How to fix/re-install grub from a live usb/cd

    First, boot the affected computer from a live usb or cd. Then mount the root file system on /mnt (assumes the hard drive you want to install grub on is /dev/sda).

    mount /dev/sda2 /mnt

    If necessary, mount /boot

    mount /dev/sda1 /mnt/boot

    Mount the virtual file systems /dev/, proc, etc

    mount --bind /dev /mnt/dev
    mount --bind /dev/pts /mnt/dev/pts
    mount --bind /proc /mnt/proc
    mount --bind /sys /mnt/sys

    Chroot into the mounted environment.

    sudo chroot /mnt

    Install grub.

    grub-install /dev/sda

    Generate a grub config file.


    Exit the chroot environment and unmount the file systems.

    umount /mnt/sys
    umount /mnt/proc
    umount /mnt/dev/pts
    umount /mnt/dev
    umount /mnt






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