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1 <?xml version='1.0' encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/genkernel.xml,v 1.18 2005/07/25 20:28:53 plasmaroo Exp $ -->
3 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
5 <guide link="/doc/en/genkernel.xml">
6 <title>Gentoo Linux Genkernel Guide</title>
8 <author title="Author">
9 <mail link="plasmaroo@gentoo.org">Tim Yamin</mail>
10 </author>
12 <!-- folajimi@speakeasy.net -->
13 <author title="Contributor">
14 Jimi Ayodele
15 </author>
17 <!-- thseiler@gmail.com -->
18 <author title="NFS Support">
19 Thomas Seiler
20 </author>
22 <abstract>
23 This guide intends to provide a reference of all the functions provided by
24 genkernel.
25 </abstract>
27 <license/>
29 <version>1.3</version>
30 <date>2005-07-24</date>
32 <chapter>
33 <title>Introduction</title>
34 <section>
35 <title>Rationale</title>
36 <body>
38 <p>
39 For users who are not privy to kernel compilation, genkernel is a tool to
40 automate this process. It can help you create a kernel image akin to those
41 available on Gentoo Installation CDs, which are designed to auto-detect the
42 hardware configuration of your system. Some users may also be interested in
43 using genkernel for hardware requiring initialization and a working kernel
44 before the system starts up. Since genkernel automatically compiles your kernel
45 modules, you can use hardware that may require certain module parameters to be
46 loaded for proper operation.
47 </p>
49 </body>
50 </section>
52 <section>
53 <title>Target Audience</title>
54 <body>
56 <p>
57 If you are either uncertain about how to compile a kernel, or are just
58 unfamiliar with your hardware configuration, genkernel is a very handy tool.
59 It is designed to take the pain out of the kernel compiling process, and
60 supports most hardware by default.
61 </p>
63 <p>
64 However, if you know what drivers are required by your system, you may be able
65 to further reduce the time taken to compile the kernel. This is possible since
66 you can direct genkernel to only build drivers relevant to your hardware.
67 Oftentimes, the number of drivers required by your system will be fewer
68 (implying a shorter kernel compilation time) than the default configuration
69 provides.
70 </p>
72 </body>
73 </section>
74 <section>
75 <title>Installing genkernel</title>
76 <body>
78 <p>
79 To obtain genkernel, run <c>emerge genkernel</c> from the command line. If you
80 are using the
81 <uri link="http://www.gentoo.org/doc/en/handbook/2005.0/hb-install-about.xml#doc_chap2_sect1">
82 Gentoo Reference Platform</uri> (GRP), remember to install binary packages by
83 passing the <c>-k</c> flag to emerge. Since the GRP is bundled with an older
84 version of genkernel, the flags may be different. In any case, consult
85 <c>genkernel --help</c> for help on how to use the version of genkernel
86 installed on your system.
87 </p>
89 </body>
90 </section>
91 </chapter>
93 <chapter>
94 <title>Working with genkernel</title>
95 <section>
96 <title>How to use genkernel</title>
97 <body>
99 <p>
100 Although there are several ways to run genkernel, the least-intrusive approach
101 is provided by <c>genkernel all</c>. Here, a generic configuration which works
102 well for most systems is used. As was mentioned earlier, this approach is not
103 without drawbacks; most of the modules created are useless to the average user
104 and may increase compile time. Below is an illustration of a more efficient
105 approach, achieved by passing certain flags to genkernel as root:
106 </p>
108 <pre caption="Running genkernel (with flags)">
109 # genkernel --bootsplash --no-install --no-clean --menuconfig all
110 </pre>
112 <p>
113 The above operation causes genkernel to create a bootsplash-enabled kernel
114 (<c>--bootsplash</c>) that will have to be manually installed
115 (<c>--no-install</c>). While preparing the kernel source tree, genkernel will
116 refrain from cleaning out any preexisting object files present in the source
117 tree (<c>--no-clean</c>). A menu-driven kernel configuration utility will be
118 displayed that allows the user to select which modules will be built for the
119 system (<c>--menuconfig</c>).
