[Beowulf] Choosing pxelinux.cfg DEFAULT via dhcpd.conf?

[David Mathog]

Is there a way to set dhcpd.conf so that it changes which pxelinux.cfg
entry (LABEL) starts on a network boot?  I think something like this can
be done with the option pxelinux.magic combined with pxelinux.config
file or pxelinux.pathprefix to specify a 2nd (or 3rd...) pxelinux.cfg
file, each of which has a different DEFAULT, but I don't see how to set
the dhcpd.conf entry for a machine to get pxelinux to effectively change
the default value for a single pxelinux.cfg file. The idea being, in a
heterogenous cluster,  to have dhcpd.conf set up so that type A nodes
boot one thing, and type B nodes boot another, without any manual
intervention required.

The pxelinux.cfg has several different LABEL entries
one of which is DEFAULT.  If dhcpd.conf has filename "/pxelinux.0" set
then when the remote node boots it network boots the DEFAULT entry from 
pxelinux.cfg.  From the keyboard one can choose an entry other than
DEFAULT to start.  I know how to pass variables to whatever comes up,
with parameters like this on the relevant line in dhcpd.conf:

  option option-200 "information passed"

but I don't see how to make the node boot, for instance,
the 3rd option on the pxelinux.cfg list, using just the one file,
other than by editing that file changing DEFAULT, and reloading the
dhcpd daemon. 

Thanks,

David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech