source: clfs-embedded/BOOK/bootable/x86/kernel.xml @ 6a3c6dc

Last change on this file since 6a3c6dc was 6a3c6dc, checked in by Jim Gifford <clfs@…>, 15 years ago

Updates to IPTables and Dropbear

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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4  <!ENTITY % general-entities SYSTEM "../../general.ent">
5  %general-entities;
6]>
7
8<sect1 id="ch-bootable-kernel" role="wrap">
9  <?dbhtml filename="kernel.html"?>
10
11  <title>Linux-&linux-version;</title>
12
13  <indexterm zone="ch-bootable-kernel">
14    <primary sortas="a-Linux">Linux</primary>
15  </indexterm>
16
17  <sect2 role="package"><title/>
18    <para>The Linux package contains the Linux kernel.</para>
19
20  </sect2>
21
22  <sect2 role="installation">
23    <title>Installation of the kernel</title>
24
25    <para os="a">Building the kernel involves a few steps&mdash;configuration,
26    compilation, and installation. Read the <filename>README</filename>
27    file in the kernel source tree for alternative methods to the way this
28    book configures the kernel.</para>
29
30    <para os="b">Prepare for compilation by running the following command:</para>
31
32<screen os="c"><userinput>make mrproper</userinput></screen>
33
34    <para os="d">This ensures that the kernel tree is absolutely clean. The
35    kernel team recommends that this command be issued prior to each
36    kernel compilation. Do not rely on the source tree being clean after
37    un-tarring.</para>
38
39    <para os="e">Configure the kernel via a menu-driven interface.
40    Please note that the udev bootscript requires "rtc" and "tmpfs" to be
41    enabled and built into the kernel, not as modules. BLFS has
42    some information regarding particular kernel configuration requirements of
43    packages outside of CLFS at <ulink
44    url="&blfs-root;view/svn/longindex.html#kernel-config-index"/>:</para>
45
46    <note os="f"><para>Since we are building for an embedded system we need to make sure
47    our key components are built into the kernel and not as modules. Our key
48    components are console/video, disk, and network. With out these built in our
49    system will not function properly. If your concerned about disk space, your kernel
50    should be without modules.</para></note>
51
52<screen os="g"><userinput>make ARCH=${CLFS_ARCH} CROSS_COMPILE=${CLFS_TARGET}- menuconfig</userinput></screen>
53
54    <para os="h">Alternatively, <command>make oldconfig</command> may be more
55    appropriate in some situations. See the <filename>README</filename>
56    file for more information.</para>
57
58    <para os="i">If desired, skip kernel configuration by copying the kernel
59    config file, <filename>.config</filename>, from the host system
60    (assuming it is available) to the root directory of the unpacked kernel
61    sources. However, we do not recommend this option. It is often better
62    to explore all the configuration menus and create the kernel configuration
63    from scratch.</para>
64
65    <para os="j">Compile the kernel image and modules:</para>
66
67<screen os="k"><userinput>make ARCH=${CLFS_ARCH} CROSS_COMPILE=${CLFS_TARGET}-</userinput></screen>
68
69    <para os="l">If using kernel modules, an
70    <filename>/etc/modprobe.conf</filename> file may be needed.
71    Information pertaining to modules and kernel configuration is
72    located in the kernel documentation in the <filename
73    class="directory">Documentation</filename> directory of the kernel
74    sources tree. Also, <filename>modprobe.conf(5)</filename> may
75    be of interest.</para>
76
77    <para os="m">Be very careful when reading other documentation relating to
78    kernel modules because it usually applies to 2.4.x kernels only. As
79    far as we know, kernel configuration issues specific to Hotplug and
80    Udev are not documented. The problem is that Udev will create a device
81    node only if Hotplug or a user-written script inserts the corresponding
82    module into the kernel, and not all modules are detectable by Hotplug.
83    Note that statements like the one below in the
84    <filename>/etc/modprobe.conf</filename> file do not work with Udev:</para>
85
86<screen os="n"><literal>alias char-major-XXX some-module</literal></screen>
87
88    <para os="o">Because of the complications with Udev and modules,
89    we strongly recommend starting with a completely non-modular kernel
90    configuration, especially if this is the first time using Udev.</para>
91
92    <para os="p">Install the modules, if the kernel configuration uses
93    them:</para>
94
95<screen os="q"><userinput>make ARCH=${CLFS_ARCH} CROSS_COMPILE=${CLFS_TARGET}- \
96    INSTALL_MOD_PATH=${CLFS} modules_install</userinput></screen>
97
98    <para os="r">After kernel compilation is complete, additional steps are
