check session php

PHP
// For PHP versions > 5.4.0

if (session_status() === PHP_SESSION_NONE) {
    session_start();
}

// For PHP Versions < 5.4.0

if(session_id() == '') {
    session_start();
}
<?php
if(session_status() == PHP_SESSION_NONE){
    //session has not started
    session_destroy();
}
Source

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