source: chapter08/kernel.xml@ edbeeb5

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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 <sect1info condition="script">
12 <productname>linux</productname>
13 <productnumber>&linux-version;</productnumber>
14 <address>&linux-url;</address>
15 </sect1info>
16
17 <title>Linux-&linux-version;</title>
18
19 <indexterm zone="ch-bootable-kernel">
20 <primary sortas="a-Linux">Linux</primary>
21 </indexterm>
22
23 <sect2 role="package">
24 <title/>
25
26 <para>The Linux package contains the Linux kernel.</para>
27
28 <segmentedlist>
29 <segtitle>&buildtime;</segtitle>
30 <segtitle>&diskspace;</segtitle>
31
32 <seglistitem>
33 <seg>&linux-ch8-sbu;</seg>
34 <seg>&linux-ch8-du;</seg>
35 </seglistitem>
36 </segmentedlist>
37
38 </sect2>
39
40 <sect2 role="installation">
41 <title>Installation of the kernel</title>
42
43 <para>Building the kernel involves a few steps&mdash;configuration,
44 compilation, and installation. Read the <filename>README</filename> file
45 in the kernel source tree for alternative methods to the way this book
46 configures the kernel.</para>
47
48 <para>Prepare for compilation by running the following command:</para>
49
50<screen><userinput remap="pre">make mrproper</userinput></screen>
51
52 <para>This ensures that the kernel tree is absolutely clean. The
53 kernel team recommends that this command be issued prior to each
54 kernel compilation. Do not rely on the source tree being clean after
55 un-tarring.</para>
56
57 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
58
59 <para>Configure the kernel via a menu-driven interface. For general
60 information on kernel configuration see <ulink
61 url="&hints-root;kernel-configuration.txt"/>. BLFS has some information
62 regarding particular kernel configuration requirements of packages outside
63 of LFS at <ulink
64 url="&blfs-book;longindex.html#kernel-config-index"/>. Additional
65 information about configuring and building the kernel can be found at
66 <ulink url="http://www.kroah.com/lkn/"/> </para>
67
68 <note><para>A good starting place for setting up the kernel configuration
69 is to run <command>make defconfig</command>. This will set the base
70 configuration to a good state that takes your current system architecture
71 into account.</para>
72
73 <para>Be sure to configure the following features as shown:</para>
74
75 <screen role="nodump">
76Device Drivers ---&gt;
77 Generic Driver Options ---&gt;
78 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
79 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]</screen></note>
80
81 <para>There are several other options that may be desired depending
82 on the requirements for the system. For a list of options needed
83 for BLFS packages, see the <ulink
84 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
85 Index of Kernel Settings</ulink>
86 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
87
88 <variablelist>
89 <title>The rationale for the above configuration items:</title>
90
91 <varlistentry>
92 <term><parameter>Support for uevent helper</parameter></term>
93 <listitem>
94 <para>Having this option set may interfere with device
95 management when using Udev/Eudev. </para>
96 </listitem>
97 </varlistentry>
98
99 <varlistentry>
100 <term><parameter>Maintain a devtmpfs</parameter></term>
101 <listitem>
102 <para>This will create automated device nodes which are populated by the
103 kernel, even without Udev running. Udev then runs on top of this,
104 managing permissions and adding symlinks. This configuration
105 item is required for all users of Udev/Eudev.</para>
106 </listitem>
107 </varlistentry>
108
109 </variablelist>
110
111<screen role="nodump"><userinput>make LANG=<replaceable>&lt;host_LANG_value&gt;</replaceable> LC_ALL= menuconfig</userinput></screen>
112
113 <variablelist>
114 <title>The meaning of the make parameters:</title>
115
116 <varlistentry>
117 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
118 <listitem>
119 <para>This establishes the locale setting to the one used on the host.
120 This is needed for a proper menuconfig ncurses interface line
121 drawing on UTF-8 linux text console.</para>
122
123 <para>Be sure to replace <replaceable>&lt;host_LANG_value&gt;</replaceable>
124 by the value of the <envar>$LANG</envar> variable from your host.
125 If not set, you could use instead the host's value of <envar>$LC_ALL</envar>
126 or <envar>$LC_CTYPE</envar>.</para>
127 </listitem>
128 </varlistentry>
129
130 </variablelist>
131
132 <para>Alternatively, <command>make oldconfig</command> may be more
133 appropriate in some situations. See the <filename>README</filename>
134 file for more information.</para>
135
136 <para>If desired, skip kernel configuration by copying the kernel
137 config file, <filename>.config</filename>, from the host system
138 (assuming it is available) to the unpacked <filename
139 class="directory">linux-&linux-version;</filename> directory. However,
140 we do not recommend this option. It is often better to explore all the
141 configuration menus and create the kernel configuration from
142 scratch.</para>
143
144 <para>Compile the kernel image and modules:</para>
145
146<screen><userinput remap="make">make</userinput></screen>
147
148 <para>If using kernel modules, module configuration in <filename
149 class="directory">/etc/modprobe.d</filename> may be required.
150 Information pertaining to modules and kernel configuration is
151 located in <xref linkend="ch-scripts-udev"/> and in the kernel
152 documentation in the <filename
153 class="directory">linux-&linux-version;/Documentation</filename> directory.
154 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
155
156 <para>Install the modules, if the kernel configuration uses them:</para>
157
158<screen><userinput remap="install">make modules_install</userinput></screen>
159
160 <para>After kernel compilation is complete, additional steps are
161 required to complete the installation. Some files need to be copied to
162 the <filename class="directory">/boot</filename> directory.</para>
163
164 <para>The path to the kernel image may vary depending on the platform being
165 used. The filename below can be changed to suit your taste, but the stem of
166 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
167 the automatic setup of the boot process described in the next section. The
168 following command assumes an x86 architecture:</para>
169
170<screen><userinput remap="install">cp -v arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
171
172 <para><filename>System.map</filename> is a symbol file for the kernel.
