By mistake, we upgraded Gitlab version from 7.4 to 10 directly. After upgraded, unicorn service failed to start so now we are in the process of downgrading the Gitlab version to the previous one. This is a production server, struggling to fix it for a couple of days.
The best thing is to recover from the backup. If you don’t have one I think you’re in a lot of trouble because gitlab version up updates some database tables and I don’t think you can recover.
However, if you only want to recover the git repo, I think that’s possible (haven’t tested this). Install a fresh new Gitlab 7.4 and copy the following directory: