xmx4G or higher
2
If upgrading from a very old version, do it in steps (1.12 > 1.13 > 1.16 > 1.18 > 1.21)
3
Backup and optimize the world in singleplayer before server use
4
Remove LazyDFU or DataFixerSlayer if they cause crashes
Common Causes
- World data from a much older version that cannot be upgraded
- Corrupted level.dat preventing data fixing
- Insufficient memory for DFU processing
- Mod interfering with data fixers
Diagnostic Steps
- Backup the world
- Increase RAM allocation
- Open in singleplayer to trigger the upgrade
- Wait for the upgrade to complete
- Then move to server
FAQ
What is DFU?
DataFixerUpper is Minecraft's system for upgrading old world data to new formats. It runs when you open a world from an older version.