It's 8:27am. I haven't slept. I am exhausted. So I'm leaving this here and going to bed. I'll check it after. Pardon me if I'm slightly south of coherent.
Ubuntu 16.04.3 LTS server running on a VPS. Got another VPS on the same host machine, CentOS6. CentOS vps is still chugging along. Ubuntu vps won't boot. Last change was adding a Virtualmin "virtual server" (really just a separate user with privileges to some daemons). And some fiddling with postfix. Everything I've read online says to rip out my graphics drivers and reinstall them. Well I don't have any graphics drivers cause I don't have graphics. No X. No window managers. And certainly not intel or nvidia graphics drivers for X.
Closest I've come to a sane-sounding solution so far is an semi-ancient forum post about Arch Linux. Same problem caused by a missing symlink from /var/run to /run. Well, I have that symlink. So that's probably not it. And other than the tremendously unhelpful message above there is nothing to indicate what might be wrong.
Silver lining... vps has an independent VNC feature built into the hypervisor... so I've still got terminal access. And I can CTRL+ALT+F2 to get a login prompt on tty2 even with the boot messages are still stuck on tty1. No network connectivity though. A sizable chunk of the systemd services/units haven't launched. Multiple reboot have produced no meaningful changes.
It does talk about "Reached target Graphical Interface" right before everything goes tits up. But again... no X. And yes, I actually checked to make sure xorg/x11 didn't get pulled in as a dependency somehow. Screenshot below.