X server not working L4T 21.3 Jetson TK1 (systemd)

I am on L4T 21.3 and Ubuntu 16.04 (recently upgraded) on my Jetson Tk1. I’m not sure what I did wrong here, maybe I updated something that I shouldn’t have, but just recently I rebooted the system to install some security updates for ubuntu and unity just crashed at the login screen. I went into console mode using Ctrl-Alt-F1 and ran startx to see what was going on, and it failed after trying to load the GLX extension. I looked into the log file that was generated for further details on the error, and found this:

Fatal server error: 
[    371.094]  (EE) AddScreen/ScreenInit failed for driver 0

I looked online and tried a few solutions I found, like deleting the xorg.conf file, but none of them worked. I have tried reinstalling the drivers from the L4T 21.3 driver package directly onto the Jetson, specifically to replace the libglx.so file. It made no difference at all, still the same problems. I also tried reinstalling unity as well as ubuntu-desktop, no change still. I feel like I’ve tried every solution I’ve found so far short of reflashing the whole thing with a brand new filesystem. I should mention that I originally installed the system using fastboot because I wanted to be able to keep the root filesystem on my SSD and boot off of that (which does work for L4T 21.3). I don’t know if that changes anything.

Update 1:

I figured out part of the problem was the rtkit service daemon was hanging for some reason. So I went in and commented out the PrivateNetwork line and now I get a very broken Unity to work with. I’m wondering if maybe there were a few more services like this that broke on my upgrade to 16.04 that just haven’t affected me until now

Update 2:

After a while of poking around at the systemd .service files, I recalled doing something similar on my laptop when I first upgraded to 16.04 and started using systemd. My solution then was to reinstall upstart with:

sudo apt-get install upstart-sysv

so I tried that on my Jetson and sure enough, after rebooting, everything works fine. It was never a problem with my L4T installation or drivers; just another faulty systemd installation. I honestly wish they’d kept upstart, it had so many fewer problems