how can i get system mac address

i'm using this code

function get_real_mac_addr(){
system('ipconfig /all');
$mycom=ob_get_contents();
$findme = "Physical";
$pmac = strpos($mycom, $findme);
$mac=substr($mycom,($pmac+36),17);
return $mac;
 }


its working in localhost and get mac address but in live server its not working

how can i get mac address in live server??