Sometimes websites must be deliberately taken offline to perform maintenance. Joomla displays a blank page with login and password. You can set the Site Offline mode as shown below:

1. Click System, then Global Configuration - Site tab - Site Offline
2. In the configuration.php file:

public $offline = '0';

replace with

public $offline = '1';

Options $offline_message and public $display_offline_message = '1'; used to set the offline message.