How to reinstall grub2 on fedora 21 using a live image and chroot

[humbleRumble]

This is applicable to LVM and UEFI (where grub2-install will fail)

This is a collection of the commands which I found necessary to reinstall grub from a live image using a chroot environment. I found all of these commands in various forum posts around the web and thought i would post them in one place as none of the individual posts worked for me while together they do have good information. please feel free to post if you think this is helpful so that it can possibly help someone else. thank you.

Notice: if anything in your system is installed in a non-standard location you may have to change some of the lines

Open a terminal and enter the following commands

su -
cd /mnt
mount /dev/fedora/root ./
mount /dev/fedora/home home/
mount -t proc proc proc/
mount --rbind /sys sys/
mount --rbind /dev dev/
mount --rbind /var/run/ var/run/
chroot /mnt/
mount /boot/efi
dhclient `/sbin/route -n | grep "^0.0.0.0" | rev | cut -d' ' -f1 | rev`
yum -y update
yum -y reinstall grub2 grub2-efi grub2-efi-modules shim
grub2-mkconfig -o /boot/grub2/grub.cfg
grub2-install /dev/sda

[wintonian]

I usually refer to the solution here for legacy BIOS.

I can attest that 'alt' method mentioned there (and linked to here) does in fact work and save some typing.

Mainly mount your root then:

# mkdir /mnt/<MYROOT>
# mount /dev/mapper/fedora-root /mnt/<MYROOT>
# grub2-install --root-directory=/mnt/<MYROOT> /dev/sd<x>

Not forgetting to mount /boot if on a different partition.

At least has worked for me without using LVM (as in the solution).

[lsatenstein]

I take the flashdrive that I used to create the Linux, I use the recovery LInux therein and follow the instructions.
Eventually a demand is to perform a chroot sysimage command. That latter command puts me into the Linux that has the invalid grub.cfg file.

You have to identify the boot volume and thereafter is perform a grub2-install /dev/boot_partition.

When you reboot grub.cfg should be in its proper place, and the boot chain (If you have uefi bios) will also be there. Your system will restart.

[humbleRumble]

@wintonian: I use lvm (as this is default in fedora 20) so your method does not work.
@isatenstein: fedora 20 workstation live image doesnt have a rescue option

It seems with lvm I cant get away with just a grub-install. just had to do this again after a failed hibernate corrupted grub yet again

---------- Post added at 12:01 PM ---------- Previous post was at 11:59 AM ----------

As it stands by modifying the first line of my example it will work for a non lvm setup as well and if no other solution works this one will, therefore i think it is very useful for others to be able to get this information.

[wintonian]

You will need to mount the LVM first.

Unfortunately I can't help you here as I don't use LVM, having found it to be more trouble than it's worth. Something which your issue illustrates again that IMO for most uses LVM creates an extra unnecessary obstacle.

Anyway here's a Google search to get you started.

[chrismurphy]

mount /boot/efi

This suggests the system has UEFI firmware, instead of legacy BIOS. If so, grub2-install is not applicable, and with default packages it will fail. Reinstalling GRUB on UEFI means reinstalling shim and grub2-efi packages.

[humbleRumble]

edited the original post to reflect that this affects LVM and UEFI.