Root into a virtual machine (KVM)

Scenario: I have a KVM virtualization server with a number of VMs defined. Suddenly, I cannot log in as root to one of the VMs. I will need to reset the root password. The "normal" methods like adding single or init=/bin/bash to the kernel boot line in GRUB do not work. The only option left is to boot from a rescue disc, but this is a virtual machine -- there is no DVD drive. Oh, no -- what to do?

NEWS FLASH: I just learned from a colleague that there is a much easier method. It is possible to chroot directly into the VM from the virtualization host. Will post detailed instructions as soon as I get them. Until then, there is always the "long route" described below.

Mount and chroot into a foreign Linux partition

Scenario: I have a Linux root partition that isn't booting properly. I need to chroot into it. How to do that?

Answer:

# mount /dev/[something] /mnt
# cd /mnt
# mount -t proc proc proc/
# mount -t sysfs sys sys/
# mount -o bind /dev dev/

After this, I should be able to chroot in and execute binaries (e.g. Yast), update grub (but watch out for /boot), etc.