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

sudo mount /dev/sda2 /mnt #sda2 is the root partition
sudo mount /dev/sda1 /mnt/boot/efi #sda1 is the 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
modprobe efivars # make sure this is loaded
sudo chroot /mnt

apt-get install --reinstall grub-efi-amd64

apt-get install --reinstall grub-efi
update-grub

yum reinstall grub-efi

efibootmgr -c --disk /dev/sdX --part Y
efibootmgr -v # verify a new record called Linux is there

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

configfile (hd0,gpt1)/EFI/ubuntu/grub.cfg

sudo grub-install

# efibootmgr -c --disk /dev/sdX --part Y
# efibootmgr -v
BootCurrent: 0004
Timeout: 1 seconds
BootOrder: 0002,0000,0003,0001,0004
Boot0000* linuxmint HD(1,800,1f4000,829f6cc9-5b17-479c-b3ea-61e43faecbf7)File(EFIlinuxmintgrubx64.efi)
Boot0001* LMDE Linux Mint Debian    HD(1,800,15d505800,934c598c-fe3c-fd43-84a1-fa38e4f72552)File(EFIlinuxmintgrubx64.efi)
Boot0002* Linux HD(1,800,1f4000,829f6cc9-5b17-479c-b3ea-61e43faecbf7)File(elilo.efi)
Boot0003* UEFI: Built-in EFI Shell  Vendor(5023b95c-db26-429b-a648-bd47664c8012,)AMBO
Boot0004* UEFI: VerbatimSTORE N GO 1.00 ACPI(a0341d0,0)PCI(1a,0)USB(1,0)USB(4,0)HD(1,80,1d70780,00000000)AMBO
mint / #

# efibootmgr -b 2 -B

#! /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

sudo su
mkdir /boot/efi

fdisk -l|grep EFI

echo "/dev/sda2 /boot/efi   vfat    defaults,sync   0   0">>/etc/fstab

mount /boot/efi

aptitude install grub-efi-amd64-bin grub-efi-ia32-bin_

grub-install --target=x86_64-efi

update-grub

aptitude install grub-efi-amd64 grub-pc_ grub-gfxpayload-lists_

apt-get install --reinstall grub-efi
update-grub