Table of Contents

GRUB rescue

GRUB_DISABLE_OS_PROBER=true

reinstall grub in chroot

export TARGET=/mnt
for i in /dev /dev/pts /proc /sys /run /run/lvm; do sudo mount --bind ${i} /${TARGET}${i}; done
chroot ${TARGET}
grub-install /dev/sdX
update-grub
update-initramfs
 
for i in /dev /dev/pts /proc /sys /run /run/lvm; do sudo umount /${TARGET}${i}; done

grub rescue

ls
ls (hd0,msdos1)/
ls (hd0,msdos7)/
set root=(hd0,msdos7)
set prefix=(hd0,msdos7)/boot/grub
insmod normal
normal

After system startup 

update-grub
grub-install /dev/sda

Early config