Cfrtjryk

My grub broke, I don't know what caused it, it happened after I booted off a usb live image of a linux distro I was going to try to install, but I was only in the anaconda setup menu, the installation itself had not started yet. he installer froze out of the blue before I could start the installation, and I had to reboot the system. After I did somehow my grub installation on /dev/sdb broke and I can't boot into my existing OSes.

My setup is as follows: /dev/sdb1 (Boot), /dev/sdb3 (Arch Linux Root) /dev/sdb2 (Windows boot) /dev/sdb4 (Empty partition, reserved to be used as an LVM for other linux distros I intend to install).

The grub prefix should be (hd1,msdos1)/grub, but when I try to reinstall grub and fix it, it for some reason always wants to put (hd1,msdos3)/boot/grub as the prefix and root.

When I try to boot it gives me the typical error: file '/grub/i386-pc/normal.mod' not found, and I'm a little bit confused since the grub-install command runs fine on arch reporting no errors, but still doesn't install grub correctly.

This is what I do to boot from grub rescue:

set prefix=(hd1,msdos1)/grub

insmod normal

normal

When I do that it loads correctly, now I only need a way to define this manually when grub is installed. Also, just to be clear, running grub-install again does not fix the problem, only repeats it. Grub seems to expect me to have it installed on /boot/grub on /dev/sdb3 when it is in fact installed on /grub on /dev/sdb1

E.G.:
grub-install --boot-directory=/media/USERNAME/Mounted_BootVolume/ --force /dev/sda3

where /dev/sda3 is the "Patch-Core-Onto-Partition" and may be (but doesnt have to be) the same as Mounted_BootVolume.

".../grub" as the trailing-target-dir obviously cannot be changed

taken from manpage: --boot-directory=...
install GRUB images under the directory DIR/grub instead of the boot/grub dir

P.S.: the new custom-dir is implicitly reflected by any boot-up of the grub-shell (i.e. grub.cfg needs no added prefix= lines) AFAIK

Have you tried Boot-Repair? It's a live USB that tries to automatically fix your Grub installation.

Was your /boot filesystem mounted when you ran grub-install?

(Unless you explicitly specify all the parameters, grub-install will attempt to auto-detect the partition that contains the /boot/grub directory, and will set the partition number and the default prefix accordingly. If /boot is a separate filesystem and not mounted while you're running grub-install, the auto-detection may get confused.)

As a partial workaround (for the directory part of the prefix), you can do this while the /boot filesystem is mounted:

cd /boot

ln -s . boot

Now there is a symbolic link /boot/bootwhich points right back to /boot, which looks nonsensical. (Don't worry, tools like find and locate are smart enough not to get trapped in an infinite loop from this.)

But when GRUB is trying to access (partition)/boot/grub, it hits the symbolic link: when replaced with the link's target, the path becomes (partition)/./grub which is equal to just (partition)/grub... which is what you want.

I spent a few hours here banging my head against the wall, the missing piece of the puzzle is that grup-install does not regenerate your grub.cfg file, you need to run update-grub or the equivalent grub-mkconfig -o /boot/grub/grub.cfg command.