99    required to complete the installation. Some files need to be copied to
100    the <filename class="directory">${CLFS}/boot</filename> directory.</para>
101
102    <para os="s">Issue the following command to install the kernel:</para>
103
104<screen os="t"><userinput>cp vmlinux ${CLFS}/boot/clfskernel-&linux-version;</userinput></screen>
105
106    <para os="u"><filename>System.map</filename> is a symbol file for the kernel.
107    It maps the function entry points of every function in the kernel API,
108    as well as the addresses of the kernel data structures for the running
109    kernel. Issue the following command to install the map file:</para>
110
111<screen os="v"><userinput>cp System.map ${CLFS}/boot/System.map-&linux-version;</userinput></screen>
112
113    <para os="w">If we compiled our kernel with modules and we made sure
114    <command>depmod.pl</command> is avaiable from BusyBox, we need to create the
115    module dependency list by issuing the following command:</para>
116
117<screen os="x"><userinput>${CLFS}/cross-tools/bin/depmod.pl -F ${CLFS}/boot/System.map \
118    -b ${CLFS}/lib/modules/&linux-version;</userinput></screen>
119
120    <para os="y">The kernel configuration file <filename>.config</filename>
121    produced by the <command>make menuconfig</command> step above contains
122    all the configuration selections for the kernel that was just compiled.
123    It is a good idea to keep this file for future reference:</para>
124
125<screen os="z"><userinput>cp .config ${CLFS}/boot/config-&linux-version;</userinput></screen>
126
127    <warning os="aa">
128      <para>Some kernel documentation recommends creating a symlink from
129      <filename class="symlink">/usr/src/linux</filename> pointing to the
130      kernel source directory. This is specific to kernels prior to the
131      2.6 series and <emphasis>must not</emphasis> be created on an CLFS
132      system as it can cause problems for packages you may wish to build
133      once your base CLFS system is complete.</para>
134
135    </warning>
136
137   <para os="ab">The bootloaders section contains more information on
138    how to configure the kernel for specifc bootloaders. Please refer
139    to this section for your specific needs.</para>
140
141  </sect2>
142
143  <sect2 id="contents-kernel" role="content">
144    <title>Contents of Linux</title>
145
146    <segmentedlist>
147      <segtitle>Installed files</segtitle>
148
149      <seglistitem>
150        <seg>config-[linux-version], clfskernel-[linux-version],
151        and System.map-[linux-version]</seg>
152      </seglistitem>
153    </segmentedlist>
154
155    <variablelist>
156      <bridgehead renderas="sect3">Short Descriptions</bridgehead>
157      <?dbfo list-presentation="list"?>
158      <?dbhtml list-presentation="table"?>
159
160      <varlistentry id="config">
161        <term><filename>config-[linux-version]</filename></term>
162        <listitem>
163          <para>Contains all the configuration selections for the kernel</para>
164          <indexterm zone="ch-bootable-kernel config">
165            <primary sortas="e-/boot/config">/boot/config-[linux-version]</primary>
166          </indexterm>
167        </listitem>
168      </varlistentry>
169
170      <varlistentry id="clfskernel">
171        <term><filename>clfskernel-[linux-version]</filename></term>
172        <listitem>
173          <para>The engine of the Linux system. When turning on the
174          computer, the kernel is the first part of the operating system
175          that gets loaded. It detects and initializes all components of
176          the computer's hardware, then makes these components available
177          as a tree of files to the software and turns a single CPU into
178          a multitasking machine capable of running scores of programs
179          seemingly at the same time.</para>
180          <indexterm zone="ch-bootable-kernel clfskernel">
181            <primary sortas="b-clfskernel">clfskernel-[linux-version]</primary>
182          </indexterm>
183        </listitem>
184      </varlistentry>
185
186      <varlistentry id="System.map">
187        <term><filename>System.map-[linux-version]</filename></term>
188        <listitem>
189          <para>A list of addresses and symbols; it maps the entry points
190          and addresses of all the functions and data structures in the
191          kernel</para>
192          <indexterm zone="ch-bootable-kernel System.map">
193            <primary sortas="e-/boot/System.map">/boot/System.map-[linux-version]</primary>
194          </indexterm>
195        </listitem>
196      </varlistentry>
197
198    </variablelist>
199
200  </sect2>
201
202</sect1>
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