source: chapter10/kernel.xml@ 7160772

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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 <para>There are several ways to configure the kernel options. Usually,
58 This is done through a menu-driven interface, for example:</para>
60<screen role="nodump"><userinput>make menuconfig</userinput></screen>
62 <variablelist>
63 <title>The meaning of optional make environment variables:</title>
65 <varlistentry>
66 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
67 <listitem>
68 <para>This establishes the locale setting to the one used on the
69 host. This may be needed for a proper menuconfig ncurses interface
70 line drawing on a UTF-8 linux text console.</para>
72 <para>If used, be sure to replace
73 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
74 the <envar>$LANG</envar> variable from your host. You can
75 alternatively use instead the host's value of <envar>$LC_ALL</envar>
76 or <envar>$LC_CTYPE</envar>.</para>
77 </listitem>
78 </varlistentry>
80 <varlistentry>
81 <term><command>make menuconfig</command></term>
82 <listitem>
83 <para>This launches an ncurses menu-driven interface. For other
84 (graphical) interfaces, type <command>make help</command>.</para>
85 </listitem>
86 </varlistentry>
87 </variablelist>
89 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
91 <para>For general information on kernel configuration see <ulink
92 url="&hints-root;kernel-configuration.txt"/>. BLFS has some information
93 regarding particular kernel configuration requirements of packages outside
94 of LFS at <ulink
95 url="&blfs-book;longindex.html#kernel-config-index"/>. Additional
96 information about configuring and building the kernel can be found at
97 <ulink url=""/> </para>
99 <note>
100 <para>A good starting place for setting up the kernel configuration is to
101 run <command>make defconfig</command>. This will set the base
102 configuration to a good state that takes your current system architecture
103 into account.</para>
105 <para>Be sure to enable/disable/set the following features or the system might
106 not work correctly or boot at all:</para>
108 <screen role="nodump" revision="sysv">Processor type and features ---&gt;
109 [*] Build a relocatable kernel [CONFIG_RELOCATABLE]
110 [*] Randomize the address of the kernel image (KASLR) [CONFIG_RANDOMIZE_BASE]
111General setup ---&gt;
112 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
113 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
114 [ ] Configure standard kernel features (expert users) [CONFIG_EXPERT]
115General architecture-dependent options ---&gt;
116 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
117 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
118Device Drivers ---&gt;
119 Firmware Drivers ---&gt;
120 EFI (Extensible Firmware Interface) Support ---&gt;
121 [*] Enable the generic EFI decompressor [CONFIG_EFI_ZBOOT]
122 Graphics support ---&gt;
123 Frame buffer Devices ---&gt;
124 &lt;*&gt; Support for frame buffer devices ---&gt;
125 Console display driver support ---&gt;
126 [*] Framebuffer Console support [CONFIG_FRAMEBUFFER_CONSOLE]
127 Generic Driver Options ---&gt;
128 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
129 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
130 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]</screen>
132 <screen role="nodump" revision="systemd">Processor type and features ---&gt;
133 [*] Build a relocatable kernel [CONFIG_RELOCATABLE]
134 [*] Randomize the address of the kernel image (KASLR) [CONFIG_RANDOMIZE_BASE]
135General setup ---&gt;
136 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
137 [ ] Auditing Support [CONFIG_AUDIT]
138 CPU/Task time and stats accounting ---&gt;
139 [*] Pressure stall information tracking [CONFIG_PSI]
140 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
141 [*] Control Group support [CONFIG_CGROUPS] ---&gt;
142 [*] Memory controller [CONFIG_MEMCG]
143 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
144 [ ] Configure standard kernel features (expert users) [CONFIG_EXPERT]
145General architecture-dependent options ---&gt;
146 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
147 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
148 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
