source: chapter10/kernel.xml@ a5de784

12.1 12.1-rc1 multilib trunk xry111/arm64 xry111/clfs-ng xry111/loongarch xry111/loongarch-12.1 xry111/mips64el xry111/update-glibc
Last change on this file since a5de784 was 3864d23, checked in by Bruce Dubbs <bdubbs@…>, 10 months ago

Package updates and misc upates/typos.

Update to vim-1837.$
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Update to sysvinit-3.08.$
Update to shadow-4.14.0.$
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Update to procps-ng-4.0.4.$
Update to pkgconf-2.0.2.$
Update to mpfr-4.2.1.$
Update to kbd-2.6.2.$
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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 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
6]>
7
8<sect1 id="ch-bootable-kernel" role="wrap">
9 <?dbhtml filename="kernel.html"?>
10
11 <sect1info condition="script">
12 <productname>kernel</productname>
13 <productnumber>&linux-version;</productnumber>
14 <address>&linux-url;</address>
15 </sect1info>
16
17 <title>Linux-&linux-version;</title>
18
19 <indexterm zone="ch-bootable-kernel">
20 <primary sortas="a-Linux">Linux</primary>
21 </indexterm>
22
23 <sect2 role="package">
24 <title/>
25
26 <para>The Linux package contains the Linux kernel.</para>
27
28 <segmentedlist>
29 <segtitle>&buildtime;</segtitle>
30 <segtitle>&diskspace;</segtitle>
31
32 <seglistitem>
33 <seg>&linux-knl-sbu;</seg>
34 <seg>&linux-knl-du;</seg>
35 </seglistitem>
36 </segmentedlist>
37
38 </sect2>
39
40 <sect2 role="installation">
41 <title>Installation of the kernel</title>
42
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>
47
48 <important>
49 <para>
50 Building the linux kernel for the first time is one of the most
51 challenging tasks in LFS. Getting it right depends on the specific
52 hardware for the target system and your specific needs. There are
53 almost 12,000 configuration items that are available for the kernel
54 although only about a third of them are needed for most computers. The
55 LFS editors recommend that users not familiar with this process follow
56 the procedures below fairly closely. The objective is to get an
57 initial system to a point where you can log in at the command line when
58 you reboot later in <xref linkend="ch-finish-reboot"/>. At this point
59 optimization and customization is not a goal.
60 </para>
61
62
63 <para>
64 For general information on kernel configuration see <ulink
65 url="&hints-root;kernel-configuration.txt"/>. Additional information
66 about configuring and building the kernel can be found at <ulink
67 url="&anduin-sources;/kernel-nutshell/"/>.
68 These references are a bit
69 dated, but still give a reasonable overview of the process.
70 </para>
71
72 <para>
73 If all else fails, you can ask for help on the <ulink
74 url="https://www.linuxfromscratch.org/mail.html">lfs-support</ulink>
75 mailing list. Note that subscribing is required in order for the list
76 to avoid spam.
77 </para>
78 </important>
79
80 <para>Prepare for compilation by running the following command:</para>
81
82<screen><userinput remap="pre">make mrproper</userinput></screen>
83
84 <para>This ensures that the kernel tree is absolutely clean. The
85 kernel team recommends that this command be issued prior to each
86 kernel compilation. Do not rely on the source tree being clean after
87 un-tarring.</para>
88
89 <para>There are several ways to configure the kernel options. Usually,
90 This is done through a menu-driven interface, for example:</para>
91
92<screen role="nodump"><userinput>make menuconfig</userinput></screen>
93
94 <variablelist>
95 <title>The meaning of optional make environment variables:</title>
96
97 <varlistentry>
98 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
99 <listitem>
100 <para>This establishes the locale setting to the one used on the
101 host. This may be needed for a proper menuconfig ncurses interface
102 line drawing on a UTF-8 linux text console.</para>
103
104 <para>If used, be sure to replace
105 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
106 the <envar>$LANG</envar> variable from your host. You can
107 alternatively use instead the host's value of <envar>$LC_ALL</envar>
108 or <envar>$LC_CTYPE</envar>.</para>
109 </listitem>
110 </varlistentry>
111
112 <varlistentry>
113 <term><command>make menuconfig</command></term>
114 <listitem>
115 <para>This launches an ncurses menu-driven interface. For other
116 (graphical) interfaces, type <command>make help</command>.</para>
117 </listitem>
118 </varlistentry>
119 </variablelist>
120
121 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
122
123
124 <note>
125 <?dbfo keep-together="auto"?>
126 <para>A good starting place for setting up the kernel configuration is to
