If you’ve updated WordPress, you should have noticed that wordpress goes into “maintenance mode” whenever mass plugins or WordPress itself is updated. What if you wanted to do some manual upgrading? Then you can manually put wordpress into maintenance mode.
To put wordpress into maintenance mode, just add a .maintenance file (notice the leading dot) in the same folder that contains wp-settings.php. Then in the file add this:
<?php $upgrading = time(); ?>
When you’re done with your maintenance simply remove the .maintenance file.
There’s also a way to update what the maintenance page displays. The default is a white page with a brief message.