How to Set Up an External CRON Job in WordPress and speed up email sending

WordPress has a built-in scheduling system called WP-Cron, designed to handle time-based tasks. This is what Noptin uses when sending emails in the background.

However, it is not often reliable as it is tied to your website traffic.

This guide will walk you through the process of setting up an external CRON job for WordPress, including special considerations for multisite setups.

Why Use an External CRON Job?

Before we dive into the setup, let’s briefly discuss why you might want to use an external CRON job:

1. Reliability: WP-Cron is triggered by site visits, which can lead to missed or delayed tasks on low-traffic sites.
2. Performance: External CRON jobs reduce the load on your WordPress site, as they don’t rely on page loads to trigger scheduled tasks.
3. Precision: External CRON jobs can be set to run at exact times, providing better control over task scheduling.

Setting Up an External CRON Job

Step 1: Disable WP-Cron

First, you need to disable the built-in WP-Cron. Add the following line to your wp-config.php file:

define('DISABLE_WP_CRON', true);

Step 2: Set Up the External CRON Job

The exact method for setting up a CRON job depends on your hosting environment. Here are general steps for cPanel and command-line setups:

For cPanel:

1. Log in to your cPanel account.
2. Find the “Cron Jobs” or “Scheduled Tasks” section.
3. Click “Add New Cron Job.”
4. Set the frequency (e.g., every 5 minutes).
5. In the command field, enter:

wget -q -O - http://your-domain.com/wp-cron.php?doing_wp_cron >/dev/null 2>&1

Replace your-domain.com with your actual domain.

For Command Line:

1. Access your server via SSH.
2. Type crontab -e to edit the crontab file.
3. Add the following line:

*/5 * * * * wget -q -O - http://your-domain.com/wp-cron.php?doing_wp_cron >/dev/null 2>&1

This sets the CRON job to run every 15 minutes. Adjust the frequency as needed.

Step 3: Verify the Setup

To ensure your external CRON job is working:

1. Install a plugin like WP Crontrol.
2. Check the “Cron Events” page to see if tasks are being executed at the scheduled times.

Setting Up CRON Jobs for WordPress Multisite

If you’re running a WordPress multisite installation, you’ll need to take a few extra steps to ensure CRON jobs run for all sites in your network.

Method 1: Individual CRON Jobs

Create a separate CRON job for each site in your network. This method gives you the most control but can be cumbersome for large networks.

For each site, create a CRON job using this format:

*/5 * * * * wget -q -O - http://site1.your-domain.com/wp-cron.php?doing_wp_cron >/dev/null 2>&1
*/5 * * * * wget -q -O - http://site2.your-domain.com/wp-cron.php?doing_wp_cron >/dev/null 2>&1
# ... and so on for each site

Method 2: Using a Custom Script

For larger networks, create a PHP script that loops through all sites:

1. Create a file named multisite-cron.php in your WordPress root directory.
2. Add the following code:

<?php
define('WP_USE_THEMES', false);
require_once('wp-load.php');

$sites = get_sites();

foreach ($sites as $site) {
    switch_to_blog($site->blog_id);
    $cron_url = get_site_url(null, 'wp-cron.php?doing_wp_cron');
    $result = wp_remote_post($cron_url);
    restore_current_blog();
}

3. Set up a single CRON job to run this script:

*/5 * * * * php /path/to/your/wordpress/multisite-cron.php

This method is more efficient for large multisite networks since it only requires one CRON job entry.

Conclusion

Setting up an external CRON job for WordPress can significantly improve your site’s performance and reliability.

For multisite setups, choose the method that best fits your network’s size and your management preferences.

Remember to monitor your CRON jobs regularly to ensure they’re running as expected and adjust as necessary.