php中的include_path相关问题

I have a PHP application where the autoloader is situated in /var/www/html/example.com/src/vendors/autoloader.php

var/
  www/
    html/
      example.com
        app/
        vendors/
          vendor_a/
           example.php
          vendor_b/
          vendor_c/
          autoloader.php
        public/

In autoloader.php I have a line that requires example.php from the vedor_a/ folder. although this works in my local virtual box running centos, php-fpm, nginx it fails to work in my vps, which has the same version of every program I am running in my localhost.

I am using php5.5.14

and I get this error when I require the above file.

Warning: require(vendor_a/example.php): failed to open stream: No such file or directory in /var/www/html/example.com/vendors/autoloader.php on line 2

Fatal error: require(): Failed opening required 'vendor_a/example.php' (include_path='.:/usr/share/pear:/usr/share/php') in /var/www/html/example.com/vendors/autoloader.php on line 2

I haven't modified anything from my php.ini where the include_path defaults to

; UNIX: "/path1:/path2"
;include_path = ".:/php/includes"

I am looking more than a solution here. Because I can see the include_path looks for php/includes dir when constructs such as require, include, include_once... at-least according to the manual but I can't find a directory called php/includes so why is that setting even there?