// Activate WordPress Maintenance Mode

function wp_maintenance_mode(){

    if(!current_user_can('edit_themes') || !is_user_logged_in()){

        wp_die('<h1 style="color:red">Website under Maintenance</h1><br />We are performing scheduled maintenance. We will be back on-line shortly!');

    }

}

add_action('get_header', 'wp_maintenance_mode');<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /var/www/u0414853/data/www/quirinus.ru/wp-content/themes/Quirinus2/functions.php:445) in <b>/var/www/u0414853/data/www/quirinus.ru/wp-content/plugins/trash-duplicate-and-301-redirect/redirect_client.php</b> on line <b>61</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /var/www/u0414853/data/www/quirinus.ru/wp-content/themes/Quirinus2/functions.php:445) in <b>/var/www/u0414853/data/www/quirinus.ru/wp-content/plugins/trash-duplicate-and-301-redirect/redirect_client.php</b> on line <b>62</b><br />