PHP

php start session if not started

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

php check if session is running

<?php
if(session_status() == PHP_SESSION_ACTIVE){
    //a session is already running
    session_destroy(); //stops the session
}
?>

check if session is started

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

php start session if not started

#you could just ignore warnings messages
@session_start();