It was a routine update, you’ve done it a thousand times. You select the plugins that need updating, hit update, and browse away while its all happening. Big mistake. You have to stay on the WordPress page for the update to finish. Now when you go to visit any page on your site, you see a dreaded 503 error!
Oh no! Did one of the plugins only half-update? Do you need to go to a backup? What’s in the logs? PHP Fatal errors? The sky is falling!
Fortunately its not that bad. Go to your WordPress root directory. Locate a file called .maintenance. Delete it. All good.