efi

UEFI/GPT 
https://unix.stackexchange.com/questions/83669/how-to-recreate-efi-boot-partition
https://docs.fedoraproject.org/en-US/Fedora/22/html/Multiboot_Guide/common_operations_appendix.html#common-chroot_from_live
https://docs.fedoraproject.org/en-US/Fedora/22/html/Multiboot_Guide/GRUB-reinstalling.html
https://forums.gentoo.org/viewtopic-t-1002254-start-0.html

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init 3

su - root
modprobe efivarfs

mkdosfs -F 32 -n EFI /dev/sdEFIx # !!!!!!!!!!!!!! CAREFUL WITH NUMBER if needed to create EFI partition from scratch

mkdir /mounted
mount /dev/sdOSx /mounted
mount /dev/sdEFIx /mounted/boot/efi
for i in /dev /dev/pts /proc /sys /sys/firmware/efi/efivars /run; do sudo mount -B $i /mounted$i; done
mkdir -p /mounted/boot/efi/EFI/fedora/
cp -R /boot/efi/EFI/fedora/* /mounted/boot/efi/EFI/fedora/

cp /etc/resolv.conf /mounted/resolv.conf

sudo chroot /mounted

yum install grub2-efi-x64 shim-x64  && yum reinstall grub2-efi-x64 shim-x64

efibootmgr -D
efibootmgr -B -b 000X ## clear old entries

blkid -s UUID -o value /dev/sdX # disk_uuid
echo 'LABEL=EFI /boot/efi vfat defaults 0 2' >> /etc/fstab ## check for existing efi entry; replace UUID or remove

efibootmgr -c -w -L Fedora -d /dev/sdz -p 1 -l \EFI\fedora\shimx64.efi

grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg