network-diskless.html

FreeBSD操作系统的详细使用手册

use).</p>

<p>Build the kernel (see <a href="kernelconfig.html">Chapter 8</a>), and copy it to the
place specified in <tt class="FILENAME">dhcpd.conf</tt>.</p>

<div class="NOTE">
<blockquote class="NOTE">
<p><b>Note:</b> When using <acronym class="ACRONYM">PXE</acronym>, building a kernel with
the above options is not strictly necessary (though suggested). Enabling them will cause
more <acronym class="ACRONYM">DHCP</acronym> requests to be issued during kernel startup,
with a small risk of inconsistency between the new values and those retrieved by <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=pxeboot&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">pxeboot</span>(8)</span></a> in some
special cases. The advantage of using them is that the host name will be set as a side
effect. Otherwise you will need to set the host name by another method, for example in a
client-specific <tt class="FILENAME">rc.conf</tt> file.</p>
</blockquote>
</div>

<div class="NOTE">
<blockquote class="NOTE">
<p><b>Note:</b> In order to be loadable with <b class="APPLICATION">Etherboot</b>, a 5.X
kernel needs to have the device hints compiled in. You would typically set the following
option in the configuration file (see the <tt class="FILENAME">NOTES</tt> configuration
comments file):</p>

<pre class="PROGRAMLISTING">
hints      "GENERIC.hints"
</pre>
</blockquote>
</div>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN37388" name="AEN37388">24.6.2.7 Preparing the Root
Filesystem</a></h3>

<p>You need to create a root filesystem for the diskless workstations, in the location
listed as <var class="LITERAL">root-path</var> in <tt class="FILENAME">dhcpd.conf</tt>.
The following sections describe two ways to do it.</p>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN37396" name="AEN37396">24.6.2.7.1 Using the <tt
class="FILENAME">clone_root</tt> Script</a></h4>

<p>This is the quickest way to create a root filesystem, but currently it is only
supported on FreeBSD&nbsp;4.X. This shell script is located at <tt
class="FILENAME">/usr/share/examples/diskless/clone_root</tt> and needs customization, at
least to adjust the place where the filesystem will be created (the <var
class="LITERAL">DEST</var> variable).</p>

<p>Refer to the comments at the top of the script for instructions. They explain how the
base filesystem is built, and how files may be selectively overridden by versions
specific to diskless operation, to a subnetwork, or to an individual workstation. They
also give examples for the diskless <tt class="FILENAME">/etc/fstab</tt> and <tt
class="FILENAME">/etc/rc.conf</tt> files.</p>

<p>The <tt class="FILENAME">README</tt> files in <tt
class="FILENAME">/usr/share/examples/diskless</tt> contain a lot of interesting
background information, but, together with the other examples in the <tt
class="FILENAME">diskless</tt> directory, they actually document a configuration method
which is distinct from the one used by <tt class="FILENAME">clone_root</tt> and the
system startup scripts in <tt class="FILENAME">/etc</tt>, which is a little confusing.
Use them for reference only, except if you prefer the method that they describe, in which
case you will need customized <tt class="FILENAME">rc</tt> scripts.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN37412" name="AEN37412">24.6.2.7.2 Using the Standard <tt
class="COMMAND">make world</tt> Procedure</a></h4>

<p>This method can be applied to either FreeBSD&nbsp;4.X or 5.X and will install a
complete virgin system (not only the root filesystem) into <tt
class="ENVAR">DESTDIR</tt>. All you have to do is simply execute the following
script:</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
export DESTDIR=/data/misc/diskless
mkdir -p ${DESTDIR}
cd /usr/src; make world &#38;&#38; make kernel
cd /usr/src/etc; make distribution
</pre>

<p>Once done, you may need to customize your <tt class="FILENAME">/etc/rc.conf</tt> and
<tt class="FILENAME">/etc/fstab</tt> placed into <tt class="ENVAR">DESTDIR</tt> according
to your needs.</p>
</div>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN37422" name="AEN37422">24.6.2.8 Configuring Swap</a></h3>

<p>If needed, a swap file located on the server can be accessed via <acronym
class="ACRONYM">NFS</acronym>. One of the methods commonly used to do this has been
discontinued in release 5.X.</p>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN37426" name="AEN37426">24.6.2.8.1 <acronym
class="ACRONYM">NFS</acronym> Swap with FreeBSD&nbsp;4.X</a></h4>

<p>The swap file location and size can be specified with BOOTP/<acronym
class="ACRONYM">DHCP</acronym> FreeBSD-specific options 128 and 129. Examples of
configuration files for <b class="APPLICATION">ISC DHCP 3.0</b> or <b
class="APPLICATION">bootpd</b> follow:</p>

<div class="PROCEDURE">
<ol type="1">
<li>
<p>Add the following lines to <tt class="FILENAME">dhcpd.conf</tt>:</p>