127 run <command>make defconfig</command>. This will set the base
128 configuration to a good state that takes your current system architecture
129 into account.</para>
130
131 <para>Be sure to enable/disable/set the following features or the system might
132 not work correctly or boot at all:</para>
133
134 <!-- To editors: for updating kernel configuration, edit
135 kernel/*.toml and regenerate kernel/*.xml with
136 "make -C kernel KERNEL_TREE=</usr/src/linux-&linux-version> -->
137
138 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
139 href="kernel/sysv.xml"/>
140
141 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
142 href="kernel/systemd.xml"/>
143
144 <para>Enable some additional features if you are building a 64-bit
145 system. If you are using menuconfig, enable them in the order of
146 <parameter>CONFIG_PCI_MSI</parameter> first, then
147 <parameter>CONFIG_IRQ_REMAP</parameter>, at last
148 <parameter>CONFIG_X86_X2APIC</parameter> because an option only
149 shows up after its dependencies are selected.</para>
150
151 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
152 href="kernel/x2apic.xml"/>
153
154 <para>If you are building a 32-bit system running on a hardware
155 with RAM more than 4GB, adjust the configuration so the kernel will
156 be able to use up to 64GB physical RAM:</para>
157
158 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
159 href="kernel/highmem.xml"/>
160
161 <para>If the partition for the LFS system is in a NVME SSD (i. e. the
162 device node for the partition is <filename>/dev/nvme*</filename>
163 instead of <filename>/dev/sd*</filename>), enable NVME support or
164 the LFS system won't boot:</para>
165
166 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
167 href="kernel/nvme.xml"/>
168 </note>
169
170 <note revision="systemd">
171 <para>While "The IPv6 Protocol" is not strictly
172 required, it is highly recommended by the systemd developers.</para>
173 </note>
174
175 <para>There are several other options that may be desired
176 depending on the requirements for the system. For a list of options needed
177 for BLFS packages, see the <ulink
178 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
179 Index of Kernel Settings</ulink>.</para>
180
181 <note>
182 <para>If your host hardware is using UEFI and you wish to boot the
183 LFS system with it, you should adjust some kernel configuration
184 following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
185 the BLFS page</ulink> <emphasis role='bold'>even if you'll use the
186 UEFI bootloader from the host distro</emphasis>.</para>
187 </note>
188
189 <variablelist>
190 <title>The rationale for the above configuration items:</title>
191
192 <varlistentry>
193 <term><parameter>Randomize the address of the kernel image (KASLR)</parameter></term>
194 <listitem>
195 <para>Enable ASLR for kernel image, to mitigate some attacks based
196 on fixed addresses of sensitive data or code in the kernel.</para>
197 </listitem>
198 </varlistentry>
199
200 <varlistentry>
201 <term>
202 <parameter>
203 Compile the kernel with warnings as errors
204 </parameter>
205 </term>
206 <listitem>
207 <para>This may cause building failure if the compiler and/or
208 configuration are different from those of the kernel
209 developers.</para>
210 </listitem>
211 </varlistentry>
212
213 <varlistentry>
214 <term>
215 <parameter>
216 Enable kernel headers through /sys/kernel/kheaders.tar.xz
217 </parameter>
218 </term>
219 <listitem>
220 <para>This will require <command>cpio</command> building the kernel.
221 <command>cpio</command> is not installed by LFS.</para>
222 </listitem>
223 </varlistentry>
224
225 <varlistentry>
226 <term>
227 <parameter>
228 Configure standard kernel features (expert users)
229 </parameter>
230 </term>
231 <listitem>
232 <para>This will make some options show up in the configuration
233 interface but changing those options may be dangerous. Do not use
234 this unless you know what you are doing.</para>
235 </listitem>
236 </varlistentry>
237
238 <varlistentry>
239 <term><parameter>Strong Stack Protector</parameter></term>
240 <listitem>
241 <para>Enable SSP for the kernel. We've enabled it for the entire
242 userspace with <parameter>--enable-default-ssp</parameter>
243 configuring GCC, but the kernel does not use GCC default setting
244 for SSP. We enable it explicitly here.</para>
245 </listitem>
246 </varlistentry>
247
248 <varlistentry>
249 <term><parameter>Support for uevent helper</parameter></term>
250 <listitem>
251 <para>Having this option set may interfere with device
252 management when using Udev.</para>
253 </listitem>
254 </varlistentry>
255
256 <varlistentry>
257 <term><parameter>Maintain a devtmpfs</parameter></term>
