Re: ISO installer image: GPT versus MBR partitions

["pelzflorian (Florian Pelz)" <pelzflorian@pelzflorian.de>]

On Wed, Apr 17, 2019 at 05:51:41PM +0200, Thomas Schmitt wrote:
> Hi,
> 
> here are instructions to repack a Guix ISO with EFI support (via GPT)
> to an ISO with MBR-only partition table.
> 

Thank you!  However, even though Linux is happy about the repacked
ISO, my Macbook still does not like it.  I wonder what makes Debian so
likable.  I will investigate tomorrow.

(The ISO image file size is reproducable, the content is not, of
course, as before.)




> The result may be inspected by
> 
>   xorriso \
>      -indev "$REPACKED_ISO" \
>      -report_system_area plain \
>      -report_el_torito plain
> 
> which should say
> 
>   ...
>   Volume id    : 'GUIXSD_IMAGE'
>   System area options: 0x00004a00
>   System area summary: MBR grub2-mbr cyl-align-off
>   ISO image size/512 : 2071064
>   Partition offset   : 16
>   MBR heads per cyl  : 64
>   MBR secs per head  : 32
>   MBR partition table:   N Status  Type        Start       Blocks
>   MBR partition      :   1   0x80  0x83           64      2065240
>   MBR partition      :   2   0x00  0xef      2065304         5760
>   El Torito catalog  : 17333  1
>   El Torito cat path : /boot.catalog
>   El Torito images   :   N  Pltf  B   Emul  Ld_seg  Hdpt  Ldsiz         LBA
>   El Torito boot img :   1  BIOS  y   none  0x0000  0x00      4       17334
>   El Torito boot img :   2  UEFI  y   none  0x0000  0x00   5760      516326
>   El Torito img path :   1  /boot/grub/i386-pc/eltorito.img
>   El Torito img opts :   1  boot-info-table grub2-boot-info
>   El Torito img blks :   2  1440
> 

Looks good, I believe:

florian@florianmacbook ~$   xorriso \
>      -indev "$REPACKED_ISO" \
>      -report_system_area plain \
>      -report_el_torito plain
GNU xorriso 1.5.0 : RockRidge filesystem manipulator, libburnia project.

xorriso : NOTE : ISO image bears MBR with  -boot_image any partition_offset=16
xorriso : NOTE : Loading ISO image tree from LBA 0
xorriso : UPDATE :   32980 nodes read in 1 seconds
xorriso : UPDATE :   56154 nodes read in 2 seconds
libisofs: NOTE : Found hidden El-Torito image for EFI.
libisofs: NOTE : EFI image start and size: 742333 * 2048 , 5760 * 512
xorriso : NOTE : Detected El-Torito boot information which currently is set to be discarded
Drive current: -indev 'g7.iso'
Media current: stdio file, overwriteable
Media status : is written , is appendable
Boot record  : El Torito , MBR grub2-mbr cyl-align-off
Media summary: 1 session, 743725 data blocks, 1453m data, 58.4g free
Volume id    : 'GUIXSD_IMAGE'
System area options: 0x00004a00
System area summary: MBR grub2-mbr cyl-align-off
ISO image size/512 : 2975092
Partition offset   : 16
MBR heads per cyl  : 91
MBR secs per head  : 32
MBR partition table:   N Status  Type        Start       Blocks
MBR partition      :   1   0x80  0x83           64      2969268
MBR partition      :   2   0x00  0xef      2969332         5760
El Torito catalog  : 21669  1
El Torito cat path : /boot.catalog
El Torito images   :   N  Pltf  B   Emul  Ld_seg  Hdpt  Ldsiz         LBA
El Torito boot img :   1  BIOS  y   none  0x0000  0x00      4       21670
El Torito boot img :   2  UEFI  y   none  0x0000  0x00   5760      742333
El Torito img path :   1  /boot/grub/i386-pc/eltorito.img
El Torito img opts :   1  boot-info-table grub2-boot-info
El Torito img blks :   2  1440







> For eyes which are not accustomed to xorriso's native command set, here is
> the same with mkisofs emulation options (without trying to exclude
> /mnt/iso/efi.img from the filesystem):
> 

This yields a differently sized ISO (perhaps because of not excluding
/mnt/iso/efi.img) which too is now liked by Linux but still not by my
Macbook:

$ ls -l g7.iso g8.iso
-rw-r--r-- 1 florian users 1523580928 17. Apr 21:26 g7.iso
-rw-r--r-- 1 florian users 1525852160 17. Apr 22:03 g8.iso



$ xorriso      -indev "$REPACKED_ISO"      -report_system_area plain      -report_el_torito plain
GNU xorriso 1.5.0 : RockRidge filesystem manipulator, libburnia project.

xorriso : NOTE : ISO image bears MBR with  -boot_image any partition_offset=16
xorriso : NOTE : Loading ISO image tree from LBA 0
xorriso : UPDATE :   33890 nodes read in 1 seconds
xorriso : UPDATE :   56155 nodes read in 2 seconds
libisofs: NOTE : Found hidden El-Torito image for EFI.
libisofs: NOTE : EFI image start and size: 743455 * 2048 , 5760 * 512
xorriso : NOTE : Detected El-Torito boot information which currently is set to be discarded
Drive current: -indev 'g8.iso'
Media current: stdio file, overwriteable
Media status : is written , is appendable
Boot record  : El Torito , MBR grub2-mbr cyl-align-off
Media summary: 1 session, 745045 data blocks, 1455m data, 57.0g free
Volume id    : 'GUIXSD_IMAGE'
System area options: 0x00004a00
System area summary: MBR grub2-mbr cyl-align-off
ISO image size/512 : 2980180
Partition offset   : 16
MBR heads per cyl  : 0
MBR secs per head  : 0
MBR partition table:   N Status  Type        Start       Blocks
MBR partition      :   1   0x80  0x83           64      2973756
MBR partition      :   2   0x00  0xef      2973820         5760
El Torito catalog  : 21351  1
El Torito cat path : /boot.catalog
El Torito images   :   N  Pltf  B   Emul  Ld_seg  Hdpt  Ldsiz         LBA
El Torito boot img :   1  BIOS  y   none  0x0000  0x00      4       21352
El Torito boot img :   2  UEFI  y   none  0x0000  0x00   5760      743455
El Torito img path :   1  /boot/grub/i386-pc/eltorito.img
El Torito img opts :   1  boot-info-table grub2-boot-info
El Torito img blks :   2  1440

Again, thank you!  (Even though I would prefer if it worked on
Macbooks.  Many people I know own one of those.  I do not know if
newer Macbooks are as picky as mine.)

Regards,
Florian