CentOS - May 2018 - CentOS 7 system unsable after "yum update" (with some errors on the way)

God dag,

I've been trying to run a "yum update" (without additional
arguments) to install the latest system updates on my CentOS 7 machine. It's
no going so well. What happens is this:

  1.  The process gets stuck a couple of places as a "post" script or
similar tries to run "dbus-send"; the problem looks awfully similar to
what's described in https://bugzilla.redhat.com/show_bug.cgi?id=1186018.
More specifically, this happens on installation of package
"setroubleshoot" and "avahi". As a workaround, I'm using
a manual kill to get rid of the hung process.
  2.  There is a similar hang related to "systemctl try-restart". This
happens on "wpa_supplicant" clean-up.
  3.  When I restart the system after the installation is done (with
work-arounds), it won't boot properly - I don't get a login screen or
console login prompt. I notice two error messages on the boot console:
Failed to start login service
Failed to start WPA supplicant daemon


I've tried the operation twice with the same result. First time was just
after the release of CentOS 7.5, I believe. I've done similar upgrades
before that, too, and they've completed without problems.


Has anyone else seen this? Any ideas what I can do to make the system usable
again, besides restoring from back-up (as I'm doing now)?


There is info on the net that suggests that the problem is related to SELinux
and that a relabel operation and/or policy change would help, but I tried all
sorts of things related to that the first time around, and nothing seemed to
help. (I was working partly in rescue mode booted from an installer USB and
partly in single user mode, which does work.)


TIA


- Toralf