The quick and easy way
The problem is probably that you try to include wp-load.php from a wrong path. In a CLI environment, the path would not be the same as when you do an HTTP request to the file. So with this you should fixed your issue:
require(dirname(__FILE__) . '/../../../wp-config.php');
The proper but longer way
Based on cale_b comments and this article he linked, there is a much proper way to go by doing a Wordpress Cron job.
First in your plugin add a function that will contain the code needed to be executed, let's call it my_cron_job(). You can eventually just include the script you already wrote in this function. Then add the following to schedule the execution of this every 5min:
// Define a new interval (5 minutes)
add_filter('cron_schedules', 'fively_interval');
function fively_interval($interval) {
$interval['fively'] = array('interval' => 5*60, 'display' => 'Once 5 minutes');
return $interval;
}
// Register the hook on plugin activation
register_activation_hook(__FILE__, 'my_cron_job_activation');
add_action('my_cron_event', 'my_cron_job');
function my_cron_job_activation() {
wp_schedule_event(time(), 'fively', 'my_cron_event');
}
// Unregister the hook on plugin deactivation
register_deactivation_hook( __FILE__, 'my_cron_job_deactivation' );
function my_cron_job_deactivation(){
wp_clear_scheduled_hook( 'my_cron_event' );
}
Then set up your cron to execute wp-cron.php every 5 minutes:
*/5 * * * * php-cli -f [path to your WP]/wp-cron.php
Update
First when choosing the option of executing wp-cron.php with a server cron you should disable the default WP Cron behaviour (execution of cron through web visits):
define('DISABLE_WP_CRON', true);
Secondly, as for your question about WP Cron reliability I see a potential flaw indeed. I'm not 100% sure of that, but I think it is possible that wp_schedule_event get desynchronized with the server cron, as the job get executed only if the interval is past. As it will be re-scheduled depending of the execution time of the script which is slightly different with the server cron time.
For example:
00:00:00:000 Server cron execute wp-cron.php
00:00:00:100 The job can be executed, so let it run
00:00:00:200 Wordpress finished to execute the job - it schedule the event in 5min
00:05:00:000 Server cron execute wp-cron.php
00:05:00:100 The job is planned for 00:05:00:200, no execution !
00:10:00:000 Server cron execute wp-cron.php
00:10:00:100 The job is executed
That's theory of course, maybe this is not accurate. I suggest doing some test and see how it behave. If it indeed behave like I think it did, I suggest as easy workaround to change the wp_schedule_event to a lower interval - 4min for example.
add_filter('cron_schedules', 'fourly_interval');
function fourly_interval($interval) {
$interval['fourly'] = array('interval' => 4*60, 'display' => 'Once 4 minutes');
return $interval;
}
So we'll have the following:
00:00:00:000 Server cron execute wp-cron.php
00:00:00:100 The job can be executed, so let it run
00:00:00:200 Wordpress finished to execute the job - it schedule the event in 4min
00:05:00:000 Server cron execute wp-cron.php
00:05:00:100 The job is planned for 00:04:00:200, so let it run!
00:10:00:000 Server cron execute wp-cron.php
00:00:00:200 Wordpress finished to execute the job - it schedule the event in 4min
00:10:00:100 The job is executed (planned for 00:09:00:200)
With the default WP Cron behaviour disabled it should work flawlessly.
