Make a symbolic link to a relative pathname

 If you create a symbolic link to a relative path, it will store it as a relative symbolic link, not absolute like your example shows. This is generally a good thing. Absolute symbolic links don't work when the filesystem is mounted elsewhere.

The reason your example doesn't work is that it's relative to the parent directory of the symbolic link and not where ln is run.

You can do:

$ pwd
/home/beau
$ ln -s foo/bar.txt bar.txt
$ readlink -f /home/beau/bar.txt
/home/beau/foo/bar.txt

Or for that matters:

$ cd foo
$ ln -s foo/bar.txt ../bar.txt

from: https://unix.stackexchange.com/questions/10370/make-a-symbolic-link-to-a-relative-pathname