Comment 2 for bug 1826656

UbiquitySyslog.txt reports (timestamps/hostname removed):

efi: EFI v2.31 by American Megatrends
efi: ACPI=0xd9ae0000 ACPI 2.0=0xd9ae0000 SMBIOS=0xf04c0 MPS=0xfd430
secureboot: Secure boot could not be determined (mode 0)
SMBIOS 2.7 present.
DMI: Gigabyte Technology Co., Ltd. To be filled by O.E.M./Z77X-D3H, BIOS F16 10/24/2012
...
grub-installer: info: Installing grub on '/dev/sda'
grub-installer: info: grub-install does not support --no-floppy
grub-installer: info: Running chroot /target grub-install --force "/dev/sda"
grub-installer: Installing for x86_64-efi platform.
grub-installer: Could not prepare Boot variable: Function not implemented
grub-installer: grub-install: error: efibootmgr failed to register the boot entry: Input/output error.
grub-installer: error: Running 'grub-install --force "/dev/sda"' failed.

efibootmgr fails to write EFI variables. This is similar to https://bugs.debian.org/923235

This mainboard is either HW rev 1.0 or 1.1 - which use identical firmware:
https://www.gigabyte.com/Motherboard/GA-Z77X-D3H-rev-10#support-dl-bios
https://www.gigabyte.com/Motherboard/GA-Z77X-D3H-rev-11#support-dl-bios
FW changelog states on the next newer version: "Support Secure boot option".