Deletes records from WHMCS's `tbllog_register` table that pile up because it logs every freaking thing.

clean_whmcs_logs.php

<?php
/**
 * Clean WHMCS Logs
 *
 * Based on the script by @linux4me at:
 * https://whmcs.community/topic/289637-database-cleanup-operations-tbllog_register-and-tblactivitylog/
 *
 * This script deletes records from the WHMCS `tbllog_register` table that are older than the specified date.
 * This is useful for keeping the database size down because WHMCS adds records every 5 minutes when the cron runs.
 *
 * CAUTION: Clearing this table will lose historical data from the Utilities > Automation Status page.
 *          Only run this if you do not need this data.
 *
 * 1. Replace the database credentials and email address in the constructor.
 * 2. Save the script as `clean_whmcs_logs.php`.
 * 3. Upload it to a non-public directory above your public_html directory.
 * 4. Set its permissions to 600, as it contains sensitive info.
 * 5. Add a cron job to run this script once a week with `/path/to/php -q /path/to/clean_whmcs_logs.php >/dev/null 2>&1`
 *
 * @package CleanWHMCSLogs
 */

namespace CleanWHMCSLogs;

/**
 * Class Cleaner
 *
 * @package CleanWHMCSLogs
 */
class Cleaner {

	private $host;
	private $dbname;
	private $dbuser;
	private $dbpass;
	private $to;
	private $date;

	/**
	 * Constructor.
	 * Insert your database credentials. The database user must have DELETE and SELECT permissions.
	 */
	public function __construct() {
		$this->host   = 'localhost';
		$this->dbname = ''; // WHMCS database name.
		$this->dbuser = ''; // WHMCS database user.
		$this->dbpass = ''; // WHMCS database password for that user.
		$this->to     = ''; // Email address to send notices to.
		$this->date   = date_create( '-1 year' ); // Delete records prior to this date. Default is 1 year ago.
	}

	/**
	 * Run the cleaner.
	 */
	public function run() {

		// Delete the records prior to $this->date.
		$sql = 'DELETE FROM tbllog_register WHERE created_at < :date';

		try {

			$dbh = new \PDO( "mysql:host={$this->host};dbname={$this->dbname}", $this->dbuser, $this->dbpass );
			$dbh->setAttribute( \PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION );
			$sth = $dbh->prepare( $sql );
			$sth->bindValue( ':date', date_format( $this->date, 'Y-m-d' ), \PDO::PARAM_STR );
			$sth->execute();
			$deleted = $sth->rowCount();
			$this->send_email( "Clean WHMCS Logs ran successfully, deleting {$deleted} records." );

		} catch ( \PDOException $e ) {

			error_log( "Error - Clean WHMCS Logs not run: {$e->getMessage()}" );
			$this->send_email( "Error - Clean WHMCS Logs did not run: {$e->getMessage()}" );

		}
	}

	/**
	 * Send an email.
	 *
	 * @param string $message The message to send.
	 */
	private function send_email( $message ) {

		$subject = 'Clean WHMCS Logs Notice';

		if ( ! mail( $this->to, $subject, $message ) ) {
			error_log( 'The script clean_whmcs_logs.php was unable to send a notice email: ' . $message );
		}
	}
}

// Run the cleaner.
$cleaner = new Cleaner();
$cleaner->run();

?>