PHP warning session_start() - SOLVED

Description: PHP Warning:  session_start(): Cannot send session cache limiter - headers already sent
It's hard to check. So wast much time to debug.

On internet guide is session_start() is the top code+html : YES- this right
BUT: it's really hard debug on big site working.-> waste much time

The simple way is: 
1. Create 1 file testsession.php 
Add code
<?php  
session_start();
error_reporting(E_ALL ^ E_NOTICE);
?>
2. Upload to host
3. Run file testsession.php 
Check view error_log at root folder: No error_log, NO waring -> is GOOD status. This mean is OK
4. Check many parts source: this is the important step
Check above HTML
Check head
Check body
....
I found issue so easy.
Good luck