mount boot partition

sudo mount /dev/sda1 /opt

sudo vi /opt/grub/grub.cfg

menuentry

search –no-floppy –fs-uuid –set $UUID_OF_BOOT_PARTITION
linux /vmlinuz root=/dev/mapper/vg-root

mount root partition on lvm

sudo apt-get install lvm2

sudo lvdisplay

sudo lvchange -ay /dev/vg-label

sudo mount /dev/mapper/vg-root /mnt

sudo vi /mnt/etc/fstab

UUID=$UUID_OF_BOOT_PARTITION /boot ext2 defaults 0 2
/dev/mapper/vg-root / ext4 defaults 0 2
/dev/mapper/vg-home /home ext4 defaults 0 2