I’m getting this error on another machine, but I remember this happened on the first one. Once you run yum everything slows down / halts. Yum with dificulties won’t install anything giving diferent errors, in this case for example
Warning: RPMDB altered outside of yum.
** Found 1 pre-existing rpmdb problem(s), 'yum check' output follows:
kbd-1.15.5-15.el7.x86_64 has missing requires of kbd-misc = ('0', '1.15.5', '15.