A hard link is a nice disk-saving Unix feature whereby one file can appear
in more than one directory, but only resides on disk once. If anyone
deletes it (including the original owner), the file is removed from
the current directory but still appears in all other directories. The
file itself only disappears if it deleted from ALL directories which
point to it.
The command to do this is ln source_file which creates a hard link
to the file source_file in the current directory.
man ln describes it so: A hard link is a pointer to a file and is
indistinguishable from the original directory entry. Any
changes to a file are effective independent of the name used
to reference the file. Hard links may not span file systems
and may not refer to directories.
When you issue ls -l, the little number (usually 1) in the second
column tells you how many hard links (including the original)
point to the file.
This file is maintained by Mark Baker, George Heintzelman