The "Rescue Installed system" is the option you want. It'll fire up off the DVD and give you a command prompt at the end of it. Along the way it will ask if you want to mount your cu... [by TrevorH]
'chroot /mnt/sysimage' command in rescue mode ,Followed below mentioned procedure
1.Boot the system from the binary DVD or boot disc1 of the same major release as the system. Once the system has successfully booted from the ISO image and Red Hat Enterprise Linux boot screen will appear.