Syslinux - Aug 2019 - Getting classic BIOS and UEFI boot on the same disk?

Hi all,

We're using the classic boot BIOS syslinux successfully for many years, but
meanwhile it's getting harder to buy hardware the still supports this boot
mode.
The option for us would be syslinux EFI boot.
To avoid too many changes we would like to generate an image for our different
hardware parts that supports both - classic BIOS boot and (U)EFI boot.
This would allow us to leave the BIOS in whatever state it is and the system
will simply boot.

I read some articles on how to install each version - from that I would
carefully say that this is not possible... At least not when following the
install instructions.
The biggest gap seems to be the MBR and the GPT...

Might there be a way to handle this actually? Or do both modes completely
exclude each other? I won't mind duplicating some files that are required
for
each boot process but could not be placed in the same location...

And - if there is already a howto for this topic - blame me, I didn't find
it :-)

Thanks in advance.

Best regards,

Erik

> We're using the classic boot BIOS syslinux successfully for many years,
> but meanwhile it's getting harder to buy hardware the still supports
> this boot mode. The option for us would be syslinux EFI boot. To avoid
> too many changes we would like to generate an image for our different
> hardware parts that supports both - classic BIOS boot and (U)EFI boot.
> This would allow us to leave the BIOS in whatever state it is and the
> system will simply boot.
> 
> I read some articles on how to install each version - from that I would
> carefully say that this is not possible... At least not when following
> the install instructions. The biggest gap seems to be the MBR and the
> GPT...
> 
> Might there be a way to handle this actually? Or do both modes
> completely exclude each other? I won't mind duplicating some files that
> are required for each boot process but could not be placed in the same
> location...
> 
> And - if there is already a howto for this topic - blame me, I didn't
> find it :-)
 
 
To me, it is not so clear what exactly is your goal.

Do you want to build an image for an internal HDD that could be capable 
of booting in both, BIOS mode and UEFI mode?

Or, is this for a portable (USB) device?

Or, is this for some kind of ISO image?

Or, is this for some kind of network-booting, in order to install OSes 
to the internal HDD?

Additionally, what OS(es) are you planning to boot from Syslinux (in 
either BIOS mode and/or UEFI mode)?

Is the resulting image expected to support multiple OSes? Which ones 
(e.g. Windows, Linux)?


Depending on the answers to these questions, the answers to your 
original questions (might) vary.

Regards,
Ady.

Hi Ady,

Ady Ady via Syslinux wrote:
>  
> To me, it is not so clear what exactly is your goal.
sorry for not being detailed enough.
> Do you want to build an image for an internal HDD that could be capable 
> of booting in both, BIOS mode and UEFI mode?
Yes. This would make us independent from the BIOS boot mode.
> Or, is this for a portable (USB) device?
Maybe - would be nice if this would work, but not
required.
> Or, is this for some kind of ISO image?
No.
> Or, is this for some kind of network-booting, in order to install OSes 
> to the internal HDD?
No. We put in a disk that is already ready to use.
> Additionally, what OS(es) are you planning to boot from Syslinux (in 
> either BIOS mode and/or UEFI mode)?
Linux. 32 bit (and 64 bit if this alternative is possible). Vanilla kernel +
Linux from scratch.
> Is the resulting image expected to support multiple OSes? Which ones 
> (e.g. Windows, Linux)?
Linux - as written above 32 and 64 bit but not at the same time of course. So
one image for 32 bit and one for 64 bit. No boot option to choose.
No Windows, nothing else.
> Depending on the answers to these questions, the answers to your 
> original questions (might) vary.
I'll cross fingers!
> Regards,
> Ady.
Thanks a lot!

Best regards,

Erik

Hi,

only speaking theoretically from the disk view, as i'm not SYSLINUX expert
but rather provide a program to pack up bootable ISO 9660 images,
Ady surely has more experience with installation, but since he did not
mention the following facts, i add my two cents.

Erik Rull wrote:
> we would like to generate an image for our different
> hardware parts that supports both - classic BIOS boot and (U)EFI boot
This combination is present in many GNU/Linux installation ISO 9660
images which work from DVD and from USB stick. But because of a
shortcomming in SYSLINUX EFI with booting from optical media, the EFI
equipment is GRUB2, except Knoppix 8, which fails accordingly from DVD
via EFI. From USB stick it works fine.
Most x86 firmwares interpret USB sticks and hard disks identically.

So, since you seem to speak of hard disk images, if there is a problem,
then only with the installation software, not with the goal.

> I read some articles on how to install each version - from that I would
> carefully say that this is not possible...
Care to share the links ?

> The biggest gap seems to be the MBR and the GPT...
GPT specifies as block 0 a "Protective MBR" which is allowed to
contain
BIOS boot code. The constraint given by GPT is in respect to the partition
table, which may only contain a single partition, which must have type 0xee
and cover the whole disk from block 1 up to the last block.

But EFI does not demand GPT. It specifies as alternative an MBR partition
table layout with one partition of type 0xef and possibly more partitions.
The 0xef partition must not have the Boot/Active flag set.

