How to fix "Briefly unavailable for scheduled maintenance" in WordPress

Why does this message appear?

When WordPress updates itself, a plugin or a theme, it puts your site in maintenance mode. This keeps visitors away while files change. WordPress does this by making a small file named .maintenance in your site folder.

When the update ends, WordPress deletes that file. If the update stops halfway, the file stays. Your site then keeps showing this message:

Briefly unavailable for scheduled maintenance. Check back in a minute.

An update can stop if you close the browser, lose your connection, or the server runs out of time.

Steps to fix it

First wait one or two minutes. The update may still be running. If the message stays, do this.

Log in to the client area at https://secure.hostvento.com/clientarea.php.
Open your hosting service and go to your control panel.
Open File Manager.
Go to the folder that holds your WordPress files. This is often public_html.
Open the settings and turn on Show Hidden Files. The file name starts with a dot, so it is hidden by default.
Find the file named .maintenance.
Right-click it and choose Delete.
Reload your website. It should work again.

You can also use FTP or SSH. FTP is a way to move files to and from your server. With SSH you can run this command inside the WordPress folder:

rm .maintenance

This removes the maintenance file.

After the site is back

Log in to the WordPress dashboard.
Go to Dashboard and then Updates.
Run the failed update again.

The update may have stopped halfway, so some files could be damaged. Running it again usually repairs them.

Tip: Take a backup before updates. Update one plugin at a time, and do not close the page until it finishes.

If the message stays after you delete the file, open a support ticket.

Quick recap

The message comes from a leftover .maintenance file.
Wait a minute, then delete the file in File Manager.
Show hidden files to see it.
Run the update again and keep backups.