173 It maps the function entry points of every function in the kernel API,
174 as well as the addresses of the kernel data structures for the running
175 kernel. It is used as a resource when investigating kernel problems.
176 Issue the following command to install the map file:</para>
177
178<screen><userinput remap="install">cp -v System.map /boot/System.map-&linux-version;</userinput></screen>
179
180 <para>The kernel configuration file <filename>.config</filename>
181 produced by the <command>make menuconfig</command> step
182 above contains all the configuration selections for the kernel
183 that was just compiled. It is a good idea to keep this file for future
184 reference:</para>
185
186<screen><userinput remap="install">cp -v .config /boot/config-&linux-version;</userinput></screen>
187
188 <para>Install the documentation for the Linux kernel:</para>
189
190<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
191cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
192
193 <para>It is important to note that the files in the kernel source
194 directory are not owned by <emphasis>root</emphasis>. Whenever a
195 package is unpacked as user <emphasis>root</emphasis> (like we did
196 inside chroot), the files have the user and group IDs of whatever
197 they were on the packager's computer. This is usually not a problem
198 for any other package to be installed because the source tree is
199 removed after the installation. However, the Linux source tree is
200 often retained for a long time. Because of this, there is a chance
201 that whatever user ID the packager used will be assigned to somebody
202 on the machine. That person would then have write access to the kernel
203 source.</para>
204
205 <note>
206 <para>In many cases, the configuration of the kernel will need to be
207 updated for packages that will be installed later in BLFS. Unlike
208 other packages, it is not necessary to remove the kernel source tree
209 after the newly built kernel is installed.</para>
210
211 <para>If the kernel source tree is going to be retained, run
212 <command>chown -R 0:0</command> on the <filename
213 class="directory">linux-&linux-version;</filename> directory to ensure
214 all files are owned by user <emphasis>root</emphasis>.</para>
215 </note>
216
217 <warning>
218 <para>Some kernel documentation recommends creating a symlink from
219 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
220 source directory. This is specific to kernels prior to the 2.6 series and
221 <emphasis>must not</emphasis> be created on an LFS system as it can cause
222 problems for packages you may wish to build once your base LFS system is
223 complete.</para>
224 </warning>
225
226 <warning>
227 <para>The headers in the system's <filename
228 class="directory">include</filename> directory (<filename
229 class="directory">/usr/include</filename>) should
230 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
231 that is, the sanitised headers installed in <xref
232 linkend="ch-system-linux-headers"/>. Therefore, they should
233 <emphasis>never</emphasis> be replaced by either the raw kernel headers
234 or any other kernel sanitized headers.</para>
235 </warning>
236
237 </sect2>
238
239 <sect2 id="conf-modprobe" role="configuration">
240 <title>Configuring Linux Module Load Order</title>
241
242 <indexterm zone="conf-modprobe">
243 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
244 </indexterm>
245
246 <para>Most of the time Linux modules are loaded automatically, but
247 sometimes it needs some specific direction. The program that loads
248 modules, <command>modprobe</command> or <command>insmod</command>, uses
249 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
250 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
251 uhci_hcd) have been built as modules, they will be loaded in the correct
252 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
253 to avoid a warning being output at boot time.</para>
254
255 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
256 the following:</para>
257
258<screen><userinput>install -v -m755 -d /etc/modprobe.d
259cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
260<literal># Begin /etc/modprobe.d/usb.conf
261
262install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
263install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
264
265# End /etc/modprobe.d/usb.conf</literal>
266EOF</userinput></screen>
267
268 </sect2>
269
270 <sect2 id="contents-kernel" role="content">
271 <title>Contents of Linux</title>
272
273 <segmentedlist>
274 <segtitle>Installed files</segtitle>
275 <segtitle>Installed directories</segtitle>
276
277 <seglistitem>
278 <seg>config-&linux-version;,
279 vmlinuz-&linux-version;-lfs-&version;, and
280 System.map-&linux-version;</seg>
281 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
282 </seglistitem>
283 </segmentedlist>
284
285 <variablelist>
286 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
287 <?dbfo list-presentation="list"?>
288 <?dbhtml list-presentation="table"?>
289
290 <varlistentry id="config">
291 <term><filename>config-&linux-version;</filename></term>
292 <listitem>
293 <para>Contains all the configuration selections for the kernel</para>
294 <indexterm zone="ch-bootable-kernel config">
295 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
296 </indexterm>
297 </listitem>
298 </varlistentry>
299
300 <varlistentry id="lfskernel">
301 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
302 <listitem>
303 <para>The engine of the Linux system. When turning on the computer,
304 the kernel is the first part of the operating system that gets loaded.
305 It detects and initializes all components of the computer's hardware,
306 then makes these components available as a tree of files to the
307 software and turns a single CPU into a multitasking machine capable
308 of running scores of programs seemingly at the same time</para>
309 <indexterm zone="ch-bootable-kernel lfskernel">
310 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
311 </indexterm>
312 </listitem>
313 </varlistentry>
314
315 <varlistentry id="System.map">
316 <term><filename>System.map-&linux-version;</filename></term>
317 <listitem>
318 <para>A list of addresses and symbols; it maps the entry points and
319 addresses of all the functions and data structures in the
320 kernel</para>
321 <indexterm zone="ch-bootable-kernel System.map">
322 <primary sortas="e-/boot/System.map">/boot/System.map-&linux-version;</primary>
323 </indexterm>
324 </listitem>
325 </varlistentry>
326
327 </variablelist>
328
329 </sect2>
330
331</sect1>
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