[syslinux] isohybrid --uefi - resulting EF00 partition too small

Mattias Schlenker ms at mattiasschlenker.de
Tue Mar 12 07:23:19 PDT 2013

Hello everyone,

I am maintaining a distribution loosely based on LFS and am now trying 
to add UEFI support. Integrating a FAT formatted partition image 
containing, preloader, gummiboot, kernel and initramfs correctly results 
in a ISO image that is bootable on BIOS and UEFI systems if booted from 
the optical drive.

However, when I run

isohybrid --uefi name-of.iso

the resulting GPT entry for the EF00 partition is just 19MB. It should 
be around 53MB:

root at barium:/tmp# gdisk -l 
GPT fdisk (gdisk) version 0.8.5

Partition table scan:
MBR: MBR only
BSD: not present
APM: not present
GPT: present

Found valid MBR and GPT. Which do you want to use?
1 - MBR
2 - GPT
3 - Create blank GPT

Your answer: 2
Using GPT and creating fresh protective MBR.
Warning! Main partition table overlaps the first partition by 34 blocks!
You will need to delete this partition or resize it in another utility.
Disk lesslinux-search-and-rescue-uluru-20130312-110347.iso: 1413120 
sectors, 690.0 MiB
Logical sector size: 512 bytes
Disk identifier (GUID): 3F6E0DF3-466E-4B62-9BCC-14303CE24ADF
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 1413086
Partitions will be aligned on 8-sector boundaries
Total free space is 514 sectors (257.0 KiB)

Number Start (sector) End (sector) Size Code Name
2 212648 251559 19.0 MiB 0700 卉䡏批楲d灁汰e灁汰

I have to note that all kernel modules and quite some binaries are part 
of the initramfs, which is responsible for the large size. This has 
never been a problem since the distribution is not intended for low 
memory applications. Thus I assume the chinese characters say "Mattias, 
you fucked it up!".

The ISO image was built using xorriso 1.1.8 (from Ubuntu 12.04) with the 
command line:

xorriso -as mkisofs -graft-points -b boot/isolinux/isolinux.bin 
-no-emul-boot -boot-info-table -boot-load-size 4 -c 
boot/isolinux/boot.cat --efi-boot boot/efi.img -V 
lesslinux-search-and-rescue-uluru-20130312-110347.iso -r cdmaster 
--sort-weight 0 / --sort-weight 1 /boot

Isohybrid capability was added by using a statically linked isohybrid 
binary built from the sources of syslinux 5.02pre3:

/mnt/archiv/LessLinux/llbuild/stage01/chroot/usr/bin/isohybrid --uefi 

If you want to examine the resulting ISO image, it can be downloaded here:


Am I wrong with the assumption that it should be possible to create a 
valid ISO image that boots on all four boot systems: BIOS-El-Torito, 
UEFI-El-Torito, BIOS from MBR (respectively compatibility MBR) and UEFI 
from EF00 partition mapped to the El-Torito image? Or did just my large 
FAT image make me run into some side effects? If there will be no 
possibility of supporting all four methods in one image I will move to 
creating separate images for USB drives, something I outlined here 
Of course in this case I would neither blame Thomas Schmitt nor Matthew 
Garrett nor anyone else who did a great job on making isohybrid work for 
so many use cases, neither would I blame my large initramfs - I think in 
some cases it is just fate that jigsaw puzzle of four boot standards 
does not fit together.


PS: Sorry for posting twice... Is the list initially moderated until 
someone's first post is accepted? I sent this mail immediately after 
subscribing and did neither receive a copy or find it in the archives. 
Let's see...

Mattias Schlenker - Redaktion + EDV-Beratung + Linux-CD/DVD-Konzepte
Dietrich-Bonhoeffer-Str. 3 - 40667 MEERBUSCH - GERMANY

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