How to Fix "Failed to Check Session Lock" on a Minecraft Server
This error means two copies of the world tried to open at once, or the lock file is stuck. Here's how to clear it on Beacon.
Failed to check session lock, aborting appears when Minecraft can't take the lock on your world folder. Each world has a small file called session.lock; the server holds it while the world is open so nothing else changes it at the same time.
Why it happens
- The server was started twice, or an old process hadn't finished shutting down when a new one started.
- The server crashed and left the lock behind.
- The world was edited while the server was running, for example by uploading a world over SFTP or running a map editor on it.
How to fix it
- Open your server and go to Console.
- Click Stop. If it hasn't stopped after a minute, use Kill.
- Wait until the status shows the server is offline.
- Go to Files and open your world folder (usually
world). - Delete
session.lock. Minecraft makes a new one on the next start, so this is safe. - Go back to Console and click Start.
Warning
Never edit or replace world files while the server is running. Stop it first, make your change, then start it again.
If it keeps happening
- Check that only one process uses the world. A plugin or mod that copies or backs up worlds while the server runs can cause it.
- Look at the full log in
logs/latest.log(in Files) for the first error, not just the last one. - Restore a recent backup from Backups if the world won't load at all.
Still stuck? Open a ticket and include your latest.log.