[syslinux] PXELINUX based kickstart query (probably OT)

[Coe, Colin C. (Unix Engineer)]

Hi all

I'm guessing this is a little off topic but here goes...

We use PXELINUX and kickstart to automate our RHEL deployments and
updates.  Recently we started using PXELINUX/memdisk and an MS-DOS image
to update the workstation BIOS'es.  After selecting <F12> (network boot)
and picking the update BIOS option, the BIOS is flashed, BIOS
configuration made standard and then the workstation reboots needing a
second <F12> to kick off the kickstart.  I'd like to do this in a single
step so the result would be:
- Select <F12> during boot
- Choose PXELINUX BIOS update option
- BIOS gets flashed
- BIOS gets configured
- Boot info is wiped from /dev/sda (leaving partitions intact)
- automatic reboot
- PXELINUX is automatically selected as no bootable media
- Kickstart commenses

What I'd like to know is how do I wipe the boot info from /dev/sda to
force a network boot?  

I tried:
- wiping the MBR which works but also wipes the partition tables which
we don't want.
- removing the boot flag from the first partition (not the MBR I know
but I thought I'd try it anyway).
- based on the info in http://www.ata-atapi.com/hiwmbr.htm I tried
wiping the first 138 bytes of /dev/sda

Any pointers on where to try next?

Thanks

CC