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#1 (**permalink**) 01-18-2008, 07:48 AM

Hi all,

I have an external USB harddisk and installed Linux (SUSE 9.3) on it.
Unfortunately my BIOS does not support direct booting from USB harddisks.
I suppose it is possible to setup e.g. a small boot CD (booting from CD
is supported), which loads a USB driver and finally boots Linux from the
USB harddisk.
Can anyone please give me some hints how to do this? Or does anyone have
a better idea how to boot from the harddisk?

Thanks and Best Regards, Stephan

P.S.: Background: My system is a Medion MD8383XL with Phoenix 6.0 BIOS.
The main harddisk is a SATA device, which is full of <shame> Windows XP
</shame>.

#2 (**permalink**) 01-18-2008, 07:48 AM

Stephan Keil wrote:
> Hi all,
>
> I have an external USB harddisk and installed Linux (SUSE 9.3) on it.
> Unfortunately my BIOS does not support direct booting from USB harddisks.
> I suppose it is possible to setup e.g. a small boot CD (booting from CD
> is supported), which loads a USB driver and finally boots Linux from the
> USB harddisk.
> Can anyone please give me some hints how to do this? Or does anyone have
> a better idea how to boot from the harddisk?
>
> Thanks and Best Regards, Stephan
>
> P.S.: Background: My system is a Medion MD8383XL with Phoenix 6.0 BIOS.
> The main harddisk is a SATA device, which is full of <shame> Windows XP
> </shame>.

The bootable CD contains a floppy image (usually 2.88.Mbytes)
which is shown as a floppy to the BIOS during booting.

So, you need a floppy image that contains the required drivers and
is bootable (first 512 bytes read via int 0x13 to 0x7c00 and
started up at the first byte).

For details, Google for 'El Torito Specification'.

The Linux mkisofs utility can insert the boot diskette image
into a CD file system image.

--

Tauno Voipio
tauno voipio (at) iki fi

#3 (**permalink**) 01-18-2008, 07:48 AM

>> I suppose it is possible to setup e.g. a small boot CD (booting from
>> CD is supported), which loads a USB driver and finally boots Linux
>> from the USB harddisk.

> The bootable CD contains a floppy image (usually 2.88.Mbytes)
> which is shown as a floppy to the BIOS during booting.
>
> So, you need a floppy image that contains the required drivers and
> is bootable (first 512 bytes read via int 0x13 to 0x7c00 and
> started up at the first byte).
>
> For details, Google for 'El Torito Specification'.
>
> The Linux mkisofs utility can insert the boot diskette image
> into a CD file system image.

Hm, sounds like a lot of low-level work :-o.
My approach was more like installing a Linux kernel with builtin
USB-drivers on the CD. But actually I would prefer to not install my
"production kernel" on the CD but some kind of "boot only" kernel. Is it
possible to "swap" the kernel after booting?

#4 (**permalink**) 01-18-2008, 07:48 AM

Stephan Keil wrote:
>>> I suppose it is possible to setup e.g. a small boot CD (booting from
>>> CD is supported), which loads a USB driver and finally boots Linux
>>> from the USB harddisk.
>
>
>> The bootable CD contains a floppy image (usually 2.88.Mbytes)
>> which is shown as a floppy to the BIOS during booting.
>>
>> So, you need a floppy image that contains the required drivers and
>> is bootable (first 512 bytes read via int 0x13 to 0x7c00 and
>> started up at the first byte).
>>
>> For details, Google for 'El Torito Specification'.
>>
>> The Linux mkisofs utility can insert the boot diskette image
>> into a CD file system image.
>
>
> Hm, sounds like a lot of low-level work :-o.
> My approach was more like installing a Linux kernel with builtin
> USB-drivers on the CD. But actually I would prefer to not install my
> "production kernel" on the CD but some kind of "boot only" kernel. Is it
> possible to "swap" the kernel after booting?

There's no easy way - the kernel runs in 32 bit mode and the
booting runs in 16 bit (real) mode. You'd need to do some serious
kernel hacking to return to the real mode.

