I have already set it.
pls see below
title CentOS (2.6.9-42.0.8.EL)
root (hd0,0)
kernel /vmlinuz-2.6.9-42.0.8.EL ro root=LABEL=/ rhgb quiet
initrd /initrd-2.6.9-42.0.8.EL.img
You can set your grub.conf back to the label /.