Due to some reason, I was in need to replace existing HDD with new one. So I cloned it using CloneZilla. It was a GNU/Linux Machine. First of all CloneZilla refuses copy partitions, one after another and flagged error for each of one. I remembered the reason for errors and turned off the machine. Turned on again and SHUTDOWN properly. The point is, if Machine is not shutdown properly, file system is unclean and ColneZilla will complaint while cloning. So I fixed that first. Then cloned without any error. But Computer refuses to boot from newly cloned HDD. It stayed at grub> prompt
Then I did the following to troubleshoot
Step1. grub> set root=(hd0,1) # / (root) partition was /dev/sda1
Step2. grub> linux /vmlinuz root=/dev/sda ro
step 3 grub> initrd /initrd.img
on the command prompt as a root
Rebooted again. Its done.