How do I turn off my website for maintenance?

To redirect all requests for your site to a "maintenance" url, use mod_rewrite.  I also found this useful when migrating a site to another server, so people hitting the old site don't add / modify any content.

In your document root, create a file called .htaccess (notice the .) , and add these lines:

RewriteEngine On
RewriteRule ^(.*) down.html [L]

Now, you'll need to create a file called "down.html" with just some plain html in it to notify users that the site is not available.  Note - don't reference any images, or other server files, or those requests will also get rewritten, causing an ugly mess.