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Clarify introduction.

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Sponsored by: iXsystems
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Dru Lavigne 2014-03-05 17:26:02 +00:00
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Notes: svn2git 2020-12-08 03:00:23 +00:00 
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en_US.ISO8859-1/books/handbook/advanced-networking/chapter.xml
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@ -3855,146 +3855,62 @@ ifconfig_<literal>lagg0</literal>="laggproto failover laggport <replaceable>bge0
<primary>diskless operation</primary>
</indexterm>
<para>A &os; machine can boot over the network and operate
without a local disk, using file systems mounted from an
<acronym>NFS</acronym> server. No system modification is
necessary, beyond standard configuration files. Such a system
is relatively easy to set up because all the necessary elements
are readily available:</para>
<itemizedlist>
<listitem>
<para>The &intel; Preboot eXecution Environment
(<acronym>PXE</acronym>) can be used to load the kernel over
the network. It provides a form of smart boot
<acronym>ROM</acronym> built into some networking cards or
motherboards. See &man.pxeboot.8; for more details.</para>
</listitem>
(<acronym>PXE</acronym>) allows an operating system to boot
over the network. For example, a &os; system can boot over the network and operate
without a local disk, using file systems mounted from an
<acronym>NFS</acronym> server. <acronym>PXE</acronym> support is usually
available in the <acronym>BIOS</acronym>. To use
<acronym>PXE</acronym> when the machine starts,
select the <literal>Boot from network</literal> option in
the <acronym>BIOS</acronym> setup or type a function key
during system initialization.</para>
<listitem>
<para>A sample script
(<filename>/usr/share/examples/diskless/clone_root</filename>)
eases the creation and maintenance of the workstation's root
file system on the server. The script will probably require
a little customization.</para>
</listitem>
<listitem>
<para>Standard system startup files exist in
<filename>/etc</filename> to detect and support a diskless
system startup.</para>
</listitem>
<listitem>
<para>Swapping, if needed, can be done either to an
<acronym>NFS</acronym> file or to a local disk.</para>
</listitem>
</itemizedlist>
<para>To use <acronym>PXE</acronym> when the machine starts,
select the <literal>Boot from network</literal> option in
the <acronym>BIOS</acronym> setup or type a function key
during system initialization.</para>
<para>There are many ways to set up diskless workstations. Many
elements are involved, and most can be customized to suit local
taste. The following will describe variations on the setup of a
complete system, emphasizing simplicity and compatibility with
the standard &os; startup scripts. The system described has
the following characteristics:</para>
<itemizedlist>
<listitem>
<para>The diskless workstations use a shared, read-only
<filename>/</filename> and
<filename>/usr</filename>.</para>
</listitem>
<listitem>
<para>The root file system is a copy of a standard &os; root,
with some configuration files overridden by ones specific to
diskless operation or, possibly, to the workstation they
belong to.</para>
</listitem>
<listitem>
<para>The parts of the root which have to be writable are
overlaid with &man.md.4; file systems. Any changes will be
lost when the system reboots.</para>
</listitem>
</itemizedlist>
<caution>
<para>As described, this system is insecure. It should live in
a protected area of a network and be untrusted by other
hosts.</para>
</caution>
<sect2>
<title>Background Information</title>
<para>When setting up diskless workstations, several operations
need to be performed for a successful
bootstrap:</para>
<para>In order to provide the files needed for an operating system
to boot over the network, a
<acronym>PXE</acronym> setup also requires properly configured
<acronym>DHCP</acronym>, <acronym>TFTP</acronym>, and <acronym>NFS</acronym>
servers, where:</para>
<itemizedlist>
<listitem>
<para>The machine needs to obtain initial parameters such as
its <acronym>IP</acronym> address, executable filename,
server name, and root path. This is done using the
<acronym>DHCP</acronym> or <acronym>BOOTP</acronym>
protocols. <acronym>DHCP</acronym> is a compatible
extension of <acronym>BOOTP</acronym>, and uses the same
port numbers and basic packet format. It is possible to
configure a system to use only <acronym>BOOTP</acronym>
and &man.bootpd.8; is included in the base &os;
system.</para>
<para><acronym>DHCP</acronym> has a number of advantages
over <acronym>BOOTP</acronym> such as nicer configuration
files and support for <acronym>PXE</acronym>. This
section describes mainly a <acronym>DHCP</acronym>
configuration, with equivalent examples using
&man.bootpd.8; when possible. The sample configuration
uses <application>ISC DHCP</application> which is
available in the Ports Collection.</para>
</listitem>
<para>Initial parameters, such as an
<acronym>IP</acronym> address, executable boot filename and location,
server name, and root path are obtained from the
<acronym>DHCP</acronym> server.</para>
</listitem>
<listitem>
<para>The machine needs to boot the loader using
<para>The operating system loader file is booted using
<acronym>TFTP</acronym>.</para>
</listitem>
<listitem>
<para>The root filesystem needs to be loaded using
<para>The file systems are loaded using
<acronym>NFS</acronym>.</para>
</listitem>
<listitem>
<para>The possible intermediate bootstrap programs and the
kernel need to be initialized and executed.
