[syslinux] Boot from CD -> system + data on USB storage

[Luciano Miguel Ferreira Rocha]

On Fri, Nov 12, 2004 at 04:35:10PM +0100, Marc Haisenko wrote:
> On Friday 12 November 2004 10:48, you wrote:
> > Hi,
> > I am looking for a solution to boot MY system on any PC.
> >
> > To store most of the system and all of my data I want to use an USB
> > storage (in my case an external USB harddisk (2.0 capable)).
> > Since booting off an USB device is not an universal thing I would prefer
> > to have a boot disk with a minimal system - just enough to load most
> > (all?) of the system from the attached USB device.
> >
> > Is this an easy thing - are there ready to use solutions out there?
> >
> > Thanks in advance.
> 
> Problem is the USB part...  ISOLINUX does not know a thing about USB, AFAIK, 
> as it would require some drivers to do so (the BIOS does some tricks to boot 
> from USB, IIRC).
> 
> You could do the following: have ISOLINUX, a kernel and an initrd on the CD 
> and the rest of the system on USB. The kernel could either have USB support 
> built in or have initrd load the modules. The initrd then searches all SCSI 
> partitions for your root partition (e.g. by having a file "this_is_my_root" 
> on that partition, and the initrd searches for a partition that has this file 
> on it). When you've found the partition you set the device number 
> in /proc/sys/kernel/real-root-dev.

The initrd created by RedHat Linux or Fedora Core searches the root
filesystem by label, so it is only needed to define an unique label to
the root filesystem.

> I've written such an linuxrc in assembler that does just this for IDE. It 
> probes all IDE partitions until it finds one that has a "/sbin/init" on it 
> and then sets real-root-dev accordingly. I've attached the source. You 
> need /dev/console and /dev/hd* to be in the initrd as well and an empty 
> directory /proc.  My source is surely not very efficient but you should be 
> able to adapt it easily (you only need to change the strings at the top of 
> the source).

Not to other archs ;)

> Problem is that if you want to upgrade your kernel you have to burn another 
> CD.

True, so a cd-rw would be the best choice. I tried kexec and loadlin but
the booted kernel didn't like the initialization of usb hardware by the
previous one or the DOS USB drivers.

Regards,
Luciano Rocha