source: chapter08/kernel.xml@ 8eb3fe4

multilib-10.1 multilib-before-cross
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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>
70 <para>A good starting place for setting up the kernel configuration is to
71 run <command>make defconfig</command>. This will set the base
72 configuration to a good state that takes your current system architecture
73 into account.</para>
75 <para>Be sure to enable/disable/set the following features or the system might
76 not work correctly or boot at all:</para>
78 <screen role="nodump" revision="sysv">
79Device Drivers ---&gt;
80 Generic Driver Options ---&gt;
81 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
82 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
84Kernel hacking ---&gt;
85 Choose kernel unwinder (Frame pointer unwinder) ---&gt; [CONFIG_UNWINDER_FRAME_POINTER]</screen>
87 <screen role="nodump" revision="systemd">
88General setup -->
89 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
90 [ ] Enable deprecated sysfs features by default [CONFIG_SYSFS_DEPRECATED_V2]
91 [*] open by fhandle syscalls [CONFIG_FHANDLE]
92 [ ] Auditing support [CONFIG_AUDIT]
93 [*] Control Group support [CONFIG_CGROUPS]
94Processor type and features ---&gt;
95 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
96Networking support ---&gt;
97 Networking options ---&gt;
98 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
99Device Drivers ---&gt;
100 Generic Driver Options ---&gt;
101 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
102 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
103 [ ] Fallback user-helper invocation for firmware loading [CONFIG_FW_LOADER_USER_HELPER]
104Firmware Drivers ---&gt;
105 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
106File systems ---&gt;
107 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
108 &lt;*&gt; Kernel automounter version 4 support (also supports v3) [CONFIG_AUTOFS4_FS]
109 Pseudo filesystems ---&gt;
110 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]
111 [*] Tmpfs extended attributes [CONFIG_TMPFS_XATTR]
112Kernel hacking ---&gt;
113 Choose kernel unwinder (Frame pointer unwinder) ---&gt; [CONFIG_UNWINDER_FRAME_POINTER]</screen>
114 </note>
116 <note revision="systemd">
117 <para>While "The IPv6 Protocol" is not strictly
118 required, it is highly recommended by the systemd developers.</para>
119 </note>
121 <para revision="sysv">There are several other options that may be desired
122 depending on the requirements for the system. For a list of options needed
123 for BLFS packages, see the <ulink
124 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
125 Index of Kernel Settings</ulink>
126 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
128 <note>
129 <para>If your host hardware is using UEFI, then the 'make defconfig'
130 above should automatically add in some EFI-related kernel options.</para>
132 <para>In order to allow your LFS kernel to be booted from within your
133 host's UEFI boot environment, your kernel must have this option
134 selected:</para>
136<screen role="nodump">Processor type and features ---&gt;
137 [*] EFI stub support [CONFIG_EFI_STUB]</screen>
139 <para>A fuller description of managing UEFI environments from within LFS
140 is covered by the lfs-uefi.txt hint at
141 <ulink
142 url=""/>.
143 </para>
144 </note>
146 <variablelist>
147 <title>The rationale for the above configuration items:</title>
149 <varlistentry>
150 <term><parameter>Support for uevent helper</parameter></term>
151 <listitem>
152 <para>Having this option set may interfere with device
153 management when using Udev/Eudev. </para>
154 </listitem>
155 </varlistentry>
157 <varlistentry>
158 <term><parameter>Maintain a devtmpfs</parameter></term>
159 <listitem>
160 <para>This will create automated device nodes which are populated by the
161 kernel, even without Udev running. Udev then runs on top of this,
162 managing permissions and adding symlinks. This configuration
163 item is required for all users of Udev/Eudev.</para>
164 </listitem>
165 </varlistentry>
167 </variablelist>
169<screen role="nodump"><userinput>make menuconfig</userinput></screen>
171 <variablelist>
172 <title>The meaning of optional make environment variables:</title>
174 <varlistentry>
175 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
176 <listitem>
177 <para>This establishes the locale setting to the one used on the
178 host. This may be needed for a proper menuconfig ncurses interface
179 line drawing on a UTF-8 linux text console.</para>
181 <para>If used, be sure to replace
182 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
183 the <envar>$LANG</envar> variable from your host. You can
184 alternatively use instead the host's value of <envar>$LC_ALL</envar>
185 or <envar>$LC_CTYPE</envar>.</para>
186 </listitem>
187 </varlistentry>
189 </variablelist>
191 <para>Alternatively, <command>make oldconfig</command> may be more
192 appropriate in some situations. See the <filename>README</filename>
193 file for more information.</para>
195 <para>If desired, skip kernel configuration by copying the kernel
196 config file, <filename>.config</filename>, from the host system
197 (assuming it is available) to the unpacked <filename
198 class="directory">linux-&linux-version;</filename> directory. However,
199 we do not recommend this option. It is often better to explore all the
200 configuration menus and create the kernel configuration from
201 scratch.</para>
203 <para>Compile the kernel image and modules:</para>
205<screen><userinput remap="make">make</userinput></screen>
207 <para>If using kernel modules, module configuration in <filename
208 class="directory">/etc/modprobe.d</filename> may be required.
