source: chapter10/kernel.xml@ a1ad522

Last change on this file since a1ad522 was a1ad522, checked in by Thomas Trepl <thomas@…>, 16 months 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 The kernel on a multilib system needs to be able to
143 identify and start binaries compiled for different architectures
144 than the default.
145 </para>
147 <para arch="ml_32,ml_all">
148 If support for any 32bit ABI was built, make sure that the option
149 "IA32 Emulation" is selected. The option 'IA32 a.out support' is
150 optional.
151 </para>
153 <para arch="ml_x32,ml_all">
154 If support for the x32bit ABI was built, make sure that the option
155 "x32 ABI for 64-bit mode" is selected.
156 </para>
158<screen arch="ml_32">Binary Emulations ---&gt;
159 [*] IA32 Emulation
160 &lt;M&gt; IA32 a.out support
162<screen arch="ml_x32">Binary Emulations ---&gt;
163 [*] x32 ABI for 64-bit mode
165<screen arch="ml_all">Binary Emulations ---&gt;
166 [*] IA32 Emulation
167 &lt;M&gt; IA32 a.out support
168 [*] x32 ABI for 64-bit mode
171 </note>
173 <variablelist>
174 <title>The rationale for the above configuration items:</title>
176 <varlistentry>
177 <term><parameter>Support for uevent helper</parameter></term>
178 <listitem>
179 <para>Having this option set may interfere with device
180 management when using Udev/Eudev. </para>
181 </listitem>
182 </varlistentry>
184 <varlistentry>
185 <term><parameter>Maintain a devtmpfs</parameter></term>
186 <listitem>
187 <para>This will create automated device nodes which are populated by the
188 kernel, even without Udev running. Udev then runs on top of this,
189 managing permissions and adding symlinks. This configuration
190 item is required for all users of Udev/Eudev.</para>
191 </listitem>
192 </varlistentry>
194 </variablelist>
196<screen role="nodump"><userinput>make menuconfig</userinput></screen>
198 <variablelist>
199 <title>The meaning of optional make environment variables:</title>
201 <varlistentry>
202 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
203 <listitem>
204 <para>This establishes the locale setting to the one used on the
205 host. This may be needed for a proper menuconfig ncurses interface
206 line drawing on a UTF-8 linux text console.</para>
208 <para>If used, be sure to replace
209 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
210 the <envar>$LANG</envar> variable from your host. You can
211 alternatively use instead the host's value of <envar>$LC_ALL</envar>
212 or <envar>$LC_CTYPE</envar>.</para>
213 </listitem>
214 </varlistentry>
216 </variablelist>
218 <para>Alternatively, <command>make oldconfig</command> may be more
219 appropriate in some situations. See the <filename>README</filename>
220 file for more information.</para>
222 <para>If desired, skip kernel configuration by copying the kernel
223 config file, <filename>.config</filename>, from the host system
224 (assuming it is available) to the unpacked <filename
225 class="directory">linux-&linux-version;</filename> directory. However,
226 we do not recommend this option. It is often better to explore all the
227 configuration menus and create the kernel configuration from
228 scratch.</para>
230 <para>Compile the kernel image and modules:</para>
232<screen><userinput remap="make">make</userinput></screen>
234 <para>If using kernel modules, module configuration in <filename
235 class="directory">/etc/modprobe.d</filename> may be required.
236 Information pertaining to modules and kernel configuration is
237 located in <xref linkend="ch-config-udev"/> and in the kernel
238 documentation in the <filename
239 class="directory">linux-&linux-version;/Documentation</filename> directory.
240 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
242 <para>Unless module support has been disabled in the kernel configuration,
243 install the modules with:</para>
245<screen><userinput remap="install">make modules_install</userinput></screen>
247 <para>After kernel compilation is complete, additional steps are
248 required to complete the installation. Some files need to be copied to
249 the <filename class="directory">/boot</filename> directory.</para>
251 <caution>
252 <para>If the host system has a separate /boot partition, the files copied
253 below should go there. The easiest way to do that is to bind /boot on the
254 host (outside chroot) to /mnt/lfs/boot before proceeding. As the root
255 user in the <emphasis>host system</emphasis>:</para>
257<screen role="nodump"><userinput>mount --bind /boot /mnt/lfs/boot</userinput></screen>
258 </caution>
260 <para>The path to the kernel image may vary depending on the platform being
261 used. The filename below can be changed to suit your taste, but the stem of
262 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
263 the automatic setup of the boot process described in the next section. The
264 following command assumes an x86 architecture:</para>
266<screen revision="sysv"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
268<screen revision="systemd"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&versiond;</userinput></screen>
270 <para><filename></filename> is a symbol file for the kernel.
271 It maps the function entry points of every function in the kernel API,
272 as well as the addresses of the kernel data structures for the running
273 kernel. It is used as a resource when investigating kernel problems.
