[syslinux] chainloading syslinux problem

[Gregory Lee Bartholomew]

On Wed, 2019-12-18 at 00:26 +0100, David Balažic wrote:
> 
> On Tue, 17 Dec 2019 at 23:19, Gregory Lee Bartholomew <gregory.lee.bartholomew at gmail.com> wrote:
> > On Tue, 2019-12-17 at 22:46 +0100, David Balažic via Syslinux wrote:
> > > Hi!
> > > I have bootable (USB flash) disk, that _appears_ to be using syslinux.
> > > (the word syslinux is in the PBR, in the hexdump).
> > > How can I chainload it? The payload seems to be a file that I tried
> > > load with COMBOOT, COM32 etc, but nothing works (they report that the
> > > file is not in proper format, wrong magic number or simply crash). How
> > > to proceed?
> > > 
> > 
> > I'm not sure how to chainload the PBR, but assuming that syslinux is in the MBR,
> > you might be able to boot it with QEMU.
> > 
> 
> I guess I was not clear enough.
> The current state is:
> MBR loads PBR which eventually loads the "app"
> 
> What I want is:
> put grub2 on MBR (possibly also overwriting PBR) and in the grub2 menu add an item the (chain)loads the previously mentioned "app" (there would of course be other menu items in grub2...)
> 
> Hope this is more clear now.
> 

In that case, I would suggest putting grub2 on a separate usb/floppy disk and
booting to its interactive command line. I think you should be able to get the
command line by pressing "c" when the menu comes up.

Once you are at grub2's command line, "ls" should list the available devices.
One of them should be the other usb flash drive on your system that has syslinux
in its PBR.

>From there, I think commands like the following should work:

> set root=(hd1,1)
> chainload +1
> boot

The above is assuming that the PBR you are trying to chainload is the first
partition on the second drive.

I'm not 100% sure about these instructions. I don't use grub2 much these days.
You might want to try a different mail list to get better advice.