source: chapter10/kernel.xml@ 588c7a0

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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>kernel</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-knl-sbu;</seg>
34 <seg>&linux-knl-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 <para>There are several ways to configure the kernel options. Usually,
58 This is done through a menu-driven interface, for example:</para>
60<screen role="nodump"><userinput>make menuconfig</userinput></screen>
62 <variablelist>
63 <title>The meaning of optional make environment variables:</title>
65 <varlistentry>
66 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
67 <listitem>
68 <para>This establishes the locale setting to the one used on the
69 host. This may be needed for a proper menuconfig ncurses interface
70 line drawing on a UTF-8 linux text console.</para>
72 <para>If used, be sure to replace
73 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
74 the <envar>$LANG</envar> variable from your host. You can
75 alternatively use instead the host's value of <envar>$LC_ALL</envar>
76 or <envar>$LC_CTYPE</envar>.</para>
77 </listitem>
78 </varlistentry>
80 <varlistentry>
81 <term><command>make menuconfig</command></term>
82 <listitem>
83 <para>This launches an ncurses menu-driven interface. For other
84 (graphical) interfaces, type <command>make help</command>.</para>
85 </listitem>
86 </varlistentry>
87 </variablelist>
89 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
91 <para>For general information on kernel configuration see <ulink
92 url="&hints-root;kernel-configuration.txt"/>. BLFS has some information
93 regarding particular kernel configuration requirements of packages outside
94 of LFS at <ulink
95 url="&blfs-book;longindex.html#kernel-config-index"/>. Additional
96 information about configuring and building the kernel can be found at
97 <ulink url=""/> </para>
99 <note>
100 <para>A good starting place for setting up the kernel configuration is to
101 run <command>make defconfig</command>. This will set the base
102 configuration to a good state that takes your current system architecture
103 into account.</para>
105 <para>Be sure to enable/disable/set the following features or the system might
106 not work correctly or boot at all:</para>
108 <screen role="nodump" revision="sysv">General setup -->
109 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
110 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
111Device Drivers ---&gt;
112 Graphics support ---&gt;
113 Frame buffer Devices ---&gt;
114 [*] Support for frame buffer devices ----
115 Generic Driver Options ---&gt;
116 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
117 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
118 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]</screen>
120 <screen role="nodump" revision="systemd">General setup -->
121 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
122 [ ] Auditing Support [CONFIG_AUDIT]
123 CPU/Task time and stats accounting ---&gt;
124 [*] Pressure stall information tracking [CONFIG_PSI]
125 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
126 [*] Control Group support [CONFIG_CGROUPS] ---&gt;
127 [*] Memory controller [CONFIG_MEMCG]
128 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
129 [*] Configure standard kernel features (expert users) [CONFIG_EXPERT] ---&gt;
130 [*] open by fhandle syscalls [CONFIG_FHANDLE]
131General architecture-dependent options ---&gt;
132 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
133Networking support ---&gt;
134 Networking options ---&gt;
135 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
136Device Drivers ---&gt;
137 Generic Driver Options ---&gt;
138 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
139 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
140 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]
141 Firmware Loader ---&gt;
142 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
143 Firmware Drivers ---&gt;
144 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
145 Graphics support ---&gt;
146 Frame buffer Devices ---&gt;
147 &lt;*&gt; Support for frame buffer devices ---&gt;
148File systems ---&gt;
149 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
150 Pseudo filesystems ---&gt;
151 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]</screen>
152 </note>
154 <note revision="systemd">
155 <para>While "The IPv6 Protocol" is not strictly
156 required, it is highly recommended by the systemd developers.</para>
157 </note>
159 <para revision="sysv">There are several other options that may be desired
160 depending on the requirements for the system. For a list of options needed
161 for BLFS packages, see the <ulink
162 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
163 Index of Kernel Settings</ulink>
164 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
166 <note>
167 <para>If your host hardware is using UEFI and you wish to boot the
168 LFS system with it, you should adjust some kernel configuration
169 following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
170 the BLFS page</ulink>.</para>
171 </note>
173 <note arch="ml_32,ml_x32,ml_all">
174 <para>
175 The kernel on a multilib system needs to be able to
176 identify and start binaries compiled for different architectures
177 than the default.
178 </para>
180 <para arch="ml_32,ml_all">
181 If support for any 32bit ABI was built, make sure that the option
182 "IA32 Emulation" is selected. The option 'IA32 a.out support' is
183 optional.
184 </para>
186 <para arch="ml_x32,ml_all">
187 If support for the x32bit ABI was built, make sure that the option
188 "x32 ABI for 64-bit mode" is selected.
