Re: Booting from USB

[zunda]

Hello Salvatore,

This is zunda, who is also playing with a small Linux booted from
USB memory: http://zunda.freeshell.org/docomomo/dist/

I saw what happens on my system (Dell Latitude X1, BIOS Rev A04).
Boot priority is set as 1st: CD/DVD/CD-RW Drive, 2nd: USB Storage
Device, and 3rd: Internal HDD.

--- Salvatore De Paolis <address@hidden> wrote:

> I installed grub into the MBR of USB (which as an ext3 partition) and when i
> boot on my laptop i get that (hd0,0) is currently the usb pendrive and (hd1,0)
> the hard disk.
> Kernel seems to be loaded from usb but after that it switch to hard disk and
> after it boots, i get the prompt to the hard disk..

On GRUB booted from MBR on my UBS memory (Sandisk Cruzer Mini),
hd0 is the USB drive and hd1 is the internal HDD. On the kernel
booted from the USB memory, the internal HDD is seen as /dev/hda
and the UBS drive is seen as /dev/sda. The device files are the
same when kernel is booted from the internal HDD.

My guess it that you would have to provide the root= kernel
parameter correctly. GRUB loads the kernel (and initrd) from the
USB drive and starts the kernel. The kernel may see the internal
HDD as /dev/hda and the USB memory as /dev/sda. So, I guess if we
could tell the kernel to mount the USB memory as the root file
system, i.e. if root=/dev/sda1 is provided as a kernel parameter,
it would use the file system in the USB as the root file system.

> Launching again grub from command line i see that (hd0,0) now is the hard disk
> and (hd1,0) changed to the usb pendrive.

Yes, I saw the same change. I am not sure but I guess that the
numbering convention are different on BIOS and on Linux. On my
system, drive numbers on GRUB booted from the MBR changes when I
change boot priority on BIOS, i.e., hd0 is the internal HDD and
hd1 is the USB memory when the boot priority is higher for the
internal HDD than for the USB memory.

My two cents,
zunda

P.S. Salvatore, sorry to have sent an e-mail directly to you.
I send the same message to the bug-grub ML.


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