also, this code will let you put it where You want on a Web Page.
$uptime_array = explode(" ", exec("cat /proc/uptime"));
$seconds = round($uptime_array[0], 0);
$minutes = $seconds / 60;
$hours = $minutes / 60;
$days = floor($hours / 24);
$hours = floor($hours - ($days * 24));
$minutes = floor($minutes - ($days * 24 * 60) - ($hours * 60));
$seconds = floor($seconds - ($days * 24 * 60 * 60) - ($hours * 60 * 60) - ($minutes * 60));
$uptime_array = array($days, $hours, $minutes, $seconds);
print("Uptime : " . $uptime_array[0] . " jour(s) " . $uptime_array[1] . " heure(s) " . $uptime_array[2] . " minute(s) " . $uptime_array[3] . " seconde(s)");
?>