It is increasingly common to encounter this error when updating several plugins simultaneously.
When WordPress performs updates, it creates a file in the root of the installation with the name .maintenance starting with dot, which are the hidden files in Linux.
This file contains a PHP variable ($upgrading) whose value is a date timestamp that if we convert it to a date and time, it is the same as the creation date of the file.
.maintenance in the root of the installation, showing date and time
.maintenance with the date and time variable
That file prevents us from doing anything in WordPress while the update is taking place, so if we refresh the page or go to the frontend we will see the message “Briefly Unavailable for Scheduled Maintenance. Check Back in a Minute.”
At the end of the updates, you will exit the maintenance mode by deleting this file and everything will be correct.
But if for any reason, the process is interrupted and the file is not deleted, we will have a beautiful blank web page with this permanent message.
Troubleshooting the error
As you may have deduced, the solution to this error is very easy and quick: delete the file.
The method is indifferent, either by SSH, connecting via FTP, from the file manager of the hosting … just keep in mind that if the file is not displayed in your FTP program, it is because it is a hidden file (dotfiles), you will have to select in the program of turn, that it shows you the hidden files.
Delete the file and voilà, web up and running.
