source: chapter10/kernel.xml@ 111194c

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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 <para>Prepare for compilation by running the following command:</para>
49
50<screen><userinput remap="pre">make mrproper</userinput></screen>
51
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>
56
57 <para>There are several ways to configure the kernel options. Usually,
58 This is done through a menu-driven interface, for example:</para>
59
60<screen role="nodump"><userinput>make menuconfig</userinput></screen>
61
62 <variablelist>
63 <title>The meaning of optional make environment variables:</title>
64
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>
71
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>
79
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>
88
89 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
90
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="http://www.kroah.com/lkn/"/> </para>
98
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>
104
105 <para>Be sure to enable/disable/set the following features or the system might
106 not work correctly or boot at all:</para>
107
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]
114General architecture-dependent options ---&gt;
115 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
116 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
117Device Drivers ---&gt;
118 Graphics support ---&gt;
119 Frame buffer Devices ---&gt;
120 &lt;*&gt; Support for frame buffer devices ---&gt;
121 Console display driver support ---&gt;
122 [*] Framebuffer Console support [CONFIG_FRAMEBUFFER_CONSOLE]
123 Generic Driver Options ---&gt;
124 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
125 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
126 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]</screen>
127
128 <screen role="nodump" revision="systemd">Processor type and features ---&gt;
129 [*] Build a relocatable kernel [CONFIG_RELOCATABLE]
130 [*] Randomize the address of the kernel image (KASLR) [CONFIG_RANDOMIZE_BASE]
131General setup ---&gt;
132 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
133 [ ] Auditing Support [CONFIG_AUDIT]
134 CPU/Task time and stats accounting ---&gt;
135 [*] Pressure stall information tracking [CONFIG_PSI]
136 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
137 [*] Control Group support [CONFIG_CGROUPS] ---&gt;
138 [*] Memory controller [CONFIG_MEMCG]
139 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
140 [*] Configure standard kernel features (expert users) [CONFIG_EXPERT] ---&gt;
141 [*] open by fhandle syscalls [CONFIG_FHANDLE]
142General architecture-dependent options ---&gt;
143 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
144 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
145 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
146Networking support ---&gt;
147 Networking options ---&gt;
148 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
149Device Drivers ---&gt;
150 Generic Driver Options ---&gt;
151 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
152 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
153 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]
154 Firmware Loader ---&gt;
155 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
156 Firmware Drivers ---&gt;
157 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
158 Graphics support ---&gt;
159 Frame buffer Devices ---&gt;
160 &lt;*&gt; Support for frame buffer devices ---&gt;
161 Console display driver support ---&gt;
162 [*] Framebuffer Console support [CONFIG_FRAMEBUFFER_CONSOLE]
163File systems ---&gt;
164 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
165 Pseudo filesystems ---&gt;
166 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]</screen>
167 </note>
168
169 <note revision="systemd">
170 <para>While "The IPv6 Protocol" is not strictly
171 required, it is highly recommended by the systemd developers.</para>
172 </note>
173
174 <para revision="sysv">There are several other options that may be desired
175 depending on the requirements for the system. For a list of options needed
176 for BLFS packages, see the <ulink
177 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
178 Index of Kernel Settings</ulink>
179 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</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>.</para>
186 </note>
187
188 <variablelist>
189 <title>The rationale for the above configuration items:</title>
190
191 <varlistentry>
192 <term><parameter>Randomize the address of the kernel image (KASLR)</parameter></term>
193 <listitem>
194 <para>Enable ASLR for kernel image, to mitigate some attacks based
195 on fixed addresses of sensitive data or code in the kernel.</para>
196 </listitem>
197 </varlistentry>
198
199 <varlistentry>
200 <term>
201 <parameter>
202 Compile the kernel with warnings as errors
203 </parameter>
204 </term>
205 <listitem>
206 <para>This may cause building failure if the compiler and/or
207 configuration are different from those of the kernel
208 developers.</para>
209 </listitem>
210 </varlistentry>
211
212 <varlistentry>
213 <term>
214 <parameter>
215 Enable kernel headers through /sys/kernel/kheaders.tar.xz
216 </parameter>
217 </term>
218 <listitem>
219 <para>This will require <command>cpio</command> building the kernel.
