This is a simple check script we use on a number of servers to make sure PHP -> Apache -> Server is running ok.

check.php

<?php
// start the output from scratch
ob_start();

// some older PHP configs need this setting
date_default_timezone_set('Europe/London');

// collect some other useful information
$json_array = array(
	"status" 	=> null,
	"dt" 		=> date("Y-m-d H:i:s"),
	"load" 		=> null,
	"remote"	=> $_SERVER['REMOTE_ADDR']
);

// check that the headers have not already been sent
if(!headers_sent()){
	
	// HTTP/1.1
	header( 'Cache-Control: no-store, no-cache, must-revalidate' );
	header( 'Cache-Control: post-check=0, pre-check=0', false );
	header( 'Pragma: no-cache' ); 

	// date in the past
	header("Expires: Sat, 26 Jul 1997 05:00:00 GMT");
	
	// load is useful
	$load = sys_getloadavg();

	// check if you get a result
	// windows servers will fail here
	if (is_array($load)){
		if ($load[0] > 80) {
			$status = "busy";
		} else {
			$status = "ok";
		}
	} else {
		$status = "error";
	}
	
	// collect some other useful information
	$json_array["status"] = $status;
	$json_array["load"] = $load;
		
	// output any info, we'll only check for OK
	echo json_encode($json_array);
	
	// all ok
	exit(0);
}

// if we are here there is something very wrong
$json_array["status"] = "emergency";
echo json_encode($json_array);
?>