149Networking support ---&gt;
150 Networking options ---&gt;
151 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
152Device Drivers ---&gt;
153 Generic Driver Options ---&gt;
154 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
155 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
156 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]
157 Firmware Loader ---&gt;
158 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
159 Firmware Drivers ---&gt;
160 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
161 EFI (Extensible Firmware Interface) Support ---&gt;
162 [*] Enable the generic EFI decompressor [CONFIG_EFI_ZBOOT]
163 Graphics support ---&gt;
164 Frame buffer Devices ---&gt;
165 &lt;*&gt; Support for frame buffer devices ---&gt;
166 Console display driver support ---&gt;
167 [*] Framebuffer Console support [CONFIG_FRAMEBUFFER_CONSOLE]
168File systems ---&gt;
169 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
170 Pseudo filesystems ---&gt;
171 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]</screen>
172 </note>
174 <note revision="systemd">
175 <para>While "The IPv6 Protocol" is not strictly
176 required, it is highly recommended by the systemd developers.</para>
177 </note>
179 <para revision="sysv">There are several other options that may be desired
180 depending on the requirements for the system. For a list of options needed
181 for BLFS packages, see the <ulink
182 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
183 Index of Kernel Settings</ulink>
184 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
186 <note>
187 <para>If your host hardware is using UEFI and you wish to boot the
188 LFS system with it, you should adjust some kernel configuration
189 following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
190 the BLFS page</ulink>.</para>
191 </note>
193 <variablelist>
194 <title>The rationale for the above configuration items:</title>
196 <varlistentry>
197 <term><parameter>Randomize the address of the kernel image (KASLR)</parameter></term>
198 <listitem>
199 <para>Enable ASLR for kernel image, to mitigate some attacks based
200 on fixed addresses of sensitive data or code in the kernel.</para>
201 </listitem>
202 </varlistentry>
204 <varlistentry>
205 <term>
206 <parameter>
207 Compile the kernel with warnings as errors
208 </parameter>
209 </term>
210 <listitem>
211 <para>This may cause building failure if the compiler and/or
212 configuration are different from those of the kernel
213 developers.</para>
214 </listitem>
215 </varlistentry>
217 <varlistentry>
218 <term>
219 <parameter>
220 Enable kernel headers through /sys/kernel/kheaders.tar.xz
221 </parameter>
222 </term>
223 <listitem>
224 <para>This will require <command>cpio</command> building the kernel.
225 <command>cpio</command> is not installed by LFS.</para>
226 </listitem>
227 </varlistentry>
229 <varlistentry>
230 <term>
231 <parameter>
232 Configure standard kernel features (expert users)
233 </parameter>
234 </term>
235 <listitem>
236 <para>This will make some options show up in the configuration
237 interface but changing those options may be dangerous. Do not use
238 this unless you know what you are doing.</para>
239 </listitem>
240 </varlistentry>
242 <varlistentry>
243 <term><parameter>Strong Stack Protector</parameter></term>
244 <listitem>
245 <para>Enable SSP for the kernel. We've enabled it for the entire
246 userspace with <parameter>--enable-default-ssp</parameter>
247 configuring GCC, but the kernel does not use GCC default setting
248 for SSP. We enable it explicitly here.</para>
249 </listitem>
250 </varlistentry>
252 <varlistentry>
253 <term><parameter>Support for uevent helper</parameter></term>
254 <listitem>
255 <para>Having this option set may interfere with device
256 management when using Udev/Eudev. </para>
257 </listitem>
258 </varlistentry>
260 <varlistentry>
261 <term><parameter>Maintain a devtmpfs</parameter></term>
262 <listitem>
263 <para>This will create automated device nodes which are populated by the
264 kernel, even without Udev running. Udev then runs on top of this,
265 managing permissions and adding symlinks. This configuration
266 item is required for all users of Udev/Eudev.</para>
267 </listitem>
268 </varlistentry>
270 <varlistentry>
