Directory lost+found is a system directory placed on the root partition of the file system. e2fsck uses this special directory to deposit unlinked files after a file system repair.
Extracted from the man help: “mklost+found pre-allocates disk blocks to the lost+found directory so that when e2fsck is being run to recover a filesystem, it does not need to allocate blocks in the filesystem to store a large number of unlinked files. This ensures that e2fsck will not have to allocate data blocks in the filesystem during recovery.”
So it’s important this directory exists, if it was erased accidentally it’s necessary to create it:
~ $ cd / ~ $ mklost+found ~ $ cd /lost+found ~ $ ls -lha total 20K drwx------ 2 root root 16K May 3 2016 . drwxr-x--x 24 root root 4.0K Nov 1 23:23 ..
On the file system root partition.