When you install Windows, Windows assumes it is the only operating system (OS) on the machine, or at least it does not account for Linux. So it replaces GRUB with its own boot loader. What you have to do is replace the Windows boot loader with GRUB. I've seen various instructions for replacing GRUB by mucking around with GRUB commands or some such, but to me the easiest way is to simply
chroot
into your install and runupdate-grub
.chroot
is great because it allows you to work on your actual install, instead of trying to redirect things here and there. It is really clean.Here's how:
- Boot from the live CD or live USB, in "Try Ubuntu" mode.
- Determine the partition number of your main partition. GParted (which should already be installed, by default, on the live session) can help you here. I'm going to assume in this answer that it's
/dev/sda2
, but make sure you use the correct partition number for your system!Mount your partition:
sudo mount /dev/sda2 /mnt #Replace sda2 with your partition number
Bind mount some other necessary stuff:
for i in /sys /proc /run /dev; do sudo mount --bind "$i" "/mnt$i"; done
If Ubuntu is installed in EFI mode ([see this answer if you're unsure][efi]), use GParted to find your EFI partition. It will have a label of
EFI
. Mount this partition, replacingsdXY
with the actual partition number for your system:sudo mount /dev/sdXY /mnt/boot/efi
chroot
into your Ubuntu install:sudo chroot /mnt
At this point, you're in your install, not the live session, and running as root. Update grub:
update-grub
If you get errors or if going up to step 7 didn't fix your problem, go to step 8. (Otherwise, it is optional.)
Depending on your situation, you might have to reinstall grub:
grub-install /dev/sda update-grub # In order to find and add windows to grub menu.
If everything worked without errors, then you're all set:
exit sudo reboot
At this point, you should be able to boot normally.
If you cannot boot normally, and didn't do step 8 because there were no error messages, try again with step 8.
- Sometimes giving GRUB2 the correct configuration for your partitions is not enough, and you must actually install it (or reinstall it) to the Master Boot Record, which step 8 does. Experience helping users in chat has shown that step 8 is sometimes necessary even when no error messages are shown.
[efi]: https://askubuntu.com/a/764702/13398
copied from https://askubuntu.com/a/88432