Rescue System - Grub reinstall

This is the proper way of chrooting on a rescue system so you can have the most cpapbilites to run any program you need in rescue mode with the apropriate devices / configs:

Boot with your Rescue disk and:

mount /dev/sda1 /mnt
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
chroot /mnt

Re-installing grub on CentOS or Suse SLES respectively:

grub-install /dev/sda

or

grub --batch < /etc/grub.conf

if you have no errors... job done

:)