Can't create hard links as you want

In Unix like system, it's not possible for your create a hard link everywhere you like. For example, hard links cannot be created between directories. Also, they cannot be created between files in different filesystems.

That means if there is a file "/home/xxx/hello", you can't just create a hard link in /boot or /tmp, if you separate /home as a solo tree.
because that confuse the OS,


[freakrobot@acm lisp]$ ln /home/freakrobot/Code/lisp/dbmanage.lisp /boot
ln: creating hard link `/boot/dbmanage.lisp' => `/home/freakrobot/Code/lisp/dbmanage.lisp': Invalid cross-device link


reference: http://www.cyberciti.biz/tips/why-isnt-it-possible-to-create-hard-links-across-file-system-boundaries.html