BIOS does not directly demand partitions, but many MBR boot programs look
for a partition with Active/Boot flag in order to chainload the boot loader
found there. (ISOLINUX "isohdp[fp]x*.bin" do not look for the flag.)

  https://wiki.syslinux.org/wiki/index.php?title=Install#UEFI
mentions special MBR boot code images "gptmbr*.bin" for GPT but does
not say
much about how to install them.
Further it says:
  There are no "installers" for syslinux.efi. Copy the relevant
syslinux.efi
  file to an appropriate location, and rename it if necessary or desired.
  Additionally, copy the necessary core module file (either
"ldlinux.e32" or
  "ldlinux.e64", according to the architecture of the firmware) to the
same
  directory.
This looks like you are supposed to create an EFI System partition (either
MBR type 0xef or GPT type GUID C12A7328-F81F-11D2-BA4B-00A0C93EC93B),
format it as FAT12 or FAT16, and to put efi32/efi/syslinux.efi and
efi64/efi/syslinux.efi in there, naming them /EFI/BOOT/BOOTIA32.EFI and
/EFI/BOOT/BOOTX64.EFI, respectively. (On Microsoft it's "\" rather
than "/",
of course.)
Then put ldlinux.e32 and ldlinux.e64 into /EFI/BOOT of the partition.
I'd start with a readily installed BIOS-capable SYSLINUX image and use a
partition editor to create an 0xef MBR partition. MBR partition table
has the advantage that it does not tell the full disk size. So one image
fits all disks if they are large enough.

The rest seems to be a matter of customization needs. For example the
EFI partition content of Knoppix 8 (seen by GNU/Linux find(1)) is this:

  ./efi
  ./efi/boot
  ./efi/boot/BOOTX64.efi
  ./efi/boot/hashtool.efi
  ./efi/boot/keytool.efi
  ./efi/boot/loader.efi
  ./efi/boot/BOOTIA32.efi
  ./efi/boot/ldlinux.e32
  ./efi/boot/ldlinux.e64
  ./boot
  ./boot/syslinux
  ./boot/syslinux/linux
  ./boot/syslinux/linux64
  ./boot/syslinux/minirt.gz
  ./boot/syslinux/syslnx32.cfg
  ./boot/syslinux/syslnx64.cfg
  ./boot/syslinux/f2
  ./boot/syslinux/f3
  ./boot/syslinux/bootefi.msg
  ./boot/syslinux/german.kbd
  ./NvVars

I assume that "linux", "linux64" and "minirt.gz"
belong to a bootable Linux.
Why Klaus Knopper put it there is not clear to me.


Have a nice day :)

Thomas

I'm not sure if it is useful, but with the advent of UEFI only machines,
we've run into a similar problem w/ out custom CentOS 7 USB installation
keys.

Basically, we create a gpt device w/ a single FAT16 partition (this
would be your /boot partition for a full installation) containing an
EFI/BOOT/ directory with the syslinux-efi files and a SYSLINUX/
directory with the syslinux-bios files.

Would further info on this be helpful?

- WRSomsky


On Wed, Aug 21, 2019 at 12:57:05PM +0200, Erik Rull via Syslinux
wrote:
> Hi all,
> 
> We're using the classic boot BIOS syslinux successfully for many years,
but
> meanwhile it's getting harder to buy hardware the still supports this
boot
> mode.
> The option for us would be syslinux EFI boot.
> To avoid too many changes we would like to generate an image for our
different
> hardware parts that supports both - classic BIOS boot and (U)EFI boot.
> This would allow us to leave the BIOS in whatever state it is and the
system
> will simply boot.
> 
> [[...]]
-- 
Dr. William R. Somsky           	                   somsky at uw.edu
Department of Physics, Box 351560		    B217 Phys-Astro Bldg
Univ. of Washington, Seattle WA 98195-1560		    206-616-2954

I just created something very similar for one of my own projects. I have a
disk image that you can "dd" onto a hard drive or USB drive and a bash
script demonstrating how it was done here:

https://www.syslinux.org/archives/2019-July/026476.html

You don't actually need the patch for the dual BIOS/UEFI support. The patch
in the above link is just to enable the reading of config "snippits"
from a
"entries" directory. Feel free to try out the provided disk image to
see if
it meets your needs and reverse-engineer the bash script to suit your needs.


On Wed, Aug 21, 2019 at 1:34 PM William R. Somsky via Syslinux <
syslinux at syslinux.org> wrote:
>
> I'm not sure if it is useful, but with the advent of UEFI only
machines,
> we've run into a similar problem w/ out custom CentOS 7 USB
installation
> keys.
>
> Basically, we create a gpt device w/ a single FAT16 partition (this
> would be your /boot partition for a full installation) containing an
> EFI/BOOT/ directory with the syslinux-efi files and a SYSLINUX/
> directory with the syslinux-bios files.
>
> Would further info on this be helpful?
>
> - WRSomsky
>
>
> On Wed, Aug 21, 2019 at 12:57:05PM +0200, Erik Rull via Syslinux wrote:
> > Hi all,
> >
> > We're using the classic boot BIOS syslinux successfully for many
years,
> but
> > meanwhile it's getting harder to buy hardware the still supports
this
> boot
> > mode.
> > The option for us would be syslinux EFI boot.
> > To avoid too many changes we would like to generate an image for our
> different
> > hardware parts that supports both - classic BIOS boot and (U)EFI boot.
> > This would allow us to leave the BIOS in whatever state it is and the
> system
> > will simply boot.
> >
> > [[...]]
>
> --
> Dr. William R. Somsky                                      somsky at uw.edu
> Department of Physics, Box 351560                   B217 Phys-Astro Bldg
> Univ. of Washington, Seattle WA 98195-1560                  206-616-2954
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