<acronym>PXE</acronym> loads &man.pxeboot.8;, which is
a modified version of the &os; third stage loader,
&man.loader.8;. The third stage loader will obtain most
parameters necessary to system startup and leave them
in the kernel environment before transferring control.
It is possible to use a <filename>GENERIC</filename>
kernel in this case.</para>
</listitem>
<listitem>
<para>Finally, the machine needs to access its file systems
using <acronym>NFS</acronym>.</para>
</listitem>
</itemizedlist>
<para>Place <filename>tftpboot</filename>
anywhere on the server. Make sure that the location is
set in both <filename>/etc/inetd.conf</filename> and
<filename>/usr/local/etc/dhcpd.conf</filename>.</para>
<para>When a computer <acronym>PXE</acronym> boots, it receives information over
<acronym>DHCP</acronym> about where to obtain the initial boot
loader file. After the host computer
receives this information, it downloads the boot loader via
<acronym>TFTP</acronym> and then executes the boot loader.
In &os;, the boot loader file is
<filename>/boot/pxeboot</filename>. After
<filename>/boot/pxeboot</filename> executes, the &os; kernel is
loaded and the rest of the &os; bootup sequence proceeds, as described in
<xref linkend="boot"/>.</para>
<para>Refer to &man.diskless.8; for more information.</para>
</sect2>
<para>This section describes how to configure these services
on a &os; system so that other systems can
<acronym>PXE</acronym> boot into &os;. Refer to &man.diskless.8; for more information.</para>
<caution>
<para>As described, the system providing these services is insecure. It should live in
a protected area of a network and be untrusted by other
hosts.</para>
</caution>
<sect2 xml:id="network-pxe-nfs">
<info>
@ -4015,32 +3931,6 @@ ifconfig_<literal>lagg0</literal>="laggproto failover laggport <replaceable>bge0
</authorgroup>
</info>
<para>The &intel; Preboot eXecution Environment
(<acronym>PXE</acronym>) allows booting the operating system
over the network. <acronym>PXE</acronym> support is usually
provided in the <acronym>BIOS</acronym> where it can be enabled
in the <acronym>BIOS</acronym> settings which enable booting
from the network. A fully functioning
<acronym>PXE</acronym> setup also requires properly configured
<acronym>DHCP</acronym> and <acronym>TFTP</acronym>
servers.</para>
<para>When the host computer boots, it receives information over
<acronym>DHCP</acronym> about where to obtain the initial boot
loader via <acronym>TFTP</acronym>. After the host computer
receives this information, it downloads the boot loader via
<acronym>TFTP</acronym> and then executes the boot loader.
This is documented in section 2.2.1 of the <link
xlink:href="http://download.intel.com/design/archives/wfm/downloads/pxespec.pdf">Preboot
Execution Environment (<acronym>PXE</acronym>)
Specification</link>. In &os;, the boot loader retrieved
during the <acronym>PXE</acronym> process is
<filename>/boot/pxeboot</filename>. After
<filename>/boot/pxeboot</filename> executes, the &os; kernel is
loaded and the rest of the &os; bootup sequence proceeds.
Refer to <xref linkend="boot"/> for more information about the
&os; booting process.</para>
<procedure>
<step>
<para>Choose a directory which will have a &os;
@ -4051,6 +3941,11 @@ ifconfig_<literal>lagg0</literal>="laggproto failover laggport <replaceable>bge0
<screen>&prompt.root; <userinput>export NFSROOTDIR=/b/tftpboot/FreeBSD/install</userinput>
&prompt.root; <userinput>mkdir -p ${NFSROOTDIR}</userinput></screen>
<para>Place <filename>tftpboot</filename>
anywhere on the server. Make sure that the location is
set in both <filename>/etc/inetd.conf</filename> and
<filename>/usr/local/etc/dhcpd.conf</filename>.</para>
</step>
<step>