189 </para>
191<screen arch="ml_32">Binary Emulations ---&gt;
192 [*] IA32 Emulation [CONFIG_IA32_EMULATION]
193 &lt;M&gt; IA32 a.out support [CONFIG_IA32_AOUT]
195<screen arch="ml_x32">Binary Emulations ---&gt;
196 [*] x32 ABI for 64-bit mode [CONFIG_X86_X32]
198<screen arch="ml_all">Binary Emulations ---&gt;
199 [*] IA32 Emulation [CONFIG_IA32_EMULATION]
200 &lt;M&gt; IA32 a.out support [CONFIG_IA32_AOUT]
201 [*] x32 ABI for 64-bit mode [CONFIG_X86_X32]
203 </note>
205 <variablelist>
206 <title>The rationale for the above configuration items:</title>
208 <varlistentry>
209 <term>
210 <parameter>
211 Compile the kernel with warnings as errors
212 </parameter>
213 </term>
214 <listitem>
215 <para>This may cause building failure if the compiler and/or
216 configuration are different from those of the kernel
217 developers.</para>
218 </listitem>
219 </varlistentry>
221 <varlistentry>
222 <term>
223 <parameter>
224 Enable kernel headers through /sys/kernel/kheaders.tar.xz
225 </parameter>
226 </term>
227 <listitem>
228 <para>This will require <command>cpio</command> building the kernel.
229 <command>cpio</command> is not installed by LFS.</para>
230 </listitem>
231 </varlistentry>
233 <varlistentry>
234 <term><parameter>Support for uevent helper</parameter></term>
235 <listitem>
236 <para>Having this option set may interfere with device
237 management when using Udev/Eudev. </para>
238 </listitem>
239 </varlistentry>
241 <varlistentry>
242 <term><parameter>Maintain a devtmpfs</parameter></term>
243 <listitem>
244 <para>This will create automated device nodes which are populated by the
245 kernel, even without Udev running. Udev then runs on top of this,
246 managing permissions and adding symlinks. This configuration
247 item is required for all users of Udev/Eudev.</para>
248 </listitem>
249 </varlistentry>
251 <varlistentry>
252 <term><parameter>Automount devtmpfs at /dev</parameter></term>
253 <listitem>
254 <para>This will mount the kernel view of the devices on /dev
255 upon switching to root filesystem just before starting
256 init.</para>
257 </listitem>
258 </varlistentry>
260 </variablelist>
262 <para>Alternatively, <command>make oldconfig</command> may be more
263 appropriate in some situations. See the <filename>README</filename>
264 file for more information.</para>
266 <para>If desired, skip kernel configuration by copying the kernel
267 config file, <filename>.config</filename>, from the host system
268 (assuming it is available) to the unpacked <filename
269 class="directory">linux-&linux-version;</filename> directory. However,
270 we do not recommend this option. It is often better to explore all the
271 configuration menus and create the kernel configuration from
272 scratch.</para>
274 <para>Compile the kernel image and modules:</para>
276<screen><userinput remap="make">make</userinput></screen>
278 <para>If using kernel modules, module configuration in <filename
279 class="directory">/etc/modprobe.d</filename> may be required.
280 Information pertaining to modules and kernel configuration is
281 located in <xref linkend="ch-config-udev"/> and in the kernel
282 documentation in the <filename
283 class="directory">linux-&linux-version;/Documentation</filename> directory.
284 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
286 <para>Unless module support has been disabled in the kernel configuration,
287 install the modules with:</para>
289<screen><userinput remap="install">make modules_install</userinput></screen>
291 <para>After kernel compilation is complete, additional steps are
292 required to complete the installation. Some files need to be copied to
293 the <filename class="directory">/boot</filename> directory.</para>
295 <caution>
296 <para>If the host system has a separate /boot partition, the files copied
297 below should go there. The easiest way to do that is to bind /boot on the
298 host (outside chroot) to /mnt/lfs/boot before proceeding. As the
299 &root; user in the <emphasis>host system</emphasis>:</para>
301<screen role="nodump"><userinput>mount --bind /boot /mnt/lfs/boot</userinput></screen>
302 </caution>
304 <para>The path to the kernel image may vary depending on the platform being
305 used. The filename below can be changed to suit your taste, but the stem of
306 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
307 the automatic setup of the boot process described in the next section. The
308 following command assumes an x86 architecture:</para>
310<screen><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
312 <para><filename></filename> is a symbol file for the kernel.
313 It maps the function entry points of every function in the kernel API,
314 as well as the addresses of the kernel data structures for the running
315 kernel. It is used as a resource when investigating kernel problems.
