Assume the following scenario you've done something and you and crushed the MBR record. And then I don't have or I just get an error message in GRUB. His recovery is a trivial operation from anywhere to look

1. Make yourself a Live CD/DVD/USB whatever you have on hand with any distro

2. A switch in the chroot you launch OS will save the settings and will use the version of grub with which they were to me, and I have a lot of things described in CMD on Grub

mount /dev/sda1 /mnt
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
chroot /mnt

3. Now we chroot to your distro to be reinstalled only left rough and ″pdejtne (for each case)

grub-install /dev/sda
update-grub

Restart the veil and we are ready to work as before and everything we ate was onion intact onion 😉 mirisali us restore GRUB