258 <listitem>
259 <para>This will create automated device nodes which are populated by the
260 kernel, even without Udev running. Udev then runs on top of this,
261 managing permissions and adding symlinks. This configuration
262 item is required for all users of Udev.</para>
263 </listitem>
264 </varlistentry>
265
266 <varlistentry>
267 <term><parameter>Automount devtmpfs at /dev</parameter></term>
268 <listitem>
269 <para>This will mount the kernel view of the devices on /dev
270 upon switching to root filesystem just before starting
271 init.</para>
272 </listitem>
273 </varlistentry>
274
275 <varlistentry>
276 <term><parameter>Framebuffer Console support</parameter></term>
277 <listitem>
278 <para>This is needed to display the Linux console on a frame
279 buffer device. To allow the kernel to print debug messages at an
280 early boot stage, it shouldn't be built as a kernel module
281 unless an initramfs will be used. And, if
282 <option>CONFIG_DRM</option> (Direct Rendering Manager) is enabled,
283 it's likely <option>CONFIG_DRM_FBDEV_EMULATION</option> (Enable
284 legacy fbdev support for your modesetting driver) should be
285 enabled as well.</para>
286 </listitem>
287 </varlistentry>
288
289 <varlistentry>
290 <term><parameter>Support x2apic</parameter></term>
291 <listitem>
292 <para>Support running the interrupt controller of 64-bit x86
293 processors in x2APIC mode. x2APIC may be enabled by firmware on
294 64-bit x86 systems, and a kernel without this option enabled will
295 panic on boot if x2APIC is enabled by firmware. This option
296 has no effect, but also does no harm if x2APIC is disabled by the
297 firmware.</para>
298 </listitem>
299 </varlistentry>
300
301 </variablelist>
302
303 <para>Alternatively, <command>make oldconfig</command> may be more
304 appropriate in some situations. See the <filename>README</filename>
305 file for more information.</para>
306
307 <para>If desired, skip kernel configuration by copying the kernel
308 config file, <filename>.config</filename>, from the host system
309 (assuming it is available) to the unpacked <filename
310 class="directory">linux-&linux-version;</filename> directory. However,
311 we do not recommend this option. It is often better to explore all the
312 configuration menus and create the kernel configuration from
313 scratch.</para>
314
315 <para>Compile the kernel image and modules:</para>
316
317<screen><userinput remap="make">make</userinput></screen>
318
319 <para>If using kernel modules, module configuration in <filename
320 class="directory">/etc/modprobe.d</filename> may be required.
321 Information pertaining to modules and kernel configuration is
322 located in <xref linkend="ch-config-udev"/> and in the kernel
323 documentation in the <filename
324 class="directory">linux-&linux-version;/Documentation</filename> directory.
325 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
326
327 <para>Unless module support has been disabled in the kernel configuration,
328 install the modules with:</para>
329
330<screen><userinput remap="install">make modules_install</userinput></screen>
331
332 <para>After kernel compilation is complete, additional steps are
333 required to complete the installation. Some files need to be copied to
334 the <filename class="directory">/boot</filename> directory.</para>
335
336 <caution>
337 <para>If you've decided to use a separate &boot-dir; partition for the
338 LFS system (maybe sharing a &boot-dir; partition with the host
339 distro) , the files copied below should go there. The easiest way to
340 do that is to create the entry for &boot-dir; in &fstab; first (read
341 the previous section for details), then issue the following command
342 as the &root; user in the
343 <emphasis>chroot environment</emphasis>:</para>
344
345<screen role="nodump"><userinput>mount /boot</userinput></screen>
346
347 <para>The path to the device node is omitted in the command because
348 <command>mount</command> can read it from &fstab;.</para>
349 </caution>
350
351 <para>The path to the kernel image may vary depending on the platform being
352 used. The filename below can be changed to suit your taste, but the stem of
353 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
354 the automatic setup of the boot process described in the next section. The
355 following command assumes an x86 architecture:</para>
356
357<screen><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
358
359 <para><filename>System.map</filename> is a symbol file for the kernel.
360 It maps the function entry points of every function in the kernel API,
361 as well as the addresses of the kernel data structures for the running
362 kernel. It is used as a resource when investigating kernel problems.
363 Issue the following command to install the map file:</para>
364
365<screen><userinput remap="install">cp -iv System.map /boot/System.map-&linux-version;</userinput></screen>
366
367 <para>The kernel configuration file <filename>.config</filename>
368 produced by the <command>make menuconfig</command> step
369 above contains all the configuration selections for the kernel
370 that was just compiled. It is a good idea to keep this file for future
371 reference:</para>
372
373<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
374
375 <para>Install the documentation for the Linux kernel:</para>
376
377<screen><userinput remap="install">cp -r Documentation -T /usr/share/doc/linux-&linux-version;</userinput></screen>
378
379 <para>It is important to note that the files in the kernel source
380 directory are not owned by <emphasis>root</emphasis>. Whenever a
381 package is unpacked as user <emphasis>root</emphasis> (like we did
382 inside chroot), the files have the user and group IDs of whatever
383 they were on the packager's computer. This is usually not a problem
384 for any other package to be installed because the source tree is
385 removed after the installation. However, the Linux source tree is
386 often retained for a long time. Because of this, there is a chance
387 that whatever user ID the packager used will be assigned to somebody
388 on the machine. That person would then have write access to the kernel
389 source.</para>
390
391 <note>
392 <para>In many cases, the configuration of the kernel will need to be
393 updated for packages that will be installed later in BLFS. Unlike
394 other packages, it is not necessary to remove the kernel source tree
395 after the newly built kernel is installed.</para>
396
397 <para>If the kernel source tree is going to be retained, run
398 <command>chown -R 0:0</command> on the <filename
399 class="directory">linux-&linux-version;</filename> directory to ensure
400 all files are owned by user <emphasis>root</emphasis>.</para>
401 </note>
402
403 <warning>
404 <para>Some kernel documentation recommends creating a symlink from
405 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
406 source directory. This is specific to kernels prior to the 2.6 series and
407 <emphasis>must not</emphasis> be created on an LFS system as it can cause
408 problems for packages you may wish to build once your base LFS system is
409 complete.</para>
410 </warning>
411
412 <warning>
413 <para>The headers in the system's <filename
414 class="directory">include</filename> directory (<filename
415 class="directory">/usr/include</filename>) should
416 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
417 that is, the sanitised headers installed in <xref
418 linkend="ch-tools-linux-headers"/>. Therefore, they should
419 <emphasis>never</emphasis> be replaced by either the raw kernel headers
420 or any other kernel sanitized headers.</para>
421 </warning>
422
423 </sect2>
424
425 <sect2 id="conf-modprobe" role="configuration">
426 <title>Configuring Linux Module Load Order</title>
427
428 <indexterm zone="conf-modprobe">
429 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
430 </indexterm>
431
432 <para>Most of the time Linux modules are loaded automatically, but
433 sometimes it needs some specific direction. The program that loads
434 modules, <command>modprobe</command> or <command>insmod</command>, uses
435 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
436 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
437 uhci_hcd) have been built as modules, they will be loaded in the correct
438 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
439 to avoid a warning being output at boot time.</para>
440
441 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
442 the following:</para>
443
444<screen><userinput>install -v -m755 -d /etc/modprobe.d
445cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
446<literal># Begin /etc/modprobe.d/usb.conf
447
448install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
449install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
450
451# End /etc/modprobe.d/usb.conf</literal>
452EOF</userinput></screen>
453
454 </sect2>
455
456 <sect2 id="contents-kernel" role="content">
457 <title>Contents of Linux</title>
458
459 <segmentedlist>
460 <segtitle>Installed files</segtitle>
461 <segtitle>Installed directories</segtitle>
462
463 <seglistitem>
464 <seg>config-&linux-version;,
465 vmlinuz-&linux-version;-lfs-&version;,
466 and System.map-&linux-version;</seg>
467 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
468 </seglistitem>
469 </segmentedlist>
470
471 <variablelist>
472 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
473 <?dbfo list-presentation="list"?>
474 <?dbhtml list-presentation="table"?>
475
476 <varlistentry id="config">
477 <term><filename>config-&linux-version;</filename></term>
478 <listitem>
479 <para>Contains all the configuration selections for the kernel</para>
480 <indexterm zone="ch-bootable-kernel config">
481 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
482 </indexterm>
483 </listitem>
484 </varlistentry>
485
486 <varlistentry id="lfskernel">
487 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
488 <listitem>
489 <para>The engine of the Linux system. When turning on the computer,
490 the kernel is the first part of the operating system that gets loaded.
491 It detects and initializes all components of the computer's hardware,
492 then makes these components available as a tree of files to the
493 software and turns a single CPU into a multitasking machine capable
494 of running scores of programs seemingly at the same time</para>
495 <indexterm zone="ch-bootable-kernel lfskernel">
496 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
497 </indexterm>
498 </listitem>
499 </varlistentry>
500
501 <varlistentry id="System.map">
502 <term><filename>System.map-&linux-version;</filename></term>
503 <listitem>
504 <para>A list of addresses and symbols; it maps the entry points and
505 addresses of all the functions and data structures in the
506 kernel</para>
507 <indexterm zone="ch-bootable-kernel System.map">
508 <primary sortas="e-/boot/System.map">/boot/System.map-&linux-version;</primary>
509 </indexterm>
510 </listitem>
511 </varlistentry>
512
513 </variablelist>
514
515 </sect2>
516
517</sect1>
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