Here’s how to fix the ‘Cannot open theme file /usr/share/apps/kdm/themes/CentOSCubes’ error message on CentOS.
It wasn’t a critical error – more of an annoyance. Dismissing the message box displayed a basic-looking KDM that allowed me to log in.
The problem on my system was that the default CentOS KDM theme was updated and the old one, CentOSCubes, dropped from the artwork package. Here’s a (resolved) CentOS bug report on the issue.
Thank you! It worked on my box. I was looking for a way to change the theme and finally I found the best one by reading the article!