This isn't the problem everyone else has been talking about, but...
I made sure that yum update offered the packages Johnny said it should then updated. when I rebooted everything looked normal except it was taking a long time to bring up the login screen.
Flipped over to ALT-F2 and saw a message about waiting for Plymouth boot screen to quit. I waited a while and it went up to (and past) 15 minutes. It said "no limit" so it apparently would have gone on forever.
I couldn't get to a text-mode screen with ALT-f[2-6] so I went down to my Linux laptop to see if I could ssh into this box. Lo and behold, ssh worked fine. So I ran top and saw a plymouth (or plymouthd, I forget which) at the top of the list. killed it, came back upstairs and it was no longer spewing that message.
now ALT-f2 gave me a text login, that I'm using now.
I ran startx and after a long-seeming wait I get a desktop, but it is NOT my normal Mate desktop. Might be Gnome (since I installed a Centos Gnome system and retrofitted Mate from EPEL).
Johnny had said we needed to make sure the kernel was installed along with the shim, et al. I looked at the list of files YUM wanted to install and saw some kernel files, so I assumed all was well. But maybe I missed something.
What info can I provide to help figure this out? Or, what Kernel files should I force to be (re)installed?
Also, I don't very often manually force a kernel install, but I know that some of the files are updates and some are installs, I'd appreciate a reminder of which is which so I can force it.
Thanks in advance!
Fred