“Briefly unavailable for scheduled maintenance” message after doing automatic upgrade in WordPress?
As part of the automatic upgrade WordPress places a file named .maintenance in the blog base folder (folder that contains the wp-admin folder). If that file exists, then visitors will see the message “Briefly unavailable for scheduled maintenance. Check back in a minute“.
To stop that message from being displayed to visitors, just delete the .maintenance file. The automatic upgrade should be executed again, just in case it failed.