set up multiple applications

Are there any reason you need to do it like that? Because that just look like you are going to dig a big hole in the ground and never get out of it.

I would recommend setting up virtual hosts (multiple domains) and send environment variables from apache into CI. And change your application directory path. So you can access it normally.

The document https://codeigniter.com/user_guide/gener..._apps.html describes the configuration I set, but things are missing about htaccess, routes.php, config.php,