Created attachment 142636 [details]
The various logs

Dear AMD Team,

unfortunately installation of your amdgpu-pro-18.40-676022-rhel-6 driver in CentOS 6.10 goes wrong at many spots.

So far I had been using fglrx happily, but now I needed Vulkan support, so I decided to upgrade.
Since I got a AMD Radeon R9 290X I followed instructions at 
https://amdgpu-install.readthedocs.io/en/latest/
and used

amdgpu-pro-install --opencl=legacy

the script ran through, I rebooted, and got a black screen.
Logging in remotely and looking at /var/log/Xorg.0.log I saw lots of entries about fglrx.
Since your instructions don't mention uninstalling old drivers, and your amdgpu-pro-install doesn't complain, I don't think that's my fault.

Next, I uninstalled fglrx, to be sure also amdgpu-pro-uninstall, rebooted, and went for another

amdgpu-pro-install --opencl=legacy

After another reboot, a 'startx' finally gave me a running X-server, but no OpenGL/GLX (running glxinfo yielded 'no GLX visual found').

Next I checked what amdgpu-pro-install did to my /etc/X11/xorg.conf and found this:

Section "ServerLayout"
   Identifier   "Main"
   Option "AIGLX" "false"
EndSection

Section "Device"
        Identifier "Videocard0"
        Driver "radeon"
EndSection

This doesn't look like it's a proper xorg.conf for amdgpu-pro. After some googling, I replaced xorg.conf with this file:
/usr/share/X11/xorg.conf.d/00-amdgpu-pro.conf 

After an X-server restart, 'glxinfo' in a terminal gave a different error:

libGL error: failed to open drm device: Permission denied
libGL error: failed to load driver: radeonsi             
libGL error: failed to open drm device: Permission denied
libGL error: failed to load driver: radeonsi             
libGL error: failed to open drm device: Permission denied
libGL error: failed to load driver: radeonsi             

Whenever there is a permission problem, I try again as 'root', and indeed, things worked.
After some googling, I did

cd /dev/dri
ls -l
crw-rw----+ 1 root video 226,   0 Nov 27 23:06 card0
crw-rw----. 1 root video 226,  64 Nov 27 23:06 controlD64
crw-rw----+ 1 root video 226, 128 Nov 27 23:06 renderD128

Then I did
chmod a+rw *
and got

crw-rw-rw-+ 1 root video 226,   0 Nov 27 23:06 card0
crw-rw-rw-. 1 root video 226,  64 Nov 27 23:06 controlD64
crw-rw-rw-+ 1 root video 226, 128 Nov 27 23:06 renderD128

And magically, after many hours of fiddling, OpenGL and OpenCL worked for a normal user. Yupppie!

So I figured it's time to file a bug report, ended up at

https://amdgpu-install.readthedocs.io/en/latest/install-bugrep.html#generating-a-bug-report

This page shows countless commands to run to save my system config. And amazingly, each command is shown with a '$' in front.
This means that I cannot just copy the entire script into a terminal, but instead have to do it line-by-line manually, or copy it to a text editor and cut the $s out.
Seriously?

Hope this report helped to improve things...

Regards,
Elmar