source: chapter10/kernel.xml@ 1203312

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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">General setup -->
109 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
110 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
111Device Drivers ---&gt;
112 Graphics support ---&gt;
113 Frame buffer Devices ---&gt;
114 [*] Support for frame buffer devices ----
115 Generic Driver Options ---&gt;
116 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
117 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
118 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]</screen>
119
120 <screen role="nodump" revision="systemd">General setup -->
121 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
122 [ ] Auditing Support [CONFIG_AUDIT]
123 CPU/Task time and stats accounting ---&gt;
124 [*] Pressure stall information tracking [CONFIG_PSI]
125 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
126 [*] Control Group support [CONFIG_CGROUPS] ---&gt;
127 [*] Memory controller [CONFIG_MEMCG]
128 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
129 [*] Configure standard kernel features (expert users) [CONFIG_EXPERT] ---&gt;
130 [*] open by fhandle syscalls [CONFIG_FHANDLE]
131General architecture-dependent options ---&gt;
132 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
133Networking support ---&gt;
134 Networking options ---&gt;
135 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
136Device Drivers ---&gt;
137 Generic Driver Options ---&gt;
138 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
139 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
140 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]
141 Firmware Loader ---&gt;
142 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
143 Firmware Drivers ---&gt;
144 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
145 Graphics support ---&gt;
146 Frame buffer Devices ---&gt;
147 &lt;*&gt; Support for frame buffer devices ---&gt;
148File systems ---&gt;
149 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
150 Pseudo filesystems ---&gt;
151 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]</screen>
152
153 <para>Enable some additional features if you are building a 64-bit
154 system. If you are using menuconfig, enable them in the order of
155 <parameter>CONFIG_PCI_MSI</parameter> first, then
156 <parameter>CONFIG_IRQ_REMAP</parameter>, at last
157 <parameter>CONFIG_X86_X2APIC</parameter> because an option only
158 shows up after its dependencies are selected.</para>
159
160 <screen role="nodump">Processor type and features ---&gt;
161 [*] Support x2apic [CONFIG_X86_X2APIC]
162Memory Management options ---&gt;
163 [ ] Enable userfaultfd() system call [CONFIG_USERFAULTFD]
164Device Drivers ---&gt;
165 [*] PCI Support ---&gt; [CONFIG_PCI]
166 [*] Message Signaled Interrupts (MSI and MSI-X) [CONFIG_PCI_MSI]
167 [*] IOMMU Hardware Support ---&gt; [CONFIG_IOMMU_SUPPORT]
168 [*] Support for Interrupt Remapping [CONFIG_IRQ_REMAP]</screen>
169 </note>
170
171 <note revision="systemd">
172 <para>While "The IPv6 Protocol" is not strictly
173 required, it is highly recommended by the systemd developers.</para>
174 </note>
175
176 <para revision="sysv">There are several other options that may be desired
177 depending on the requirements for the system. For a list of options needed
178 for BLFS packages, see the <ulink
179 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
180 Index of Kernel Settings</ulink>
181 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
182
183 <note>
184 <para>If your host hardware is using UEFI and you wish to boot the
185 LFS system with it, you should adjust some kernel configuration
186 following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
187 the BLFS page</ulink>.</para>
188 </note>
189
190 <variablelist>
191 <title>The rationale for the above configuration items:</title>
192
193 <varlistentry>
194 <term>
195 <parameter>
196 Compile the kernel with warnings as errors
197 </parameter>
198 </term>
199 <listitem>
200 <para>This may cause building failure if the compiler and/or
201 configuration are different from those of the kernel
202 developers.</para>
203 </listitem>
204 </varlistentry>
205
206 <varlistentry>
207 <term>
208 <parameter>
209 Enable kernel headers through /sys/kernel/kheaders.tar.xz
210 </parameter>
211 </term>
212 <listitem>
213 <para>This will require <command>cpio</command> building the kernel.
