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I'm trying to start a 64 bits machine from USB where the EFI is only 32 bits compatible, which is a Lenovo Ideapad 100S.

When I boot on full 32 bits USB dongle (obtained from a .iso), it works. But with the same revision in 64 bits, it doesn't.

To solve that, I'm following tutorials suggesting to modify a 64 bits usb key and to add a 32 bits EFI file in the /efi/boot directory.

Such as https://medium.com/@realzedgoat/a-sorta-beginners-guide-to-installing-ubuntu-linux-on-32-bit-uefi-machines-d39b1d1961ec

It doesn't work in 2018 with Debian.

A nowadays Debian install usb dongle contains many things called EFI.

/boot/grub/efi.img
/boot/grub/
/boot/grub/x86_64-efi    <-- a dir with many driver modules
/efi/boot/bootx64.efi    <-- the original file
/efi/boot/bootia32.efi   <-- the file added thanks to tutorials

So ether I really missed something, or boot disk have changed and I have to modify more.

So do you know which files are implicated in the EFI load-up sequence?

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When booting from removable media, /efi/boot/boot<architecture>.efi is the file the UEFI firmware should be looking for, according to the UEFI specifications.

But then, the GRUB bootloader as packaged by Debian probably also needs the corresponding GRUB module directory and its contents: for 32-bit GRUB, it would be /boot/grub/i386-efi/. I think Ubuntu and Fedora configure their versions of GRUB slightly differently, and their GRUB configurations pack more of the GRUB modules into the main GRUB .efi binary.

The modules are in grub-efi-ia32-bin package, and in a working OS installation, they are initially located under /usr/lib/grub/<module directory> and the bootloader installation process will copy them from there to their final location at /boot/grub/<module directory>.

I think the /boot/grub/efi.img contains a CD-ROM boot image that is needed by the "El Torito" extension to the ISO-9660 standard, and it's not actually used when booting from a FAT32-formatted USB dongle.

  • I am a bit further, it was not a problem of efi files, but of .iso corruption after modification (don't use Iso Master). There is a second partition on usb live dungles, in R/W where the .efi stay, that's where you can modify files. But now I'm stuck with Grub2, who also searches some EFI files. – Sandburg May 20 '18 at 13:06

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