Na página rename(2)
man:
EBUSY The rename fails because oldpath or newpath is a directory that
is in use by some process (perhaps as current working directory,
or as root directory, or because it was open for reading) or is
in use by the system (for example as mount point), while the
system considers this an error. (Note that there is no require‐
ment to return EBUSY in such cases — there is nothing wrong with
doing the rename anyway — but it is allowed to return EBUSY if
the system cannot otherwise handle such situations.)