214 <command>cpio</command> is not installed by LFS.</para>
215 </listitem>
216 </varlistentry>
217
218 <varlistentry>
219 <term><parameter>Support for uevent helper</parameter></term>
220 <listitem>
221 <para>Having this option set may interfere with device
222 management when using Udev/Eudev. </para>
223 </listitem>
224 </varlistentry>
225
226 <varlistentry>
227 <term><parameter>Maintain a devtmpfs</parameter></term>
228 <listitem>
229 <para>This will create automated device nodes which are populated by the
230 kernel, even without Udev running. Udev then runs on top of this,
231 managing permissions and adding symlinks. This configuration
232 item is required for all users of Udev/Eudev.</para>
233 </listitem>
234 </varlistentry>
235
236 <varlistentry>
237 <term><parameter>Automount devtmpfs at /dev</parameter></term>
238 <listitem>
239 <para>This will mount the kernel view of the devices on /dev
240 upon switching to root filesystem just before starting
241 init.</para>
242 </listitem>
243 </varlistentry>
244
245 <varlistentry>
246 <term><parameter>Support x2apic</parameter></term>
247 <listitem>
248 <para>Support running the interrupt controller of 64-bit x86
249 processors in x2APIC mode. x2APIC may be enabled by firmware on
250 64-bit x86 systems, and a kernel without this option enabled will
251 panic on boot if x2APIC is enabled by firmware. This option has
252 has no effect, but also does no harm if x2APIC is disabled by the
253 firmware.</para>
254 </listitem>
255 </varlistentry>
256
257 <varlistentry>
258 <term><parameter>Enable userfaultfd() system call</parameter></term>
259 <listitem>
260 <para>If this option is enabled, a security vulnerability not
261 resolved in Linux-&linux-version; yet will be exploitable.
262 Disable this option to avoid the vulnerability. This system call
263 is not used by any part of LFS or BLFS.</para>
264 </listitem>
265 </varlistentry>
266
267 </variablelist>
268
269 <para>Alternatively, <command>make oldconfig</command> may be more
270 appropriate in some situations. See the <filename>README</filename>
271 file for more information.</para>
272
273 <para>If desired, skip kernel configuration by copying the kernel
274 config file, <filename>.config</filename>, from the host system
275 (assuming it is available) to the unpacked <filename
276 class="directory">linux-&linux-version;</filename> directory. However,
277 we do not recommend this option. It is often better to explore all the
278 configuration menus and create the kernel configuration from
279 scratch.</para>
280
281 <para>Compile the kernel image and modules:</para>
282
283<screen><userinput remap="make">make</userinput></screen>
284
285 <para>If using kernel modules, module configuration in <filename
286 class="directory">/etc/modprobe.d</filename> may be required.
287 Information pertaining to modules and kernel configuration is
288 located in <xref linkend="ch-config-udev"/> and in the kernel
289 documentation in the <filename
290 class="directory">linux-&linux-version;/Documentation</filename> directory.
291 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
292
293 <para>Unless module support has been disabled in the kernel configuration,
294 install the modules with:</para>
295
296<screen><userinput remap="install">make modules_install</userinput></screen>
297
298 <para>After kernel compilation is complete, additional steps are
299 required to complete the installation. Some files need to be copied to
300 the <filename class="directory">/boot</filename> directory.</para>
301
302 <caution>
303 <para>As the cross-built LFS system has a separate /boot partition,
304 the files copied below should go there. The easiest way to do that is
305 to mount <filename class="directory">/boot</filename> before
306 proceeding. As the &root; user:</para>
307
308<screen role="nodump"><userinput>mount /boot</userinput></screen>
309
310 <para>We don't need to specify the path to the device node, as it's
311 already given in <filename>/etc/fstab</filename>.</para>
312 </caution>
313
314 <para>The path to the kernel image may vary depending on the platform being
315 used. The filename below can be changed to suit your taste, but the stem of
316 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
317 the automatic setup of the boot process described in the next section. The
318 following command assumes an x86 architecture:</para>
319
320<screen><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
321
322 <para><filename>System.map</filename> is a symbol file for the kernel.
323 It maps the function entry points of every function in the kernel API,
324 as well as the addresses of the kernel data structures for the running
325 kernel. It is used as a resource when investigating kernel problems.
