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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' (see section GRUB image files). 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="/tftpboot/menu.lst.foo":

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

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