120 </p>
122 <p>
123 There are other flags which alter the result provided by genkernel. For
124 instance, replacing <c>--no install</c> with the <c>--install</c> flag allows
125 genkernel to automatically install the new kernel in the <path>/boot</path>
126 directory. Using the <c>--mountboot</c> flag allows genkernel to mount your
127 <path>/boot</path> partition automatically, if necessary.
128 </p>
130 <p>
131 Remember, genkernel is designed to make kernel compilation easy and
132 stress-free. For this reason, genkernel features several flags to ease the
133 kernel compilation effort. For example, there are flags to help with kernel
134 configuration, while others affect the actual compilation. Some flags even help
135 debug the compilation process. For those interested in further optimization,
136 there are flags that affect kernel assembling, packaging and even kernel
137 initialization.
138 </p>
140 <p>
141 The rest of this chapter examines the functionality of various flags and
142 actions available for genkernel. Some of the flags have variants which perform
143 a converse operation. The converse variants carry the <b><c>no-</c></b> prefix,
144 and their effects are enclosed within the square brackets, [].
145 </p>
147 </body>
148 </section>
150 <section>
151 <title>Configuration Flags</title>
152 <body>
154 <p>
155 The configuration flags listed below exist to help you decide what features
156 should be enabled or disabled in the kernel prior to compilation. You can even
157 choose whether or not the configuration file created in the process should be
158 saved. The following are the primary configuration flags:
159 </p>
161 <ul>
162 <li>
163 <b>--<c>no-</c>menuconfig</b>: Activates <e>[or deactivates]</e> the
164 <c>make menuconfig</c> command (which invokes an interactive, menu-based
165 kernel configuration utility), before building the kernel.
166 </li>
167 <li>
168 <b>--gconfig</b>: Provides a kernel configuration utility which depends
169 on the GTK+ libraries. The advantage of this option is that most users
170 find it easier and clearer to configure the kernel using this tool, since
171 it relies on the X-windowing system. The disadvantage of this option is
172 that you <b>need</b> the X-windowing system to use it, so it will not
173 work on the command line.
174 </li>
175 <li>
176 <b>--xconfig</b>: Provides a kernel configuration utility which depends
177 on the QT libraries. The advantage of this option is that most users find
178 it easier and clearer to configure the kernel using this tool, since it
179 relies on the X-windowing system. The disadvantage of this option is that
180 you <b>need</b> the X-windowing system to use it, so it will not work on
181 the command line.
182 </li>
183 <li>
184 <b>--<c>no-</c>save-config</b>: Saves [or does not save] the kernel
185 configuration to a file in the <path>/etc/kernels/</path> directory for
186 later use.
187 </li>
188 </ul>
190 </body>
191 </section>
193 <section>
194 <title>Compilation Flags</title>
195 <body>
197 <p>
198 The following flags usually take effect during the actual compilation:
199 </p>
201 <ul>
202 <li>
203 <b>--kerneldir=<path>/path/to/sources/</path></b>: Specifies an
204 alternative kernel source location, rather than the default
205 <path>/usr/src/linux/</path> location.
206 </li>
207 <li>
208 <b>--kernel-config=<path>/path/to/config-file</path></b>: Specifies what
209 alternative kernel configuration will be used, rather than the default
210 <path>/path/to/sources/.config</path> file.
211 </li>
212 <li>
213 <b>--module-prefix=<path>/path/to/prefix-directory/</path></b>: Specifies
214 a prefix to the directory where kernel modules will be installed (default
215 path is the <path>/lib/modules/</path> directory.)
216 </li>
217 </ul>
219 <ul>
220 <li>
221 <b>--<c>no-</c>clean</b>: Activates <e>[or deactivates]</e> the
222 <c>make clean</c> command before compiling your kernel. The
223 <c>make clean</c> command removes all object files and dependencies from
224 the kernel's source tree.
225 </li>
226 <li>
227 <b>--<c>no-</c>mrproper</b>: Activates <e>[or deactivates]</e> the
228 <c>make mrproper</c> command before kernel compilation. Like the
229 <c>make clean</c> command, <c>make mrproper</c> removes all object files
230 and dependencies from the kernel's source tree. However, any previous
231 configuration files (in <path>/path/to/sources/.config</path> or
232 <path>/path/to/sources/.config.old</path>) will <b>also</b> be purged
233 from the kernel's source tree.
234 </li>
235 <li>
236 <b>--oldconfig</b>: Issues the <c>make oldconfig</c> command, which
237 attempts to collect configuration information for the system's
238 architecture from a generic script in <path>/usr/share/genkernel/</path>.
239 This is a non-interactive process; no user input is entertained. Also, if
240 <c>--oldconfig</c> is used in conjunction with <c>--clean</c>, the latter
241 flag is negated, resulting in the activation of the <c>--no-clean</c>
242 flag.
243 </li>
244 </ul>
246 <ul>
247 <li>
248 <b>--callback="<c>echo hello</c>"</b>: Calls the specified arguments
249 (<c>echo hello</c>, in this case) after the kernel and the relevant
250 modules have been built, but before building the initrd image. This may
251 be useful if you want to install external modules in the initrd image by
252 emerging the relevant item(s) with the callback feature, and then
253 redefining a genkernel module group.
254 </li>
255 </ul>
257 <ul>
258 <li>
259 <b>--<c>no-</c>install</b>: Activates <e>[or deactivates]</e> the
260 <c>make install</c> command, which installs your new kernel image,
261 configuration file, initrd image and system map onto your mounted boot
262 partition. Any compiled modules will be installed as well.
263 </li>
264 <li>
265 <b>--<c>no-</c>initrdmodules</b>: Refrains from copying any modules to
266 the genkernel-created initrd image. This flag is an exception to the rule
267 about the <c>no-</c> prefix; omission of this prefix creates an invalid
268 genkernel flag.
269 </li>
270 <li>
271 <b>--genzimage</b>: Creates the initrd image, prior to the kernel image.
272 (This hack currently applies only to PPC Pegasos systems.)
273 </li>
274 </ul>
276 </body>
277 </section>
279 <section>
280 <title>Compiler Flags</title>
281 <body>
283 <p>
284 The following flags are supported by genkernel, and are passed to the relevant
285 applications while the kernel is being assembled. These flags affect the
286 <e>compiler</e> used for the kernel compilation process, albeit at a much lower
287 level.
288 </p>
290 <ul>
291 <li>
292 <b>--kernel-cc=<c>someCompiler</c></b>: Specifies the compiler employed
293 during the kernel compilation process.
294 </li>
295 <li>
296 <b>--kernel-ld=<c>someLinker</c></b>: Specifies the linker employed
297 during the kernel compilation process.
298 </li>
299 <li>
300 <b>--kernel-as=<c>someAssembler</c></b>: Specifies the assembler employed
301 during the kernel compilation process.
302 </li>
303 <li>
304 <b>--kernel-make=<c>someMake</c></b>: Specifies an alternative to the
305 <e>GNU make</e> utility employed during the kernel compilation process.
306 </li>
307 </ul>
309 <ul>
310 <li>
311 <b>--utils-cc=<c>someCompiler</c></b>: Specifies the compiler employed
312 during the compilation of support utilities.
313 </li>
314 <li>
315 <b>--utils-ld=<c>someLinker</c></b>: Specifies the linker employed during
316 the compilation of support utilities.
317 </li>
318 <li>
319 <b>--utils-as=<c>someAssembler</c></b>: Specifies the assembler employed
320 during the compilation of support utilities.
321 </li>
322 <li>
323 <b>--utils-make=<c>someMake</c></b>: Specifies an alternative to the
324 <e>GNU make</e> utility employed during the compilation of support
325 utilities.
