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Etherboot is a free software package for building boot ROMs to boot computers over a TCP/IP network. It makes use of DHCP (or bootp) and TFTP during booting. Etherboot contains its own drivers for several commonly used network cards, along with the ability to build ROM images for them, as well as .COM programs that can be run from DOS. The LTSP uses Etherboot for booting their workstations.
Netboot is the original free software network boot code designed for making boot ROMs. It makes use of the "packet" network drivers included with many network cards to build a ROM image that can boot from the network. While this approach does allow it to cover a large range of network cards it is at the mercy of the quality of the packet drivers included with the network card (often marginal since the packet drivers are not extensively used these days), and in some cases the packet drivers are far too big to be usable (in one case the packet driver file was nearly 64MB, about 4 times what will fit in a boot ROM). If the network card you are attempting to boot will not work with Etherboot, Netboot might be worth investigating.
NILO is the successor project to Etherboot. It is attempting to create a product that can be put into a network card boot ROM which will support the PXE standard. At present it isn't really ready for use, but looks very promising.
Linux Terminal Server Project (LTSP)
The Linux Terminal Server Project (LTSP) provides a Linux distribution (for want of a better term) that is customised towards network booting multiple diskless workstations using Etherboot. They have a series of RPM files available including pre-compiled kernels, X servers, and a base package including all the necessary files for a root file system, along with a central configuration file. Their distribution is set up to work with a read only NFS file system, and they make use of symlinks into a ram disk for things that need to be updated. These features make it quite feasible to network boot a dozen or more diskless workstations from a single configuration. Their site also includes a lot of very useful information on how to boot diskless workstations from the network, as well as notes from the various talks they have given on the concept. One of their sponsors DisklessWorkstations.com is able to provide ready to use boot roms to work with the LTSP software.
Diskless Nodes HOWTO
The Diskless Nodes HOWTO describes how to set up a diskless computer that boots over the network, using a boot rom and a root NFS file system (exported read/write). This technique described in the HOWTO is close to the example configuration described in this article. It includes a useful description of how the network booting process works down to identifying individual machines.
pxelinux, by H Peter Anvin, is distributed with the syslinux package, and at present is in BETA form. It provides a second stage boot loader that works in the PXE (Preboot Execution Environment) to give a configurable boot loader that can load a Linux kernel (and optionally a ram disk image) via TFTP. The current BETA versions work reliably with only a few quirks; the most annoying one found with the hardware in the example in this paper was that pxelinux's messages wouldn't display on the PCI video card making diagnosis difficult. They did display properly on the built in video, so this may be a hardware specific problem. pxelinux requires the use of a slightly customised TFTP server available from the same kernel.org mirror sites as syslinux/pxelinux.
BpBatch is a PXE second stage boot loader that is very configurable and able to perform a wide variety of tasks prior to booting an operating system including partitioning and formatting a hard drive, making it suitable for use as the basis of a replication server. It also has considerably support for interacting with the user in the form of menus (text and graphical) and fairly extensive scripting support. By default BpBatch is set up to cache files it downloads from the network on a local hard drive partition (only downloading a new copy if the original changes), but it is apparently possible to disable this for a truly diskless system. While the source to BpBatch is not available, the package itself is available for free download.
Boot Linux, FreeBSD, FreeDOS from PXE
This short document describes how Linux, FreeDOS and FreeBSD can be booted via PXE, using pxelinux. FreeBSD is booted by booting FreeDOS and then using an Etherboot boot loader in a .COM file.
Preboot Execution Environment (PXE)
PXE is a part of the Intel lead Wired for Management initiative. PXE provides a programming environment for code to execute prior to loading an operating system accessing services over the network and on the local machine. Increasing numbers of PCs are being supplied with support for PXE built in, and there are several second stage boot loaders that make use of PXE.
Network Audio System (NAS)
The Network Audio System provides a network transparent, client server audio system, and was originally developed at NCD. It can be used to "pipe" the audio from an application to another machine for output.
Audio Forwarder (afwd)
A somewhat experimental Linux kernel modification (for 2.3/2.4 kernels) which will transparently forward attempts to open a /dev/audio (and other audio character devices) to another machine across the network.

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