search for: your_test_mbr

...can boot these with qemu. But where > shall I insert this creation of mine. Just overwrite the first 432 bytes of the ISO. Make a backup of the original bytes, so you can restore it later. dd bs=1 count=432 if=debian-8.7.1-i386-xfce-CD-1.iso of=mbr.backup dd conv=notrunc bs=1 count=432 if=your_test_mbr \ of=debian-8.7.1-i386-xfce-CD-1.iso To restore the original MBR code: dd conv=notrunc bs=1 count=432 if=mbr.backup \ of=debian-8.7.1-i386-xfce-CD-1.iso Have a nice day :) Thomas

Thomas Schmitt wrote: > So if we had a MBR which prints the content of the first 512 read bytes > we could tell whether they are block aligned and from which block they > come. Ok. I'll try. Is it the isohdppx or isohdpfx (or both) that is relevant? Meanwhile I have a hacked isohdppx.bin that prints: G if GPT M if MBR <nothing> if no partition info E if EBIOS C if not EBIOS