<pre class="PROGRAMLISTING">
# Global section
option swap-path code 128 = string;
option swap-size code 129 = integer 32;

host margaux {
  ... # Standard lines, see above
  option swap-path <var class="REPLACEABLE">"192.168.4.4:/netswapvolume/netswap"</var>;
  option swap-size <var class="REPLACEABLE">64000</var>;
}
       
</pre>

<p><var class="LITERAL">swap-path</var> is the path to a directory where swap files will
be located. Each file will be named <tt class="FILENAME">swap.<var
class="REPLACEABLE">client-ip</var></tt>.</p>

<p>Older versions of <b class="APPLICATION">dhcpd</b> used a syntax of <var
class="LITERAL">option option-128 "...</var>, which is no longer supported.</p>

<p><tt class="FILENAME">/etc/bootptab</tt> would use the following syntax instead:</p>

<pre class="PROGRAMLISTING">
T128="192.168.4.4:/netswapvolume/netswap":T129=0000fa00
</pre>

<div class="NOTE">
<blockquote class="NOTE">
<p><b>Note:</b> In <tt class="FILENAME">/etc/bootptab</tt>, the swap size must be
expressed in hexadecimal format.</p>
</blockquote>
</div>
</li>

<li>
<p>On the <acronym class="ACRONYM">NFS</acronym> swap file server, create the swap
file(s):</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">mkdir <var
class="REPLACEABLE">/netswapvolume/netswap</var></kbd>
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">cd <var
class="REPLACEABLE">/netswapvolume/netswap</var></kbd>
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">dd if=/dev/zero bs=1024 count=<var
class="REPLACEABLE">64000</var> of=swap.<var class="REPLACEABLE">192.168.4.6</var></kbd>
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">chmod 0600 swap.<var
class="REPLACEABLE">192.168.4.6</var></kbd>
           
</pre>

<p><var class="REPLACEABLE">192.168.4.6</var> is the IP address for the diskless
client.</p>
</li>

<li>
<p>On the <acronym class="ACRONYM">NFS</acronym> swap file server, add the following line
to <tt class="FILENAME">/etc/exports</tt>:</p>

<pre class="PROGRAMLISTING">
<var class="REPLACEABLE">/netswapvolume</var>  -maproot=0:10 -alldirs <var
class="REPLACEABLE">margaux corbieres</var>
       
</pre>

<p>Then tell <b class="APPLICATION">mountd</b> to reread the <tt
class="FILENAME">exports</tt> file, as above.</p>
</li>
</ol>
</div>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN37482" name="AEN37482">24.6.2.8.2 <acronym
class="ACRONYM">NFS</acronym> Swap with FreeBSD&nbsp;5.X</a></h4>

<p>The kernel does not support enabling <acronym class="ACRONYM">NFS</acronym> swap at
boot time. Swap must be enabled by the startup scripts, by mounting a writeable file
system and creating and enabling a swap file. To create a swap file of appropriate size,
you can do like this:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">dd if=/dev/zero of=<var
class="REPLACEABLE">/path/to/swapfile</var> bs=1k count=1 oseek=<var
class="REPLACEABLE">100000</var></kbd>
</pre>

<p>To enable it you have to add the following line to your <tt
class="FILENAME">rc.conf</tt>:</p>

<pre class="PROGRAMLISTING">
swapfile=<var class="REPLACEABLE">/path/to/swapfile</var>
</pre>
</div>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN37496" name="AEN37496">24.6.2.9 Miscellaneous Issues</a></h3>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN37498" name="AEN37498">24.6.2.9.1 Running with a Read-only
<tt class="FILENAME">/usr</tt></a></h4>

<p>If the diskless workstation is configured to run X, you will have to adjust the <b
class="APPLICATION">XDM</b> configuration file, which puts the error log on <tt
class="FILENAME">/usr</tt> by default.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN37507" name="AEN37507">24.6.2.9.2 Using a Non-FreeBSD
Server</a></h4>

<p>When the server for the root filesystem is not running FreeBSD, you will have to
create the root filesystem on a FreeBSD machine, then copy it to its destination, using
<tt class="COMMAND">tar</tt> or <tt class="COMMAND">cpio</tt>.</p>

<p>In this situation, there are sometimes problems with the special files in <tt
class="FILENAME">/dev</tt>, due to differing major/minor integer sizes. A solution to
this problem is to export a directory from the non-FreeBSD server, mount this directory
onto a FreeBSD machine, and run <tt class="COMMAND">MAKEDEV</tt> on the FreeBSD machine
to create the correct device entries (FreeBSD 5.0 and later use <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=devfs&sektion=5&manpath=FreeBSD+6-current">
<span class="CITEREFENTRY"><span class="REFENTRYTITLE">devfs</span>(5)</span></a> to
allocate device nodes transparently for the user, running <tt
class="COMMAND">MAKEDEV</tt> on these versions is pointless).</p>
</div>
</div>
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