316 Issue the following command to install the map file:</para>
318<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
320 <para>The kernel configuration file <filename>.config</filename>
321 produced by the <command>make menuconfig</command> step
322 above contains all the configuration selections for the kernel
323 that was just compiled. It is a good idea to keep this file for future
324 reference:</para>
326<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
328 <para>Install the documentation for the Linux kernel:</para>
330<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
331cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
333 <para>It is important to note that the files in the kernel source
334 directory are not owned by <emphasis>root</emphasis>. Whenever a
335 package is unpacked as user <emphasis>root</emphasis> (like we did
336 inside chroot), the files have the user and group IDs of whatever
337 they were on the packager's computer. This is usually not a problem
338 for any other package to be installed because the source tree is
339 removed after the installation. However, the Linux source tree is
340 often retained for a long time. Because of this, there is a chance
341 that whatever user ID the packager used will be assigned to somebody
342 on the machine. That person would then have write access to the kernel
343 source.</para>
345 <note>
346 <para>In many cases, the configuration of the kernel will need to be
347 updated for packages that will be installed later in BLFS. Unlike
348 other packages, it is not necessary to remove the kernel source tree
349 after the newly built kernel is installed.</para>
351 <para>If the kernel source tree is going to be retained, run
352 <command>chown -R 0:0</command> on the <filename
353 class="directory">linux-&linux-version;</filename> directory to ensure
354 all files are owned by user <emphasis>root</emphasis>.</para>
355 </note>
357 <warning>
358 <para>Some kernel documentation recommends creating a symlink from
359 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
360 source directory. This is specific to kernels prior to the 2.6 series and
361 <emphasis>must not</emphasis> be created on an LFS system as it can cause
362 problems for packages you may wish to build once your base LFS system is
363 complete.</para>
364 </warning>
366 <warning>
367 <para>The headers in the system's <filename
368 class="directory">include</filename> directory (<filename
369 class="directory">/usr/include</filename>) should
370 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
371 that is, the sanitised headers installed in <xref
372 linkend="ch-tools-linux-headers"/>. Therefore, they should
373 <emphasis>never</emphasis> be replaced by either the raw kernel headers
374 or any other kernel sanitized headers.</para>
375 </warning>
377 </sect2>
379 <sect2 id="conf-modprobe" role="configuration">
380 <title>Configuring Linux Module Load Order</title>
382 <indexterm zone="conf-modprobe">
383 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
384 </indexterm>
386 <para>Most of the time Linux modules are loaded automatically, but
387 sometimes it needs some specific direction. The program that loads
388 modules, <command>modprobe</command> or <command>insmod</command>, uses
389 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
390 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
391 uhci_hcd) have been built as modules, they will be loaded in the correct
392 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
393 to avoid a warning being output at boot time.</para>
395 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
396 the following:</para>
398<screen><userinput>install -v -m755 -d /etc/modprobe.d
399cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
400<literal># Begin /etc/modprobe.d/usb.conf
402install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
403install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
405# End /etc/modprobe.d/usb.conf</literal>
408 </sect2>
410 <sect2 id="contents-kernel" role="content">
411 <title>Contents of Linux</title>
413 <segmentedlist>
414 <segtitle>Installed files</segtitle>
415 <segtitle>Installed directories</segtitle>
417 <seglistitem>
418 <seg>config-&linux-version;,
419 vmlinuz-&linux-version;-lfs-&version;,
420 and;</seg>
421 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
422 </seglistitem>
423 </segmentedlist>
425 <variablelist>
426 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
427 <?dbfo list-presentation="list"?>
428 <?dbhtml list-presentation="table"?>
430 <varlistentry id="config">
431 <term><filename>config-&linux-version;</filename></term>
432 <listitem>
433 <para>Contains all the configuration selections for the kernel</para>
434 <indexterm zone="ch-bootable-kernel config">
435 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
436 </indexterm>
437 </listitem>
438 </varlistentry>
440 <varlistentry id="lfskernel">
441 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
442 <listitem>
443 <para>The engine of the Linux system. When turning on the computer,
444 the kernel is the first part of the operating system that gets loaded.
445 It detects and initializes all components of the computer's hardware,
446 then makes these components available as a tree of files to the
447 software and turns a single CPU into a multitasking machine capable
448 of running scores of programs seemingly at the same time</para>
449 <indexterm zone="ch-bootable-kernel lfskernel">
450 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
451 </indexterm>
452 </listitem>
453 </varlistentry>
455 <varlistentry id="">
456 <term><filename>;</filename></term>
457 <listitem>
458 <para>A list of addresses and symbols; it maps the entry points and
459 addresses of all the functions and data structures in the
460 kernel</para>
461 <indexterm zone="ch-bootable-kernel">
462 <primary sortas="e-/boot/">/boot/;</primary>
463 </indexterm>
464 </listitem>
465 </varlistentry>
467 </variablelist>
469 </sect2>
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