CMS and Displaying custom 404 page [closed]

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. 开发者_如何学JAVA Closed 11 years ago.

This is just a random question. I've heard of a few CMS making it easily manageable to where the root site can display a 404 page if the admin tells it to display it instead of the website just in case the user wants to put the site down for maintenance. I was just trying to seeif I could understand how this sort of task is accomplished.

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if ($down_flag === true) {
    header('HTTP/1.0 404 Not Found');
    include('404.php');
    exit;
}