326 Issue the following command to install the map file:</para>
327
328<screen><userinput remap="install">cp -iv System.map /boot/System.map-&linux-version;</userinput></screen>
329
330 <para>The kernel configuration file <filename>.config</filename>
331 produced by the <command>make menuconfig</command> step
332 above contains all the configuration selections for the kernel
333 that was just compiled. It is a good idea to keep this file for future
334 reference:</para>
335
336<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
337
338 <para>Install the documentation for the Linux kernel:</para>
339
340<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
341cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
342
343 <para>It is important to note that the files in the kernel source
344 directory are not owned by <emphasis>root</emphasis>. Whenever a
345 package is unpacked as user <emphasis>root</emphasis> (like we did
346 inside chroot), the files have the user and group IDs of whatever
347 they were on the packager's computer. This is usually not a problem
348 for any other package to be installed because the source tree is
349 removed after the installation. However, the Linux source tree is
350 often retained for a long time. Because of this, there is a chance
351 that whatever user ID the packager used will be assigned to somebody
352 on the machine. That person would then have write access to the kernel
353 source.</para>
354
355 <note>
356 <para>In many cases, the configuration of the kernel will need to be
357 updated for packages that will be installed later in BLFS. Unlike
358 other packages, it is not necessary to remove the kernel source tree
359 after the newly built kernel is installed.</para>
360
361 <para>If the kernel source tree is going to be retained, run
362 <command>chown -R 0:0</command> on the <filename
363 class="directory">linux-&linux-version;</filename> directory to ensure
364 all files are owned by user <emphasis>root</emphasis>.</para>
365 </note>
366
367 <warning>
368 <para>Some kernel documentation recommends creating a symlink from
369 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
370 source directory. This is specific to kernels prior to the 2.6 series and
371 <emphasis>must not</emphasis> be created on an LFS system as it can cause
372 problems for packages you may wish to build once your base LFS system is
373 complete.</para>
374 </warning>
375
376 <warning>
377 <para>The headers in the system's <filename
378 class="directory">include</filename> directory (<filename
379 class="directory">/usr/include</filename>) should
380 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
381 that is, the sanitised headers installed in <xref
382 linkend="ch-tools-linux-headers"/>. Therefore, they should
383 <emphasis>never</emphasis> be replaced by either the raw kernel headers
384 or any other kernel sanitized headers.</para>
385 </warning>
386
387 </sect2>
388
389 <sect2 id="conf-modprobe" role="configuration">
390 <title>Configuring Linux Module Load Order</title>
391
392 <indexterm zone="conf-modprobe">
393 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
394 </indexterm>
395
396 <para>Most of the time Linux modules are loaded automatically, but
397 sometimes it needs some specific direction. The program that loads
398 modules, <command>modprobe</command> or <command>insmod</command>, uses
399 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
400 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
401 uhci_hcd) have been built as modules, they will be loaded in the correct
402 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
403 to avoid a warning being output at boot time.</para>
404
405 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
406 the following:</para>
407
408<screen><userinput>install -v -m755 -d /etc/modprobe.d
409cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
410<literal># Begin /etc/modprobe.d/usb.conf
411
412install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
413install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
414
415# End /etc/modprobe.d/usb.conf</literal>
416EOF</userinput></screen>
417
418 </sect2>
419
420 <sect2 id="contents-kernel" role="content">
421 <title>Contents of Linux</title>
422
423 <segmentedlist>
424 <segtitle>Installed files</segtitle>
425 <segtitle>Installed directories</segtitle>
426
427 <seglistitem>
428 <seg>config-&linux-version;,
429 vmlinuz-&linux-version;-lfs-&version;,
430 and System.map-&linux-version;</seg>
431 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
432 </seglistitem>
433 </segmentedlist>
434
435 <variablelist>
436 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
437 <?dbfo list-presentation="list"?>
438 <?dbhtml list-presentation="table"?>
439
440 <varlistentry id="config">
441 <term><filename>config-&linux-version;</filename></term>
442 <listitem>
443 <para>Contains all the configuration selections for the kernel</para>
444 <indexterm zone="ch-bootable-kernel config">
445 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
446 </indexterm>
447 </listitem>
448 </varlistentry>
449
450 <varlistentry id="lfskernel">
451 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
452 <listitem>
453 <para>The engine of the Linux system. When turning on the computer,
454 the kernel is the first part of the operating system that gets loaded.
455 It detects and initializes all components of the computer's hardware,
456 then makes these components available as a tree of files to the
457 software and turns a single CPU into a multitasking machine capable
458 of running scores of programs seemingly at the same time</para>
459 <indexterm zone="ch-bootable-kernel lfskernel">
460 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
461 </indexterm>
462 </listitem>
463 </varlistentry>
464
465 <varlistentry id="System.map">
466 <term><filename>System.map-&linux-version;</filename></term>
467 <listitem>
468 <para>A list of addresses and symbols; it maps the entry points and
469 addresses of all the functions and data structures in the
470 kernel</para>
471 <indexterm zone="ch-bootable-kernel System.map">
472 <primary sortas="e-/boot/System.map">/boot/System.map-&linux-version;</primary>
473 </indexterm>
474 </listitem>
475 </varlistentry>
476
477 </variablelist>
478
479 </sect2>
480
481</sect1>
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