Changing root filesystem from CD to USB drive

[dmly...@gmail.com]

Hi,
I have this isse: my PC cannot boot from USB drive. I am thinking of
two possible solutions here.
1. Create an initrd with USB support, then modify the linuxrc to find
the USB device, mount it, then change root to the newly mounted root
filesystem.
2. Boot from a live CD (Ubuntu) for example to a console. Then change
root to the USB device which now connected.

I think method #1 is more difficult but it is more efficient than
method number 2.
Could somebody help me to solve the problem?
Thanks a lot

[Douglas Mayne]

Is the problem that the system won't boot from the USB device or that you
need to use the USB as the root filesystem? AFAIK, if your system won't
boot from USB, then the only way to fix it is via a BIOS upgrade.

If your root filesystem is entirely on a partition on the USB device,
then your bootstrap program should load the kernel, the initrd and specify
the root filesystem. The initrd will need to load the modules necessary
for the device and filesystem on the USB device. The grub loader is
versatile bootstrap loader and should meet your needs. Grub will load from
a CD or from an internal disc. Maybe, a grub stanza similar to that shown
below would work for you. (Substitute values as appropriate for your
system.)

title GNU/Linux Distro on USB External Device
root (cd)
kernel /boot/vmlinuz ro root=/dev/sda1
initrd /boot/initrd

Apparently, grub will also load kernel modules, which means you may not
even need an initrd. I haven't used that feature: module
http://www.gnu.org/software/grub/manual/html_node/module.html#module

--
Douglas Mayne

[dmly...@gmail.com]

Thank you,
But this PC won't allow you to boot from USB. I hope you could point me
to the correct direction of how to bootstrap into the USb drive after
booting from the initrd of the Cd-ROM.
Doug

[Douglas Mayne]

I thought I did, but maybe we're having trouble communicating. Please,
reread my last post and see if you can tell where we went separate
directions.

Is anything installed on the USB disc now? If not, is part of your plan
to use it as the root filesystem for a the GNU/Linux distribution of your
choice?

BTW, you need to improve your posting style. Apparently, you are
posting from google groups, and their default setting does not include any
context of the thread. This is bad form. Remember, this is Usenet not
Google Groups.

--
Douglas Mayne