aren't cookies global?

OK. Your problem is that when using $config['sess_driver'] = 'files'; the $config['sess_save_path'] MUST describe the absolute path to the folder used for the files. On a linux system that might be something like `/var/www/project_folder/sessions/`. The point is it must be a complete path from the root of the drive to the folder to hold the files.

Read the Files Driver section of the documentation carefully for other vital information about using the files driver.

Depending on your server, you might need a different value for $config['cookie_domain']. If the empty string does not work then you might want to try '.example.com'; or maybe '.example.com/' .

If you are going to use cookies to hold data (instead of sessions) it is strongly recommended to use SSL (https://) and use these cookie settings

PHP Code:

$config['cookie_secure'] = TRUE;
$config['cookie_httponly'] = TRUE;