Dies with a maintenance message when conditions are met.
Checks for a file in the WordPress root directory named ".maintenance". This file will contain the variable $upgrading, set to the time the file was created. If the file was created less than 10 minutes ago, WordPress enters maintenance mode and displays a message.
The default message can be replaced by using a drop-in (maintenance.php in the wp-content directory).
<?php wp_maintenance( ); ?>
wp_maintenance() is located in