Ce script utilise la commande système uptime.
On l'exécute en PHP, puis on affiche un compteur en Javascript :

<?php
$uptime = exec("cat /proc/uptime");
$uptime = split(" ",$uptime);
$uptime = $uptime[0];
?>
<html>
<head>
<script language="javascript">
var upSeconds=<?php echo $uptime; ?>;
function doUptime() {
	var uptimeString = "Server Uptime: ";
	var secs = parseInt(upSeconds % 60);
	var mins = parseInt(upSeconds / 60 % 60);
	var hours = parseInt(upSeconds / 3600 % 24);
	var days = parseInt(upSeconds / 86400);
	if (days > 0) {
		uptimeString += days;
		uptimeString += ((days == 1) ? " day" : " days") + ", ";
	}
	if (hours > 0) {
		uptimeString += hours;
		uptimeString += ((hours == 1) ? " hour" : " hours") + ", ";
	}
	if (mins > 0) {
		uptimeString += mins;
		uptimeString += ((mins == 1) ? " minute" : " minutes") + ", ";
	}
	uptimeString += secs;
	uptimeString += ((secs == 1) ? " second" : " seconds");
	uptime.innerHTML = uptimeString;
	upSeconds++;
	setTimeout("doUptime()",1000);
}
</script>
</head>
<body onLoad="doUptime();">
 
<div id="uptime">&nbsp;</div>
 
</body>
</html>

voilà c'est tout con, ça sert pas à grand chose mais ca peut-être utile pour vérifier le statut de son serveur ...
Exemple ici -> http://www.tatane.com/uptime.php