Ubuntu 15.10 multiboot with Windows 7 & 10

Nor

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Jan 9, 2016, 4:41:29 PM1/9/16

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I currently have Windows 7 & 10 duel setup-works fine. I am trying to get Ubuntu 15.10 installed on a usb pen drive to work with the Windows boot loader. Referring to "Dual boot Windows 7 and Linux/Unix" for guidance, I can't get it to work; item 3 doesn't work, and with Alternative 1: B: I can't find the proper file to use. What is the proper file?

My system is a Dell 7500 workstation, two 500 gb hard disks as a raid mirror, both Windows operating systems are on the hard drive, 3 usb hard disks, in addition to the usb pen drive.

I had no trouble getting Ubuntu installed on the pen drive with Grub2 or then removing Grub 2.

I need some help!

Nor

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Jan 10, 2016, 8:34:05 AM1/10/16

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Some additional info. While I still cannot boot Ubuntu with the Windows boot loader, I've found a work around that might shed some more light on my problem. If I disconnect all of the USB drives except the one containing Ubuntu 15.10 and change my
BIOS settings to boot first from USB device, my computer boots into Ubuntu using Grub2(guess I didn't get Grub2 removed after all), and it is usable. I would prefer to boot Ubuntu from the Windows loader, so I still need help.

boyans.net

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Jan 12, 2016, 7:47:36 PM1/12/16

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It depends on firmware.

A.) If you have UEFI firmware and UEFI boot is enabled by default then Windows 10 allows booting to USB going through:

Settings - Update & Security - Recovery - Advanced StartUp (here you can choose to restart to DVD or USB or into Recovery)

Alternative: Using BootNext tool allows rebooting to any installed Windows on disk or any bootable device.

B.) If you have BIOS firmware you can chainload PLOP boot manager which can boot USB or GRUB4DOS which can chainload almost everything.

boyans.net

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Feb 25, 2016, 1:43:52 PM2/25/16

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Just have reread the question.

You have to chainload either the boot sector (eventually MBR) from USB or the file "boot.img" found in /boot/grub[/i386-pc] (size is also 512 bytes).

A possible reason for the method not to work on different disk is that the boot sector file addresses same disk e.g. disk is represented as constant 0x80 in boot sector file.

To chainload disk 1 for example the constant should be 0x81.

To chainload disk 2 - constant 0x82.

So we have a fixed scheme for addressing disks - you cannot freely move/remove disks or boot will break!

The position of this disk addressing byte is 0x40 for GRUB legacy or 0x64 for GRUB2 in boot sector file.

Version 0.9.4 of Visual BCD Editor is handling this addressing (version still not available to public, sorry).