How is it possible for rm to throw “not a directory” and “is a directory errors”?

Question

I got a strange error the other day. Attempting to rm -rf nav/ a directory threw "not a directory", but trying to rm nav errored with "is a directory".

How is this possible?

Answer 1

You may have some filesystem corruption. Notice the 1 between the permission and the owner? That's the number of links to the directory inode. A directory should normally have a minimum of two, because it is linked to by the parent directory, and by itself (the . entry it contains). I would guess there is some corruption and your nav directory does not contain a . entry. Can you get anything with ls -la nav?