source: chapter10/kernel.xml@ 70f30e9

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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 <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 his point
59 optimization and customization is not a goal.
60 </para>
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>
72 <para>
73 If all else fails, you can ask for help on the <ulink
74 url="">lfs-support</ulink>
75 mailing list. Note that subscribing is required in order for the list
76 to avoid spam.
77 </para>
78 </important>
80 <para>Prepare for compilation by running the following command:</para>
82<screen><userinput remap="pre">make mrproper</userinput></screen>
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>
89 <para>There are several ways to configure the kernel options. Usually,
90 This is done through a menu-driven interface, for example:</para>
92<screen role="nodump"><userinput>make menuconfig</userinput></screen>
94 <variablelist>
95 <title>The meaning of optional make environment variables:</title>
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>
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>
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>
121 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
124 <note>
125 <para>A good starting place for setting up the kernel configuration is to
126 run <command>make defconfig</command>. This will set the base
127 configuration to a good state that takes your current system architecture
128 into account.</para>
130 <para>Be sure to enable/disable/set the following features or the system might
131 not work correctly or boot at all:</para>
133 <screen role="nodump" revision="sysv">Processor type and features ---&gt;
134 [*] Build a relocatable kernel [CONFIG_RELOCATABLE]
135 [*] Randomize the address of the kernel image (KASLR) [CONFIG_RANDOMIZE_BASE]
136General setup ---&gt;
137 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
138 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
139 [ ] Configure standard kernel features (expert users) [CONFIG_EXPERT]
140General architecture-dependent options ---&gt;
141 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
142 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
143Device Drivers ---&gt;
144 Firmware Drivers ---&gt;
145 EFI (Extensible Firmware Interface) Support ---&gt;
146 [*] Enable the generic EFI decompressor [CONFIG_EFI_ZBOOT]
147 Graphics support ---&gt;
148 Frame buffer Devices ---&gt;
149 &lt;*&gt; Support for frame buffer devices ---&gt;
150 Console display driver support ---&gt;
151 [*] Framebuffer Console support [CONFIG_FRAMEBUFFER_CONSOLE]
152 Generic Driver Options ---&gt;
153 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
154 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
155 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]</screen>
157 <screen role="nodump" revision="systemd">Processor type and features ---&gt;
158 [*] Build a relocatable kernel [CONFIG_RELOCATABLE]
159 [*] Randomize the address of the kernel image (KASLR) [CONFIG_RANDOMIZE_BASE]
160General setup ---&gt;
161 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
162 [ ] Auditing Support [CONFIG_AUDIT]
163 CPU/Task time and stats accounting ---&gt;
164 [*] Pressure stall information tracking [CONFIG_PSI]
165 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
166 [*] Control Group support [CONFIG_CGROUPS] ---&gt;
167 [*] Memory controller [CONFIG_MEMCG]
168 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
169 [ ] Configure standard kernel features (expert users) [CONFIG_EXPERT]
170General architecture-dependent options ---&gt;
171 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
172 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
173 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
174Networking support ---&gt;
175 Networking options ---&gt;
176 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
177Device Drivers ---&gt;
178 Generic Driver Options ---&gt;
179 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
180 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
181 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]
182 Firmware Loader ---&gt;
183 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
184 Firmware Drivers ---&gt;
