Linking files -Linux File system

Linking files

A link is nothing more than a way of matching two or more file names to the same set of file data. There are two ways to achieve this:

• Hard link: Associate two or more file names with the same inode. Hard links share the same data blocks on the hard disk, while they continue to behave as independent files.

  There is an immediate disadvantage: hard links can't span partitions, because inode numbers are only unique within a given partition.

• Soft link or symbolic link (or for short: symlink): a small file that is a pointer to another file. A symbolic link contains the path to the target file instead of a physical location on the hard disk. Since inodes are not used in this system, soft links can span across partitions.

Creating symbolic links

The symbolic link is particularly interesting for beginning users: they are fairly obvious to see and you don't need to worry about partitions.

The command to make links is ln. In order to create symlinks, you need to use the -s option:

ln -s targetfile linkname

The application of symbolic links is widespread. They are often used to save disk space, to make a copy of a file in order to satisfy installation requirements of a new program that expects the file to be in another location, they are used to fix scripts that suddenly have to run in a new environment and can generally save a lot of work. A system admin may decide to move the home directories of the users to a new location, disk2 for instance, but if he wants everything to work like before, like the /etc/passwd file, with a minimum of effort he will create a symlink from /home to the new location /disk2/home.