custom pve iso


New Member
Apr 28, 2015
hi all,
I recompile the pve kernel and I want to use it to replace the kernel in iso.
How to use 'xorriso' command to rebuild the iso?


Proxmox Staff Member
Staff member
Aug 29, 2006
No, building ISO is not documented and AFAIK, only done by Proxmox.


New Member
Apr 29, 2015

thanks to proxmox for flying xorriso.

You may mount the ISO via a loop device (or as virtual CD-ROM)
and let xorriso pack up the mounted directory tree at the
root of the new ISO, overwrite the kernel by a subsequent
pathspec, and apply the necessary options for booting.

The demanding part is about the boot options.
You will have to analyze the boot equipment of the original
image. Released xorriso-1.3.8 can do:
  xorriso -indev proxmox-ve_3.4-3f2d890e-1.iso \
          -toc \
          -pvd_info \
          -report_el_torito plain \
          -report_system_area plain
and reveils that the image has the full {BIOS, EFI, Mac} x {CD, HD}
equipment of GRUB2:
  Volume Id    : PVE
  Modif. Time  : 2015021906085500
  El Torito images   :   N  Pltf  B   Emul  Ld_seg  Hdpt  Ldsiz         LBA
  El Torito boot img :   1  BIOS  y   none  0x0000  0x00      4       35033
  El Torito boot img :   2  UEFI  y   none  0x0000  0x00   5760        6790
  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 path :   2  /efi.img
  System area summary: MBR protective-msdos-label grub2-mbr cyl-align-off GPT APM
  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x00  0xee            1      1298567
  GPT partname local :   2  EFI boot partition
  GPT partition path :   2  /efi.img
  APM partition name :   2  HFSPLUS_Hybrid
  APM partition type :   2  Apple_HFS
  APM start and size :   2  8230  316250
The APM/HFS+ stuff is a speciality of grub-mkrescue which uses
xorriso -as mkisofs option -hfsplus. By a lengthy xorriso -find
command i can see that the following file is blessed in HFS+ as
"Intel Boot File":
But actually i am unable to test APM/HFS+. Most of this was
contributed to xorriso by Vladimir Serbinenko of GRUB2.

Let's assume you don't want to boot the ISO on a HFS+ Mac,
but only prepare for BIOS and EFI:
  # Need an MBR. After inspection of the first 32 KB by od -c
  # i am sure that there is no code outside the MBR and the
  # partition tables. So i just cout out the first 512 bytes.
  dd if=proxmox-ve_3.4-3f2d890e-1.iso bs=512 count=1 of=proxmox.mbr

  # Mount the original image in order to copy its directory tree
  mount -o loop proxmox-ve_3.4-3f2d890e-1.iso /mnt/iso

  # Prepare the paths for kernel swap. The new kernel gets the old name
  # in the hope that this suffices to integrate it into the old system.

  # Now repack while overwriting the kernel from /mnt/iso by the new one.
  # Keep volume id and modification time. The booting system might
  # search for them among disk identifiers.
  xorriso -as mkisofs \
     -o repacked.iso \
     -r -V 'PVE' \
     --modification-date=2015021906085500 \
     --grub2-mbr proxmox.mbr \
     --protective-msdos-label \
     -efi-boot-part --efi-boot-image \
     -c '/boot/' \
     -b '/boot/grub/i386-pc/eltorito.img' \
       -no-emul-boot -boot-load-size 4 -boot-info-table --grub2-boot-info \
     -eltorito-alt-boot \
     -e '/efi.img' -no-emul-boot \
     /mnt/iso \
     -graft-points "$old_kernel"="$my_new_kernel"
The used options are explained in

When presented on an USB stick, the resulting repacked.iso
booted my BIOS equipped test machine up to a bright
screen which offered me to install Proxmox or to test
I did not replace the kernel when repacking.

There remains the problem that the file repacked.iso is
50 percent larger than the original ISO. tar produces a
similarly large result. This is due to zisofs compression
applied to 11787 of the 14170 data files in the original
If ISO size matters, then one could apply zisofs compression
to those data files which will surely be opened only via
a zisofs enabled Linux kernel. GRUB2 and early boot stages
of proxmox might not be able to deal with compressed file

Have a nice day :)

Last edited:


The Proxmox community has been around for many years and offers help and support for Proxmox VE and Proxmox Mail Gateway. We think our community is one of the best thanks to people like you!

Get your subscription!

The Proxmox team works very hard to make sure you are running the best software and getting stable updates and security enhancements, as well as quick enterprise support. Tens of thousands of happy customers have a Proxmox subscription. Get your own in 60 seconds.

Buy now!