Location: PHPKode > scripts > PHP Cron > php-cron/example.php
 * This file illustrates how PHP Cron might be used.  It constitutes a check in
 * a database (MySQL sql source included below), and logs if the application
 * runs.  Here's an application overview:
 * Purpose:  To provide failover support for cron jobs on a secondary server
 * Requirements:  Cron, Database, command-line PHP support.  Non-PHP apps can be
 * wrapped in a PHP program that will exit or run and log as appropriate.
 * Your crontab needs the hostname set as an environment variable so PHP can
 * pick up on it.  Put the following at the top of your crontab:
 *  HOSTNAME="hostA"
 * SQL consists of two tables:  One to define the cron jobs that are being
 * monitored, a second to log events.  Here is the SQL:
 * CREATE TABLE projects (
  id int(10) NOT NULL default '0',
  name varchar(200) NOT NULL default '',
  notes text,
  cron_schedule varchar(30) NOT NULL default ''

CREATE TABLE monitor (
  id int(10) default '0',
  project_id int(3) NOT NULL default '0',
  event_date datetime NOT NULL default '0000-00-00 00:00:00',
  event_type varchar(50) NOT NULL default '',
  hostname varchar(20) default NULL,
  notes text

 * I leave it to the reader to implement a front-end to add and show monitoring
 * information for projects.
 //The project id needs to match the id of the project you enter into the projects table
$project_id = 1;  
 //If the host is the failover host, we check if the cron ran on the primary	
 if (didCronRun($project_id, "hostA") && $_ENV['HOSTNAME'] == "hostB"){
 	$debug_msg .= "$project cron ran on ".$_ENV['HOSTNAME']." !!!\n";
 	//Since the cron ran on the main host, we can exit the script.
 } else {
 	$debug_msg .= "Hostname is set to ".$_ENV['HOSTNAME'];
 	//OK, the job didn't run on the primary host.  Log the fact that this cron is running:
 	@db_log($project_id, "CRON", $_ENV['HOSTNAME']." starting my cron job");
 	//Now continue to run your cron application.  If you're running a perl/shell script, you can just exec it
 	//Otherwise, you'll probably want to just set the $project_id in your
 	//code and include this file.  

 * Utility function to determine if the cron job (id) ran normally for a
 * given host.
function didCronRun($id, $host){
	//Implement your own db connection here.
	$db = db();
	//Get the schedule of the cron from the database (e.g. "0 5 * * *")
	$q = "select cron_schedule from projects where id='".$id."'";
	$cron_schedule = mysql_result(mysql_query($q, $db),0,0);
	//Start new cron parser instance    	
	$cron = new CronParser($cron_schedule);
	$lastRan = $cron->getLastRan(); //Array (0=minute, 1=hour, 2=dayOfMonth, 3=month, 4=week, 5=year) 	
	//Convert to Unix timestamp
	$cron_ran = mktime ( $lastRan[1] ,$lastRan[0],0 , $lastRan[3] ,$lastRan[2], $lastRan[5]); 
	//Now, we look for a log entry for this app's cron job running OK
	//We're looking for a time within 45 secs or so of the $cron_ran time.  
	//You may want to adjust this if your job takes a while to run... 		
	$q = "SELECT * FROM `monitor` WHERE event_date > from_unixtime(".($cron_ran-45).") " .
			" and event_type = 'CRON' " .
			" and project_id='".$id."' " .
			" order by event_date desc ";
	$r = @mysql_query($q, $db);
	$row = @mysql_fetch_array($r);
	//Return either true or false depending on whether the job has run OK since given time.
	if (isset($row['hostname']) && $row['hostname'] == $host){
		//Job ran on the specified host
		return true ; 
	} else {
		//Job didn't run on the specified host, so it needs to run on failover host.
		return false;

  * Log application cron event in the database
 function db_log($id, $type, $notes){
	$logConn = db(); //Implement your own connection here
	$q = "insert into monitor values ('', '".$id."', now(), '".$type."', '".$_ENV['HOSTNAME']."',  '".$notes."')";
	$r = @mysql_query($q, $logConn);			
	if (@mysql_affected_rows()< 1){
		//Query seems to have failed.  Email it instead:
		mail ("your email", "Log failed ($type) for app id $id", $notes, "");			

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