274 Issue the following command to install the map file:</para>
276<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
278 <para>The kernel configuration file <filename>.config</filename>
279 produced by the <command>make menuconfig</command> step
280 above contains all the configuration selections for the kernel
281 that was just compiled. It is a good idea to keep this file for future
282 reference:</para>
284<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
286 <para>Install the documentation for the Linux kernel:</para>
288<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
289cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
291 <para>It is important to note that the files in the kernel source
292 directory are not owned by <emphasis>root</emphasis>. Whenever a
293 package is unpacked as user <emphasis>root</emphasis> (like we did
294 inside chroot), the files have the user and group IDs of whatever
295 they were on the packager's computer. This is usually not a problem
296 for any other package to be installed because the source tree is
297 removed after the installation. However, the Linux source tree is
298 often retained for a long time. Because of this, there is a chance
299 that whatever user ID the packager used will be assigned to somebody
300 on the machine. That person would then have write access to the kernel
301 source.</para>
303 <note>
304 <para>In many cases, the configuration of the kernel will need to be
305 updated for packages that will be installed later in BLFS. Unlike
306 other packages, it is not necessary to remove the kernel source tree
307 after the newly built kernel is installed.</para>
309 <para>If the kernel source tree is going to be retained, run
310 <command>chown -R 0:0</command> on the <filename
311 class="directory">linux-&linux-version;</filename> directory to ensure
312 all files are owned by user <emphasis>root</emphasis>.</para>
313 </note>
315 <warning>
316 <para>Some kernel documentation recommends creating a symlink from
317 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
318 source directory. This is specific to kernels prior to the 2.6 series and
319 <emphasis>must not</emphasis> be created on an LFS system as it can cause
320 problems for packages you may wish to build once your base LFS system is
321 complete.</para>
322 </warning>
324 <warning>
325 <para>The headers in the system's <filename
326 class="directory">include</filename> directory (<filename
327 class="directory">/usr/include</filename>) should
328 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
329 that is, the sanitised headers installed in <xref
330 linkend="ch-tools-linux-headers"/>. Therefore, they should
331 <emphasis>never</emphasis> be replaced by either the raw kernel headers
332 or any other kernel sanitized headers.</para>
333 </warning>
335 </sect2>
337 <sect2 id="conf-modprobe" role="configuration">
338 <title>Configuring Linux Module Load Order</title>
340 <indexterm zone="conf-modprobe">
341 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
342 </indexterm>
344 <para>Most of the time Linux modules are loaded automatically, but
345 sometimes it needs some specific direction. The program that loads
346 modules, <command>modprobe</command> or <command>insmod</command>, uses
347 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
348 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
349 uhci_hcd) have been built as modules, they will be loaded in the correct
350 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
351 to avoid a warning being output at boot time.</para>
353 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
354 the following:</para>
356<screen><userinput>install -v -m755 -d /etc/modprobe.d
357cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
358<literal># Begin /etc/modprobe.d/usb.conf
360install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
361install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
363# End /etc/modprobe.d/usb.conf</literal>
366 </sect2>
368 <sect2 id="contents-kernel" role="content">
369 <title>Contents of Linux</title>
371 <segmentedlist>
372 <segtitle>Installed files</segtitle>
373 <segtitle>Installed directories</segtitle>
375 <seglistitem>
376 <seg>config-&linux-version;,
377 <phrase revision="sysv">vmlinuz-&linux-version;-lfs-&version;,</phrase>
378 <phrase revision="systemd">vmlinuz-&linux-version;-lfs-&versiond;,</phrase>
379 and;</seg>
380 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
381 </seglistitem>
382 </segmentedlist>
384 <variablelist>
385 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
386 <?dbfo list-presentation="list"?>
387 <?dbhtml list-presentation="table"?>
389 <varlistentry id="config">
390 <term><filename>config-&linux-version;</filename></term>
391 <listitem>
392 <para>Contains all the configuration selections for the kernel</para>
393 <indexterm zone="ch-bootable-kernel config">
394 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
395 </indexterm>
396 </listitem>
397 </varlistentry>
399 <varlistentry id="lfskernel">
400 <term revision="sysv"><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
401 <term revision="systemd"><filename>vmlinuz-&linux-version;-lfs-&versiond;</filename></term>
402 <listitem>
403 <para>The engine of the Linux system. When turning on the computer,
404 the kernel is the first part of the operating system that gets loaded.
405 It detects and initializes all components of the computer's hardware,
406 then makes these components available as a tree of files to the
407 software and turns a single CPU into a multitasking machine capable
408 of running scores of programs seemingly at the same time</para>
409 <indexterm zone="ch-bootable-kernel lfskernel">
410 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
411 </indexterm>
412 </listitem>
413 </varlistentry>
415 <varlistentry id="">
416 <term><filename>;</filename></term>
417 <listitem>
418 <para>A list of addresses and symbols; it maps the entry points and
419 addresses of all the functions and data structures in the
420 kernel</para>
421 <indexterm zone="ch-bootable-kernel">
422 <primary sortas="e-/boot/">/boot/;</primary>
423 </indexterm>
424 </listitem>
425 </varlistentry>
427 </variablelist>
429 </sect2>
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