How to Reinstall GRUB

Follow the steps below to reinstall GRUB on your Linux system:

Reinstalling GRUB in the Linux terminal.

1. Mount the partition containing the OS installation. 
The example mounts the /dev/sda1 partition to the /mnt directory.

sudo mount /dev/sda1 /mnt

2. Bind the /dev, /dev/pts, /proc, and /sys directories 
to the corresponding directories in the /mnt folder.

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

3. Install GRUB.

sudo grub-install --root-directory=/mnt/ /dev/sda
#
or
#
sudo chroot /mnt
#
grub-install /dev/sda --force
#
or
#
dpkg-reconfigure grub-pc
#
update-grub
#
update-initramfs -c -k all
#
exit

4. Unmount the directories when the installation completes successfully.

sudo umount /mnt/sys &&
sudo umount /mnt/proc &&
sudo umount /mnt/dev/pts &&
sudo umount /mnt/dev &&
sudo umount /mnt

5. reboot

sudo reboot

## error ##
grub2-install: "this GPT partition label contains no BIOS Boot Partition"

You need to change the label type, from boot to bios_grub for example through parted:

parted /dev/sd[x]
set 1 boot off
set 1 bios_grub on
q

Then again:

grub2-install /dev/sd[x]

or

dpkg-reconfigure grub-pc
#
Reinstalling GRUB in the Linux terminal LVM.

1. Mount the partition containing the LVM OS installation. 
The example mounts the /dev/mapper/vgname-lvname partition to the /mnt directory.

sudo mount /dev/mapper/vgname--lvname /mnt
ex.:
sudo mount /dev/mapper/vgname--lvname-root /mnt
sudo mount /dev/mapper/vgname--lvname-var /mnt/var
sudo mount /dev/mapper/vgname--lvname-home /mnt/home
#
#part boot ex.: ext2 file system
sudo mount /dev/sd[x][1-9] /mnt/boot

2. Bind the /dev, /dev/pts, /proc, and /sys directories 
to the corresponding directories in the /mnt folder.

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

3. Install GRUB.

sudo grub-install --root-directory=/mnt/ /dev/sd[x]
#
or
#
sudo chroot /mnt
#
grub-install /dev/sd[x] --force
#
or
#
dpkg-reconfigure grub-pc
#
update-grub
#
update-initramfs -c -k all
#
exit

4. Unmount the directories when the installation completes successfully.

sudo umount /mnt/sys &&
sudo umount /mnt/proc &&
sudo umount /mnt/dev/pts &&
sudo umount /mnt/dev &&
#
sudo umount /mnt/boot &&
sudo umount /mnt/var &&
sudo umount /mnt/home &&
sudo umount /mnt

5. reboot

sudo reboot