Reinstalling GRUB2

Somehow I managed to completely mangle grub2 to the point even grub's self-repair couldn't work things out.

The usual method of fixing grub2 is to dnf reinstall grub2-common shim and maybe some other packages however this wasn't helping at all. I also use grub-btrfs (which, now that I think of it, I could have used to repair in this scenario too 🤔).

Anyway, I can never find one guide that's complete or up-to-date on fixing a completely messed up grub2. So here it is. Mostly for myself when I do it the next time! 😊

Note: This guide is intended for UEFI and Fedora systems only. The order is similar and can be adapted to other systems, if you know their peculiarities.

Where is stuff?

Step 1. Boot from the Fedora Live CD...

First of all, run lsblk to remember your partition structure which you haven't looked at for 10 months. You can also use Gnome Disks:

> lsblk
nvme0n1     259:0    0   1.8T  0 disk 
├─nvme0n1p1 259:1    0   100M  0 part 
├─nvme0n1p2 259:2    0    16M  0 part 
├─nvme0n1p3 259:3    0 117.2G  0 part 
├─nvme0n1p4 259:4    0   707M  0 part 
├─nvme0n1p5 259:5    0   512M  0 part
└─nvme0n1p6 259:6    0   1.1T  0 part

Get set up

Great, so now I remember nvme0n1p6 is my Fedora install (Btrfs), and nvme0n1p5 is my Linux EFI partition (FAT32).

Note also here: My Windows has its nice own EFI partition—nvme0n1p1 FAT32 of 100MB. If you have separate EFI partitions for Windows & Linux, they are unlikely to ever fight and kill each others' boot systems, and if they do, it's a lot simpler to fix it.

Let's mount my filesystem. Thankfully I no longer need to remember Btrfs commands, mount is smart enough to recognise it's mounting Btrfs.

You will need to examine the following commands, because your mount points might be different from mine.

# Mount my main root '/' folder the new mount point:
sudo mount /dev/nvme0n1p6 /mnt

# If your `/boot` is its own partition, mount it now with:
sudo mount /dev/nvme0n1p4

# Otherwise if your `/boot` is a just a folder within root `/`, mount it like this:
sudo mount -o bind /boot /mnt/boot

# Tell chroot where other important folders are:
sudo mount -o bind /dev /mnt/dev
sudo mount -o bind /proc /mnt/proc
sudo mount -o bind /sys /mnt/sys
sudo mount -o bind /run /mnt/run

# And tell the kernel how to access to the efivars directory and mount the EFI system partition:
sudo mount -o bind /sys/firmware/efi/efivars /mnt/sys/firmware/efi/efivars

# Then lastly, mount the EFI partition inside /boot
sudo mount /dev/nvme0n1p5 /mnt/boot/efi

Okay, we are ready to switch control to your normal Fedora install! We do this with chroot:

sudo chroot /mnt

Resetting and reinstalling grub2

Now you're chroot, you no longer need to use sudo for things. You are su already. So excercise appropriate care.

For grub to completely regenerate itself, you need to clear several files.

**Important. If you've customised any files in /etc/grub.d/ (for grub-btrfs, or chainloading, etc.) copy these files somewhere safe (e.g. /home/<yourusername>/backup. For the reinstall to work, only copy the minimum of files you are sure are correct/working.

What we need to do now is delete ALL of grub's configuration files and shim (except your /etc/default/grub config). This is what triggers grub to re-create them for you. If you miss one, reinstalling grub will do nothing.

We will also delete the symbolic links (grub will recreate these too).

rm /boot/efi/EFI/fedora/grub.cfg

rm /etc/grub2.cfg
rm /etc/grub2-efi.cfg

rm /etc/grub.d/*
rm /etc/sysconfig/grub

With all this gone, and everything mounted correctly, grub should now regenerate correctly them on reinstall:

dnf reinstall grub2-* shim-*

If you backed up any configs in /etc/grub.d/, copy them back now.

Now that all the original configs are reset, you should be able to build working grub2 configs:

grub2-mkconfig -o /boot/grub2/grub.cfg

Note: After this on Feodra just use grub2-mkconfig -o /etc/grub2.cfg.

