I did an apt-get upgrade on my clusters's head node (13.04 server) and since then it won't boot at all. The system kernel panics very early in boot with the message: run-init: nuking initramfs contents: directory not empty. According to the logs, the only packages that were updated are: python3, libplymouth2, whoopsie, plymouth-theme-ubuntu-text, and plymouth. I have no idea what the problem could be. Any help is appreciated.