Reinstall GRUB on a dual boot setup with Arch Linux and Windows

In this post, I’ll walk through how to reinstall GRUB on a dual-boot system with Arch Linux and Windows.

This morning, I upgraded my BIOS using a Lenovo installer from within Windows. That ended up messing with GRUB—on reboot, I was dropped into a GRUB shell instead of seeing the familiar boot options. Worse, GRUB couldn’t even detect the Linux filesystems using ls, which made things look pretty bad.

I’m writing this partly as a personal note in case it happens again, and partly to help anyone else who runs into the same problem.

I use Arch Linux, so the instructions are Arch-specific, but many of the steps should apply to other distributions too. My system uses UEFI and GPT; if you’re using legacy BIOS, the steps will differ.

---

Step 1: Make sure Windows is still bootable

Reboot your computer and enter the BIOS setup (on my Lenovo laptop, this means pressing F2 during startup).

In the BIOS settings:

• Make sure the Windows boot entry comes before the GRUB entry in the boot order.
• Save and reboot.

With luck, Windows should boot normally. If not, you may need to do more serious recovery steps—up to and including a factory reset.

---

Step 2: Create a bootable USB with Arch Linux

Skip this if you already have one.

1. Download the Arch ISO.
2. Use Rufus or a similar tool to write the ISO to a USB stick.
3. Plug in the USB, reboot, and ensure the USB drive is first in the boot order.

You should now boot into a live Arch environment.

---

Step 3: Identify and mount your partitions

First, list available partitions:

lsblk

This might show something like:

NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
nvme0n1     259:0    0 476.9G  0 disk
├─nvme0n1p1 259:1    0   260M  0 part
├─nvme0n1p2 259:2    0    16M  0 part
├─nvme0n1p3 259:3    0 377.1G  0 part
├─nvme0n1p4 259:4    0     2G  0 part
├─nvme0n1p5 259:5    0    40G  0 part 
├─nvme0n1p6 259:6    0    50G  0 part 
└─nvme0n1p7 259:7    0   7.7G  0 part

For more detail, run:

fdisk -l

This might show something like:

Device             Start        End   Sectors   Size Type
/dev/nvme0n1p1      2048     534527    532480   260M EFI System
/dev/nvme0n1p2    534528     567295     32768    16M Microsoft reserved
/dev/nvme0n1p3    567296  791318527 790751232 377.1G Microsoft basic data
/dev/nvme0n1p4 996118528 1000214527   4096000     2G Windows recovery environment
/dev/nvme0n1p5 791318528  875204607  83886080    40G Linux filesystem
/dev/nvme0n1p6 875204608  980062207 104857600    50G Linux filesystem
/dev/nvme0n1p7 980062208  996118527  16056320   7.7G Linux swap

Partition table entries are not in disk order.

You’ll need to figure out which partition contains your root (/) filesystem. In my case:

• /dev/nvme0n1p5 is root (/)
• /dev/nvme0n1p6 is /home
• /dev/nvme0n1p7 is swap

Mount the root partition:

mount /dev/nvme0n1p5 /mnt
ls /mnt

If you see typical root directories (bin/, boot/, etc/, etc.), you’ve got the right partition. Otherwise, unmount and try the other one.

If you have a separate /home, mount it too:

mount /dev/nvme0n1p6 /mnt/home

Enable swap:

swapon /dev/nvme0n1p7

Verify with:

lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
nvme0n1     259:0    0 476.9G  0 disk
├─nvme0n1p1 259:1    0   260M  0 part
├─nvme0n1p2 259:2    0    16M  0 part
├─nvme0n1p3 259:3    0 377.1G  0 part
├─nvme0n1p4 259:4    0     2G  0 part
├─nvme0n1p5 259:5    0    40G  0 part /
├─nvme0n1p6 259:6    0    50G  0 part /home
└─nvme0n1p7 259:7    0   7.7G  0 part [SWAP]

Look for correct mount points, like /, /home, and [SWAP].

Step 4: Reinstall GRUB

First, chroot into your system:

arch-chroot /mnt

If you’re using a non-Arch distro, use chroot directly but make sure to mount proc, sys, dev, and other required filesystems.

Next, mount the EFI partition (this is crucial for UEFI setups):

mount /dev/nvme0n1p1 /boot/efi/

Then reinstall GRUB:

grub-install --target=x86_64-efi --bootloader-id=grub_uefi --recheck

Generate the GRUB configuration:

grub-mkconfig -o /boot/grub/grub.cfg

Exit the chroot environment, unmount the partitions (optional), and reboot:

exit
reboot

Remove the USB stick, and hopefully you’ll see the GRUB menu again.

---

If Windows doesn’t show up in GRUB

Sometimes GRUB won’t detect Windows while you’re in the chroot environment. If that happens, boot into Arch normally, then:

• Ensure the EFI partition is mounted:

  mount /dev/nvme0n1p1 /boot/efi
  

• Regenerate the GRUB config:

  grub-mkconfig -o /boot/grub/grub.cfg
  

Now GRUB should detect both Arch and Windows.

Additional resources

• This video guide helped me install Arch and fix dual-boot issues.
• The Arch wiki page on GRUB is also very useful.
• This guide contains some useful tips for GRUB package updates.