boota ubuntu från usb

i konsoll, skriv:

mkdir /tmp/installed
sudo mount /dev/sda3 (eller vad nu / hette) /tmp/installed
sudo mount -o bind /dev /tmp/installed/dev
sudo mount -o bind /proc /tmp/installed/proc
sudo mount -o bind /sys /tmp/installed/sys

sudo chroot /tmp/installed /bin/bash

grub-install /dev/sda