[GTALUG] urgent: Red Hat distros have an update that renders some systems unbootable

[D. Hugh Redelmeier]

https://access.redhat.com/solutions/5272311
https://arstechnica.com/gadgets/2020/07/red-hat-and-centos-systems-arent-booting-due-to-boothole-patches/

Don't do upgrades to Fedora, RHEL, CentOS until you read those.

This seems to have bitten me, making one of my routers (running CentOS 7).
I'm still not sure if this is what has happened to my system.
The symptoms looked like an SSD failure: nothing past POST on the screen.

So I spent a fair bit of time trying to work around the loss.  Now that 
I've seen this error report, I will redirect my efforts