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In our company we use a modified Ubuntu installation ISO image. Since Ubuntu 22.04 has changed the structure of the installation image (ISOLINUX has been removed, in favor of GRUB2), I would need advice on how to build a new ISO that would support both MBR and EFI at the same time (on same image), as Ubuntu 22.04.

In Ubuntu 20.04, I built the ISO image using the commands below.

So the question is: How to build an ISO image for Ubuntu 22.04? Thanks.

Commands for create ISO image with Ubuntu 20.04 LTS

Extract content from image:
dd if="/opt/ubnt/ubuntu-20.04.4-desktop-amd64.iso" bs=1 count=432 of="/opt/ubnt/isohdpfx.bin"
xorriso -osirrox on -indev /opt/ubnt/ubuntu-20.04.4-desktop-amd64.iso -extract / /opt/ubnt/ubuntu-MODIF

... Some customizations here ...

Build Ubuntu 20.04 LTS
xorriso -as mkisofs -r  
  -V 'Ubuntu 20.04 LTS MODIF (EFIBIOS)' 
  -o /opt/ubnt/ubuntu-modif.iso 
  -isohybrid-mbr /opt/ubnt/isohdpfx.bin 
  -J -joliet-long -b isolinux/isolinux.bin 
  -c isolinux/boot.cat 
  -boot-load-size 4 
  -boot-info-table -no-emul-boot -eltorito-alt-boot 
  -e boot/grub/efi.img 
  -no-emul-boot 
  -isohybrid-gpt-basdat /opt/ubnt/ubuntu-MODIF
Jakub Franek
  • 53

1 Answers1

9

Ubuntu 22.04 build ISO (Both: MBR and EFI )

The youngest release of xorriso (1.5.4) can tell:


$ xorriso -indev ubuntu-22.04-desktop-amd64.iso -report_el_torito as_mkisofs
-V 'Ubuntu 22.04 LTS amd64'
--modification-date='2022041910231900'
--grub2-mbr --interval:local_fs:0s-15s:zero_mbrpt,zero_gpt:'ubuntu-22.04-desktop-amd64.iso'
--protective-msdos-label
-partition_cyl_align off
-partition_offset 16
--mbr-force-bootable
-append_partition 2 28732ac11ff8d211ba4b00a0c93ec93b --interval:local_fs:7129428d-7137923d::'ubuntu-22.04-desktop-amd64.iso'
-appended_part_as_gpt
-iso_mbr_part_type a2a0d0ebe5b9334487c068b6b72699c7
-c '/boot.catalog'
-b '/boot/grub/i386-pc/eltorito.img'
-no-emul-boot
-boot-load-size 4
-boot-info-table
--grub2-boot-info
-eltorito-alt-boot
-e '--interval:appended_partition_2_start_1782357s_size_8496d:all::'
-no-emul-boot
-boot-load-size 8496

Older versions guess wrong. The new layout surprises them somewhat. But they can create it. The original was made by xorriso-1.5.2.

The shown options are for reproducing the ISO as exactly as possible. For a modified ISO one will want to omit some of them to get default settings and replace others by actions which later don't need the presence of the original ISO image.


# Extract the MBR template for --grub2-mbr
# We only need the x86 code. All partition stuff will be newly created.
dd if=ubuntu-22.04-desktop-amd64.iso bs=1 count=432 of=/opt/ubnt/boot_hybrid.img

The EFI partition is not a data file inside the ISO any more.


So extract the EFI partition image image for -append_partition


7129428d-7137923d : 7137923 - 7129428 + 1 = 8496


dd if=ubuntu-22.04-desktop-amd64.iso bs=512 skip=7129428 count=8496 of=/opt/ubnt/efi.img


Extract file tree as usual ...


Finally pack up an ISO the new way


xorriso -as mkisofs -r 

  -V 'Ubuntu 22.04 LTS MODIF (EFIBIOS)' 

  -o /opt/ubnt/ubuntu-modif.iso 

  --grub2-mbr /opt/ubnt/boot_hybrid.img 

  -partition_offset 16 

  --mbr-force-bootable 

  -append_partition 2 28732ac11ff8d211ba4b00a0c93ec93b /opt/ubnt/efi.img 

  -appended_part_as_gpt 

  -iso_mbr_part_type a2a0d0ebe5b9334487c068b6b72699c7 

  -c '/boot.catalog' 

  -b '/boot/grub/i386-pc/eltorito.img' 

    -no-emul-boot -boot-load-size 4 -boot-info-table --grub2-boot-info 

  -eltorito-alt-boot 

  -e '--interval:appended_partition_2:::' 

    -no-emul-boot 

  /opt/ubnt/ubuntu-MODIF

The advantage is that the ISO on USB stick will be recognized as GPT partitioned with neatly separated partitions.


$ /sbin/fdisk -l ubuntu-22.04-desktop-amd64.iso

Disk ubuntu-22.04-desktop-amd64.iso: 3.4 GiB, 3654957056 bytes, 7138588 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: A09DB2B8-B5F6-43AE-AFB3-91E0A90189A1


Device                            Start     End Sectors  Size Type
ubuntu-22.04-desktop-amd64.iso1      64 7129427 7129364  3.4G Microsoft basic da
ubuntu-22.04-desktop-amd64.iso2 7129428 7137923    8496  4.2M EFI System
ubuntu-22.04-desktop-amd64.iso3 7137924 7138523     600  300K Microsoft basic da

(Partition 3 covers the traditional end padding of 300 KiB which is actually needed only on CD media written by write type Track-At-Once. Option -no-pad would prevent it.)

Thomas Schmitt
  • 151
  • 2