how to expire php session if user is inactive for 15 mins

Question

i have created one project in PHP, into which i am managing sessions.

I am creating session in my config.php file by writing following line of code.

Answer 1

try

  ini_set('session.gc_maxlifetime',54000);  
  ini_set('session.gc_probability',1);
  ini_set('session.gc_divisor',1); 

use this before calling session_start()