Take care with your site settings if you want your users to see your maintenance mode messages.
When upgrading a site the site admin can put the site into maintenance mode. A great feature is the ability to add an information message for users about what is happening and when the site will be available.
But if you have forced login to your site at /admin/settings.php the message won’t be seen!
So remember to temporarily turn the “Force users to log in” setting off if you want you users to see the helpful message.