Ubuntu – Installing grub2 in efi-mode in usb flash drive

The hard disk is definitely set up for BIOS-style booting. Specific evidence of this includes:

• The partition table is MBR. Although it's theoretically possible to boot in EFI mode from an MBR partition table, to the best of my knowledge Windows does not support this configuration. Certainly its installer doesn't; the Windows installer supports MBR-on-BIOS or GPT-on-EFI, but not MBR-on-EFI or GPT-on-BIOS.
• There's no ESP on /dev/sda. (There are EFI boot files on /dev/sdb1, but that looks like a USB flash drive, not your regular boot disk.)
• The Boot Info Script output identifies GRUB as being installed in the MBR of /dev/sda. This is consistent with a BIOS-mode GRUB installation.
• The Boot Info Script output has identified /Windows/System32/winload.exe as a boot file on /dev/sda2. If this were an EFI installation of Windows, you'd see a reference to winload.efi somewhere.

Thus, whatever the source of the problem, it doesn't seem to have anything to do with EFI; it's a straight-up GRUB-on-BIOS problem.

The biggest clue I see is this, from the Boot Info Script output:

=> Grub2 (v1.99) is installed in the MBR of /dev/sda and looks at sector 1 of 
   the same hard drive for core.img. core.img is at this location and looks 
   for (,msdos6)/root/grub on this drive.

Note in particular the reference to (,msdos6)/root/grub. Later in the Boot Info Script output, there's a list of boot files on /dev/sda6 ((,msdos6) in GRUB-speak). This list includes /boot/grub/grub.cfg, but there's no mention of anything in the root directory. In fact, the root directory (not to be confused with the / directory, whose name is pronounced "root") is the superuser's home directory, and it doesn't ordinarily hold boot files. Thus, I suspect that GRUB was mis-installed. Perhaps you used options to grub-install that you didn't mention and that were inappropriate, or perhaps there's a bug in the installation script. In any event, I recommend re-installing GRUB using the usual procedures for doing this on a BIOS-based computer. Note, however, that if your emergency system boots in EFI mode, that could create complications, so you should be sure to boot your emergency system in BIOS mode.

You can check your boot mode in Linux by looking for the /sys/firmware/efi directory. If it's present, you've booted in EFI mode. If it's absent, you've probably booted in BIOS mode (although there are conditions when that file will be absent even though you've booted in EFI mode).

You cannot set two /boot partitions with boot-flag ! There is only one boot-flag necessary for grub2 in /boot partition - so simply deactivate boot-flag in your partition /dev/sda1

After this activate boot-flag in /boot partition of /dev/sdi - sure ? this is correct ? You have a /boot partition in /dev/sdi ? So there you need to activate boot-flag ( simply with gparted ).

As you say ... grub2 is already installed in /dev/sdi ? If not now follows (necessary because you modified boot-flags) :

sudo grub-install /dev/sdi

sudo update-grub2

Before this all your machine was booting into Windows 7 of /dev/sda3 via /dev/sda1 - but now boot-flag is deactivated and set to /boot partition of /dev/sdi - and your machine should now boot to installation of your usb-drive.

Only in case that in UEFI-mode your machine is not able to boot into usb-drive - then you should disable UEFI-mode in BIOS-settings and enable there EFI-mode instead.