WordPress Cron Jobs Explained: Schedule Tasks Without Server Access (wppioneer.com)

01-wp-schedule-event.php

<?php
/**
 * Schedule a custom cron event on plugin activation.
 *
 * Hooks into 'wp_schedule_event' to register a task that runs
 * once every hour starting from the current time.
 */
function myplugin_activate() {
    if ( ! wp_next_scheduled( 'myplugin_hourly_event' ) ) {
        wp_schedule_event( time(), 'hourly', 'myplugin_hourly_event' );
    }
}
register_activation_hook( __FILE__, 'myplugin_activate' );

/**
 * The callback that fires when the cron event runs.
 */
add_action( 'myplugin_hourly_event', 'myplugin_do_this_hourly' );

function myplugin_do_this_hourly() {
    // Your scheduled task logic goes here.
    error_log( 'myplugin_hourly_event fired at ' . current_time( 'mysql' ) );
}

/**
 * Clean up the scheduled event on plugin deactivation.
 * Always do this — orphaned cron entries slow every page load.
 */
function myplugin_deactivate() {
    $timestamp = wp_next_scheduled( 'myplugin_hourly_event' );
    if ( $timestamp ) {
        wp_unschedule_event( $timestamp, 'myplugin_hourly_event' );
    }
}
register_deactivation_hook( __FILE__, 'myplugin_deactivate' );

02-custom-interval.php

<?php
/**
 * Register custom cron intervals.
 *
 * WordPress ships with 'hourly', 'twicedaily', and 'daily'.
 * Use this filter to add any interval your plugin needs.
 */
add_filter( 'cron_schedules', 'myplugin_add_cron_intervals' );

function myplugin_add_cron_intervals( $schedules ) {
    // Every 15 minutes
    $schedules['every_fifteen_minutes'] = array(
        'interval' => 15 * MINUTE_IN_SECONDS, // 900 seconds
        'display'  => __( 'Every 15 minutes', 'myplugin' ),
    );

    // Every 6 hours
    $schedules['every_six_hours'] = array(
        'interval' => 6 * HOUR_IN_SECONDS, // 21600 seconds
        'display'  => __( 'Every 6 hours', 'myplugin' ),
    );

    // Weekly
    $schedules['weekly'] = array(
        'interval' => WEEK_IN_SECONDS, // 604800 seconds
        'display'  => __( 'Once a week', 'myplugin' ),
    );

    return $schedules;
}

// Now register an event with your custom interval:
function myplugin_schedule_custom() {
    if ( ! wp_next_scheduled( 'myplugin_fifteen_min_event' ) ) {
        wp_schedule_event( time(), 'every_fifteen_minutes', 'myplugin_fifteen_min_event' );
    }
}
add_action( 'wp', 'myplugin_schedule_custom' );

03-disable-wp-cron.php

<?php
/**
 * Step 1 — Add this constant to wp-config.php to disable WP-Cron.
 *
 * Place it ABOVE the "That's all, stop editing!" line.
 */
define( 'DISABLE_WP_CRON', true );

/*
 * Step 2 — Add a real server cron job via crontab.
 *
 * Run:  crontab -e
 *
 * Then add one of the following lines:
 *
 * Every minute (recommended for busy sites):
 *   * * * * * php /var/www/html/wp-cron.php > /dev/null 2>&1
 *
 * Or using WP-CLI (preferred — bootstraps WordPress properly):
 *   * * * * * wp cron event run --due-now --path=/var/www/html --quiet
 *
 * Every 5 minutes (for lighter sites):
 *   *\/5 * * * * php /var/www/html/wp-cron.php > /dev/null 2>&1
 *
 * Replace /var/www/html with the actual path to your WordPress root.
 * For WP-CLI, make sure wp is in the system PATH or use the full path:
 *   /usr/local/bin/wp cron event run --due-now --path=/var/www/html --quiet
 */

04-debug-cron.php

<?php
/**
 * Debug helper: list all scheduled WP-Cron events with their
 * next run time and recurrence interval.
 *
 * Drop this in a plugin or a quick throwaway file, then visit
 * your site as an admin.  Remove it after debugging.
 */
add_action( 'admin_notices', 'myplugin_debug_cron_events' );

function myplugin_debug_cron_events() {
    if ( ! current_user_can( 'manage_options' ) ) {
        return;
    }

    $crons = _get_cron_array();

    if ( empty( $crons ) ) {
        echo '<div class="notice notice-info"><p>No cron events scheduled.</p></div>';
        return;
    }

    echo '<div class="notice notice-info" style="overflow:auto;max-height:400px;">';
    echo '<p><strong>Scheduled Cron Events</strong></p>';
    echo '<table style="border-collapse:collapse;width:100%;">';
    echo '<tr><th style="text-align:left;border-bottom:1px solid #ccc;padding:4px 8px;">Hook</th>';
    echo '<th style="text-align:left;border-bottom:1px solid #ccc;padding:4px 8px;">Next Run</th>';
    echo '<th style="text-align:left;border-bottom:1px solid #ccc;padding:4px 8px;">Schedule</th></tr>';

    foreach ( $crons as $timestamp => $hooks ) {
        foreach ( $hooks as $hook => $events ) {
            foreach ( $events as $event ) {
                $next_run  = human_time_diff( $timestamp, time() );
                $direction = ( $timestamp > time() ) ? 'in ' . $next_run : $next_run . ' ago (overdue!)';
                $schedule  = isset( $event['schedule'] ) ? $event['schedule'] : 'single';

                echo '<tr>';
                echo '<td style="padding:4px 8px;font-family:monospace;">' . esc_html( $hook ) . '</td>';
                echo '<td style="padding:4px 8px;">' . esc_html( $direction ) . '</td>';
                echo '<td style="padding:4px 8px;">' . esc_html( $schedule ) . '</td>';
                echo '</tr>';
            }
        }
    }

    echo '</table></div>';
}

05-wp-cli-cron.sh

#!/usr/bin/env bash
# WP-CLI cron management cheatsheet
# Run all commands from your WordPress root directory
# or pass --path=/var/www/html to each command.

# ─── List all scheduled events ─────────────────────────────────────────────
wp cron event list

# ─── Run all due events right now ──────────────────────────────────────────
wp cron event run --due-now

# ─── Run a specific hook ───────────────────────────────────────────────────
wp cron event run myplugin_hourly_event

# ─── Schedule a one-time event (epoch timestamp) ───────────────────────────
wp cron event schedule myplugin_hourly_event 1735689600

# ─── Delete a specific event ───────────────────────────────────────────────
wp cron event delete myplugin_hourly_event

# ─── Test whether WP-Cron is functioning correctly ─────────────────────────
wp cron test

# ─── List cron schedules (built-in + custom intervals) ─────────────────────
wp cron schedule list