Network booting FreeBSD with gpxelinx almost works

[Daniel Feenberg]

We have been network booting FreeBSD for some time with pxeboot. So I am 
confident that we have the dhcpd.conf and the root filesystem sufficient 
for diskless booting. But now we would like to have menu of OSs to boot 
and got the idea somewhere that gpxelinux could do that for us. We copied 
gpxelinux.0 from the syslinux-4.02 distribution and replaced pxeboot with 
"gpxelinux" in the dhcpd.conf file. Indeed with a configuration file in 
pxelinux.cfg like this:

   default freebsd
   label freebsd
     PXE pxeboot

and the root path still specified as a DHCP option, FreeBSD 8.1 does boot. 
If I replace the first line with:

   UI menu.c32

the client does display the menu and but if one hits return to select the 
single item offered the client merely hangs for a minute, then announces 
"boot failure". I am guessing that once the UI is interposed, somehow the 
root path isn't getting transmitted to pxeboot. All the other gpxelinux 
boot kernels seem to expect the information about the root filesystem to 
be specified in the pxelinux.cfg file, rather than in dhcpd.conf. Does 
anyone have experience with this? FreeBSD isn't mentioned anywhere I can 
find in the syslinux or gpxelinux documentation, and the various web 
posting I have found linking FreeBSD to gpxelinux are all about do 
installations of iso files over the net.

Daniel Feenberg
NBER
http://www.nber.org/sys-admin/FreeBSD-diskless.html