The ln command is used on the Linux command line to create either hard or symbolic links. It is used in one of two ways:
ln file link
to create a hard link
ln -s item link
to create a symbolic link where “item” is either a file or a directory.
Hard links are the original Unix way of creating links, compared to symbolic links, which are more modern. By default, every file has a single hard link that gives the file its name. When we create a hard link, we create an additional directory entry for a file.
Hard links have two important limitations:
A hard link cannot reference a file outside its own file system. This means a link may not reference a file that is not on the same disk partition as the link itself.
A hard link may not reference a directory.
A hard link is indistinguishable from the file itself. Unlike a symbolic link, when you list a directory containing a hard link you will see no special indication of the link. When a hard link is deleted, the link is removed but the contents of the file itself continue to exist (that is, its space is not deallocated) until all links to the file are deleted.
It is important to be aware of hard links because you might encounter them from time to time, but modern practice prefers symbolic links, which we will cover next.
Symbolic links were created to overcome the limitations of hard links. Symbolic links work by creating a special type of file that contains a text pointer to the referenced file or directory. In this regard, they operate in much the same way as a Windows shortcut though of course, they predate the Windows feature by many years.
A file pointed to by a symbolic link, and the symbolic link itself are largely indistinguishable from one another. For example, if you write some something to the symbolic link, the referenced file is also written to. However when you delete a symbolic link, only the link is deleted, not the file itself. If the file is deleted before the symbolic link, the link will continue to exist, but will point to nothing. In this case, the link is said to be broken. In many implementations, the ls command will display broken links in a distinguishing color, such as red, to reveal their presence.
Published on Wed 08 April 2009 by Larry Epson in Linux with tag(s): ln linux