Re: USB boot from HardDisk

[Stefan Monnier <monnier@iro.umontreal.ca>]

> But if the computer starts I do get a grub menu from the Ubuntu
> distrobution. Would it be possible to use this grub setup from Ubuntu to
> boot my pendrive usb ?

One way or another, your Ubuntu can read the pendrive, then you can
do it.  There are various ways to boot over USB; by order of increased
reliance on your harddisk:
0- Let the BIOS boot directly from the pendrive.  You say this doesn't
   work for you for some reason.
1- Let the BIOS boot from the harddisk, but then let Grub fetch the
   kernel and initrd from the USB.  This requires that Grub sees the
   pendrive: if your BIOS doesn't see it you'll need Grub2 and you may
   need to tell Grub to load some usb modules.
2- Boot Grub from the harddisk, and let Grub fetch the kernel and initrd
   from the harddisk, but pass a rootfs argument that points to
   the pendrive.

Assuming that the Ubuntu and Debian kernels are sufficiently similar
(likely) you could do (2) simply by booting to Grub2 and selecting your
usual Ubuntu entry but modifying it so as to replace "root=<blabla>"
with "root=/dev/sdb1 rootdelay=10" (tho I'm not sure the rootdelay=10
arg is still needed nowadays), where /dev/sdb is the name under which
your USB pendrive should appear (that's not very reliable, so you can
use UUID, labels, LVM volume names, you name it if you want it to be
more robust).


        Stefan