LPI Linux Certification/Create And Change Hard And Symbolic Links

Detailed Objectives

(LPIC‑1 Version 5.0)

Weight

2

Description

Candidates should be able to create and manage hard and symbolic links to a file.

Key Knowledge Areas

Create links.
Identify hard and/or softlinks.
Copying versus linking files.
Use links to support system administration tasks.

The following is a partial list of the used files, terms and utilities

ln
ls

Links

Use links when:

You want to create a pathname to a file.
Set a shorter or fixed pathname to a file.

To link one file to another, use ln:

ln [options] filename linkname
ln [options] filename linkdirectory

Common options are:

‐f, force: clobber existing link
‐s, symbolic link: The default links are hard links (ln without ‑s option). A hard link can only be created to an existing file on the same physical device, after creation no visible association can be displayed between a link name and a file name.
Symbolic links – also known as soft links – are like shortcuts in Windows®, in the sense that the file may be removed but the link will remain (although useless). Unlike in Windows®, however, a symbolic link can be created on a file that does not exist yet. The association between the link name and the file name can be viewed with the ls command.

Linking to a file

The symbolic and hard link can be displayed with ls ‑l. Symbolic link are indicated with a dash, greater than, resembling a rightward arrow (→) with most monospace fonts: link_name‑>real_filename.

$ ls -l /dev/midi
lrwxrwxrwx   1   root   root        6    Feb 10 15:37   /dev/midi -> midi00

Hard links are indicated with the number of links counter (3 − 1 = 2 in this case).

$ ls -l readme
-rwxrwxrwx   3   yann   users       677  Feb 10 15:37   readme

When removing a link name, use rm. Only the link will be removed not the linked file.

Exercises

Answer key

Create directories etc and bin in your home directory.
Copy all the files in recursive mode from /etc to your etc directory and do the same for /bin to bin.
In your local etc directory rename all *.conf files to *.conf.bak.
Create in your home directory a symbolic link called dir that points to your local bin/ls. Check if dir does execute ls.
Remove the dir link. Is bin/ls still there?