[syslinux] dual disk netboot approach

[Jeffrey Hutzelman]

On Fri, 2011-06-03 at 00:16 +0200, Geert Stappers wrote:
> Hello,
> 
> My challenge is to run Linux on a computer
> where I don't dare to touch the Microsoft Windows harddisk.
> 
> Fifthteen years ago would be trick to attach a second harddisk to the
> computer and boot from floppy disk. In 2011 is the idea to attach a
> second disk and netboot it.
> 
> One approach is to TFTP the kernel and append 'root=/dev/sdb1'

Or perhaps something less device-specific, like a reference to a UUID or
an LVM volume.

> This E-mail is however to seek advice for another approach.
> In this approach is the kernel also on the second harddisk.
> 
> I see two possible roads, both with dragons on it.
> 
> The PXELINUX only road: Will PXELINUX load a kernel from disk?
>
> The PXELINUX with EXTLINUX road: When PXELINUX loads and starts EXTLINUX
>  will EXTLINUX load a config file from the network?

No and no.  Syslinux of any flavor can read only from its configuration
filesystem.  PXELINUX reads configuration and boot files only from TFTP
(or some other URL, if using gpxelinux); EXTLINUX reads only from an
EXT2/3/4 filesystem (and only the device/partition it was loaded from).

You may be able to accomplish your goal with a slightly more hideous
alternative.  In ISOLINUX only, the 'localboot' command supports an
option to boot from a particular local disk, by providing a BIOS drive
number.  So, try using PXELINUX to load MEMDISK and a CD-ROM image
containing ISOLINUX and a config file that chains to your second disk.


Of course, it may be simpler to do as others have suggested, and simply
boot from USB or by configuring the BIOS to boot from the second disk
(in fact, on some machines, if you hit the right key during POST, you
can select which disk to boot from).

-- Jeff