If you can get a version of GRUB able to boot your disk,
a floppy with that GRUB diskette image might be the solution.

--

Tauno Voipio
tauno voipio (at) iki fi

#5 (**permalink**) 01-18-2008, 07:49 AM

On 2005-06-13, Stephan Keil <Stephan.Keil@gmx.de> wrote:

> I have an external USB harddisk and installed Linux (SUSE 9.3) on it.
> Unfortunately my BIOS does not support direct booting from USB harddisks.
> I suppose it is possible to setup e.g. a small boot CD (booting from CD
> is supported), which loads a USB driver and finally boots Linux from the
> USB harddisk.
> Can anyone please give me some hints how to do this? Or does anyone have
> a better idea how to boot from the harddisk?

What you'll want to do is create a bootable CD with the linux kernel image
and a a compressed root filesystem that will load into a temporary
ramdisk (see "initrd"). This initrd filesystem will contain the needed USB
drivers to allow the kernel to find your USB hard drive and remount that
as the root filesystem once the kernel can recognize it.

Check your distribution's web site to see if they already have an ISO file
(or instructions on how to make one) to do this. If so, all you'll need to
do is burn that to a cd and you're good to go.

--

John (john@os2.dhs.org)

#6 (**permalink**) 01-18-2008, 07:49 AM

On 2005-06-14, Stephan Keil <Stephan.Keil@gmx.de> wrote:

> My approach was more like installing a Linux kernel with builtin
> USB-drivers on the CD. But actually I would prefer to not install my
> "production kernel" on the CD but some kind of "boot only" kernel. Is it
> possible to "swap" the kernel after booting?

No, not rally. But you don't really need to swap the kernel; just change
the root filesystem from something on the CD or on a ramdisk to the
filesystem on the USB HD once the system's up and running.

--

John (john@os2.dhs.org)

#7 (**permalink**) 01-18-2008, 07:49 AM

Thank you, John & Tauno, for your answers.

> What you'll want to do is create a bootable CD with the linux kernel image
> and a a compressed root filesystem that will load into a temporary
> ramdisk (see "initrd"). This initrd filesystem will contain the needed USB
> drivers to allow the kernel to find your USB hard drive and remount that
> as the root filesystem once the kernel can recognize it.

I will give it (and me

a try. Actually I would prefer to have the
kernel on a harddisk for easy kernel updates, but that's not so
important, a CD-RW would also do the job. (I'm out of Linux for some
years now, but in former times I compiled a new kernel approx. once a
week; may be times have changed here ?!)

#8 (**permalink**) 01-18-2008, 07:49 AM

Stephan Keil wrote:
> Hi all,
>
> I have an external USB harddisk and installed Linux (SUSE 9.3) on it.
> Unfortunately my BIOS does not support direct booting from USB harddisks.
> I suppose it is possible to setup e.g. a small boot CD (booting from CD
> is supported), which loads a USB driver and finally boots Linux from the
> USB harddisk.
> Can anyone please give me some hints how to do this? Or does anyone have
> a better idea how to boot from the harddisk?
>
> Thanks and Best Regards, Stephan
>
> P.S.: Background: My system is a Medion MD8383XL with Phoenix 6.0 BIOS.
> The main harddisk is a SATA device, which is full of <shame> Windows XP
> </shame>.

What you need is to boot from CD with an initial ramdisk including
the usb-storage support (mkinitrd --with=uhci-hcd --with=ohci-hcd
--with=ehci-hcd --with=usb-storage)
The initial ramdisk including the usb-storage is crucial to be able to
mount the root fs on the USB drive.

Then Google search for "grub on CD" to learn how to make a grub-bootable
cd-rom.

The typical grub.conf entry should be as follows:

title USB boot
root(cd)
kernel /vmlinuz-2.6.X-Y root=/dev/sdaZ
initrd /ramdisk-2.6.X.Y.img

I made all that in practice and it works.

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Booting from USB HDD without BIOS support