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Booting from a network
======================

   It is sometimes very useful to boot from a network, especially, when
you use a machine which has no local disk. In this case, you need to
obtain a kind of Net Boot ROM, such as a PXE ROM or a free software
package like Etherboot. Such a Boot ROM first boots the machine, sets
up the network card installed into the machine, and downloads a second
stage boot image from the network. Then, the second image will try to
boot an operating system from the network actually.

   GRUB provides two second stage images, `nbgrub' and `pxegrub' (Note:
Images). Those images are the same as the normal Stage 2, except that
they set up a network automatically, and try to load a configuration
file from the network, if specified. The usage is very simple: If the
machine has a PXE ROM, use `pxegrub'. If the machine has a NBI loader
such as Etherboot, use `nbgrub'. There is no difference between them
but their formats. As how to load a second stage image you want to use
should be described in the manual on your Net Boot ROM, please refer to
the manual, for more information.

   However, there is one thing specific to GRUB. Namely, how to specify
a configuration file in a BOOTP/DHCP server. For now, GRUB uses the tag
`150', to get the name of a configuration file. This below is an
example about a BOOTP configuration:

     .allhost:hd=/tmp:bf=null:\
             :ds=145.71.35.1 145.71.32.1:\
             :sm=255.255.254.0:\
             :gw=145.71.35.1:\
             :sa=145.71.35.5:
     
     foo:ht=1:ha=63655d0334a7:ip=145.71.35.127:\
             :bf=/nbgrub:\
             :tc=.allhost:\
             :T150="(nd)/tftpboot/menu.lst.foo":

   Note that you should specify the drive name `(nd)' in the name of
the configuration file. That is because you can change the root drive
before downloading the configuration from the TFTP server, when the
preset menu feature is used (Note: Preset Menu).

   See the manual about your BOOTP/DHCP server, for more information.
The exact syntax should differ from the example, more or less.