Hardlink

Also the article for:

• filename

A hardlink associates a filename with a file. That name is an entry in a directory listing. Of course a file can have more hardlinks to it (usually the number of hardlinks to a file is limited), but all hardlinks to a file must reside on the same filesystem than the file itself!

What you usually call a file is just a name for that file, and thus, a hardlink.

The difference between a sym link and a hard link is that there is no easy way to differ between a 'real' file and a hard link, let's take a look at the example:

* create an empty file

$ touch a

* create a hard link 'b' and sym link 'c' to empty file

$ ln a b
$ ln -s a c

as you can see file(1) can't differ between a real file 'a' and a hard link 'b', but it can tell 'c' is a sym link

$ file *
a: empty
b: empty
c: symbolic link to `a'

ls -i prints out the inode numbers of files, if two files have the same inode number AND are on the same file system it means they are hardlinked.

$ ls -i *
5262 a  5262 b  5263 c

hard links don't consume additional space on the hard drive, the space is freed when the last hard link pointing to it is deleted.

• file
• filesystem
• symlink