way 1
failed~
sudo su
mount /dev/sda5 /mnt
mount --bind /dev /mnt/dev
mount --bind /dev/pts /mnt/dev/pts
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
chroot /mnt
grub-install --root-directory=/mnt /dev/sda5
grub-install --recheck /dev/sda5
update-grub
way 2
use ISO to boot and try repair
add ppa
deb http://ppa.launchpad.net/yannubuntu/boot-repair/ubuntu eoan main
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys <PUBKEY>
apt-get install -y boot-repair && boot-repair
