[Synology] PHP Mysqli no such file or directory

PHP Mysqli no such file or directory 

I am using apache server 2.2 + php 5.6

In my php file,

the line
$conn = new mysqli($servername, $username, $password);

causes error "no such file or directory ".

Here we go

1. Login your DSM
2. Open web station > php settings
3. Choose a php profile > Edit > Select tab "Core" > Search for "socket"
4. Set the socket value of mysqli to "/run/mysqld/mysqld10.sock"
5. Click OK