When updating to a new version of WordPress, the installation hangs and system returns the following message when users attempt to view the public web site:
Briefly unavailable for scheduled maintenance. Check back in a minute.
In WordPress dashboard, the screenshot below shows how WP hangs at “copying required files” when updating to a new WordPress version:
Cause of the Maintenance Message
During an automatic upgrade, WordPress places a file in the blog root directory called “.maintenance” to prevent visitors from being confronted with ugly, broken pages during the upgrade process. That’s a great little built-in feature, but if the upgrade gets interrupted or fails for any reason, that file doesn’t get deleted and nobody, including you, can access your blog. No worries, this is (most likely) the simplest fix on Earth.
Removing the Maintenance Message
Delete the .maintenance file from WP’s root directory. In this example, WordPress in installed in \public_html\: