Syslinux - Nov 2024 - Fail to boot ISOs using EFI

Hi,

I run a distro that uses Syslinux and I'm failing to see a way to boot an
ISO using EFI. I noticed no other distro that uses Syslinux managed to
accomplish that.

1. booting Syslinux using EFI on a system copied to a storage unit works
just fine -- Syslinux menu shows up; it's all good
2. booting the ISO using EFI via, let's say VirtualBox, fails -- VirtualBox
says it can't find any EFI file, but by disabling EFI in the VM setting
allows Syslinux to boot normally

So I read that Syslinux can only boot an ISO using EFI if we use a .img
file with Syslinux inside it, and then generate the ISO using mkisofs
passing the following parameter: -eltorito-alt-boot -eltorito-platform 0xEF
-eltorito-boot boot/syslinux/efiboot.img.

Now, the problem is that once Syslinux is running from inside this .img, it
can't see the external world, which means we need to also include the
kernel and initrd in the .img file, which is a deal breaker for me because
I would have to duplicate big files.

Is there a cleaner/easier solution?

Thanks a lot!

Hi,

Fulalas Caos wrote:
> So I read that Syslinux can only boot an ISO using EFI if we use a .img
> file with Syslinux inside it, and then generate the ISO using mkisofs
> passing the following parameter: -eltorito-alt-boot -eltorito-platform 0xEF
> -eltorito-boot boot/syslinux/efiboot.img.
To my knowledge the problem with SYSLINUX and EFI is reladed to CD-ROM,
not to ISO 9660. If the ISO is treated with program "isohybrid" and
its
option --uefi, then it is supposed to boot as (virtual) USB stick or
hard disk.
See:
  https://wiki.syslinux.org/wiki/index.php?title=Isohybrid#UEFI

For copying onto a real USB stick:
 
https://wiki.syslinux.org/wiki/index.php?title=Isohybrid#Copying_onto_USB_stick_by_shell_commands


Have a nice day :)

Thomas

On Fri, Nov 29, 2024 at 04:20:58PM +0100, Fulalas Caos via Syslinux
wrote:
> Hi,
> 
> I run a distro that uses Syslinux and I'm failing to see a way to boot
an
> ISO using EFI. I noticed no other distro that uses Syslinux managed to
> accomplish that.
> 
> 1. booting Syslinux using EFI on a system copied to a storage unit works
> just fine -- Syslinux menu shows up; it's all good
> 2. booting the ISO using EFI via, let's say VirtualBox, fails --
VirtualBox
> says it can't find any EFI file, but by disabling EFI in the VM setting
> allows Syslinux to boot normally
> 
> So I read that Syslinux can only boot an ISO using EFI if we use a .img
> file with Syslinux inside it, and then generate the ISO using mkisofs
> passing the following parameter: -eltorito-alt-boot -eltorito-platform 0xEF
> -eltorito-boot boot/syslinux/efiboot.img.
> 
> Now, the problem is that once Syslinux is running from inside this .img, it
> can't see the external world, which means we need to also include the
> kernel and initrd in the .img file, which is a deal breaker for me because
> I would have to duplicate big files.
> 
> Is there a cleaner/easier solution?
Devuan (daedalus) has installer ISOs that handle the use case of UEFI
with CDROM media. One part of that solution is to have two root
pivots, with a smaller "preamble" initrd that only has the task of
finding and unpacking the initrd proper, which resides outside the
embedded image. I'm not sure it's a clean solution, but it's a good
way of handling a range of diffrent media drives.

The solution also included a syslinux-efi patch dealing with the
"differing drive blocksize problem" (though this might not arise for
virtualbox's emulated drive).

Ralph.
> 
> Thanks a lot!
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