how to require_once in codeigniter

I am trying to extend a library in codeigniter. The only way to do so seems to include the original library using `require_once` then load the extended library using `$this->load->library()` right now I have tried - `require_once('ion_auth.php');` - `require_once('home/SITE_NAME/public_html/FOLDER_NAME/application/libraries/ion_auth.php')` - `require_once('/home/SITE_NAME/public_html/FOLDER_NAME/application/libraries/ion_auth.php')` but unfortunately not luck..... I keep getting this error ``` Message: require_once(...) [function.require-once]: failed to open stream: No such file or directory ``` Weird thing is though this works on my local xampp environment but not on the actual server.