source: chapter10/kernel.xml@ e9a3e8f

Last change on this file since e9a3e8f was e9a3e8f, checked in by Thomas Trepl <thomas@…>, 3 years ago

Merge changes from trunk to multilib

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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 <!-- 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">Device Drivers ---&gt;
79 Generic Driver Options ---&gt;
80 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
81 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]</screen>
83 <screen role="nodump" revision="systemd">General setup -->
84 [*] Control Group support [CONFIG_CGROUPS]
85 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
86 [*] Configure standard kernel features (expert users) [CONFIG_EXPERT] ---&gt;
87 [*] open by fhandle syscalls [CONFIG_FHANDLE]
88 [ ] Auditing support [CONFIG_AUDIT]
89Processor type and features ---&gt;
90 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
91Firmware Drivers ---&gt;
92 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
93Networking support ---&gt;
94 Networking options ---&gt;
95 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
96Device Drivers ---&gt;
97 Generic Driver Options ---&gt;
98 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
99 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
100 Firmware Loader ---&gt;
101 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
102File systems ---&gt;
103 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
104 &lt;*&gt; Kernel automounter support (supports v3, v4, and v5) [CONFIG_AUTOFS_FS]
105 Pseudo filesystems ---&gt;
106 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]
107 [*] Tmpfs extended attributes [CONFIG_TMPFS_XATTR]</screen>
108 </note>
110 <note revision="systemd">
111 <para>While "The IPv6 Protocol" is not strictly
112 required, it is highly recommended by the systemd developers.</para>
113 </note>
115 <para revision="sysv">There are several other options that may be desired
116 depending on the requirements for the system. For a list of options needed
117 for BLFS packages, see the <ulink
118 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
119 Index of Kernel Settings</ulink>
120 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
122 <note>
123 <para>If your host hardware is using UEFI, then the 'make defconfig'
124 above should automatically add in some EFI-related kernel options.</para>
126 <para>In order to allow your LFS kernel to be booted from within your
127 host's UEFI boot environment, your kernel must have this option
128 selected:</para>
130<screen role="nodump">Processor type and features ---&gt;
131 [*] EFI stub support [CONFIG_EFI_STUB]</screen>
133 <para>A fuller description of managing UEFI environments from within LFS
134 is covered by the lfs-uefi.txt hint at
135 <ulink
136 url="&hints-root;lfs-uefi.txt"/>.
137 </para>
138 </note>
140 <note arch="ml_32,ml_x32,ml_all">
141 <para>
142 Running a multilib system means also that the kernel has to be
143 configured proper. It is required that the kernel is able to
144 identify and start binaries compiled for different architectures
145 than the default. Setup the required parameter in the kernel
146 config:
147 </para>
148<screen>Binary Emulations ---&gt;
149 [*] IA32 Emulation
150 &lt;M&gt; IA32 a.out support
151 [*] x32 ABI for 64-bit mode
153 <para>Make sure that the option
154 'IA32 Emulation' is set if you built support for the 32bit ABI.
155 If you selected the x32 ABI or built support for both, also select
156 'x32 ABI for 64-bit mode'. The option 'IA32 a.out support' is
157 optional.
158 </para>
159 </note>
161 <variablelist>
162 <title>The rationale for the above configuration items:</title>
164 <varlistentry>
165 <term><parameter>Support for uevent helper</parameter></term>
166 <listitem>
167 <para>Having this option set may interfere with device
168 management when using Udev/Eudev. </para>
169 </listitem>
170 </varlistentry>
172 <varlistentry>
173 <term><parameter>Maintain a devtmpfs</parameter></term>
174 <listitem>
175 <para>This will create automated device nodes which are populated by the
176 kernel, even without Udev running. Udev then runs on top of this,
177 managing permissions and adding symlinks. This configuration
178 item is required for all users of Udev/Eudev.</para>
179 </listitem>
180 </varlistentry>
182 </variablelist>
184<screen role="nodump"><userinput>make menuconfig</userinput></screen>
186 <variablelist>
187 <title>The meaning of optional make environment variables:</title>
189 <varlistentry>
190 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
191 <listitem>
192 <para>This establishes the locale setting to the one used on the
193 host. This may be needed for a proper menuconfig ncurses interface
194 line drawing on a UTF-8 linux text console.</para>
196 <para>If used, be sure to replace
197 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
198 the <envar>$LANG</envar> variable from your host. You can
199 alternatively use instead the host's value of <envar>$LC_ALL</envar>
200 or <envar>$LC_CTYPE</envar>.</para>
201 </listitem>
202 </varlistentry>
204 </variablelist>
206 <para>Alternatively, <command>make oldconfig</command> may be more
207 appropriate in some situations. See the <filename>README</filename>
208 file for more information.</para>
210 <para>If desired, skip kernel configuration by copying the kernel
211 config file, <filename>.config</filename>, from the host system
212 (assuming it is available) to the unpacked <filename
213 class="directory">linux-&linux-version;</filename> directory. However,
214 we do not recommend this option. It is often better to explore all the
215 configuration menus and create the kernel configuration from
216 scratch.</para>
218 <para>Compile the kernel image and modules:</para>
220<screen><userinput remap="make">make</userinput></screen>
222 <para>If using kernel modules, module configuration in <filename
223 class="directory">/etc/modprobe.d</filename> may be required.
224 Information pertaining to modules and kernel configuration is
225 located in <xref linkend="ch-config-udev"/> and in the kernel
226 documentation in the <filename
227 class="directory">linux-&linux-version;/Documentation</filename> directory.
228 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
230 <para>Unless module support has been disabled in the kernel configuration,
231 install the modules with:</para>
233<screen><userinput remap="install">make modules_install</userinput></screen>
235 <para>After kernel compilation is complete, additional steps are
236 required to complete the installation. Some files need to be copied to
237 the <filename class="directory">/boot</filename> directory.</para>
239 <caution>
240 <para>If the host system has a separate /boot partition, the files copied
241 below should go there. The easiest way to do that is to bind /boot on the
242 host (outside chroot) to /mnt/lfs/boot before proceeding. As the root
243 user in the <emphasis>host system</emphasis>:</para>
245<screen role="nodump"><userinput>mount --bind /boot /mnt/lfs/boot</userinput></screen>
246 </caution>
248 <para>The path to the kernel image may vary depending on the platform being
249 used. The filename below can be changed to suit your taste, but the stem of
250 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
251 the automatic setup of the boot process described in the next section. The
252 following command assumes an x86 architecture:</para>
254<screen revision="sysv"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
256<screen revision="systemd"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&versiond;</userinput></screen>
258 <para><filename></filename> is a symbol file for the kernel.
259 It maps the function entry points of every function in the kernel API,
260 as well as the addresses of the kernel data structures for the running
261 kernel. It is used as a resource when investigating kernel problems.
262 Issue the following command to install the map file:</para>
264<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
266 <para>The kernel configuration file <filename>.config</filename>
267 produced by the <command>make menuconfig</command> step
268 above contains all the configuration selections for the kernel
269 that was just compiled. It is a good idea to keep this file for future
270 reference:</para>
272<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
274 <para>Install the documentation for the Linux kernel:</para>
276<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
277cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
279 <para>It is important to note that the files in the kernel source
280 directory are not owned by <emphasis>root</emphasis>. Whenever a
281 package is unpacked as user <emphasis>root</emphasis> (like we did
282 inside chroot), the files have the user and group IDs of whatever
283 they were on the packager's computer. This is usually not a problem
284 for any other package to be installed because the source tree is
285 removed after the installation. However, the Linux source tree is
286 often retained for a long time. Because of this, there is a chance
287 that whatever user ID the packager used will be assigned to somebody
288 on the machine. That person would then have write access to the kernel
289 source.</para>
291 <note>
292 <para>In many cases, the configuration of the kernel will need to be
293 updated for packages that will be installed later in BLFS. Unlike
294 other packages, it is not necessary to remove the kernel source tree
295 after the newly built kernel is installed.</para>
297 <para>If the kernel source tree is going to be retained, run
298 <command>chown -R 0:0</command> on the <filename
299 class="directory">linux-&linux-version;</filename> directory to ensure
300 all files are owned by user <emphasis>root</emphasis>.</para>
301 </note>
303 <warning>
304 <para>Some kernel documentation recommends creating a symlink from
305 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
306 source directory. This is specific to kernels prior to the 2.6 series and
307 <emphasis>must not</emphasis> be created on an LFS system as it can cause
308 problems for packages you may wish to build once your base LFS system is
309 complete.</para>
310 </warning>
312 <warning>
313 <para>The headers in the system's <filename
314 class="directory">include</filename> directory (<filename
315 class="directory">/usr/include</filename>) should
316 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
317 that is, the sanitised headers installed in <xref
318 linkend="ch-tools-linux-headers"/>. Therefore, they should
319 <emphasis>never</emphasis> be replaced by either the raw kernel headers
320 or any other kernel sanitized headers.</para>
321 </warning>
323 </sect2>
325 <sect2 id="conf-modprobe" role="configuration">
326 <title>Configuring Linux Module Load Order</title>
328 <indexterm zone="conf-modprobe">
329 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
330 </indexterm>
332 <para>Most of the time Linux modules are loaded automatically, but
333 sometimes it needs some specific direction. The program that loads
334 modules, <command>modprobe</command> or <command>insmod</command>, uses
335 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
336 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
337 uhci_hcd) have been built as modules, they will be loaded in the correct
338 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
339 to avoid a warning being output at boot time.</para>
341 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
342 the following:</para>
344<screen><userinput>install -v -m755 -d /etc/modprobe.d
345cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
346<literal># Begin /etc/modprobe.d/usb.conf
348install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
349install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
351# End /etc/modprobe.d/usb.conf</literal>
354 </sect2>
356 <sect2 id="contents-kernel" role="content">
357 <title>Contents of Linux</title>
359 <segmentedlist>
360 <segtitle>Installed files</segtitle>
361 <segtitle>Installed directories</segtitle>
363 <seglistitem>
364 <seg>config-&linux-version;,
365 <phrase revision="sysv">vmlinuz-&linux-version;-lfs-&version;,</phrase>
366 <phrase revision="systemd">vmlinuz-&linux-version;-lfs-&versiond;,</phrase>
367 and;</seg>
368 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
369 </seglistitem>
370 </segmentedlist>
372 <variablelist>
373 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
374 <?dbfo list-presentation="list"?>
375 <?dbhtml list-presentation="table"?>
377 <varlistentry id="config">
378 <term><filename>config-&linux-version;</filename></term>
379 <listitem>
380 <para>Contains all the configuration selections for the kernel</para>
381 <indexterm zone="ch-bootable-kernel config">
382 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
383 </indexterm>
384 </listitem>
385 </varlistentry>
387 <varlistentry id="lfskernel">
388 <term revision="sysv"><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
389 <term revision="systemd"><filename>vmlinuz-&linux-version;-lfs-&versiond;</filename></term>
390 <listitem>
391 <para>The engine of the Linux system. When turning on the computer,
392 the kernel is the first part of the operating system that gets loaded.
393 It detects and initializes all components of the computer's hardware,
394 then makes these components available as a tree of files to the
395 software and turns a single CPU into a multitasking machine capable
396 of running scores of programs seemingly at the same time</para>
397 <indexterm zone="ch-bootable-kernel lfskernel">
398 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
399 </indexterm>
400 </listitem>
401 </varlistentry>
403 <varlistentry id="">
404 <term><filename>;</filename></term>
405 <listitem>
406 <para>A list of addresses and symbols; it maps the entry points and
407 addresses of all the functions and data structures in the
408 kernel</para>
409 <indexterm zone="ch-bootable-kernel">
410 <primary sortas="e-/boot/">/boot/;</primary>
411 </indexterm>
412 </listitem>
413 </varlistentry>
415 </variablelist>
417 </sect2>
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