LPI Linux Certification/Create And Change Hard And Symbolic Links

Detailed Objectives edit

(LPIC-1 Version 5.0)

Weight: 2

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 edit

Use link 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:

-f force: clobber existing link
-s symbolic link

The default links are hard links (ln without an 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 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 doesn’t exist yet. The association between the link name and the file name can be viewed with the ls command.

Linking to a file edit

The symbolic and hard link can be displayed with ls -l. Symbolic link are indicated with an arrow: link_name->real_filename.

$ ls -l /dev/midi
lrwxrwxrwx   1   root   root        6    Jul 4 21:50   /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  Jul 4 21:50   readme

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

Exercises edit

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