The root device is not configured to be read-write

"The root device is not configured to be read-write", this is the message that I was greeted with, during boot, when starting up my HTPC yesterday.

The HTPC is running Arch Linux with XBMC, and XBMC started up just fine afterwards and everything seemed to be working. Nevertheless, I thought it strange, since I hadn't updated the system or changed any settings recently.

First I thought it might be a one-off event, but rebooting displayed the same message. A little googling told me that at least a few others had seen the same thing and that the solution was simple: just rebuild the grub configuration file.

sudo grub-mkconfig -o /boot/grub/grub.cfg

It looks like somehow something had gone wrong with my GRUB installation, I noticed also that the changes that I had made to /etc/default/grub had also disappeared, so I made the changes and rebuilt the configuration file again.

It bugs me a bit that I don't know the cause of this, but at least it was fixed quickly and without any real difficulties.