source: chapter10/kernel.xml@ 08a6368

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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">Device Drivers ---&gt;
109 Generic Driver Options ---&gt;
110 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
111 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]</screen>
113 <screen role="nodump" revision="systemd">General setup -->
114 [ ] Auditing Support [CONFIG_AUDIT]
115 [*] Control Group support [CONFIG_CGROUPS]
116 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
117 [*] Configure standard kernel features (expert users) [CONFIG_EXPERT] ---&gt;
118 [*] open by fhandle syscalls [CONFIG_FHANDLE]
119Firmware Drivers ---&gt;
120 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
121General architecture-dependent options ---&gt;
122 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
123Networking support ---&gt;
124 Networking options ---&gt;
125 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
126Device Drivers ---&gt;
127 Generic Driver Options ---&gt;
128 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
129 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
130 Firmware Loader ---&gt;
131 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
132File systems ---&gt;
133 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
134 Pseudo filesystems ---&gt;
135 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]</screen>
136 </note>
138 <note revision="systemd">
139 <para>While "The IPv6 Protocol" is not strictly
140 required, it is highly recommended by the systemd developers.</para>
141 </note>
143 <para revision="sysv">There are several other options that may be desired
144 depending on the requirements for the system. For a list of options needed
145 for BLFS packages, see the <ulink
146 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
147 Index of Kernel Settings</ulink>
148 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
150 <note>
151 <para>If your host hardware is using UEFI and you wish to boot the
152 LFS system with it, you should adjust some kernel configuration
153 following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
154 the BLFS page</ulink>.</para>
155 </note>
157 <note arch="ml_32,ml_x32,ml_all">
158 <para>
159 The kernel on a multilib system needs to be able to
160 identify and start binaries compiled for different architectures
161 than the default.
162 </para>
164 <para arch="ml_32,ml_all">
165 If support for any 32bit ABI was built, make sure that the option
166 "IA32 Emulation" is selected. The option 'IA32 a.out support' is
167 optional.
168 </para>
170 <para arch="ml_x32,ml_all">
171 If support for the x32bit ABI was built, make sure that the option
172 "x32 ABI for 64-bit mode" is selected.
173 </para>
175<screen arch="ml_32">Binary Emulations ---&gt;
176 [*] IA32 Emulation
177 &lt;M&gt; IA32 a.out support
179<screen arch="ml_x32">Binary Emulations ---&gt;
180 [*] x32 ABI for 64-bit mode
182<screen arch="ml_all">Binary Emulations ---&gt;
183 [*] IA32 Emulation
184 &lt;M&gt; IA32 a.out support
185 [*] x32 ABI for 64-bit mode
188 </note>
190 <variablelist>
191 <title>The rationale for the above configuration items:</title>
193 <varlistentry>
194 <term><parameter>Support for uevent helper</parameter></term>
195 <listitem>
196 <para>Having this option set may interfere with device
197 management when using Udev/Eudev. </para>
198 </listitem>
199 </varlistentry>
201 <varlistentry>
202 <term><parameter>Maintain a devtmpfs</parameter></term>
203 <listitem>
204 <para>This will create automated device nodes which are populated by the
205 kernel, even without Udev running. Udev then runs on top of this,
206 managing permissions and adding symlinks. This configuration
207 item is required for all users of Udev/Eudev.</para>
208 </listitem>
209 </varlistentry>
211 </variablelist>
213 <para>Alternatively, <command>make oldconfig</command> may be more
214 appropriate in some situations. See the <filename>README</filename>
215 file for more information.</para>
217 <para>If desired, skip kernel configuration by copying the kernel
218 config file, <filename>.config</filename>, from the host system
219 (assuming it is available) to the unpacked <filename
220 class="directory">linux-&linux-version;</filename> directory. However,
221 we do not recommend this option. It is often better to explore all the
222 configuration menus and create the kernel configuration from
223 scratch.</para>
225 <para>Compile the kernel image and modules:</para>
227<screen><userinput remap="make">make</userinput></screen>
229 <para>If using kernel modules, module configuration in <filename
230 class="directory">/etc/modprobe.d</filename> may be required.
231 Information pertaining to modules and kernel configuration is
232 located in <xref linkend="ch-config-udev"/> and in the kernel
233 documentation in the <filename
234 class="directory">linux-&linux-version;/Documentation</filename> directory.
235 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
237 <para>Unless module support has been disabled in the kernel configuration,
238 install the modules with:</para>
240<screen><userinput remap="install">make modules_install</userinput></screen>
242 <para>After kernel compilation is complete, additional steps are
243 required to complete the installation. Some files need to be copied to
244 the <filename class="directory">/boot</filename> directory.</para>
246 <caution>
247 <para>If the host system has a separate /boot partition, the files copied
248 below should go there. The easiest way to do that is to bind /boot on the
249 host (outside chroot) to /mnt/lfs/boot before proceeding. As the root
250 user in the <emphasis>host system</emphasis>:</para>
252<screen role="nodump"><userinput>mount --bind /boot /mnt/lfs/boot</userinput></screen>
253 </caution>
255 <para>The path to the kernel image may vary depending on the platform being
256 used. The filename below can be changed to suit your taste, but the stem of
257 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
258 the automatic setup of the boot process described in the next section. The
259 following command assumes an x86 architecture:</para>
261<screen><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
263 <para><filename></filename> is a symbol file for the kernel.
