Reinstall GRUB with a GNU\Linux LiveCD or LiveUSB

Sometimes, I had to install Windows in addition to GNU\Linux on the same machine. Sad days.

Best way to do this, is to start with the Linux installation -that opens the partition program- to have a right division of your disk. After this installation, I install Windows in its own partition, but this OS doesn’t like the linux bootloader and it rewrite the disk MBR with the reference to start the Microsoft Bootloader.

So in this condition, to reinstall the GRUB bootloader (the best used bootloader with new GNU\Linux distros) you can use the live distro on the CD or pendrive.
When the live-system starts, you need to know the system name of the linux partition. To know that, use the command

$ sudo fdisk -l

that shows the various partitions of the machine. Then you can identify your linux partition and know the system name that is “/dev/sdaX” or “/dev/hdaX” where X is a number.

Then, you only need to write these commands:

$ su
# mkdir /disk
# mount /dev/sdaX disk
# mount --bind /dev disk/dev
# mount -t proc none disk/proc
# chroot disk /bin/bash
# grub-install /dev/sda
# update-grub

In case you have the /boot folder into a different partition, you need to write also

# mount /dev/sdaX disk/boot

before the chroot command.

After that, you can do a normal restart of your system from HD and the bootloader is restored!

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