How to Fix a SkyFactory 5 Server That Keeps Crashing
SkyFactory 5 runs on Forge 1.20.1, and most server crashes come down to one of a few specific, well-documented causes rather than a mystery mod conflict.
See the SkyFactory 5 pack page for boot-tested RAM data before you chase anything else.
1. Corrupted jei-server.toml
A crash right after the "reading world data" log line is often a corrupted jei-server.toml config file rather than a world problem at all.
Fix: rename the file to jei-server.toml.bak (or delete it) and let the server regenerate a clean copy on the next boot.
2. Client/server version mismatch
Clients need the exact same pack version as the server — a mismatch causes join failures or crashes that look server-side but aren't. Check this before troubleshooting anything else if the problem is isolated to specific players connecting.
3. Controllable mod conflict
This mod was flagged as a crash contributor and made optional in a past pack update specifically to alleviate the issue. If you're on an older release and seeing related instability, updating or removing it from the server is worth trying.
4. RAM below the 8 GB floor — and sometimes above it too
8 GB is the pack's own recommended floor, and 6 GB is the hard minimum. Below that, expect lag building into tick-timeout crashes rather than a clean error.
Late-game worlds with large auto-farms and built-out resource chains have pushed past 10 GB in reported cases — if you've ruled out the config and version issues above and memory errors persist at a reasonable allocation, heavier automation is the likely reason, not a bug.
FAQ
My server crashes right after 'reading world data' — what's wrong?+
This is often a corrupted jei-server.toml config file. Rename it (to jei-server.toml.bak, for example) or delete it so the server generates a fresh copy on next boot.
I allocated 10 GB and I'm still crashing with memory errors — why?+
Large auto-farms and fully built-out resource chains can push even well above the 8 GB floor in late-game SkyFactory 5 worlds. If you've ruled out a config or version issue, treat heavy automation as a real reason to go past the baseline, not just a buffer.
Is the Controllable mod a known problem?+
It was flagged as a crash contributor and made optional in a past SkyFactory 5 update. If you're on an older pack version and seeing related crashes, updating or removing it is worth trying.
Host SkyFactory 5 on hardware sized for its real floor
CoalHost starts SkyFactory 5 servers at the pack's measured 8 GB floor by default, with backups in place before anything risky.
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