326 </li>
327 </ul>
329 <ul>
330 <li>
331 <b>--makeopts=<c>-jX</c></b>: Specifies the number of concurrent threads
332 that the make utility can implement while the kernel (and utilities) are
333 being compiled. The variable <b>'X'</b> is a number obtained by adding
334 one (1) to the number of CPUs used by the system. So, for a system with
335 one CPU, the appropriate flag is <c>-j2</c>; a system with two CPUs will
336 use the <c>-j3</c> flag, and so on. <e>(A system with one processor that
337 supports Hyper-Threading&#8482; (HT) Technology can use the</e><c>-j3</c>
338 <e>flag, provided Symmetric Multi-Processing (SMP) support is enabled in
339 the kernel.)</e>
340 </li>
341 </ul>
343 </body>
344 </section>
346 <section>
347 <title>Debugging Flags</title>
348 <body>
350 <p>
351 The use debugging flags during the kernel compilation process controls the
352 amount of information reported, as well as the presentation of said data.
353 </p>
355 <ul>
356 <li>
357 <b>--debuglevel=<c>verblevel</c></b>: Controls the level of
358 verbosity for information provided by genkernel. The variable
359 <c>verblevel</c> is an integer between 0 and 5. The level '0' represents
360 minimal output, while '5' provides as much information as possible about
361 genkernel's activities during the kernel compilation process.
362 </li>
363 <li>
364 <b>--debugfile=<path>/path/to/outputfile</path></b>: Ignores the value
365 set by the <c>--debuglevel</c> argument, and sends <b>all</b> debugging
366 data produced by genkernel to the specified output file, which is located
367 at <path>/var/log/genkernel.log</path> by default.
368 </li>
369 <li>
370 <b>--no-color</b>: Activates [or deactivates] colored output of debugging
371 information (reported by genkernel) using escape sequences.
372 </li>
373 </ul>
375 </body>
376 </section>
378 <section>
379 <title>Initialization Flags</title>
380 <body>
382 <p>
383 The flags here are used to create certain effects during system startup. Some
384 of these flags are primarily for aesthetics, while others may be essential for
385 enabling certain features on the system.
386 </p>
388 <ul>
389 <li>
390 <b>--<c>no-</c>bootsplash</b>: Activates <e>[or deactivates]</e> support
391 for <uri link="http://www.bootsplash.org/">bootsplash</uri> in the
392 genkernel-built initrd image. The bootsplash feature is supported on a
393 limited number of architectures, and a kernel that supports bootsplash
394 is also required.
395 </li>
396 <li>
397 <b>--<c>no-</c>gensplash</b>: Activates <e>[or deactivates]</e> support
398 for <uri link="http://dev.gentoo.org/~spock/projects/gensplash/">gensplash</uri>
399 support in the genkernel-built initrd image. The gensplash utility is
400 intended to be a replacement for bootsplash, and is designed for use with
401 2.6.x series kernels. To override the default theme used by gensplash,
402 use <b>--gensplash=<c>PreferredTheme</c></b> (where <c>PreferredTheme</c>
403 is the title of one of the directories inside the
404 <path>/etc/splash/</path> directory.
405 </li>
406 <li>
407 <b>--gensplash-res=<c>PreferredResolution</c></b>: This flag allows you
408 to select which splash screen resolutions will be supported in the initrd
409 during the start-up of the system. This is useful for two reasons: First,
410 you are able to select only the splash screen resolution(s) relevant to
411 your system. Second, you avoid the unnecessary increase in the disk space
412 required by initrd (since the initrd does not have to support resolutions
413 that are irrelevant for your system configuration.) However, you may want
414 to omit this flag if the kernel is being compiled for an Installation CD;
415 this allows gensplash support for all possible resolutions.
416 </li>
417 <li>
418 <b>--do-keymap-auto</b>: Force keymap selection during the boot
419 sequence.
