function cwc_maintenance_mode() {
    if ( !current_user_can( 'edit_themes' ) || !is_user_logged_in() ) {
        wp_die('Maintenance, please come back soon.');
    }
}
add_action('get_header', 'cwc_maintenance_mode');

Just paste the following snippet into your functions.php file and save it.

When you need to put your wordpress blog on hold while performing some maintenance.

wordpress

PHP