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If you're looking to perform a lot of system recovery, or system installation, then network booting with PXE is ideal. PXE allows you to boot up a system and have it automatically get an IP address via DHCP and start booting a kernel over the network.

PXE itself stands for "Pre-boot eXecution Environment", which describes how it works in the sense that the clients using it haven't booted in a traditional manner.

In order to use PXE you need to setup a boot-server which will allow client systems to :

With both of these services in place any system which supports PXE/network-booting (you might need to enable it in the BIOS) should be able to gain an IP address, fetch a kernel, and boot without an installed operating system.

(This is ideal for systems which can't be booted by a traditional approach; for example your new AMD-64 system which doesn't have a CD/DVD drive!)

Our Setup
For the purposes of this article we'll assume:

In our example we'll configure a PXE-server which will allow remote systems to run the Debian Etch installer, but nothing here is specific to that. PXE allows you to configure a system to boot from an arbitrary kernel (and matching ramdisk if you wish to use one). With the correct configuration you can even cause the clients to mount a remote file-system via NFS and have a diskless thin-client system.
TFTP Setup
TFTP is a very simple file-transfer protocol, which is very similar to FTP but which doesn't use any kind of authentication. If you're not already running a TFTP server you can install one by running:

root@itchy:~# apt-get install tftpd-hpa

Once installed you'll need to enable it by editing the file /etc/default/tftpd-hpa. You should change RUN_DAEMON to yes, leaving you with contents like these:

#Defaults for tftpd-hpa
OPTIONS="-l -s /var/lib/tftpboot"

Now create the root directory, if it is missing, and start the server:

root@itchy:~# mkdir -p /var/lib/tftpboot
root@itchy:~# /etc/init.d/tftpd-hpa start
Starting HPA's tftpd: in.tftpd.

Once our systems have retrieved an IP address via DHCP they will request files from beneath the /var/lib/tftpboot root directory. We'll come back to the contents of this directory shortly.
DHCP Setup
If you don't already have a DHCP server configured upon your LAN you'll need to install one. If you're using a small home router, or similar, to provide local DHCP services you must disable this first. (Since we require the DHCP server to pass back some extra options to clients which the majority of routers won't allow).

Discussing a full DHCP installation is mostly beyond the scope of this introduction but the thing we're trying to do is fairly simple. The goal of the DHCP server in this setup is twofold: