Proxmox and fixing GRUB after rsync'ing bootable disks


# mount /dev/sda1 /mnt
# mount --bind /dev/ /mnt/dev
# mount --bind /dev/pts /mnt/dev/pts
# mount --bind /proc /mnt/proc
# mount --bind /sys /mnt/sys
# chroot /mnt
# grub-install /dev/sda
# grub-install --recheck /dev/sda
# update-grub
# exit

reboot