Today i have just tried to upgrade WordPress. it could not and i got this message “Briefly unavailable for scheduled maintenance. Check back in a minute” my blog didn’t show up at all even after I’ve tried to reload the page for several times. it was totally worry. 🙁
Then i login my FTP server and i saw one new a small file called .maintenance. 😮
I deleted a small file called .maintenance and loaded my blog and i got my blog back 😀
So, if you are facing the problem too, you can follow this solution. Hopefully, this solution will solve your problem.You will only get this problem when an update is not successful.