Did a mysterious Lost & Found folder just appear on your Mac? It could mean trouble

If you can't empty that folder, beware!

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Joseph Pierpoint discovered a folder in his Trash labeled “Lost & Found.” When he opened it, he found it contained over 50,000 files. Worse, “Any attempts to send these files to the Trash are thwarted by interruptions that state that this kind of solution is infeasible for one reason or another.”

The Lost & Found folder relates to a low-level Unix filesystem-recovery utility. When fsck (filesystem check) runs, it looks not just at files that appear properly referenced in a filesystem’s directory, but also at anything it finds that looks like a file but isn’t appropriately noted in that record structure. In Unix, it stores these recovered bits in a folder named lost+found. macOS exposes recovered files in Lost & Found, and drops it in the Trash because these items typically aren’t useful, but it doesn’t delete them in case a user wants to examine what was recovered.

The “journaled” part of Apple’s HFS+ Journaled disk partition type refers to tracking and recording changes so that they can be applied later if there’s a failure while they’re being made directly. In this case, it’s macOS updating the HFS+ directory. If something goes wrong while that’s happening, before the Journaled format, if you’re as old as I am, you might recall having to run repair operations that could take tens of minutes or hours to rebuild directory structures. Journaling largely prevents that.

However, after a crash or a forced reboot, macOS (like most Unix and Unix-variant systems) runs fsck at startup. Any files it finds as pieces that aren’t referenced in the filesystem’s index, it drops into lost+found. Files being in that folder don’t necessarily mean your drive is in trouble, but it’s not great news, either. Being unable to delete Lost & Found in the Trash also could mean something’s wrong.

I’d suggest first restarting a Mac and trying to empty the Trash again. If that fails, follow these steps.

  1. Restart into Recovery: select  > Restart and then hold down Command-R to start in Recovery Mode.
  2. Run Disk Utility.
  3. Select the disk and click First Aid.
  4. If all is well, restart and see if you can empty the Trash.

If First Aid finds problems, you should run it again (even a few times) to see if it ever finishes cleanly. Whether it finishes cleanly or not, you should immediately clone the drive or backup your data in some comprehensive fashion.

If you still can’t empty the Trash after all this, while it might seem extreme, it could be worthwhile to erase and restore your system using these instructions. Make sure you’re confident you have a complete and safe clone before erasing the drive.

While going through this you experience problems working with the drive, or after you go through all these steps, it could be a physical issue. Seek warranty service or replace it.

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