I nuked /usr on one of my servers for cleaning purposes some 5-6 years ago when I was still quite fresh to Unix. After reboot, I was unable to log in even as root. That was the day I learned not to change the shell of root to anything outside of /bin (I had set it to /usr/bin/bash).
I was able to recover the machine with a LiveCD but still, it was annoying.
I was able to recover the machine with a LiveCD but still, it was annoying.