220 <command>cpio</command> is not installed by LFS.</para>
221 </listitem>
222 </varlistentry>
223
224 <varlistentry>
225 <term><parameter>Strong Stack Protector</parameter></term>
226 <listitem>
227 <para>Enable SSP for the kernel. We've enabled it for the entire
228 userspace with <parameter>--enable-default-ssp</parameter>
229 configuring GCC, but the kernel does not use GCC default setting
230 for SSP. We enable it explicitly here.</para>
231 </listitem>
232 </varlistentry>
233
234 <varlistentry>
235 <term><parameter>Support for uevent helper</parameter></term>
236 <listitem>
237 <para>Having this option set may interfere with device
238 management when using Udev/Eudev. </para>
239 </listitem>
240 </varlistentry>
241
242 <varlistentry>
243 <term><parameter>Maintain a devtmpfs</parameter></term>
244 <listitem>
245 <para>This will create automated device nodes which are populated by the
246 kernel, even without Udev running. Udev then runs on top of this,
247 managing permissions and adding symlinks. This configuration
248 item is required for all users of Udev/Eudev.</para>
249 </listitem>
250 </varlistentry>
251
252 <varlistentry>
253 <term><parameter>Automount devtmpfs at /dev</parameter></term>
254 <listitem>
255 <para>This will mount the kernel view of the devices on /dev
256 upon switching to root filesystem just before starting
257 init.</para>
258 </listitem>
259 </varlistentry>
260
261 <varlistentry>
262 <term><parameter>Framebuffer Console support</parameter></term>
263 <listitem>
264 <para>This is needed to display the Linux console on a frame
265 buffer device. To allow the kernel to print debug messages at an
266 early boot stage, it shouldn't be built as a kernel module
267 unless an initramfs will be used. And, if
268 <option>CONFIG_DRM</option> (Direct Rendering Manager) is enabled,
269 it's likely <option>CONFIG_DRM_FBDEV_EMULATION</option> (Enable
270 legacy fbdev support for your modesetting driver) should be
271 enabled as well.</para>
272 </listitem>
273 </varlistentry>
274
275 </variablelist>
276
277 <para>Alternatively, <command>make oldconfig</command> may be more
278 appropriate in some situations. See the <filename>README</filename>
279 file for more information.</para>
280
281 <para>If desired, skip kernel configuration by copying the kernel
282 config file, <filename>.config</filename>, from the host system
283 (assuming it is available) to the unpacked <filename
284 class="directory">linux-&linux-version;</filename> directory. However,
285 we do not recommend this option. It is often better to explore all the
286 configuration menus and create the kernel configuration from
287 scratch.</para>
288
289 <para>Compile the kernel image and modules:</para>
290
291<screen><userinput remap="make">make</userinput></screen>
292
293 <para>If using kernel modules, module configuration in <filename
294 class="directory">/etc/modprobe.d</filename> may be required.
295 Information pertaining to modules and kernel configuration is
296 located in <xref linkend="ch-config-udev"/> and in the kernel
297 documentation in the <filename
298 class="directory">linux-&linux-version;/Documentation</filename> directory.
299 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
300
301 <para>Unless module support has been disabled in the kernel configuration,
302 install the modules with:</para>
303
304<screen><userinput remap="install">make modules_install</userinput></screen>
305
306 <para>After kernel compilation is complete, additional steps are
307 required to complete the installation. Some files need to be copied to
308 the <filename class="directory">/boot</filename> directory.</para>
309
310 <caution>
311 <para>If you've decided to use a separate &boot-dir; partition for the
312 LFS system (maybe sharing a &boot-dir; partition with the host
313 distro) , the files copied below should go there. The easiest way to
314 do that is to create the entry for &boot-dir; in &fstab; first (read
315 the previous section for details), then issue the following command
316 as the &root; user in the
317 <emphasis>chroot environment</emphasis>:</para>
318
319<screen role="nodump"><userinput>mount /boot</userinput></screen>
320
321 <para>The path to the device node is omitted in the command because
322 <command>mount</command> can read it from &fstab;.</para>
323 </caution>
324
325 <para>The path to the kernel image may vary depending on the platform being
326 used. The filename below can be changed to suit your taste, but the stem of
327 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
328 the automatic setup of the boot process described in the next section. The
329 following command assumes an ARM64 architecture:</para>
330
331<screen><userinput remap="install">cp -iv arch/arm64/boot/Image /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
332
333 <para><filename>System.map</filename> is a symbol file for the kernel.
334 It maps the function entry points of every function in the kernel API,
335 as well as the addresses of the kernel data structures for the running
336 kernel. It is used as a resource when investigating kernel problems.