185 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
186 EFI (Extensible Firmware Interface) Support ---&gt;
187 [*] Enable the generic EFI decompressor [CONFIG_EFI_ZBOOT]
188 Graphics support ---&gt;
189 Frame buffer Devices ---&gt;
190 &lt;*&gt; Support for frame buffer devices ---&gt;
191 Console display driver support ---&gt;
192 [*] Framebuffer Console support [CONFIG_FRAMEBUFFER_CONSOLE]
193File systems ---&gt;
194 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
195 Pseudo filesystems ---&gt;
196 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]</screen>
198 <para>If the partition for the LFS system is in a NVME SSD (i. e. the
199 device node for the partition is <filename>/dev/nvme*</filename>
200 instead of <filename>/dev/sd*</filename>), enable NVME support or
201 the LFS system won't boot:</para>
203 <screen role="nodump">Device Drivers ---&gt;
204 NVME Support ---&gt;
205 &lt;*&gt; NVM Express block device [CONFIG_BLK_DEV_NVME]</screen>
206 </note>
208 <note revision="systemd">
209 <para>While "The IPv6 Protocol" is not strictly
210 required, it is highly recommended by the systemd developers.</para>
211 </note>
213 <para>There are several other options that may be desired
214 depending on the requirements for the system. For a list of options needed
215 for BLFS packages, see the <ulink
216 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
217 Index of Kernel Settings</ulink>.</para>
219 <note>
220 <para>If your host hardware is using UEFI and you wish to boot the
221 LFS system with it, you should adjust some kernel configuration
222 following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
223 the BLFS page</ulink> <emphasis role='bold'>even if you'll use the
224 UEFI bootloader from the host distro</emphasis>.</para>
225 </note>
227 <variablelist>
228 <title>The rationale for the above configuration items:</title>
230 <varlistentry>
231 <term><parameter>Randomize the address of the kernel image (KASLR)</parameter></term>
232 <listitem>
233 <para>Enable ASLR for kernel image, to mitigate some attacks based
234 on fixed addresses of sensitive data or code in the kernel.</para>
235 </listitem>
236 </varlistentry>
238 <varlistentry>
239 <term>
240 <parameter>
241 Compile the kernel with warnings as errors
242 </parameter>
243 </term>
244 <listitem>
245 <para>This may cause building failure if the compiler and/or
246 configuration are different from those of the kernel
247 developers.</para>
248 </listitem>
249 </varlistentry>
251 <varlistentry>
252 <term>
253 <parameter>
254 Enable kernel headers through /sys/kernel/kheaders.tar.xz
255 </parameter>
256 </term>
257 <listitem>
258 <para>This will require <command>cpio</command> building the kernel.
259 <command>cpio</command> is not installed by LFS.</para>
260 </listitem>
261 </varlistentry>
263 <varlistentry>
264 <term>
265 <parameter>
266 Configure standard kernel features (expert users)
267 </parameter>
268 </term>
269 <listitem>
270 <para>This will make some options show up in the configuration
271 interface but changing those options may be dangerous. Do not use
272 this unless you know what you are doing.</para>
273 </listitem>
274 </varlistentry>
276 <varlistentry>
277 <term><parameter>Strong Stack Protector</parameter></term>
278 <listitem>
279 <para>Enable SSP for the kernel. We've enabled it for the entire
280 userspace with <parameter>--enable-default-ssp</parameter>
281 configuring GCC, but the kernel does not use GCC default setting
282 for SSP. We enable it explicitly here.</para>
283 </listitem>
284 </varlistentry>
286 <varlistentry>
287 <term><parameter>Support for uevent helper</parameter></term>
288 <listitem>
289 <para>Having this option set may interfere with device
290 management when using Udev/Eudev. </para>
291 </listitem>
292 </varlistentry>
294 <varlistentry>
295 <term><parameter>Maintain a devtmpfs</parameter></term>
296 <listitem>
297 <para>This will create automated device nodes which are populated by the
298 kernel, even without Udev running. Udev then runs on top of this,
299 managing permissions and adding symlinks. This configuration
300 item is required for all users of Udev/Eudev.</para>
301 </listitem>
302 </varlistentry>
304 <varlistentry>