420 </li>
421 <li>
422 <b>--lvm2</b>: Includes support for storage using via <uri
423 link="http://sources.redhat.com/lvm2/">Logical Volume Management</uri>
424 (LVM2) from <e>static</e> binaries, if available to the system. Relevant
425 (static) LVM2 binaries are compiled if they are unavailable. Be sure to
426 install the lvm2 package on your system with <c>emerge lvm2</c> before
427 enabling this flag, and review the <uri
428 link="http://www.gentoo.org/doc/en/lvm2.xml">Gentoo LVM2
429 Installation</uri> guide.
430 </li>
431 <li>
432 <b>--evms2</b>: Includes support for storage using the <uri
433 link="http://evms.sourceforge.net/">Enterprise Volume Management
434 System</uri> (EVMS2), if available. Be sure to install the evms package
435 on your system with <c>USE=static emerge evms2</c> before using this
436 (genkernel) flag. <e>(Omitting the </e><c>USE=static</c> <e>flag during
437 package installation will fail to include the necessary static binaries.)
438 </e>
439 </li>
440 <li>
441 <b>--dmraid</b>: Includes support for <uri
442 link="http://people.redhat.com/~heinzm/sw/dmraid/readme">DMRAID</uri>;
443 the utility which creates RAID mappings using the kernel device-mapper
444 subsystem. DMRAID discovers, activates, deactivates and displays
445 properties of software RAID sets (ATARAID, for example) and contained
446 DOS partitions.
447 </li>
448 <li>
449 <b>--linuxrc=/path/to/your/linuxrc</b>: Specifies a user-created
450 <e>linuxrc</e> &#8212; a script that is initialized during the start-up
451 stage of the kernel, prior to the actual boot process. (A default linuxrc
452 script should be in the <path>/usr/share/genkernel/</path> directory.)
453 This script allows you to boot into a small, modularized kernel and load
454 the drivers that are needed (as modules) by the system.
455 </li>
456 <li>
457 <b>--cachedir=/path/to/alt/dir/</b>: Overrides the default cache location
458 used while compiling the kernel.
459 </li>
460 <li>
461 <b>--tempdir=/path/to/new/tempdir/</b>: Specifies the location of the
462 temporary directory used by genkernel while compiling the kernel.
463 </li>
464 <li>
465 <b>--unionfs</b>: Includes support for the <uri
466 link="http://www.fsl.cs.sunysb.edu/project-unionfs.html">Unification File
467 System</uri> in the initrd image.
468 </li>
469 </ul>
471 </body>
472 </section>
474 <section>
475 <title>Miscellaneous Flags</title>
476 <body>
478 <p>
479 The assortment of flags listed below are supported by genkernel, but do not fit
480 neatly into any of the other categories:
481 </p>
483 <ul>
484 <li>
485 <b>--mountboot</b>: Detects whether or not the <path>/boot/</path>
486 directory needs to be mounted on a separate partition. It will check
487 <path>/etc/fstab</path> script for instructions on how to mount the boot
488 partition on a file system (if needed).
489 </li>
490 <li>
491 <b>--kernname=<c>NickName</c></b>: Allows you to modify the name of the
492 kernel and initrd images in the <path>/boot/</path> directory, so that
493 the images produced are kernel-<c>NickName</c>-version and
494 initramfs-<c>NickName</c>-version.
495 </li>
496 </ul>
498 </body>
499 </section>
502 <section>
503 <title>Possible Actions</title>
504 <body>
506 <p>
507 An action tells genkernel what to build. Currently, the following actions are
508 supported:
509 </p>
511 <ul>
512 <li><c>initrd</c>: Only builds the initrd image</li>
513 <li><c>bzImage</c>: Only builds the kernel image</li>
514 <li><c>kernel</c>: Only builds the kernel image and modules</li>
515 <li><c>all</c>: Builds all stages &#8212; the initrd, kernel image and
516 modules.</li>
517 </ul>
519 <p>
520 The last action, <c>all</c>, is recommended for most users since it builds the
521 stages required for a functional kernel. Remember, an <e>action</e> simply
522 tells genkernel what to <e>build</e>, not <e>install</e>.
