Maintenance mode or under construction mode for the public website are modes where you disable the public website, but leave the SiteManager control panel operational. These modes are useful when preparing large updates of the website which you want to hide from the users until ready. The difference between the two modes is the message that the users will see and the appropriate HTTP response codes. To enable or disable the maintenance or under construction mode for the public website. To access the website settings panel click the "Settings" link from the top menu and double click on the "Website Settings" row.
Select the mode you want to enable/disable and click on the "Update Settings!" button. The settings will be saved but will not be applied to the site. To apply the new settings you will have to rebuild the configuration file. To do that find the green "Apply Settings" button above the form and click it.