271 <term><parameter>Automount devtmpfs at /dev</parameter></term>
272 <listitem>
273 <para>This will mount the kernel view of the devices on /dev
274 upon switching to root filesystem just before starting
275 init.</para>
276 </listitem>
277 </varlistentry>
279 <varlistentry>
280 <term><parameter>Enable the generic EFI decompressor</parameter></term>
281 <listitem>
282 <para>Create the bootable image as an EFI application that carries
283 the actual kernel image in compressed form. It can make the
284 bootable image 50% smaller.</para>
285 </listitem>
286 </varlistentry>
288 <varlistentry>
289 <term><parameter>Framebuffer Console support</parameter></term>
290 <listitem>
291 <para>This is needed to display the Linux console on a frame
292 buffer device. To allow the kernel to print debug messages at an
293 early boot stage, it shouldn't be built as a kernel module
294 unless an initramfs will be used. And, if
295 <option>CONFIG_DRM</option> (Direct Rendering Manager) is enabled,
296 it's likely <option>CONFIG_DRM_FBDEV_EMULATION</option> (Enable
297 legacy fbdev support for your modesetting driver) should be
298 enabled as well.</para>
299 </listitem>
300 </varlistentry>
302 </variablelist>
304 <para>Alternatively, <command>make oldconfig</command> may be more
305 appropriate in some situations. See the <filename>README</filename>
306 file for more information.</para>
308 <para>If desired, skip kernel configuration by copying the kernel
309 config file, <filename>.config</filename>, from the host system
310 (assuming it is available) to the unpacked <filename
311 class="directory">linux-&linux-version;</filename> directory. However,
312 we do not recommend this option. It is often better to explore all the
313 configuration menus and create the kernel configuration from
314 scratch.</para>
316 <para>Compile the kernel image and modules:</para>
318<screen><userinput remap="make">make</userinput></screen>
320 <para>If using kernel modules, module configuration in <filename
321 class="directory">/etc/modprobe.d</filename> may be required.
322 Information pertaining to modules and kernel configuration is
323 located in <xref linkend="ch-config-udev"/> and in the kernel
324 documentation in the <filename
325 class="directory">linux-&linux-version;/Documentation</filename> directory.
326 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
328 <para>Unless module support has been disabled in the kernel configuration,
329 install the modules with:</para>
331<screen><userinput remap="install">make modules_install</userinput></screen>
333 <para>After kernel compilation is complete, additional steps are
334 required to complete the installation. Some files need to be copied to
335 the <filename class="directory">/boot</filename> directory.</para>
337 <caution>
338 <para>If you've decided to use a separate &boot-dir; partition for the
339 LFS system (maybe sharing a &boot-dir; partition with the host
340 distro) , the files copied below should go there. The easiest way to
341 do that is to create the entry for &boot-dir; in &fstab; first (read
342 the previous section for details), then issue the following command
343 as the &root; user in the
344 <emphasis>chroot environment</emphasis>:</para>
346<screen role="nodump"><userinput>mount /boot</userinput></screen>
348 <para>The path to the device node is omitted in the command because
349 <command>mount</command> can read it from &fstab;.</para>
350 </caution>
352 <para>The path to the kernel image may vary depending on the platform being
353 used. The filename below can be changed to suit your taste, but the stem of
354 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
355 the automatic setup of the boot process described in the next section. The
356 following command assumes an ARM64 architecture with an EFI boot loader
357 (for example, GRUB built in &ch-final;):</para>
359<screen><userinput remap="install">cp -iv arch/arm64/boot/vmlinuz.efi /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
361 <para><filename></filename> is a symbol file for the kernel.
362 It maps the function entry points of every function in the kernel API,
363 as well as the addresses of the kernel data structures for the running
364 kernel. It is used as a resource when investigating kernel problems.