523 </p>
525 </body>
526 </section>
529 <section>
530 <title>Bootloader Configuration</title>
531 <body>
533 <p>
534 To set up genkernel to work with your bootloader, three or four changes should
535 to the bootloader's configuration file:
536 </p>
538 <ol>
539 <li>
540 Add <c>root=/dev/ram0</c> and <c>init=/linuxrc</c> to the kernel
541 parameters passed to the kernel image.
542 </li>
543 <li>
544 Add <c>real_root=/dev/hda3</c>, for example, to the kernel parameters
545 passed to the kernel image, if <path>/dev/hda3</path> contains your root
546 partition.
547 </li>
548 <li>
549 If you are using bootsplash, add a suitable mode line such as
550 <c>vga=0x317</c> to the parameters passed to the kernel and also add
551 <c>splash=verbose</c> or <c>splash=silent</c> depending on the
552 verboseness you require from your bootloader.
553 </li>
554 <li>
555 Add the initrd information as required by the bootloader. Consult the
556 <uri link="/doc/en/handbook/handbook-x86.xml?part=1&amp;chap=10">
557 Bootloader Configuration Chapter</uri> of the Gentoo Handbook for details
558 on how to make your bootloader initrd-aware.
559 </li>
560 </ol>
562 </body>
563 </section>
565 </chapter>
567 <chapter>
568 <title>Configuration Options</title>
570 <section>
571 <title>Editing /etc/genkernel.conf</title>
572 <body>
574 <p>
575 Passing flags to genkernel from the command line can be cumbersome, especially
576 if you have about a dozen flags:
577 </p>
579 <pre caption="Running genkernel (overloaded with flags)">
580 # genkernel --debuglevel=5 --no-color --no-mrproper --clean --gensplash\
581 --kerneldir=/path/to/alternate/kernel/sources --install --menuconfig --udev\
582 --kernel-config=/path/to/preferred/configfile --save-config --mountboot all
583 </pre>
585 <p>Fortunately, there is a configuration file where most of the basic options
586 can be set (or changed) as necessary. What follows is a rundown of the more
587 relevant options:
588 </p>
590 <ul>
591 <li>
592 <b>MENUCONFIG=<c>[yes|no]</c></b>: This option is equivalent to the
593 <c>--menuconfig</c> flag used by genkernel, which in turn uses the
594 <c>make menuconfig</c> command to invoke a command-line based kernel
595 configuration utility. To invoke the utility automatically during kernel
596 configuration via this script, set this option to 'yes' here; otherwise,
597 choose 'no'.
598 </li>
599 <li>
600 <b>CLEAN=<c>[yes|no]</c></b>: Setting this option to 'yes' is equivalent
601 to the <c>--clean</c> flag used by genkernel, and invokes the
602 <c>make clean</c> command to remove all object files and dependencies
603 from the kernel's source tree. Setting this option to 'no' creates a
604 cascade effect &#8212; it is equivalent to genkernel's <c>--no-clean</c>
605 flag, which disables the <c>make clean</c> command and implies
606 genkernel's <c>--no-mrproper</c> flag &#8212; essentially nullifying the
607 <c>make mrproper</c> command.
608 </li>
609 <li>
610 <b>MRPROPER=<c>[yes|no]</c></b>: Setting this option to 'yes' is
611 equivalent to <c>--mrproper</c> flag used by genkernel, and invokes the
612 <c>make mrproper</c> command, which purges the kernel source tree of any
613 configuration files. Selecting 'no' here is equivalent to genkernel's
614 <c>--no-mrproper</c> flag, which disables the <c>make mrproper</c>
615 command.
616 </li>
617 <li>
618 <b>MOUNTBOOT=<c>[yes|no]</c></b>: Setting this option to 'yes' is
619 equivalent to the <c>--mountboot</c> flag, and automatically mounts the
620 <path>/boot/</path> directory (if needed) at compile time. If the
621 <path>/boot/</path> directory is on a separate partition, consider
622 enabling this option; it will make for one less (essential) step to
623 remember later.
