[CentOS] CentOS 7.5 gui login root only

isdtor writes:
> Prasad K writes:
> > I have seen similar issues when user shell profiles like .bash_profile or
> > .bashrc has some errors.
> > Are users invoking other shells from their default shell ? this usually
> > breaks X11 start-up scripts.
>  
> The same user can login find through the gui when the system was installed with the CentOS DVD directly. Package selection was the last option (create workstation or something) with most but not all extra package groups that are selectable at this point.
> 
> This is a KVM machine, I have tried the default (cirrus) and vga, no change.
 
This bug report put me on the right track: https://bugs.freedesktop.org/show_bug.cgi?id=66867, with

/var/log/messages: gnome-session-binary[12345]: ERROR: Failed to connect to system bus: Exhausted all available authentication mechanisms

and associated YPPROC_DOMAIN not found entries.

The NIS domain must be defined and correct in /etc/sysconfig/network so that it's known to dbus when it starts. This is different from CentOS6 and before where the contents of this file largely didn't matter for NIS and /etc/yp.conf was sufficient.