满足条件时，需要维护消息。

原型

wp_maintenance()

描述

检查名为“.maintenance”的WordPress根目录中的文件。此文件将包含变量$ upgrade，设置为创建文件的时间。如果文件创建时间不到10分钟，WordPress将进入维护模式并显示一条消息。

源文件

路径：wp-includes/load.php

<?php
...
function wp_maintenance() {
	if ( ! file_exists( ABSPATH . '.maintenance' ) || wp_installing() )
		return;
	global $upgrading;
	include( ABSPATH . '.maintenance' );
	// If the $upgrading timestamp is older than 10 minutes, don't die.
	if ( ( time() - $upgrading ) >= 600 )
		return;
	/**
	 * Filters whether to enable maintenance mode.
	 *
	 * This filter runs before it can be used by plugins. It is designed for
	 * non-web runtimes. If this filter returns true, maintenance mode will be
	 * active and the request will end. If false, the request will be allowed to
	 * continue processing even if maintenance mode should be active.
	 *
	 * @since 4.6.0
	 *
	 * @param bool $enable_checks Whether to enable maintenance mode. Default true.
	 * @param int  $upgrading     The timestamp set in the .maintenance file.
	 */
	if ( ! apply_filters( 'enable_maintenance_mode', true, $upgrading ) ) {
		return;
	}
	if ( file_exists( WP_CONTENT_DIR . '/maintenance.php' ) ) {
		require_once( WP_CONTENT_DIR . '/maintenance.php' );
		die();
	}
	wp_load_translations_early();
	$protocol = wp_get_server_protocol();
	header( "$protocol 503 Service Unavailable", true, 503 );
	header( 'Content-Type: text/html; charset=utf-8' );
	header( 'Retry-After: 600' );
?>
	<!DOCTYPE html>
	<html ot; />
		<title><?php _e( 'Maintenance' ); ?></title>
	</head>
	<body>
		<h1><?php _e( 'Briefly unavailable for scheduled maintenance. Check back in a minute.' ); ?></h1>
	</body>
	</html>
<?php
	die();
}
...
?>

其他

英文文档：https://developer.wordpress.org/reference/functions/wp_maintenance/