Manually open WordPress site maintenance mode

In the update program or plug-in, the front end of WordPress will show that it is in maintenance mode. If you want to temporarily enable the maintenance mode, customize the front end prompt text to let users know that your site is in maintenance, rather than running away from the door, you can use the following code to achieve this.

Enable WordPress site maintenance mode

Add the following code to the current topic function template functions.php:

 function zm_maintenancemode() { if ( !current_user_can( 'edit_themes' ) || ! is_user_logged_in() ) { Wp_die ('Please wait while the website is being maintained! '); exit; } } add_action('get_header', 'zm_maintenancemode');

After the code is added, the front end will show that the maintenance is in progress without logging in, but it will not affect the login background operation.

source: http://www.thecreativedev.com/how-to-put-wordpress-site-into-maintenance-mode/