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I am creating a boot disk (USB drive) using mkusb. mkusb gives me an option to use grub4win.img.xz:

dus-live 12.2.8 cannot install 'grub-pc' in installed systems in UEFI mode.
'grub-pc' is used to make persistent live drives bootable in BIOS mode.

Instead you can use 'grub4win.img.xz', an image with the grub content.

 Minimum 8 GB: You need a drive (USB pendrive or memory card) with
at least 8 GB because the image is expanded to 7.744 GB (to allow for
undersized 8 GB drives).
 Do you want to use 'grub4win.img.xz'? (y/N)

And after it's done:

Cannot install grub for BIOS mode from an installed system in UEFI mode.
 The created system should work in UEFI mode, 
if the ISO file is made for UEFI mode (Windows 8-10 64-bit).
If you use 'grub4win.img.xz', it should work in BIOS mode too.

My system already has secure boot in UEFI disabled. So did I need this?

qwr
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1 Answers1

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mkusb wants grub4win.img.xz if you run an installed system booted in UEFI mode. This is independent of secure boot.

You need grub4win.img.xz in order to create a drive that can boot also in BIOS mode. If it is enough for you to boot in UEFI mode, you do not need it.

But there is another issue, that might create problems for you.

The method used by mkusb was developed a few years ago. At that time it was enough to have a FAT32 partition to make an installer drive fro Windows. But nowadays there are several Windows 10 iso files that contain a version of the file install.wim with size > 4 GiB. It means that this method does not work because the FAT32 file system cannot manage it.

Such Windows iso files can be extracted into a USB pendrive with one FAT32 partition and one NTFS partition. It can be done with

Edit:

The current version of mkusb, 12.5.7, uses a new tool to create an installer drive for Windows, mkusb-tow, and it can manage versions of Windows with a huge install.wim file inside the iso file.

sudodus
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