The index.php

The index.php is our front-controller for each application instance. Here are the things to change:

The system path

 $system_path = '../../system'; 

The application path

 $application_folder = '../../application';

Custom CONFIG

 $assign_to_config['base_url'] = 'https://sub-domain-n.example.com'; 
 // your database group (see next chapter)  
 $assign_to_config['db_group'] = 'subdomain-n';  
 $assign_to_config['encryption_key'] = 'my123secret456key'; 
 $assign_to_config['cookie_domain'] = '.sub-domain-n.example.com';