Linux Secrets: How to Create a Link with ln
Use the Linux Command ln to Define Links to a File
Dec 5, 2008
As any Linux programmer goes about their daily business they'll create new programs and give them nice sensible names.
However, for the users it may be a laborious job having to type out a long file name all of the time - they wants something short and snappy - a nice little tla (three letter abreviation) for example. So, the question is - how can the two needs be reconciled? The answer is to use Linux Links.
An Example Script - the Disk Usage Checker
The starting point is a simple, yet useful, script - this will report any disk with more that 90% usage, and can be created very easily:
For the Linux programmer this has been named perfectly as check_disk_usage, but the user may want something simpler and easy to type - for example cdu; therefore, the next step is to create a link
Creating a Linux Link
The link is created by using the command:
If the directory is examined then two new files will be shown:
The files will have the same size and creation date/time:
And even the inodes are the same:
In this case a hard link has been created and, as far as the system is concerned, they are the same file; however, there is a problem with using a hard link - it doesn't always work when the file and the link are in different directories (especially if those directories are on different disks). The solution is to use a symbolic link.
Symbolic Links
Rather than being a direct link (as with the hard link) the symbolic link simply holds the path to the target file; it's created by using the -s option with ln:
This time the inodes are different:
And the link is shown as such in the directory listing:
Summary
The Linux link enables the user to reference the same file with more that one name - and to that they use the ln command; the ln command can be used in two ways:
- to create a hard link - this is the default
- to create a symbolic link - defined by using the -s option
Although the hard link is the default, it is always better to use the symbolic links so that it can be placed anywhere in the system.