305 <term><parameter>Automount devtmpfs at /dev</parameter></term>
306 <listitem>
307 <para>This will mount the kernel view of the devices on /dev
308 upon switching to root filesystem just before starting
309 init.</para>
310 </listitem>
311 </varlistentry>
313 <varlistentry>
314 <term><parameter>Enable the generic EFI decompressor</parameter></term>
315 <listitem>
316 <para>Create the bootable image as an EFI application that carries
317 the actual kernel image in compressed form. It can make the
318 bootable image 50% smaller.</para>
319 </listitem>
320 </varlistentry>
322 <varlistentry>
323 <term><parameter>Framebuffer Console support</parameter></term>
324 <listitem>
325 <para>This is needed to display the Linux console on a frame
326 buffer device. To allow the kernel to print debug messages at an
327 early boot stage, it shouldn't be built as a kernel module
328 unless an initramfs will be used. And, if
329 <option>CONFIG_DRM</option> (Direct Rendering Manager) is enabled,
330 it's likely <option>CONFIG_DRM_FBDEV_EMULATION</option> (Enable
331 legacy fbdev support for your modesetting driver) should be
332 enabled as well.</para>
333 </listitem>
334 </varlistentry>
336 </variablelist>
338 <para>Alternatively, <command>make oldconfig</command> may be more
339 appropriate in some situations. See the <filename>README</filename>
340 file for more information.</para>
342 <para>If desired, skip kernel configuration by copying the kernel
343 config file, <filename>.config</filename>, from the host system
344 (assuming it is available) to the unpacked <filename
345 class="directory">linux-&linux-version;</filename> directory. However,
346 we do not recommend this option. It is often better to explore all the
347 configuration menus and create the kernel configuration from
348 scratch.</para>
350 <para>Compile the kernel image and modules:</para>
352<screen><userinput remap="make">make</userinput></screen>
354 <para>If using kernel modules, module configuration in <filename
355 class="directory">/etc/modprobe.d</filename> may be required.
356 Information pertaining to modules and kernel configuration is
357 located in <xref linkend="ch-config-udev"/> and in the kernel
358 documentation in the <filename
359 class="directory">linux-&linux-version;/Documentation</filename> directory.
360 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
362 <para>Unless module support has been disabled in the kernel configuration,
363 install the modules with:</para>
365<screen><userinput remap="install">make modules_install</userinput></screen>
367 <para>After kernel compilation is complete, additional steps are
368 required to complete the installation. Some files need to be copied to
369 the <filename class="directory">/boot</filename> directory.</para>
371 <caution>
372 <para>If you've decided to use a separate &boot-dir; partition for the
373 LFS system (maybe sharing a &boot-dir; partition with the host
374 distro) , the files copied below should go there. The easiest way to
375 do that is to create the entry for &boot-dir; in &fstab; first (read
376 the previous section for details), then issue the following command
377 as the &root; user in the
378 <emphasis>chroot environment</emphasis>:</para>
380<screen role="nodump"><userinput>mount /boot</userinput></screen>
382 <para>The path to the device node is omitted in the command because
383 <command>mount</command> can read it from &fstab;.</para>
384 </caution>
386 <para>The path to the kernel image may vary depending on the platform being
387 used. The filename below can be changed to suit your taste, but the stem of
388 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
389 the automatic setup of the boot process described in the next section. The
390 following command assumes an ARM64 architecture with an EFI boot loader
391 (for example, GRUB built in &ch-final;):</para>
393<screen><userinput remap="install">cp -iv arch/arm64/boot/vmlinuz.efi /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
395 <para><filename></filename> is a symbol file for the kernel.
396 It maps the function entry points of every function in the kernel API,
397 as well as the addresses of the kernel data structures for the running
398 kernel. It is used as a resource when investigating kernel problems.
