source: clfs-embedded/BOOK/bootable/x86/kernel.xml @ 81d9bce

Last change on this file since 81d9bce was 81d9bce, checked in by Jim Gifford <clfs@…>, 17 years ago

Added note about what has to built into the kernel

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File size: 8.9 KB
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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
3  "http://www.oasis-open.org/docbook/xml/4.4/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 build 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.</para></note>
50
51<screen os="g"><userinput>make ARCH=i386 CROSS_COMPILE=${CLFS_TARGET}- menuconfig</userinput></screen>
52
53    <para os="h">Alternatively, <command>make oldconfig</command> may be more
54    appropriate in some situations. See the <filename>README</filename>
55    file for more information.</para>
56
57    <para os="i">If desired, skip kernel configuration by copying the kernel
58    config file, <filename>.config</filename>, from the host system
59    (assuming it is available) to the root directory of the unpacked kernel
60    sources. However, we do not recommend this option. It is often better
61    to explore all the configuration menus and create the kernel configuration
62    from scratch.</para>
63
64    <para os="j">Compile the kernel image and modules:</para>
65
66<screen os="k"><userinput>make ARCH=i386 CROSS_COMPILE=${CLFS_TARGET}-</userinput></screen>
67
68    <para os="l">If using kernel modules, an
69    <filename>/etc/modprobe.conf</filename> file may be needed.
70    Information pertaining to modules and kernel configuration is
71    located in the kernel documentation in the <filename
72    class="directory">Documentation</filename> directory of the kernel
73    sources tree. Also, <filename>modprobe.conf(5)</filename> may
74    be of interest.</para>
75
76    <para os="m">Be very careful when reading other documentation relating to
77    kernel modules because it usually applies to 2.4.x kernels only. As
78    far as we know, kernel configuration issues specific to Hotplug and
79    Udev are not documented. The problem is that Udev will create a device
80    node only if Hotplug or a user-written script inserts the corresponding
81    module into the kernel, and not all modules are detectable by Hotplug.
82    Note that statements like the one below in the
83    <filename>/etc/modprobe.conf</filename> file do not work with Udev:</para>
84
85<screen os="n"><literal>alias char-major-XXX some-module</literal></screen>
86
87    <para os="o">Because of the complications with Udev and modules,
88    we strongly recommend starting with a completely non-modular kernel
89    configuration, especially if this is the first time using Udev.</para>
90
91    <para os="p">Install the modules, if the kernel configuration uses
92    them:</para>
93
94<screen os="q"><userinput>make ARCH=i386 CROSS_COMPILE=${CLFS_TARGET}- \
95    INSTALL_MOD_PATH=${CLFS} modules_install</userinput></screen>
96
97    <para os="r">After kernel compilation is complete, additional steps are
98    required to complete the installation. Some files need to be copied to
99    the <filename class="directory">${CLFS}/boot</filename> directory.</para>
100
101    <para os="s">Issue the following command to install the kernel:</para>
102
103<screen os="t"><userinput>cp vmlinux ${CLFS}/boot/clfskernel-&linux-version;</userinput></screen>
104
105    <para os="u"><filename>System.map</filename> is a symbol file for the kernel.
106    It maps the function entry points of every function in the kernel API,
107    as well as the addresses of the kernel data structures for the running
108    kernel. Issue the following command to install the map file:</para>
109
110<screen os="v"><userinput>cp System.map ${CLFS}/boot/System.map-&linux-version;</userinput></screen>
111
112    <para os="w">If we compiled our kernel with modules and we made sure depmod.pl
113    is avaiable from busybox, we need to create the module dependency list by
114    issuing the following command:</para>
115
116<screen os="x"><userinput>${CLFS}/cross-tools/bin/depmod.pl -F ${CLFS}/boot/System.map -b ${CLFS}/lib/modules/&linux-version;</userinput></screen>
117
118    <para os="y">The kernel configuration file <filename>.config</filename>
119    produced by the <command>make menuconfig</command> step above contains
120    all the configuration selections for the kernel that was just compiled.
121    It is a good idea to keep this file for future reference:</para>
122
123<screen os="z"><userinput>cp .config ${CLFS}/boot/config-&linux-version;</userinput></screen>
124
125    <warning os="aa">
126      <para>Some kernel documentation recommends creating a symlink from
127      <filename class="symlink">/usr/src/linux</filename> pointing to the
128      kernel source directory. This is specific to kernels prior to the
129      2.6 series and <emphasis>must not</emphasis> be created on an CLFS
130      system as it can cause problems for packages you may wish to build
131      once your base CLFS system is complete.</para>
132
133      <para>Also, the headers in the system's <filename
134      class="directory">include</filename> directory should
135      <emphasis>always</emphasis> be the ones against which Glibc was
136      compiled (from the Linux-Headers package) and should
137      <emphasis>never</emphasis> be replaced by the kernel headers.</para>
138    </warning>
139
140   <para os="ab">The bootloaders section contains more information on
141    how to configure the kernel for specifc bootloaders. Please refer
142    to this section for your specific needs.</para>
143
144  </sect2>
145
146  <sect2 id="contents-kernel" role="content">
147    <title>Contents of Linux</title>
148
149    <segmentedlist>
150      <segtitle>Installed files</segtitle>
151
152      <seglistitem>
153        <seg>config-[linux-version], clfskernel-[linux-version],
154        and System.map-[linux-version]</seg>
155      </seglistitem>
156    </segmentedlist>
157
158    <variablelist>
159      <bridgehead renderas="sect3">Short Descriptions</bridgehead>
160      <?dbfo list-presentation="list"?>
161      <?dbhtml list-presentation="table"?>
162
163      <varlistentry id="config">
164        <term><filename>config-[linux-version]</filename></term>
165        <listitem>
166          <para>Contains all the configuration selections for the kernel</para>
167          <indexterm zone="ch-bootable-kernel config">
168            <primary sortas="e-/boot/config">/boot/config-[linux-version]</primary>
169          </indexterm>
170        </listitem>
171      </varlistentry>
172
173      <varlistentry id="clfskernel">
174        <term><filename>clfskernel-[linux-version]</filename></term>
175        <listitem>
176          <para>The engine of the Linux system. When turning on the
177          computer, the kernel is the first part of the operating system
178          that gets loaded. It detects and initializes all components of
179          the computer's hardware, then makes these components available
180          as a tree of files to the software and turns a single CPU into
181          a multitasking machine capable of running scores of programs
182          seemingly at the same time.</para>
183          <indexterm zone="ch-bootable-kernel clfskernel">
184            <primary sortas="b-clfskernel">clfskernel-[linux-version]</primary>
185          </indexterm>
186        </listitem>
187      </varlistentry>
188
189      <varlistentry id="System.map">
190        <term><filename>System.map-[linux-version]</filename></term>
191        <listitem>
192          <para>A list of addresses and symbols; it maps the entry points
193          and addresses of all the functions and data structures in the
194          kernel</para>
195          <indexterm zone="ch-bootable-kernel System.map">
196            <primary sortas="e-/boot/System.map">/boot/System.map-[linux-version]</primary>
197          </indexterm>
198        </listitem>
199      </varlistentry>
200
201    </variablelist>
202
203  </sect2>
204
205</sect1>
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