Re: ISO installer image: GPT versus MBR partitions

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i now look at the FAT filesystem images of Debian Live 9 and Guix 0.16.0:

Guix:

- There is an MBR partition table in the image file:
    Device            Boot Start   End Sectors  Size Id Type
    /mnt/iso/efi.img1 *        0  2879    2880  1.4M  1 FAT12

- Program "file" says:

  DOS/MBR boot sector, code offset 0x3c+2,
  OEM-ID "MTOO4021",
  root entries 224, sectors 2880 (volumes <=32 MB) ,
  sectors/FAT 9, sectors/track 18,
  serial number 0x336648a7, unlabeled,
  FAT (12 bit), followed by FAT

Debian:

- No partition table in image.

- Program "file" says:
  DOS/MBR boot sector, code offset 0x3c+2,
  OEM-ID "mkfs.fat",
  sectors/cluster 4, root entries 512, sectors 832 (volumes <=32 MB) ,
  Media descriptor 0xf8,
  sectors/FAT 1, sectors/track 32, heads 64,
  serial number 0x64c6c435, unlabeled, FAT (12 bit)

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My favorite suspect would be the partition table in Guix /efi.img.

To kill table entry 1 after having put the Guix EFI image back into
partition 2 of the USB stick:

   dd if=/dev/zero bs=1 count=16 seek=446 of=/dev/sdc1

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If this does not help, then create a new empty FAT filesystem image,
mount it, and copy the tree from the mounted Guix /efi.img into it.
The new filesystem should have between 200 KiB and 1.4 MiB.
(The Guix image of 1.4 MiB still has 90 % of its capacity free.)

Then put the new filesystem into /dev/sdc2 and see what happens.

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If this does not help, then copy again the Debian efi.img into partition 2,
mount it, and replace the file bootx64.efi by the one of the mounted
Guix efi.img.

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Have a nice day :)

Thomas