209 Information pertaining to modules and kernel configuration is
210 located in <xref linkend="ch-scripts-udev"/> and in the kernel
211 documentation in the <filename
212 class="directory">linux-&linux-version;/Documentation</filename> directory.
213 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
215 <para>Install the modules, if the kernel configuration uses them:</para>
217<screen><userinput remap="install">make modules_install</userinput></screen>
219 <para>After kernel compilation is complete, additional steps are
220 required to complete the installation. Some files need to be copied to
221 the <filename class="directory">/boot</filename> directory.</para>
223 <caution>
224 <para>If the host system has a separate /boot partition, the files copied
225 below should go there. The easiest way to do that is to bind /boot on the
226 host (outside chroot) to /mnt/lfs/boot before proceeding. As the root
227 user in the <emphasis>host system</emphasis>:</para>
229<screen role="nodump"><userinput>mount --bind /boot /mnt/lfs/boot</userinput></screen>
230 </caution>
232 <para>The path to the kernel image may vary depending on the platform being
233 used. The filename below can be changed to suit your taste, but the stem of
234 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
235 the automatic setup of the boot process described in the next section. The
236 following command assumes an x86 architecture:</para>
238<screen arch="default" revision="sysv"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
240<screen arch="multilib" revision="sysv"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;-multilib</userinput></screen>
242<screen arch="default" revision="systemd"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&versiond;</userinput></screen>
244<screen arch="multilib" revision="systemd"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&versiond;-multilib</userinput></screen>
247 <para><filename></filename> is a symbol file for the kernel.
248 It maps the function entry points of every function in the kernel API,
249 as well as the addresses of the kernel data structures for the running
250 kernel. It is used as a resource when investigating kernel problems.
251 Issue the following command to install the map file:</para>
253<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
255 <para>The kernel configuration file <filename>.config</filename>
256 produced by the <command>make menuconfig</command> step
257 above contains all the configuration selections for the kernel
258 that was just compiled. It is a good idea to keep this file for future
259 reference:</para>
261<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
263 <para>Install the documentation for the Linux kernel:</para>
265<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
266cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
268 <para>It is important to note that the files in the kernel source
269 directory are not owned by <emphasis>root</emphasis>. Whenever a
270 package is unpacked as user <emphasis>root</emphasis> (like we did
271 inside chroot), the files have the user and group IDs of whatever
272 they were on the packager's computer. This is usually not a problem
273 for any other package to be installed because the source tree is
274 removed after the installation. However, the Linux source tree is
275 often retained for a long time. Because of this, there is a chance
276 that whatever user ID the packager used will be assigned to somebody
277 on the machine. That person would then have write access to the kernel
278 source.</para>
280 <note>
281 <para>In many cases, the configuration of the kernel will need to be
282 updated for packages that will be installed later in BLFS. Unlike
283 other packages, it is not necessary to remove the kernel source tree
284 after the newly built kernel is installed.</para>
286 <para>If the kernel source tree is going to be retained, run
287 <command>chown -R 0:0</command> on the <filename
288 class="directory">linux-&linux-version;</filename> directory to ensure
289 all files are owned by user <emphasis>root</emphasis>.</para>
290 </note>
292 <warning>
293 <para>Some kernel documentation recommends creating a symlink from
294 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
295 source directory. This is specific to kernels prior to the 2.6 series and
