source: chapter08/kernel.xml@ cfb4e55

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Last change on this file since cfb4e55 was cfb4e55, checked in by Bruce Dubbs <bdubbs@…>, 7 years ago

Add role for new instruction in kernel

git-svn-id: 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

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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 "" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
8<sect1 id="ch-bootable-kernel" role="wrap">
9 <?dbhtml filename="kernel.html"?>
11 <sect1info condition="script">
12 <productname>linux</productname>
13 <productnumber>&linux-version;</productnumber>
14 <address>&linux-url;</address>
15 </sect1info>
17 <title>Linux-&linux-version;</title>
19 <indexterm zone="ch-bootable-kernel">
20 <primary sortas="a-Linux">Linux</primary>
21 </indexterm>
23 <sect2 role="package">
24 <title/>
26 <para>The Linux package contains the Linux kernel.</para>
28 <segmentedlist>
29 <segtitle>&buildtime;</segtitle>
30 <segtitle>&diskspace;</segtitle>
32 <seglistitem>
33 <seg>&linux-ch8-sbu;</seg>
34 <seg>&linux-ch8-du;</seg>
35 </seglistitem>
36 </segmentedlist>
38 </sect2>
40 <sect2 role="installation">
41 <title>Installation of the kernel</title>
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>
48 <para>Prepare for compilation by running the following command:</para>
50<screen><userinput remap="pre">make mrproper</userinput></screen>
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>
57 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
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=""/> </para>
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>
73 <para>Be sure to configure the following features as shown:</para>
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>
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>
88 <variablelist>
89 <title>The rationale for the above configuration items:</title>
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>
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>
109 </variablelist>
111<screen role="nodump"><userinput>make menuconfig</userinput></screen>
113 <variablelist>
114 <title>The meaning of optional make environment variables:</title>
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
120 host. This may be needed for a proper menuconfig ncurses interface
121 line drawing on a UTF-8 linux text console.</para>
123 <para>If used, be sure to replace
124 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
125 the <envar>$LANG</envar> variable from your host. You can
126 alternatively use instead the host's value of <envar>$LC_ALL</envar>
127 or <envar>$LC_CTYPE</envar>.</para>
128 </listitem>
129 </varlistentry>
131 </variablelist>
133 <para>Alternatively, <command>make oldconfig</command> may be more
134 appropriate in some situations. See the <filename>README</filename>
135 file for more information.</para>
137 <para>If desired, skip kernel configuration by copying the kernel
138 config file, <filename>.config</filename>, from the host system
139 (assuming it is available) to the unpacked <filename
140 class="directory">linux-&linux-version;</filename> directory. However,
141 we do not recommend this option. It is often better to explore all the
142 configuration menus and create the kernel configuration from
143 scratch.</para>
145 <para>Compile the kernel image and modules:</para>
147<screen><userinput remap="make">make</userinput></screen>
149 <para>If using kernel modules, module configuration in <filename
150 class="directory">/etc/modprobe.d</filename> may be required.
151 Information pertaining to modules and kernel configuration is
152 located in <xref linkend="ch-scripts-udev"/> and in the kernel
153 documentation in the <filename
154 class="directory">linux-&linux-version;/Documentation</filename> directory.
155 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
157 <para>Install the modules, if the kernel configuration uses them:</para>
159<screen role="nodump"><userinput remap="install">make modules_install</userinput></screen>
161 <para>After kernel compilation is complete, additional steps are
162 required to complete the installation. Some files need to be copied to
163 the <filename class="directory">/boot</filename> directory.</para>
165 <caution>
166 <para>If the host system has a separate /boot partition, the
167 files copied below should go there. The easiest way to do that
168 is to bind /boot on the host to /mnt/lfs/boot before proceeding:</para>
170<screen><userinput>mount --bind /boot /mnt/lfs/boot</userinput></screen>
171 </caution>
173 <para>The path to the kernel image may vary depending on the platform being
174 used. The filename below can be changed to suit your taste, but the stem of
175 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
176 the automatic setup of the boot process described in the next section. The
177 following command assumes an x86 architecture:</para>
179<screen><userinput remap="install">cp -v arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
181 <para><filename></filename> is a symbol file for the kernel.
182 It maps the function entry points of every function in the kernel API,
183 as well as the addresses of the kernel data structures for the running
184 kernel. It is used as a resource when investigating kernel problems.
185 Issue the following command to install the map file:</para>
187<screen><userinput remap="install">cp -v /boot/;</userinput></screen>
189 <para>The kernel configuration file <filename>.config</filename>
190 produced by the <command>make menuconfig</command> step
191 above contains all the configuration selections for the kernel
192 that was just compiled. It is a good idea to keep this file for future
