Linux - Symbolic Links

With Unix/Linux you can create links to directories/files using a symbolic link. A symbolic link is different to a hard link.

Hard Link vs. Symbolic Link

• A hard link cannot link to a directory or different filesystem/volume, and must link to an existing file.
• A symbolic link can link to a directory, different filesystem/volume, and can also link to an arbitary value that may not exist.

Create a hard link

To create a hard link you can issue the following from the command line:

$ ln source_file link_name

This creates the link from source_file to link_name. The first file is always the name of the file you want to create a link to. The second file is always the name of the link that you wish to create.

Create a symbolic link

A symbolic link is created in much the same way, however we issue the -s flag.

$ ln -s source_file link_name

Flags

-f, --force

remove existing destination files

-n, --no-dereference

treat destination that is a symlink to a directory as if it were a normal file

Example of hard link vs symbolic link when removing source file

Hard link:

To test the different between a hard link and a symbolic link I performed the following:

Create a hard link of a test source file:

$ cat test_source
This is the source test file
$ ln test_source test_link

Check the hard link works

$ cat test_link
This is the source test file

Remove the source file

$ rm test_source

Check if the link file still exists

$ ls -ltr
total 40
-rw-r--r-- 1 krobbe dba 29 Jul 6 10:31 test_link
$ cat test_link
This is the source test file

Result: the link file still contains the information that was in the source file even though the source file has been removed.

Symbolic link:

Create soft link:

$ ln -s test_link test_link2

Check the soft link works correctly

$ cat test_link2
This is the source test file
$ ls -ltr
-rw-r--r-- 1 krobbe dba 29 Jul 6 10:31 test_link
lrwxrwxrwx 1 krobbe dba 9 Jul 6 10:34 test_link2 -> test_link

Remove the source file

$ rm test_link

Check the status of the link

$ ls -ltr
total 36
lrwxrwxrwx 1 krobbe dba 9 Jul 6 10:34 test_link2 -> test_link
$ cat test_link
cat: test_link: No such file or directory

Result: The symbolic link is highlighted as there being an error and when we go to view the contents of the file, no file or directory found error is presented.