296 <emphasis>must not</emphasis> be created on an LFS system as it can cause
297 problems for packages you may wish to build once your base LFS system is
298 complete.</para>
299 </warning>
301 <warning>
302 <para>The headers in the system's <filename
303 class="directory">include</filename> directory (<filename
304 class="directory">/usr/include</filename>) should
305 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
306 that is, the sanitised headers installed in <xref
307 linkend="ch-system-linux-headers"/>. Therefore, they should
308 <emphasis>never</emphasis> be replaced by either the raw kernel headers
309 or any other kernel sanitized headers.</para>
310 </warning>
312 </sect2>
314 <sect2 id="conf-modprobe" role="configuration">
315 <title>Configuring Linux Module Load Order</title>
317 <indexterm zone="conf-modprobe">
318 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
319 </indexterm>
321 <para>Most of the time Linux modules are loaded automatically, but
322 sometimes it needs some specific direction. The program that loads
323 modules, <command>modprobe</command> or <command>insmod</command>, uses
324 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
325 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
326 uhci_hcd) have been built as modules, they will be loaded in the correct
327 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
328 to avoid a warning being output at boot time.</para>
330 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
331 the following:</para>
333<screen><userinput>install -v -m755 -d /etc/modprobe.d
334cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
335<literal># Begin /etc/modprobe.d/usb.conf
337install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
338install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
340# End /etc/modprobe.d/usb.conf</literal>
343 </sect2>
345 <sect2 id="contents-kernel" role="content">
346 <title>Contents of Linux</title>
348 <segmentedlist>
349 <segtitle>Installed files</segtitle>
350 <segtitle>Installed directories</segtitle>
352 <seglistitem>
353 <seg>config-&linux-version;,
354 <phrase arch="default" revision="sysv">vmlinuz-&linux-version;-lfs-&version;,</phrase>
355 <phrase arch="default" revision="systemd">vmlinuz-&linux-version;-lfs-&versiond;,</phrase>
356 <phrase arch="multilib" revision="sysv">vmlinuz-&linux-version;-lfs-&version;-multilib,</phrase>
357 <phrase arch="multilib" revision="systemd">vmlinuz-&linux-version;-lfs-&versiond;-multilib,</phrase>
358 and;</seg>
359 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
360 </seglistitem>
361 </segmentedlist>
363 <variablelist>
364 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
365 <?dbfo list-presentation="list"?>
366 <?dbhtml list-presentation="table"?>
368 <varlistentry id="config">
369 <term><filename>config-&linux-version;</filename></term>
370 <listitem>
371 <para>Contains all the configuration selections for the kernel</para>
372 <indexterm zone="ch-bootable-kernel config">
373 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
374 </indexterm>
375 </listitem>
376 </varlistentry>
378 <varlistentry id="lfskernel">
379 <term revision="sysv"><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
380 <term revision="systemd"><filename>vmlinuz-&linux-version;-lfs-&versiond;</filename></term>
381 <listitem>
382 <para>The engine of the Linux system. When turning on the computer,
383 the kernel is the first part of the operating system that gets loaded.
384 It detects and initializes all components of the computer's hardware,
385 then makes these components available as a tree of files to the
386 software and turns a single CPU into a multitasking machine capable
387 of running scores of programs seemingly at the same time</para>
388 <indexterm zone="ch-bootable-kernel lfskernel">
389 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
390 </indexterm>
391 </listitem>
392 </varlistentry>
394 <varlistentry id="">
395 <term><filename>;</filename></term>
396 <listitem>
397 <para>A list of addresses and symbols; it maps the entry points and
398 addresses of all the functions and data structures in the
399 kernel</para>
400 <indexterm zone="ch-bootable-kernel">
401 <primary sortas="e-/boot/">/boot/;</primary>
402 </indexterm>
403 </listitem>
404 </varlistentry>
406 </variablelist>
408 </sect2>
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