What on earth just happened?

[John Austin]

On Fri, 2014-05-09 at 08:31 -0400, Tom Horsley wrote:
> I ran yum update this morning, getting a gazillion updates.
> I rebooted the system.
> 
> When it came back up, I couldn't log in. I'd get a KDM screen,
> login, then immediately get the KDM screen again.
> 
> I tried to login with a "failsafe" session which gave me
> (apparently) an xterm that printed black rectangles
> for all characters :-).
> 
> I tried other sessions like xfce and gnome and got the
> same KDM login screen popping back up after I typed
> my password.
> 
> I got in a vterm as root, created a new user, and
> logged in as that user with a default gnome session.
> That seemed to work fine. I decided I should compare
> what is running in the session with my original
> user, so I logged out and logged in again as original
> user, and now my original user login works fine.
> 
> Logging in once as a different user appears to have
> completely fixed the system.
> 
> What the heck was that? (It will be interesting to
> see if the same sequence happens when I install the
> latest updates at home).

Glad I'm not the only one with a problem!
kdm and xfce

I have two workarounds
>From Cont/Alt/F2 window as root
systemctl disable kdm.service
systemctl stop kdm.service
systemctl enable lightdm.service
systemctl start lightdm.service
OR
yum downgrade kdm libkworkspace kgreeter-plugins  kde-workspace \
kde-workspace-libs kcm_colors kde-style-oxygen

I will try your solution next

John