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Re: grub-mkrescue: Problem with MBR partition table at start of EFI part

From: pelzflorian (Florian Pelz)
Subject: Re: grub-mkrescue: Problem with MBR partition table at start of EFI partition
Date: Fri, 10 May 2019 18:12:08 +0200
User-agent: NeoMutt/20180716

On Fri, May 10, 2019 at 03:46:56PM +0200, Thomas Schmitt wrote:
> Hi,
> Florian Pelz wrote:
> > I would like to test but on this bootable German Windows 10
> > 32-bit+64-bit USB install medium, the content is different.  How would
> > I find the offset in the USB image (you call it offset 454) which I
> > should zero out to break Windows?
> That would be offset 454 in the EFI boot image: Start LBA field of MBR
> partition 1.
> You may learn the block address of the image from xorriso:
>   xorriso -indev "$ISO" -report_el_torito plain 2>/dev/null \
>   | grep 'El Torito boot img : .* UEFI'
> should say something like
>   El Torito boot img :   2  UEFI  y   none  0x0000  0x00   1     515

This is not an install ISO but a USB install medium.  The USB drive
was written by the Windows Media Creation Tool.  Copying instead a
Windows ISO created by the Windows Media Creation Tool to a USB drive
does *not* yield a bootable USB drive; it does not even boot on other

So mine is a USB drive already, not an ISO image.  I do:

$ sudo xorriso -indev "stdio:/dev/sdb" -report_el_torito plain
GNU xorriso 1.5.0 : RockRidge filesystem manipulator, libburnia project.

xorriso : NOTE : Loading ISO image tree from LBA 0
libisoburn: WARNING : No ISO 9660 image at LBA 0. Creating blank image.
Drive current: -indev 'stdio:/dev/sdb'
Media current: stdio file, overwriteable
Media status : is written , is closed
Media summary: 1 session, 3932160 data blocks, 7680m data,     0 free
Volume id    : 'ISOIMAGE'
xorriso : NOTE : No El Torito information was loaded

Apparently it is wrong to look at such Windows 10 USB media and I
should rather look at older Windows installation media.  I will try to
procure a Windows 7 install ISO.  I will report back tomorrow.


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