337 Issue the following command to install the map file:</para>
338
339<screen><userinput remap="install">cp -iv System.map /boot/System.map-&linux-version;</userinput></screen>
340
341 <para>The kernel configuration file <filename>.config</filename>
342 produced by the <command>make menuconfig</command> step
343 above contains all the configuration selections for the kernel
344 that was just compiled. It is a good idea to keep this file for future
345 reference:</para>
346
347<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
348
349 <para>Install the documentation for the Linux kernel:</para>
350
351<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
352cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
353
354 <para>It is important to note that the files in the kernel source
355 directory are not owned by <emphasis>root</emphasis>. Whenever a
356 package is unpacked as user <emphasis>root</emphasis> (like we did
357 inside chroot), the files have the user and group IDs of whatever
358 they were on the packager's computer. This is usually not a problem
359 for any other package to be installed because the source tree is
360 removed after the installation. However, the Linux source tree is
361 often retained for a long time. Because of this, there is a chance
362 that whatever user ID the packager used will be assigned to somebody
363 on the machine. That person would then have write access to the kernel
364 source.</para>
365
366 <note>
367 <para>In many cases, the configuration of the kernel will need to be
368 updated for packages that will be installed later in BLFS. Unlike
369 other packages, it is not necessary to remove the kernel source tree
370 after the newly built kernel is installed.</para>
371
372 <para>If the kernel source tree is going to be retained, run
373 <command>chown -R 0:0</command> on the <filename
374 class="directory">linux-&linux-version;</filename> directory to ensure
375 all files are owned by user <emphasis>root</emphasis>.</para>
376 </note>
377
378 <warning>
379 <para>Some kernel documentation recommends creating a symlink from
380 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
381 source directory. This is specific to kernels prior to the 2.6 series and
382 <emphasis>must not</emphasis> be created on an LFS system as it can cause
383 problems for packages you may wish to build once your base LFS system is
384 complete.</para>
385 </warning>
386
387 <warning>
388 <para>The headers in the system's <filename
389 class="directory">include</filename> directory (<filename
390 class="directory">/usr/include</filename>) should
391 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
392 that is, the sanitised headers installed in <xref
393 linkend="ch-tools-linux-headers"/>. Therefore, they should
394 <emphasis>never</emphasis> be replaced by either the raw kernel headers
395 or any other kernel sanitized headers.</para>
396 </warning>
397
398 </sect2>
399
400 <sect2 id="conf-modprobe" role="configuration">
401 <title>Configuring Linux Module Load Order</title>
402
403 <indexterm zone="conf-modprobe">
404 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
405 </indexterm>
406
407 <para>Most of the time Linux modules are loaded automatically, but
408 sometimes it needs some specific direction. The program that loads
409 modules, <command>modprobe</command> or <command>insmod</command>, uses
410 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
411 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
412 uhci_hcd) have been built as modules, they will be loaded in the correct
413 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
414 to avoid a warning being output at boot time.</para>
415
416 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
417 the following:</para>
418
419<screen><userinput>install -v -m755 -d /etc/modprobe.d
420cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
421<literal># Begin /etc/modprobe.d/usb.conf
422
423install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
424install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
425
426# End /etc/modprobe.d/usb.conf</literal>
427EOF</userinput></screen>
428
429 </sect2>
430
431 <sect2 id="contents-kernel" role="content">
432 <title>Contents of Linux</title>
433
434 <segmentedlist>
435 <segtitle>Installed files</segtitle>
436 <segtitle>Installed directories</segtitle>
437
438 <seglistitem>
439 <seg>config-&linux-version;,
440 vmlinuz-&linux-version;-lfs-&version;,
441 and System.map-&linux-version;</seg>
442 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
443 </seglistitem>
444 </segmentedlist>
445
446 <variablelist>
447 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
448 <?dbfo list-presentation="list"?>
449 <?dbhtml list-presentation="table"?>
450
451 <varlistentry id="config">
452 <term><filename>config-&linux-version;</filename></term>
453 <listitem>
454 <para>Contains all the configuration selections for the kernel</para>
455 <indexterm zone="ch-bootable-kernel config">
456 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
457 </indexterm>
458 </listitem>
459 </varlistentry>
460
461 <varlistentry id="lfskernel">
462 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
463 <listitem>
464 <para>The engine of the Linux system. When turning on the computer,
465 the kernel is the first part of the operating system that gets loaded.
466 It detects and initializes all components of the computer's hardware,
467 then makes these components available as a tree of files to the
468 software and turns a single CPU into a multitasking machine capable
469 of running scores of programs seemingly at the same time</para>
470 <indexterm zone="ch-bootable-kernel lfskernel">
471 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
472 </indexterm>
473 </listitem>
474 </varlistentry>
475
476 <varlistentry id="System.map">
477 <term><filename>System.map-&linux-version;</filename></term>
478 <listitem>
479 <para>A list of addresses and symbols; it maps the entry points and
480 addresses of all the functions and data structures in the
481 kernel</para>
482 <indexterm zone="ch-bootable-kernel System.map">
483 <primary sortas="e-/boot/System.map">/boot/System.map-&linux-version;</primary>
484 </indexterm>
485 </listitem>
486 </varlistentry>
487
488 </variablelist>
489
490 </sect2>
491
492</sect1>
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