MultiNetBoot

Net boot chosing between multiple systems

Nowadays, many systems (Kubuntu, SuSE, Fedora, ...) allow network booting or installing. In order to do this, you usually need to copy a subfolder from the installation CD to your tftp server, and set this as your root.

However, until syslinux 3.72 and its pxechain.com module, it was not easily possible to set up a boot menu allowing to chose among one of many systems.

With pxechain.com, it has become very simple to set up a global boot menu, as described below.

Preparation

• Download syslinux-3.72 (or later) from http://www.kernel.org/pub/linux/utils/boot/syslinux/
• Compile it
• Copy modules/pxechain.com, com32/menu/menu.c32 and core/pxelinux.0 to your tftproot (usually /var/lib/tftpboot)
• Set up your DHCP server to point to the pxlinux.0 in your tftp root by putting the following into your dhcpd.conf, and restart it:

 filename "pxelinux.0";

Setting up the various systems you want to chose among

Copy the boot environments of the systems that you want to chose amongst as subdirectories of your tftp root : /var/lib/tftpboot/udpcast , /var/lib/tftpboot/kubuntu, ...

Making index file

Set up the root level's PXElinux configuration file to be an index. Create the /var/lib/tftpbot/pxelinux.cfg directory, and store the following in /var/lib/tftpboot/pxelinux.cfg/default :

default menu.c32
prompt 0
menu title Hitchhiker PXE boot menu

LABEL udpcast
        menu label Udpcast
        kernel pxechain.com
        append ::udpcast/pxelinux.0

LABEL KubuntuNet
        menu Kubuntu network install
        kernel pxechain.com
        append ::KubuntuNet/pxelinux.0

For each system you've got one paragraph, starting with a LABEL line (to give it a unique name), followed by a menu line (to set the name displayed in the menu). The kernel pxechain.com line tells pxelinux to chain another pxe boot loader (the one present in the system's image). The last line (append ...) points towards the boot loader of the system to be loaded.

How it works / why it is needed

pxechain.com works by patching the DHCP information received from the server such that the boot filename points into the subdirectory of the chosen system (parameter of the append line), rather than the root.

Directly saying kernel udpcast/pxelinux.0 would not work: Although the correct pxelinux.0 would be loaded, all dependant files (pxelinux.cfg/default, linux, initrd, ...) would again be loaded relatively to the root. Indeed the boot loader derives its "working directory" from the DHCP packet, which would not be patched using this simplistic approach.