Nothing’s more frustrating than trying to launch your Minecraft server only to see “Failed to start the minecraft server” with “The world directory is being used by another instance of Minecraft” plastered across your console. This error means exactly what it says—something’s already accessing your world files, and Minecraft won’t risk corrupting your data by letting two processes fight over the same files.
What the “World is Being Used” Error Actually Means
This error occurs when Minecraft detects a session.lock file in your world directory. When your server starts, it creates this lock file to prevent multiple server instances from accessing the same world data simultaneously. If the lock file already exists, Minecraft assumes another process is using the world and refuses to start.
The most common causes are a server that didn’t shut down cleanly, a crashed Java process still running in the background, or accidentally launching multiple server instances. Less commonly, file permission issues or antivirus software can interfere with the lock file mechanism.
Quick Fix: Stop All Running Server Instances
Before diving into file deletion, check if your server is actually still running somewhere.
Windows Users
- Press Ctrl + Shift + Esc to open Task Manager
- Click the “Details” tab
- Look for any java.exe or javaw.exe processes
- Right-click and select “End Task” for each Java process
- Try starting your server again
Linux/macOS Users
Open your terminal and run:
ps aux | grep java
Look for any Minecraft server processes. Kill them using:
kill -9 [PID]
Replace [PID] with the actual process ID number from the first column. If you’re running multiple Java applications, make sure you’re only killing the Minecraft server process.
Delete the Session Lock File
If no server processes are running but you’re still getting the error, the lock file is stuck. Here’s how to remove it safely.
Locate Your World Directory
Your world folder is typically named “world” (or whatever you specified in server.properties as level-name). Navigate to your main server directory and open the world folder.
Remove the Lock File
Inside your world directory, look for a file named session.lock. Delete it. That’s it. This file is automatically recreated when the server starts, so deleting it won’t harm your world data.
If you don’t see the file, you may need to enable viewing hidden files in your operating system. On Windows, open File Explorer, click “View,” and check “Hidden items.” On macOS, press Cmd + Shift + . in Finder.
Advanced Solutions for Persistent Problems
Check File Permissions
Sometimes the server can’t properly create or delete the session.lock file due to permission restrictions. On Linux/macOS, ensure your server has proper ownership:
sudo chown -R yourusername:yourusername /path/to/server
On Windows, right-click your server folder, select “Properties,” go to the “Security” tab, and ensure your user account has full control.
Antivirus and Backup Software Interference
Real-time antivirus scanning or automated backup tools can lock world files while scanning or copying them. Add your Minecraft server directory to your antivirus exclusion list. If you’re using backup software, configure it to skip the session.lock file or schedule backups when the server isn’t running.
Network Share and Cloud Storage Issues
Running a Minecraft server from a network drive, Dropbox, or OneDrive is asking for trouble. The lock file mechanism doesn’t work reliably across network protocols. Always run your server from local storage. If you need remote access, use proper server hosting or remote desktop solutions instead.
Preventing Future Lock File Errors
The best fix is prevention. Always shut down your server properly using the /stop command in the console rather than force-closing the window or killing the process. This gives Minecraft time to save world data and remove the session.lock file cleanly.
If you’re experiencing memory-related crashes that leave lock files behind, address the underlying stability issues. Frequent crashes often indicate insufficient RAM allocation or Java configuration problems.
Consider using a server wrapper or management tool that monitors the Java process and handles cleanup if the server crashes unexpectedly. Many server hosts include these features built-in.
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When the World Directory Is Actually Corrupted
Rarely, repeated improper shutdowns can corrupt world data beyond just the lock file. If you’ve removed session.lock and stopped all processes but still can’t start the server, check your server logs for additional error messages.
Look for errors mentioning specific region files (like “region/r.0.0.mca”). These indicate actual world corruption. You may need to delete corrupted region files (losing that chunk of your world) or restore from a backup.
This is why regular backups are non-negotiable. Before attempting any fixes beyond removing the lock file, make a complete copy of your world directory. If something goes wrong, you can always restore the backup and try again.
Multiple Server Instances on the Same Machine
If you’re intentionally running multiple Minecraft servers on one machine, each needs its own completely separate directory. You can’t run two servers from the same folder, even if they’re configured for different ports. The session.lock mechanism works at the directory level, not the server instance level.
Create separate folders like “server1,” “server2,” etc., each with its own complete server installation and world data. This prevents any conflict between instances.
Frequently Asked Questions
Can I just ignore the session.lock file?
No. While you can delete it to bypass the error, you should never actually run two server instances on the same world. The lock file exists to prevent catastrophic data corruption. If two processes write to the same world files simultaneously, you’ll lose data or corrupt the entire world.
Does this error mean my world is corrupted?
Not usually. In most cases, it’s simply a leftover lock file from an improper shutdown. The error is actually Minecraft protecting your world from potential corruption. Once you remove the lock file and ensure no other processes are running, your world should load normally.
Why does this keep happening after server crashes?
When Minecraft crashes instead of shutting down properly, it can’t remove the session.lock file. If you’re experiencing frequent crashes, the lock file is a symptom, not the disease. Address the underlying stability issues—usually related to insufficient memory allocation or incompatible mods.
Can I automate removing the lock file on startup?
Yes, but it’s risky. You could create a startup script that deletes session.lock before launching the server, but this removes the safety check that prevents running multiple instances. Only do this if you’re absolutely certain you’ll never accidentally launch two servers simultaneously.
Will this error affect my players’ data?
No. The session.lock file only affects server startup. Player data, inventories, and statistics are stored separately and aren’t impacted by this error. However, if you force multiple instances to run simultaneously by repeatedly deleting the lock file, you risk corrupting everything.
The “world is being used” error is annoying but straightforward to fix. Stop any running server processes, delete the session.lock file, and restart cleanly. If you’re constantly fighting this issue, it’s time to either improve your shutdown procedures or let someone else handle the infrastructure while you focus on what actually matters—your Minecraft community.
