How to reinstall GRUB2 EFI?

Question

After successfully updating my bios, something went wrong and I ended up with a blinking cursor on the top left corner of a black screen. No errors, no nothing. The bios now only listed a SATA: <disc name> boot option in place of the usual UEFI ubuntu one. I'm using a GPT partitioning scheme.

I eventually found that the working solution was to properly reinstall grub-efi-amd64. So, how do I do this ?

PS: Actually, i succeeded to reinstall GRUB2 EFI on my own and will post my answer here as I was unable to find any complete how-to on this.

Answer 1

• Boot your computer with a live-usb/CD in UEFI mode. I had two boot options <flash_drive> and UEFI: <flash_drive>, the second is needed to expose the efi variables in /sys/firmware/efi/ so that efibootmgr don't fail later on. Booting with the first option gives me the following error:

  Fatal: Couldn't open either sysfs or procfs directories for accessing EFI variables.
  Try 'modprobe efivars' as root.
  

  modprobe efivars did'nt work for me.

• chroot into the broken system (similar to the ubuntu grub2 help but with efi specificities):

  sudo mount /dev/sda2 /mnt #sda2 is my root partition
  sudo mount /dev/sda1 /mnt/boot/efi #sda1 is my efi partition
  for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done
  sudo cp /etc/resolv.conf /mnt/etc/ #makes the network available after chrooting
  sudo chroot /mnt
  apt-get install --reinstall grub-efi-amd64
  
  or alternatively: 
  apt-get install --reinstall grub-efi
  update-grub
  
  should the above give you a grub, but not a bootable one
  

• Now type Ctrl+D to exit chroot, unmount everything and reboot:

  for i in /sys /proc /dev/pts /dev; do sudo umount /mnt$i; done
  sudo umount /mnt/boot/efi #please do this. corrupted efi partitions are not nice
  sudo umount /mnt
  sudo reboot
  

You may need to adapt this to your needs (different partition table, separate /boot partition, etc.) and it may not be the only option but this worked just fine for me.

Answer 2

I would up-vote this, but apparently I don't have enough rep on SuperUser. I'm glad I finally found an answer to this after days of fighting clones that worked but wouldn't boot. I think it all relates to UEFI and some kind of "secure booting" mechanism or something.

I'm working off-line, so apt-get wasn't an option. What I did was put Ubuntu Desktop on a USB stick, add the grub-efi and grub-efi-amd64 packages to the root of the USB stick (grub-efi_1.99~rc1-13ubuntu3_amd64.deb and grub-efi-amd64_1.99~rc1-13ubuntu3_amd64.deb for Ubuntu 11.04 - change as appropriate for distro and architecture), and put the following in a script on the USB stick as well:

#! /bin/bash
sudo mount /dev/sda2 /mnt
sudo mount /dev/sda1 /mnt/boot/efi
dir=`dirname $0`
sudo cp $dir/grub-efi*.deb /mnt/tmp
for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt /bin/sh -c "dpkg -i /tmp/grub-efi*.deb"
sudo shutdown -r now

Boot up the Live USB stick, open a terminal, run the command, and the job is a good 'un! The only occasional problem is that UEFI sometimes got moved down the boot priority order below the HDD, at which point you need to go into the BIOS and change the boot order to stop it trying (and failing) on SATA: drive.

You can also use dpkg-reconfigure instead of dpkg -i, but that asks a couple of boot loader questions.

[edit] I also don't have enough rep to comment, so what I thought was a comment on a reply turns out to be a reply.