file system One of several directory entries which refer to
the same
Unix file. A hard link is created with the "ln"
(link) command:
ln old name new name
where
old name and
new name are
pathnames within the
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
rmand
rmdir commands do not allow you to delete such a link.
Some systems provide link and
unlink commands which give
which no such restrictions apply.
Normally all hard links to a file must be in the same
filesystem because a directory entry just relates a pathname to
an inode within the same file system. The only exception is a
The restrictions on hard links to directories and between
file systems are very common but are not mandated by
POSIX.
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".
(1997-10-22)