source: chapter08/kernel.xml@ efcb393

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Make the new book

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