PHP Web server monitor

With this simple PHP script, you’ll be able to monitor the availability of Web servers. Write a list of URLs to monitor and run the script from cron. If a site becomes unavailable, monitor PHP script will generate alert and send e-mail to the default e-mail address. Monitor script is also able to send e-mail message to the various e-mail address (e-mail address per URL).

<?
// check list of URLs (select URLs with small traffic - static content)
url_test('http://www.redips.net/my/img/b.gif');
url_test('http://raspored.hrt.hr/b.gif');

/**
 * function checks Web server and sends an e-mail if there is a problem
 * email_admin has a default value and function can be called with or without e-mail address
 * script implies that the Web server does not work if there is no response within 10 seconds
 *
 * @param string $url          URL that must be checked
 * @param string $email_admin  if there is a problem send e-mail notification to this address
 */
function url_test($url, $email_admin='your@email.address'){
	// set timeout
	$timeout = 10;
	// init url session and set curl options
	$ch = curl_init();
	curl_setopt ($ch, CURLOPT_URL, $url);
	curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
	curl_setopt ($ch, CURLOPT_TIMEOUT, $timeout);
	$http_respond = curl_exec($ch); // execute http request
	// remove all html tags from the http response
	$http_respond = trim(strip_tags($http_respond));
	// get status from the http response
	$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
	// returned http code should be 200 otherwise there is a problem
	if ($http_code != 200){
		// prepare tested server name (component parameter added in PHP 5.1.2)
		$http_server = parse_url($url, PHP_URL_HOST);
		// and who was tester
    $hostname = trim(`/bin/hostname`);
		// get an error message from the URL request
		$http_error = trim(curl_error($ch));
		// prepare e-mail message
		$email_message = "TEST URL: $url";
		if ($http_code)    $email_message .= "\n\nHTTP CODE: $http_code";
		if ($http_respond) $email_message .= "\n\nHTTP RESPOND:\n$http_respond";
		if ($http_error)   $email_message .= "\n\nHTTP ERROR:\n$http_error";
		// prepare e-mail header
		$email_header = "Content-Type: text/plain; charset=\"iso-8859-2\"\n".
		                "Subject: http://$http_server problem!\n".
		                "From: monitor@$hostname\n".
		                "X-Priority: 1\n".
		                "Priority: Urgent\n".
		                "Importance: high";
		// send e-mail message
		error_log($email_message, 1, $email_admin, $email_header);
	}
	// close url session
	curl_close($ch);
}
?>

I run monitor script every five minutes and here is my cron entry:

# PHP Web server monitor
*/5 * * * * /usr/bin/php /usr/local/scripts/monitor.php

Script was and is very useful for me, and I hope it will be for you.