On booting up a redhat 7 server, the Gnome Display Manager GDM does not start. A blank black screen appears.

The last thing to be done before it stopped working was applying a STIG to harden it. Which among the many STIGs which broke it is unknown.

On boot up am able to see that gdm attempted to start. I don't seen any errors in messages.

Was thinking that a change to ../dconf/local.d/db caused the problem. So I reinstalled package deconf and removed all those files - made no difference.

Don't think it is the graphical card because I am able to start a desktop with startx.

This really has me stumped. Suggestions?

What is STIG? Do you need to run an old version of redhat like 7? Could you substitute GDM with e.g. SDDM?

Sorry for these vague answer, perhaps if you give more details somebody really knowledgeable can help you...

STIG is US goverernmentese for "Security Technical Implementation Guidelines" and is a hardening guide. Some are OK, some have been put together by people in a closed environment that have no clue. I am not familiar with the Red hat one, only the web app one so can't speak to the Red Hat one.

Back off the changes you made until you find which one caused the issue and then add that change to a POA&M.

With over 100 changes made, haven't been able to find which one broke it. Which STIG could potentially break gdm?

I had thought reverting the changes in /etc/dconf/local.d/db would fix things. It didn't.

Unsure if this is what your issue is but could be related. I had commented the line in /etc/pam.d/postlogin that was listed as optional and didn't meet the STIG setting. After uncommenting the line back to the original, the GUI started fine.

Hope this helps.