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Re: Multiple boot from USB stick

From: Andrei Borzenkov
Subject: Re: Multiple boot from USB stick
Date: Tue, 16 Feb 2016 13:36:15 +0300

On Tue, Feb 16, 2016 at 1:08 PM, Karsten Malcher
<address@hidden> wrote:
> Hello Andrei,
> Am 16.02.2016 um 10:48 schrieb Andrei Borzenkov:
>> On Tue, Feb 16, 2016 at 12:37 PM, Karsten Malcher
>> <address@hidden> wrote:
>>>> linux16 /memdisk iso
>>>> initrd16 /fdbase.iso
>>>> boot
>>>> Does it suite as a concrete solution? :)
>>> I was talking about the file FreeDOS_1.1.iso.
>>> Where did you get this 2 iso files?
>> There is one iso file. Sorry, it was 1.0, not 1.1:
> O.K. This is clear now.
> One more interesting thing. When you use
> you can get here:
> But for me still is not clear where you get the memdisk.iso and fdbase.iso ?

There is no memdisk.iso. memdisk was from Sylinux installed on my
Linux. fdbase was a typo, it is whatever I downloaded from freedos.og.

>>> Why you can boot them without a loopback?
>> Because no loopback is needed. I want to boot from ISO, not extract
>> files from it.
> I thought grub must use loopback to access the kernel to boot within an iso 
> file?

If you want to load file that is located inside ISO image, then you
need loopback. I did *not* need any file from ISO image.

>>> But this method is working now and i can understand why:
>>> menuentry "FreeDOS ISO Image Isolinux" {
>>>         set isofile="/boot/iso/FreeDOS_1.1.iso"
>>>         loopback loop (hd0,1)$isofile
>>>         linux16 (loop)/ISOLINUX/MEMDISK
>>>         initrd16 (loop)/ISOLINUX/FDBOOT.IMG
>>> }
>> I do not know what fdboot.img does so I cannot comment.
> This is the kernel image of freedos within the iso file.

Does it explain anything?

>>> With use of loopback i am mounting the iso file.
>>> Then both files within the iso are loaded and executed.
>>> FreeDOS 1.1 is starting, but then it can't work with the files within the 
>>> ISO.
>>> So i get the message: "SETUP wasn't able to locate any disks to install 
>>> FreeDOS 1.1 from"
>> Well, I did not try to launch setup, but I can access ISO after
>> manually loading eltorito.sys and shu-bla-bla (whatever name for CD
>> shim is, do not remember).
> I think there are parts of your grub.cfg missing.

I do not have any grub.cfg. You do not need it to execute three commands.

> So i can't follow you.
>> But I am not surprised it does not work for you. I suspect fdboot.img
>> contains just enough of FreeDOS to locate and access CDROM. But with
>> the way you boot it there is no CDROM anywhere. The way I boot CDROM
>> access is emulated by memdisk.
> The role of memdisk is still not clear for me.

It provides emulated device accessible via BIOS calls. It also has a
bit more intelligence, e.g. it knows how to extract and launch boot
image from bootable ISO.

> But it does what i expected from it:
> Freedos can't access the files within the iso, because the iso file is not 
> "mounted as cdrom".
> I have no idea how to do the trick?

Why do not you simply try what I suggested? Or if you insist on doing
it using grub.cfg and loopback ...

menuentry "FreeDOS ISO Image Isolinux" {
        set isofile="/boot/iso/FreeDOS_1.1.iso"
        loopback loop (hd0,1)$isofile
        linux16 (loop)/ISOLINUX/MEMDISK iso
        initrd16 (hd0,1)$isofile

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