193 reference:</para>
195<screen><userinput remap="install">cp -v .config /boot/config-&linux-version;</userinput></screen>
197 <para>Install the documentation for the Linux kernel:</para>
199<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
200cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
202 <para>It is important to note that the files in the kernel source
203 directory are not owned by <emphasis>root</emphasis>. Whenever a
204 package is unpacked as user <emphasis>root</emphasis> (like we did
205 inside chroot), the files have the user and group IDs of whatever
206 they were on the packager's computer. This is usually not a problem
207 for any other package to be installed because the source tree is
208 removed after the installation. However, the Linux source tree is
209 often retained for a long time. Because of this, there is a chance
210 that whatever user ID the packager used will be assigned to somebody
211 on the machine. That person would then have write access to the kernel
212 source.</para>
214 <note>
215 <para>In many cases, the configuration of the kernel will need to be
216 updated for packages that will be installed later in BLFS. Unlike
217 other packages, it is not necessary to remove the kernel source tree
218 after the newly built kernel is installed.</para>
220 <para>If the kernel source tree is going to be retained, run
221 <command>chown -R 0:0</command> on the <filename
222 class="directory">linux-&linux-version;</filename> directory to ensure
223 all files are owned by user <emphasis>root</emphasis>.</para>
224 </note>
226 <warning>
227 <para>Some kernel documentation recommends creating a symlink from
228 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
229 source directory. This is specific to kernels prior to the 2.6 series and
230 <emphasis>must not</emphasis> be created on an LFS system as it can cause
231 problems for packages you may wish to build once your base LFS system is
232 complete.</para>
233 </warning>
235 <warning>
236 <para>The headers in the system's <filename
237 class="directory">include</filename> directory (<filename
238 class="directory">/usr/include</filename>) should
239 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
240 that is, the sanitised headers installed in <xref
241 linkend="ch-system-linux-headers"/>. Therefore, they should
242 <emphasis>never</emphasis> be replaced by either the raw kernel headers
243 or any other kernel sanitized headers.</para>
244 </warning>
246 </sect2>
248 <sect2 id="conf-modprobe" role="configuration">
249 <title>Configuring Linux Module Load Order</title>
251 <indexterm zone="conf-modprobe">
252 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
253 </indexterm>
255 <para>Most of the time Linux modules are loaded automatically, but
256 sometimes it needs some specific direction. The program that loads
257 modules, <command>modprobe</command> or <command>insmod</command>, uses
258 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
259 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
260 uhci_hcd) have been built as modules, they will be loaded in the correct
261 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
262 to avoid a warning being output at boot time.</para>
264 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
265 the following:</para>
267<screen><userinput>install -v -m755 -d /etc/modprobe.d
268cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
269<literal># Begin /etc/modprobe.d/usb.conf
271install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
272install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
274# End /etc/modprobe.d/usb.conf</literal>
277 </sect2>
279 <sect2 id="contents-kernel" role="content">
280 <title>Contents of Linux</title>
282 <segmentedlist>
283 <segtitle>Installed files</segtitle>
284 <segtitle>Installed directories</segtitle>
286 <seglistitem>
287 <seg>config-&linux-version;,
288 vmlinuz-&linux-version;-lfs-&version;, and
290 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
291 </seglistitem>
292 </segmentedlist>
294 <variablelist>
295 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
296 <?dbfo list-presentation="list"?>
297 <?dbhtml list-presentation="table"?>
299 <varlistentry id="config">
300 <term><filename>config-&linux-version;</filename></term>
301 <listitem>
302 <para>Contains all the configuration selections for the kernel</para>
303 <indexterm zone="ch-bootable-kernel config">
304 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
305 </indexterm>
306 </listitem>
307 </varlistentry>
309 <varlistentry id="lfskernel">
310 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
311 <listitem>
312 <para>The engine of the Linux system. When turning on the computer,
313 the kernel is the first part of the operating system that gets loaded.
314 It detects and initializes all components of the computer's hardware,
315 then makes these components available as a tree of files to the
316 software and turns a single CPU into a multitasking machine capable
317 of running scores of programs seemingly at the same time</para>
318 <indexterm zone="ch-bootable-kernel lfskernel">
319 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
320 </indexterm>
321 </listitem>
322 </varlistentry>
324 <varlistentry id="">
325 <term><filename>;</filename></term>
326 <listitem>
327 <para>A list of addresses and symbols; it maps the entry points and
328 addresses of all the functions and data structures in the
329 kernel</para>
330 <indexterm zone="ch-bootable-kernel">
331 <primary sortas="e-/boot/">/boot/;</primary>
332 </indexterm>
333 </listitem>
334 </varlistentry>
336 </variablelist>
338 </sect2>
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