index.php

<?php
/*
 * Run this script to know how many disk space is left on the server.
 * If the critical disk space limit is reached, then the script will display "CRITICAL_ALERT"
 * and send you a E-Mail.
 * Else, it'll display the disk free space (in Bytes).
 */

// Constants definition
define('ROOT', '/'); // Your disk/partition root path where you want to store data
define('ALERT_EMAIL_ADDRESS', 'you@domain.tld'); // Set your mail here, to receive alerts
define('UNIT', 1000000000); // GB (1 > B; 1000 > KB; 1000000 > MB; 1000000000 > GB; etc.)
define('UNIT_NAME', 'Go') // Must be linked to the previous constant, here I use the GB unit (in France, we say Go instead of GB)
define('CRITICAL_FREE_SPACE', 10 * UNIT); // Set your critical limit here

// Get free disk space
$free_space = disk_free_space(ROOT);

// API Logic
if ($free_space < CRITICAL_FREE_SPACE)
{
	// French
	mail(ALERT_EMAIL_ADDRESS, '[DV Storage] Seuil critique atteint sur '.$_SERVER['SERVER_ADDR'], 'Libre: '.($free_space / UNIT).' '.UNIT_NAME);
	
	// English
	//mail(ALERT_EMAIL_ADDRESS, '[DV Storage] Critical limit reached on '.$_SERVER['SERVER_ADDR'], 'Free: '.($free_space / UNIT).' '.UNIT_NAME);
	
	echo 'CRITICAL_ALERT';
}
else
{
	echo $free_space;
}

exit();