Thread:Project:Current issues/Site broken after upgrade with Call to undefined method MediaWiki::run()/reply (3)

I just had this problem on CentOS, upgrading from 1.16 to 1.20 and couldn't find any solution so I am posting here so that others may benefit.

Basically the problem was php53-xml was not installed on my system, and it looks like it's needed for the database upgrade to complete successfully - note that the upgrade without php-xml does not throw any errors so it looks like it's completed successfully, but it doesn't.