Alias Physical Files

By Danny Kalev, ITworld |  How-to

Linux allows you to associate more than one name to the same physical
file. This feature is useful, for instance, when you need to refer to
the same physical file from different directories. This week I will
explain how to create file links using the ln command.

The ln command defines a new name - commonly called a link - for an
existing file. In the following example, the user defines a new link
called "january" for the file reports01_01:

$ln reports01_01 january

The ln command takes two parameters, the first being the original
filenames and the second the new associated name. If you list the
current directory's files, you will see a new item added -- the link
january:

$ls
reports01_01 january

Remember though, only one physical file resides in the directory.
Adding a link doesn't create a new file, it merely creates an alias.

It's possible to associate more than one link per file. The
following example issustrates associating a new link with the file
reports01_01:

$ln reports01_01 inventory

As expected, the ls command now shows three different files in the
current directory, two of which are the previously defined links:

$ls
reports01_01 january inventory

To find out the number of links associated with a file, type the ls
command with the -l option. This option provides additional information
about a file such as permissions, the number of associated links, the
owner, the size, and modification date. However, this option still
doesn't reveal the names linked to the same file. To see the
associated links, use the -i option. This option displays the file's
inode - a unique identification number Linux assigns to each physical
file. If two filenames have the same inode number, then they are linked
to the same physical file. For example:

$ls -i january inventory
4577 january 4577 inventory

To delete a file, you have to remove all of its associated links. So
long as one associated link remains, the file isn't deleted; even if
the original filename has been removed, the physical file remains
intact. In the following example, the user employs the rm command to
remove the file reports01_01. However, since this file has two other
associated links, it still can be accessed through them:

$rm reports01_01
$cat january
bulbs 12
mice 56

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