Some final checks...

We're getting close. Lastly we'll check the symlinks in /etc/ are correct: ls -la /etc/grub2*

They should look exactly like this:

lrwxrwxrwx. 1 root root 20 Oct 27 23:43 /etc/grub2.cfg -> /boot/grub2/grub.cfg
lrwxrwxrwx. 1 root root 22 Oct 12 13:24 /etc/grub2-efi.cfg -> ../boot/grub2/grub.cfg

If not, you can recreate them manually, however this is an indication grub did not reinstall properly, so it's better to go back and examine your steps (and probably reboot and start from the beginning).

Great. Now list your grub2 menu options and make sure they look correct before you reboot with:

grubby --info=ALL

If some are missing or incorrect, check your /etc/default/grub config, and re-run grub2-mkconfig - /etc/grub2.cfg.

If you want to be really sure GRUB2 was properly reinstalled, you can check the files we deleted were recreated:

cat /boot/efi/EFI/fedora/grub.cfg
cat /boot/grub2/grub.cfg

...and make sure those files both have contents. The first file should only be several lines long (that's the shim).

Unmount stuff

Exit the chroot then unmount things, before finally rebooting 😊:

Note: You could probably get away with not doing this, hoewever it makes sure the file system has actually written all changes to the drive before you reboot, especially for COW (copy-on-write) filesystems like Btrfs.

sync && exit

sudo umount /mnt/boot/efi
sudo umount /mnt/sys/firmware/efi/efivars
sudo umount /mnt/sys
sudo umount /mnt/dev
sudo umount /mnt/proc
sudo umount /mnt/run
sudo umount /mnt

reboot

Legal Matters

ASUS and ROG Trademark is either a US registered trademark or trademark of ASUSTeK Computer Inc. in the United States and/or other countries.

Reference to any ASUS products, services, processes, or other information and/or use of ASUS Trademarks does not constitute or imply endorsement, sponsorship, or recommendation thereof by ASUS.

The use of ROG and ASUS trademarks within this website and associated tools and libraries is only to provide a recognisable identifier to users to enable them to associate that these tools will work with ASUS ROG laptops.

Privacy Policy

We use Matomo

Matomo is an open source web analytics platform. A web analytics platform is used by a website owner in order to measure, collect, analyse and report visitor data for purposes of understanding and optimizing their website.

Purpose of the processing

Matomo is used to get an idea how our website is used by our users so we can optimize things further so that the user may find the most relevant information more quickly.

Data Matomo is processing

  • User IP address
  • Optional User ID
  • Date and time of the request
  • Title of the page being viewed
  • URL of the page being viewed
  • Referrer URL
  • Screen resolution being used
  • Time in local user’s timezone
  • Files that were clicked and downloaded
  • Links to an outside domain that were clicked
  • Page generation time
  • User location: country, region, city, approximate latitude and longitude
  • Main Language of the browser being used
  • User Agent of the browser being used

Pick up the one you are using:

  • Cookies
  • IP address
  • User ID
  • Custom Dimensions
  • Custom Variables
  • Location of the user

And also:

  • Date and time
  • Title of the page being viewed
  • URL of the page being viewed
  • URL of the page that was viewed prior to the current page
  • Screen resolution
  • Time in local timezone
  • Files that were clicked and downloaded
  • Link clicks to an outside domain
  • Pages generation time
  • Country, region, city
  • Main Language of the browser
  • User Agent of the browser

This list can be completed with additional features such as:

  • Form interactions
  • Media interactions
  • A/B Tests

The processing of personal data with Matomo is based on legitimate interests

If you wish us to not process any personal data with Matomo, you can opt-out from it at any time. There will be no consequences at all regarding the use of our website.

You can withdraw at any time your consent by clicking here

The right to lodge a complaint with a supervisory authority

If you think that the way we process your personal data with Matomo analytics is infringing the law, you have the right to lodge a complaint with a supervisory authority.

We are not doing any profiling.