> The xorrisofs option to cause GPT during the production of an Ubuntu ISO
> would be
> -appended_part_as_gpt
Thinking it through, I am happy for us to make this change from MBR to GPT.
- optical media don't care about the partition table, only the El-Torito
boot image.
- BIOS boot of USB doesn't care about the partition table, only the MBR
- UEFI 2.0 requires systems to understand GPT
- pre-2.0 UEFI systems are mostly not guaranteed to work anyway.
I do see that the GPT has an extra partition at the end; is this required
for alignment? I haven't seen such partition entries when using MBR.
$ gdisk -l ~/devel/iso/groovy-desktop-amd64.iso
GPT fdisk (gdisk) version 1.0.5
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: present
Found valid GPT with protective MBR; using GPT.
Disk /home/vorlon/devel/iso/groovy-desktop-amd64.iso: 5736268 sectors, 2.7 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): 8897A8AA-43A3-4BD4-A4AA-C472E4376703
Partition table holds up to 248 entries
Main partition table begins at sector 2 and ends at sector 63
First usable sector is 64, last usable sector is 5736204
Partitions will be aligned on 4-sector boundaries
Total free space is 1 sectors (512 bytes)
Number Start (sector) End (sector) Size Code Name
1 64 5725651 2.7 GiB 0700 ISO9660
2 5725652 5735603 4.9 MiB EF00 Appended2
3 5735604 5736203 300.0 KiB 0700 Gap1
$
Here is the full commandline used to construct this image.
Thanks very much for the analysis, Thomas!
> There remain riddles:
> Why does the grub-mkrescue ISO not boot on V14IIL ?
> (I still wonder which other ISOs boot on that machine.)
> Why did the old Ubuntu ISOs with their invalid GPT boot on sudodus' V130
> whereas a similarly invalid GPT did not help with the 20201007.1 ISO ?
Yes, that is puzzling.
> Maybe Canonical Ltd. should ask Lenovo Group Limited for enlightenment.
I've escalated it internally to the right team, and they will follow up, but
no guarantees we'll get a meaningful answer :)
> ------- ------- ------- ------- ------- ------- ------- ------- ------- ------- ---
> The xorrisofs option to cause GPT during the production of an Ubuntu ISO
> would be
> -appended_ part_as_ gpt
Thinking it through, I am happy for us to make this change from MBR to GPT.
- optical media don't care about the partition table, only the El-Torito
boot image.
- BIOS boot of USB doesn't care about the partition table, only the MBR
- UEFI 2.0 requires systems to understand GPT
- pre-2.0 UEFI systems are mostly not guaranteed to work anyway.
I've made this switch now and confirmed the result at cdimage. ubuntu. com/ubuntu/ daily-live/ 20201009. 1>.
<http://
I do see that the GPT has an extra partition at the end; is this required
for alignment? I haven't seen such partition entries when using MBR.
$ gdisk -l ~/devel/ iso/groovy- desktop- amd64.iso
GPT fdisk (gdisk) version 1.0.5
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: present
Found valid GPT with protective MBR; using GPT. devel/iso/ groovy- desktop- amd64.iso: 5736268 sectors, 2.7 GiB 43A3-4BD4- A4AA-C472E43767 03
Disk /home/vorlon/
Sector size (logical): 512 bytes
Disk identifier (GUID): 8897A8AA-
Partition table holds up to 248 entries
Main partition table begins at sector 2 and ends at sector 63
First usable sector is 64, last usable sector is 5736204
Partitions will be aligned on 4-sector boundaries
Total free space is 1 sectors (512 bytes)
Number Start (sector) End (sector) Size Code Name
1 64 5725651 2.7 GiB 0700 ISO9660
2 5725652 5735603 4.9 MiB EF00 Appended2
3 5735604 5736203 300.0 KiB 0700 Gap1
$
Here is the full commandline used to construct this image.
xorriso -as mkisofs -r -checksum_ algorithm_ iso md5,sha1 -V Ubuntu\ 20.10\ amd64 -o /srv/cdimage. ubuntu. com/scratch/ ubuntu/ groovy/ daily-live/ debian- cd/amd64/ groovy- desktop- amd64.raw -J -joliet-long -l -b boot/grub/ i386-pc/ eltorito. img -no-emul-boot -boot-load-size 4 -boot-info-table --grub2-boot-info --grub2-mbr cd-boot- images/ usr/share/ cd-boot- images- amd64/images/ boot/grub/ i386-pc/ boot_hybrid. img -append_partition 2 0xef cd-boot- images/ usr/share/ cd-boot- images- amd64/images/ boot/grub/ efi.img -appended_ part_as_ gpt -eltorito-alt-boot -e --interval\ :appended_ partition_ 2\:all\ :\: -no-emul-boot -partition_offset 16 cd-boot- images/ usr/share/ cd-boot- images- amd64/tree CD1