Comment 10 for bug 1385630

Yes, it's certainly a race condition of some sort. Unfortunately quite impossible to debug remotely as there are no available logs/kernel traces :-( SysRQ missing is also a bit unhelpful there (yes, it's usually Alt+PrintScr); does that work if boot works normally? If it just doesn't work with that hang, then the kernel is so thoroughly locked up that not even SysRQ helps. Maybe try with a different keyboard?

> And why systemd 208 was always successful, but 215 not?

Well, that's exactly the $10,000 question that this report is about :-) It has slightly different udev rules and does different things at bootup, but there's been a lot of changes between those versions.

Do you get the hang if you boot without "quiet" and also without "splash"? That's text-mode only and might be a bit faster again.