I had a lost+found folder in all Unix file systems I used since the 80s. It's where fsck places files that it found during a scan and can't figure out to which directory they belong. Sometimes I found stuff in there.

From what I googled XFS, Btrfs and ZFS don't use lost+found. It's a thing of the old not journaled filesystems and of the ext family.

▲

jcalvinowens 2 hours ago | parent | next [-]

XFS does use /lost+found, it calls it the "orphanage directory" and xfs_repair reparents children of corrupt directories there.

Based on comments in the kernel source, it seems like the userspace fsck for JFS and F2FS will also sometimes create /lost+found. There might be more that do.

	▲	adrian_b 12 minutes ago \| parent [-]
		XFS filesystems do not have a "/lost+found" directory in their normal state. In the very rare occasions when one has to run "xfs_repair", it will create a "/lost+found" directory, if it is required for recovered files. After the repair and after investigating whether the recovered files contain useful data or not (and after moving the useful files elsewhere), one should normally delete the "/lost+found" directory, because it is no longer needed.

▲

Eikon an hour ago | parent | prev [-]

Even with journaling, you might need one. ZeroFS [0] almost had a lost+found directory (even with the WAL enabled), because you might have consistency issues between your in-memory state and what was flushed, and especially in what order.

ZeroFS ended up not needing recovery at all through atomic, strictly ordered commits [1], but it was far from trivial (and not just a matter of requiring a WAL).

[0] https://github.com/Barre/ZeroFS

[1] https://github.com/Barre/ZeroFS/blob/main/zerofs/src/fs/writ...