GRUB is abbreviated as GRand Unified Bootloader is the Boot Loader for Linux OS. The GRUB is the most important part of the Linux OS. GRUB is the Boot Loader for Linux, hence without these Linux OS cannot be booted or start. why it is called as the most important part in the Linux Booting process.

When this GRUB is damaged or corrupted its core files your Linux OS cannot be booted. Sometimes it may happen that you found your grub corrupted so that you can’t log in into your Enterprise Linux OS. So for that I am providing a technique to recover and rescue your corrupted GRUB into new one.

Step-I (Select and Hit Rescue Installed System)

Insert the RHEL/CentOS/Scientific/Oracle Linux installation DVD / USB drive and Boot with it and follow the given Steps:

The following window will open So then press on Rescue installed system or Boot from local drive (It will Boot from your local drive it takes previous stage of your) but in this tutorial I am trying it using Rescue Installed System.

Step-II (Choose the Language)

Choose the Language and hit Enter

Step-III (Select Keyboard Type)

Select the Keyboard Type and hit Enter

Step-IV (Starting of Rescue Mode Select the Rescue Image or Media)

Select Local CD/DVD

Step-V (Setup of Networking)

It will ask you about to setup Networking. To set a network you can watch my other tutorial, actually you should setup a network, but right now we are just learning about grub so don’t setup your network we will do it later. Just press on NO and proceed to further process.

Step-VI (Starting of Rescue Screen)

Now it will take you to the Rescue screen. So let’s discuss about the options which it provide.If you have a problem in the file system area I recommend Skip option. But here we want to recover our grub so we use Continue option so that it will mount your system under /mnt/sysimage.

Step-VII (Select Mount point for Rescue)

Click on OK to Mount your system under /mnt/sysimage. Now to work in the root environment runs chroot /mnt/sysimage command.

Step-VIII (Final Mount Point for Rescue Screen)

Read the info and hit OK.

Step-IX (First Aid Kit for Recovery and rescue)

After this Hit on start shell to enter in the shell prompt.

Step-X (Rescue and Recover the corrupted GRUB)

After hitting you will see the following lines below this.Now to work in root environment just press in front of bash prompt.

In Bash prompt use this command

bash-4.1# chroot /mnt/sysimage
sh-4.1# grub-install /dev/sda
sh-4.1# exit
bash-4.1# exit
Step-XI (Exit from the Rescue Mode)

Just hit on Reboot to restart the systems.

After this just let the system reboot and don’t panic if you see the overwritten screen just let it be. It will take 3 to 4 minutes, so in meanwhile hear a song and be happy. After all this process, you are now free to use your Linux.

Congratulations now you have repaired the GRUB on CentOS and RHEL.