[syslinux] Changes to get CD to boot on EFI System.

Thomas Schmitt scdbackup at gmx.net
Tue Mar 22 14:03:26 PDT 2016


Hi,

Ady wrote:
> If users want to find the "--uefi" parameter for the isohybrid command, 
> it is already there, documented. 

Yes. But it does only work with non-SYSLINUX boot images.

It is undisputed that one can work around that problem on a
hard-disk-like medium by simply not using ISO 9660 but a set
of partitions and SYSLINUX EFI software.

But this does not help with optical media. There the El Torito
specs clearly define the boot catalog and images as parasites
of an ISO 9660 filesystem. You have no chance to express this by
a set of partitions.

So for ISOLINUX and isohybrid, EFI means that you need a FAT
filesystem image with software from projects other than SYSLINUX.


> developers in popular Linux distros completely 
> "misunderstanding" (to put it gently) the matter in question.

At least they get their ISOs to boot from CD and USB stick alike.
(Some of them are my highly esteemed users. So i am biased here.)


> Let users keep asking;

Until they begin to chant

  Arise ye users from your slumber,
  Arise ye prisoners of want.

while preparing torches and pitchforks.


Didier Spaier wrote:
> why not just state clearly in the first document:
> "It is not possible to make a CD bootable on UEFI with ISOLINUX".

If we count isohybrid as part of ISOLINUX then this is not fully true,
because it enables a non-SYSLINUX boot image for USB stick booting
via EFI while it enables ISOLINUX for USB stick booting via BIOS.

Further we should give the users a hint what kind of software in a
FAT filesystem image file would be suitable for isohybrid option --uefi.

Like in ISOLUNUX wiki
  http://www.syslinux.org/wiki/index.php?title=ISOLINUX
After the text under "What is ISOLINUX":
"ISOLINUX boots only via BIOS firmware or UEFI firmware in legacy
 emulation mode. It is nevertheless possible to add a GRUB2 based
 EFI System Partition image to an ISOLINUX equipped ISO 9660
 filesystem."

In isohybrid wiki
  http://www.syslinux.org/wiki/index.php?title=Isohybrid
After "Meanwhile there is an additional isohybrid feature for UEFI":
", which can be used to enable a FAT filesystem image with e.g. GRUB2
 UEFI boot equipment for booting from USB stick."

After
"UEFI
 -----------------------------------------------------------------
 This file contains a FAT filesystem with boot equipment from which
 the UEFI firmware will be able to start the desired operating system.":
"The boot equipment in that filesystem usually stems from GRUB2,
 because the SYSLINUX EFI boot software cannot operate from a
 partition inside an ISO 9660 filesystem.
 One would have to put a whole operating system into the FAT filesystem
 which would access the content of the ISO filesystem after SYSLINUX
 is completely done with its part of the job. GRUB2 can hop out of
 the FAT filesystem on its own and make use of all files stored in there.
 See installation ISOs of Fedora or Debian for examples."


> There is also goofiboot (fork of gummiboot) and even efi-stub

Do you know an example of them booting out of an ISO ?

It would be helpful for a neutral description in the isohybrid wiki
if it was not only GRUB2 that can be shown as tested.


Have a nice day :)

Thomas



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