264 It maps the function entry points of every function in the kernel API,
265 as well as the addresses of the kernel data structures for the running
266 kernel. It is used as a resource when investigating kernel problems.
267 Issue the following command to install the map file:</para>
269<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
271 <para>The kernel configuration file <filename>.config</filename>
272 produced by the <command>make menuconfig</command> step
273 above contains all the configuration selections for the kernel
274 that was just compiled. It is a good idea to keep this file for future
275 reference:</para>
277<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
279 <para>Install the documentation for the Linux kernel:</para>
281<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
282cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
284 <para>It is important to note that the files in the kernel source
285 directory are not owned by <emphasis>root</emphasis>. Whenever a
286 package is unpacked as user <emphasis>root</emphasis> (like we did
287 inside chroot), the files have the user and group IDs of whatever
288 they were on the packager's computer. This is usually not a problem
289 for any other package to be installed because the source tree is
290 removed after the installation. However, the Linux source tree is
291 often retained for a long time. Because of this, there is a chance
292 that whatever user ID the packager used will be assigned to somebody
293 on the machine. That person would then have write access to the kernel
294 source.</para>
296 <note>
297 <para>In many cases, the configuration of the kernel will need to be
298 updated for packages that will be installed later in BLFS. Unlike
299 other packages, it is not necessary to remove the kernel source tree
300 after the newly built kernel is installed.</para>
302 <para>If the kernel source tree is going to be retained, run
303 <command>chown -R 0:0</command> on the <filename
304 class="directory">linux-&linux-version;</filename> directory to ensure
305 all files are owned by user <emphasis>root</emphasis>.</para>
306 </note>
308 <warning>
309 <para>Some kernel documentation recommends creating a symlink from
310 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
311 source directory. This is specific to kernels prior to the 2.6 series and
312 <emphasis>must not</emphasis> be created on an LFS system as it can cause
313 problems for packages you may wish to build once your base LFS system is
314 complete.</para>
315 </warning>
317 <warning>
318 <para>The headers in the system's <filename
319 class="directory">include</filename> directory (<filename
320 class="directory">/usr/include</filename>) should
321 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
322 that is, the sanitised headers installed in <xref
323 linkend="ch-tools-linux-headers"/>. Therefore, they should
324 <emphasis>never</emphasis> be replaced by either the raw kernel headers
325 or any other kernel sanitized headers.</para>
326 </warning>
328 </sect2>
330 <sect2 id="conf-modprobe" role="configuration">
331 <title>Configuring Linux Module Load Order</title>
333 <indexterm zone="conf-modprobe">
334 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
335 </indexterm>
337 <para>Most of the time Linux modules are loaded automatically, but
338 sometimes it needs some specific direction. The program that loads
339 modules, <command>modprobe</command> or <command>insmod</command>, uses
340 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
341 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
342 uhci_hcd) have been built as modules, they will be loaded in the correct
343 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
344 to avoid a warning being output at boot time.</para>
346 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
347 the following:</para>
349<screen><userinput>install -v -m755 -d /etc/modprobe.d
350cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
351<literal># Begin /etc/modprobe.d/usb.conf
353install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
354install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
356# End /etc/modprobe.d/usb.conf</literal>
359 </sect2>
361 <sect2 id="contents-kernel" role="content">
362 <title>Contents of Linux</title>
364 <segmentedlist>
365 <segtitle>Installed files</segtitle>
366 <segtitle>Installed directories</segtitle>
368 <seglistitem>
369 <seg>config-&linux-version;,
370 vmlinuz-&linux-version;-lfs-&version;,
371 and;</seg>
372 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
373 </seglistitem>
374 </segmentedlist>
376 <variablelist>
377 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
378 <?dbfo list-presentation="list"?>
379 <?dbhtml list-presentation="table"?>
381 <varlistentry id="config">
382 <term><filename>config-&linux-version;</filename></term>
383 <listitem>
384 <para>Contains all the configuration selections for the kernel</para>
385 <indexterm zone="ch-bootable-kernel config">
386 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
387 </indexterm>
388 </listitem>
389 </varlistentry>
391 <varlistentry id="lfskernel">
392 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
393 <listitem>
394 <para>The engine of the Linux system. When turning on the computer,
395 the kernel is the first part of the operating system that gets loaded.
396 It detects and initializes all components of the computer's hardware,
397 then makes these components available as a tree of files to the
398 software and turns a single CPU into a multitasking machine capable
399 of running scores of programs seemingly at the same time</para>
400 <indexterm zone="ch-bootable-kernel lfskernel">
401 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
402 </indexterm>
403 </listitem>
404 </varlistentry>
406 <varlistentry id="">
407 <term><filename>;</filename></term>
408 <listitem>
409 <para>A list of addresses and symbols; it maps the entry points and
410 addresses of all the functions and data structures in the
411 kernel</para>
412 <indexterm zone="ch-bootable-kernel">
413 <primary sortas="e-/boot/">/boot/;</primary>
414 </indexterm>
415 </listitem>
416 </varlistentry>
418 </variablelist>
420 </sect2>
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