WordPress and “Briefly unavailable for scheduled maintenance”

Do you know the message: “Briefly unavailable for scheduled maintenance. Check back in a minute.”?

But you don’t know how to get rid of it?
You get this message on your WordPress blog after you clicked to install a new version of WordPress. When you update the WordPress-core, your users (and you) will see the message “Briefly unavailable for scheduled maintenance. Check back in a minute.” appear, so that they cannot interfere with the upgrade taking place at that time.
However, sometimes, the update seems to hang, and the message simply won’t go away.
Then what to do?

Easy! Log on to your web host with your favorite FTP program (I use Filezilla btw), go to the root of your WordPress installation, and check for the file “.maintenance” (starting with the dot!). When you’ve found it, delete it! Simple as that. The presence of this one simple file tells WordPress to go in maintenance mode, and show the dreaded “Briefly unavailable for scheduled maintenance. Check back in a minute.” message to your users. Removing the file removes the message. Most of the times, you will have to restart your update, since the presence of the file mostly means that the update went berserk somewhere.
Now, if you connect to your web host with your FTP program, and you cannot find the “.mainenance” file anywhere, check the settings of your FTP program, and see if it is set to “show hidden files”. Files starting with a dot, like “.maintenance” are hidden files on Unix filesystem.

Good luck with un-maintenancing your WordPress blog again!