399 Issue the following command to install the map file:</para>
401<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
403 <para>The kernel configuration file <filename>.config</filename>
404 produced by the <command>make menuconfig</command> step
405 above contains all the configuration selections for the kernel
406 that was just compiled. It is a good idea to keep this file for future
407 reference:</para>
409<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
411 <para>Install the documentation for the Linux kernel:</para>
413<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
414cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
416 <para>It is important to note that the files in the kernel source
417 directory are not owned by <emphasis>root</emphasis>. Whenever a
418 package is unpacked as user <emphasis>root</emphasis> (like we did
419 inside chroot), the files have the user and group IDs of whatever
420 they were on the packager's computer. This is usually not a problem
421 for any other package to be installed because the source tree is
422 removed after the installation. However, the Linux source tree is
423 often retained for a long time. Because of this, there is a chance
424 that whatever user ID the packager used will be assigned to somebody
425 on the machine. That person would then have write access to the kernel
426 source.</para>
428 <note>
429 <para>In many cases, the configuration of the kernel will need to be
430 updated for packages that will be installed later in BLFS. Unlike
431 other packages, it is not necessary to remove the kernel source tree
432 after the newly built kernel is installed.</para>
434 <para>If the kernel source tree is going to be retained, run
435 <command>chown -R 0:0</command> on the <filename
436 class="directory">linux-&linux-version;</filename> directory to ensure
437 all files are owned by user <emphasis>root</emphasis>.</para>
438 </note>
440 <warning>
441 <para>Some kernel documentation recommends creating a symlink from
442 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
443 source directory. This is specific to kernels prior to the 2.6 series and
444 <emphasis>must not</emphasis> be created on an LFS system as it can cause
445 problems for packages you may wish to build once your base LFS system is
446 complete.</para>
447 </warning>
449 <warning>
450 <para>The headers in the system's <filename
451 class="directory">include</filename> directory (<filename
452 class="directory">/usr/include</filename>) should
453 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
454 that is, the sanitised headers installed in <xref
455 linkend="ch-tools-linux-headers"/>. Therefore, they should
456 <emphasis>never</emphasis> be replaced by either the raw kernel headers
457 or any other kernel sanitized headers.</para>
458 </warning>
460 </sect2>
462 <sect2 id="conf-modprobe" role="configuration">
463 <title>Configuring Linux Module Load Order</title>
465 <indexterm zone="conf-modprobe">
466 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
467 </indexterm>
469 <para>Most of the time Linux modules are loaded automatically, but
470 sometimes it needs some specific direction. The program that loads
471 modules, <command>modprobe</command> or <command>insmod</command>, uses
472 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
473 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
474 uhci_hcd) have been built as modules, they will be loaded in the correct
475 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
476 to avoid a warning being output at boot time.</para>
478 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
479 the following:</para>
481<screen><userinput>install -v -m755 -d /etc/modprobe.d
482cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
483<literal># Begin /etc/modprobe.d/usb.conf
485install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
486install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
488# End /etc/modprobe.d/usb.conf</literal>
491 </sect2>
493 <sect2 id="contents-kernel" role="content">
494 <title>Contents of Linux</title>
496 <segmentedlist>
497 <segtitle>Installed files</segtitle>
498 <segtitle>Installed directories</segtitle>
500 <seglistitem>
501 <seg>config-&linux-version;,
502 vmlinuz-&linux-version;-lfs-&version;,
503 and;</seg>
504 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
505 </seglistitem>
506 </segmentedlist>
508 <variablelist>
509 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
510 <?dbfo list-presentation="list"?>
511 <?dbhtml list-presentation="table"?>
513 <varlistentry id="config">
514 <term><filename>config-&linux-version;</filename></term>
515 <listitem>
516 <para>Contains all the configuration selections for the kernel</para>
517 <indexterm zone="ch-bootable-kernel config">
518 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
519 </indexterm>
520 </listitem>
521 </varlistentry>
523 <varlistentry id="lfskernel">
524 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
525 <listitem>
526 <para>The engine of the Linux system. When turning on the computer,
527 the kernel is the first part of the operating system that gets loaded.
528 It detects and initializes all components of the computer's hardware,
529 then makes these components available as a tree of files to the
530 software and turns a single CPU into a multitasking machine capable
531 of running scores of programs seemingly at the same time</para>
532 <indexterm zone="ch-bootable-kernel lfskernel">
533 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
534 </indexterm>
535 </listitem>
536 </varlistentry>
538 <varlistentry id="">
539 <term><filename>;</filename></term>
540 <listitem>
541 <para>A list of addresses and symbols; it maps the entry points and
542 addresses of all the functions and data structures in the
543 kernel</para>
544 <indexterm zone="ch-bootable-kernel">
545 <primary sortas="e-/boot/">/boot/;</primary>
546 </indexterm>
547 </listitem>
548 </varlistentry>
550 </variablelist>
552 </sect2>
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