Reinstall GRUB on a dual boot setup with Arch Linux and Windows
In this article, we will go through the re-installation of GRUB on a dual-boot setup. This morning, I was upgrading my BIOS through a Lenovo installer, from Windows.
This has kind of messed up my Grub setup, and when trying to boot on Grub, it just went to a Grub shell rather than presening me the usual boot options. Moreover, when trying ls on the Grub shell, it wasn’t able to detect the filesystem for the Linux partitions, so it seemed quite bad.
My motivation to write this article, is for myself, to remember how to get out of this situation again if needs be, and to help other folks who might face the same issue.
This article is mostly speaking about Arch Linux as this is the distribution I currently use, but some of the steps might be applicable to other distributions as well.
My machine uses UEFI/GPT, and if you have an older BIOS, things might be a bit different.
Ensure Windows is still bootable
When rebooting the PC, at the very beginning, enter the BIOS (for my laptop model, I need to press F2).
Make sure to change the BIOS order so that the Windows boot comes before grub.
Restart the PC, and hopefully Windows starts as usual. If that’s not the case, you might need some more heavy lifting and at worst a factory reset.
Also in the BIOS, I suggest
Create a bootable USB stick with Arch Linux
Skip this step if you already have one.
Download Arch Linux as an ISO file.
Then download Rufus or any other similar tool, to burn the ISO file on a USB stick.
Once done, plug the USB stick, reboot the PC, and ensure that the USB drive comes first in the boot order in the bios.
You should then boot in an in-memory Arch Linux distribution as root.
Identify the partitions
Run lsblk first to check the partitions:
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$ 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
└─nvme0n1p7 259:7 0 7.7G 0 part
There’s a chance that nothing is mounted, so that’s not very helpful.
Run fdisk -l and check the results. For me, it looks like something like this:
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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.
This indicates that I have created two partitions for my Linux OS, namely /dev/nvme0n1p5 and /dev/nvme0n1p6.
/dev/nvme0n1p7 is clearly identified as a swap partition, but for the other two, it might not be clear which one is what.
I generally create two partitions, one for the root folder /, and one for /home, but depending on how you did it earlier, it might be different.
Now, it’s time to try to identify them.
Let’s try to mount the first partition:
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$ mount /dev/nvme0n1p5 /mnt
Then check the contents in /mnt:
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$ ls /mnt
If you see something that loks like bin boot dev ... proc run tmp ..., then that’s probably the root of the filesystem, so all good.
If you see the contents of something else (like /home), then unmount it for now until you find the root that you can mount on /mnt.
If you have a partition for /home, you can mount it on /mnt/home:
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$ mount /dev/nvme0n1p6 /mnt/home
Then setup the swap partition:
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$ swapon /dev/nvme0n1p7
Finally, check with lsblk again that everything is in order:
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$ 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]
Reinstall grub
The first step is to chroot:
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$ arch-chroot /mnt
If you are not using Arch Linux, check if your distro includes a similar helper for chroot, or just run chroot but you might have to manually mount a few things.
Make sure to mount the EFI partition to /boot/efi/:
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$ mount /dev/nvme0n1p1 /boot/efi/
Then reinstall grub with:
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$ grub-install --target=x86_64-efi --bootloader-id=grub_uefi --recheck
And then generate the grub config file (you might want to take a copy of the old one):
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$ grub-mkconfig -o /boot/grub/grub.cfg
Once done, remove the USB stick, then reboot the PC.
Now grub should be working as per normal. At this stage, there can be one caveat - it’s possible that grub didn’t detect the Windows partition while in chroot earlier.
Just go to your Arch Linux, mount the EFI directory if it’s not already done, and rerun the grub config generation:
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$ grub-mkconfig -o /boot/grub/grub.cfg
Now it should be able to detect the Windows partition.
Additional resources
This video helped me a lot to install Arch Linux with dual boot in the first place, and to troubleshoot this issue.
The Arch wiki page on GRUB is also very useful.