365 Issue the following command to install the map file:</para>
367<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
369 <para>The kernel configuration file <filename>.config</filename>
370 produced by the <command>make menuconfig</command> step
371 above contains all the configuration selections for the kernel
372 that was just compiled. It is a good idea to keep this file for future
373 reference:</para>
375<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
377 <para>Install the documentation for the Linux kernel:</para>
379<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
380cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
382 <para>It is important to note that the files in the kernel source
383 directory are not owned by <emphasis>root</emphasis>. Whenever a
384 package is unpacked as user <emphasis>root</emphasis> (like we did
385 inside chroot), the files have the user and group IDs of whatever
386 they were on the packager's computer. This is usually not a problem
387 for any other package to be installed because the source tree is
388 removed after the installation. However, the Linux source tree is
389 often retained for a long time. Because of this, there is a chance
390 that whatever user ID the packager used will be assigned to somebody
391 on the machine. That person would then have write access to the kernel
392 source.</para>
394 <note>
395 <para>In many cases, the configuration of the kernel will need to be
396 updated for packages that will be installed later in BLFS. Unlike
397 other packages, it is not necessary to remove the kernel source tree
398 after the newly built kernel is installed.</para>
400 <para>If the kernel source tree is going to be retained, run
401 <command>chown -R 0:0</command> on the <filename
402 class="directory">linux-&linux-version;</filename> directory to ensure
403 all files are owned by user <emphasis>root</emphasis>.</para>
404 </note>
406 <warning>
407 <para>Some kernel documentation recommends creating a symlink from
408 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
409 source directory. This is specific to kernels prior to the 2.6 series and
410 <emphasis>must not</emphasis> be created on an LFS system as it can cause
411 problems for packages you may wish to build once your base LFS system is
412 complete.</para>
413 </warning>
415 <warning>
416 <para>The headers in the system's <filename
417 class="directory">include</filename> directory (<filename
418 class="directory">/usr/include</filename>) should
419 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
420 that is, the sanitised headers installed in <xref
421 linkend="ch-tools-linux-headers"/>. Therefore, they should
422 <emphasis>never</emphasis> be replaced by either the raw kernel headers
423 or any other kernel sanitized headers.</para>
424 </warning>
426 </sect2>
428 <sect2 id="conf-modprobe" role="configuration">
429 <title>Configuring Linux Module Load Order</title>
431 <indexterm zone="conf-modprobe">
432 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
433 </indexterm>
435 <para>Most of the time Linux modules are loaded automatically, but
436 sometimes it needs some specific direction. The program that loads
437 modules, <command>modprobe</command> or <command>insmod</command>, uses
438 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
439 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
440 uhci_hcd) have been built as modules, they will be loaded in the correct
441 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
442 to avoid a warning being output at boot time.</para>
444 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
445 the following:</para>
447<screen><userinput>install -v -m755 -d /etc/modprobe.d
448cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
449<literal># Begin /etc/modprobe.d/usb.conf
451install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
452install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
454# End /etc/modprobe.d/usb.conf</literal>
457 </sect2>
459 <sect2 id="contents-kernel" role="content">
460 <title>Contents of Linux</title>
462 <segmentedlist>
463 <segtitle>Installed files</segtitle>
464 <segtitle>Installed directories</segtitle>
466 <seglistitem>
467 <seg>config-&linux-version;,
468 vmlinuz-&linux-version;-lfs-&version;,
469 and;</seg>
470 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
471 </seglistitem>
472 </segmentedlist>
474 <variablelist>
475 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
476 <?dbfo list-presentation="list"?>
477 <?dbhtml list-presentation="table"?>
479 <varlistentry id="config">
480 <term><filename>config-&linux-version;</filename></term>
481 <listitem>
482 <para>Contains all the configuration selections for the kernel</para>
483 <indexterm zone="ch-bootable-kernel config">
484 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
485 </indexterm>
486 </listitem>
487 </varlistentry>
489 <varlistentry id="lfskernel">
490 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
491 <listitem>
492 <para>The engine of the Linux system. When turning on the computer,
493 the kernel is the first part of the operating system that gets loaded.
494 It detects and initializes all components of the computer's hardware,
495 then makes these components available as a tree of files to the
496 software and turns a single CPU into a multitasking machine capable
497 of running scores of programs seemingly at the same time</para>
498 <indexterm zone="ch-bootable-kernel lfskernel">
499 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
500 </indexterm>
501 </listitem>
502 </varlistentry>
504 <varlistentry id="">
505 <term><filename>;</filename></term>
506 <listitem>
507 <para>A list of addresses and symbols; it maps the entry points and
508 addresses of all the functions and data structures in the
509 kernel</para>
510 <indexterm zone="ch-bootable-kernel">
511 <primary sortas="e-/boot/">/boot/;</primary>
512 </indexterm>
513 </listitem>
514 </varlistentry>
516 </variablelist>
518 </sect2>
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