The Free On-line Dictionary of Computing (30 December 2018):

hard link
hard linking

    One of several directory entries which refer to
   the same Unix file.  A hard link is created with the "ln"
   (link) command:

   	ln  

   where  and  are pathnames within the
   same file system.  Hard links to the same file are
   indistinguishable from each other except that they have
   different pathnames.  They all refer to the same inode and
   the inode contains all the information about a file.

   The standard ln command does not usually allow you to create a
   hard link to a directory, chiefly because the standard rm
   and rmdir commands do not allow you to delete such a link.
   Some systems provide link and unlink commands which give
   direct access to the system calls of the same name, for
   which no such restrictions apply.

   Normally all hard links to a file must be in the same file
   system because a directory entry just relates a pathname to
   an inode within the same file system.  The only exception is a
   mount point.

   The restrictions on hard links to directories and between
   file systems are very common but are not mandated by POSIX.
   Symbolic links are often used instead of hard links because
   they do not suffer from these restrictions.

   The space associated with a file is not freed until all the
   hard links to the file are deleted.  This explains why the
   system call to delete a file is called "unlink".

   Microsoft Windows NTFS supports hard links via the
   fsutil command.

   Unix manual page: ln(1).


(http://microsoft.com/windowsxp/home/using/productdoc/en/fsutil_hardlink.asp).

   (2004-02-24)