624 </li>
625 <li>
626 <b>SAVE_CONFIG=<c>[yes|no]</c></b>: After configuring the kernel, the
627 selected options are stored as <path>.config</path> in the kernel source
628 tree. This script may be overwritten during the next kernel compilation,
629 or even purged from the kernel source tree. Choosing 'yes' here is
630 equivalent to the <c>--save-config</c> flag, and stores all options
631 selected during kernel configuration as a script in the
632 <path>/etc/kernels/</path> directory. Choosing 'no' preserves the
633 <e>status quo</e>.
634 </li>
635 <li>
636 <b>USECOLOR=<c>[yes|no]</c></b>: Setting this option to 'yes' is
637 equivalent to the <c>--color</c> flag, which colors genkernel's output
638 to ease debugging (when needed.)
639 </li>
640 <li>
641 <b>DEBUGLEVEL=<c>[0|1|2|3|4|5]</c></b>: This option is for adjusting the
642 verbosity of the output produced by genkernel &#8212; setting this option
643 to '0' with <c>--debuglevel=0</c> will suppress all output produced by
644 genkernel; setting this option to '5' with <c>--debuglevel=5</c>
645 provides the user with all output produced by genkernel.
646 </li>
647 </ul>
649 <p>
650 By choosing the appropriate options in <path>/etc/genkernel.conf</path>, you
651 can halve the number of flags passed to genkernel from the command line:
652 </p>
654 <pre caption="Running genkernel (with flags), after employing genkernel.conf">
655 # genkernel --gensplash --kerneldir=/path/to/alternate/kernel/sources --udev\
656 --kernel-config=/path/to/preferred/configfile --install all
657 </pre>
659 <p>
660 Identical results are obtained from both approaches, but the latter has most of
661 the options stored in a script that can be modified at a later date.
662 </p>
664 </body>
665 </section>
667 </chapter>
669 <chapter>
670 <title>Network-Booting with genkernel</title>
672 <section>
673 <title>Network Booting from an Installation CD</title>
674 <body>
676 <p>
677 The genkernel utility can build kernel and initrd images that provide support
678 for network booting, or <e>netboot</e>ing . With any luck, you should be able
679 to netboot any recent computer into the environment provided by the
680 Installation CD.
681 </p>
683 <p>
684 The magic lies in genkernel's linuxrc script: it will try to <e>netmount</e>
685 the Installation CD using NFS. From there, <e>the init scripts</e> of the
686 Installation CD can take over, as if the CD was present locally.
687 </p>
689 </body>
690 </section>
692 <section>
693 <title>Building Kernel and Initrd Images with Support for Netbooting</title>
694 <body>
696 <p>
697 To enable support for netbooting, include the following options while
698 configuring the kernel:
699 </p>
701 <warn>
702 Support for netbooting with genkernel is experimental and may contain bugs.
703 </warn>
705 <p>
706 First, the kernel image must include the drivers for your Network Interface
707 Cards (NIC). Normally, drivers for such devices will be compiled as modules.
708 However, it is essential (for netbooting) that you such drivers compiled
709 directly into the kernel image and <b>not</b> as modules.
710 </p>
712 <pre caption="Configuring a 2.6.x series kernel to support your NIC driver">
713 Device Drivers --->
714 Networking Support --->
715 Ethernet (10 or 100Mbit) --->
716 [*] Ethernet (10 or 100Mbit)
717 &lt;*&gt; the driver for your network card
718 <comment>(Be sure to select &lt;*&gt; and not &lt;m&gt;)</comment>
719 </pre>
721 <p>
722 Secondly, we suggest that you enable <c>IP: kernel level
723 autoconfiguration</c> and the <c>IP: DHCP support</c> options. This avoids an
724 unnecessary layer of complexity since the IP address and the NFS path to the
725 Installation CD can be configured on a DHCP server. Of course, this means the
726 kernel command line will remain constant for any machine &#8212; which is very
727 important for <e>etherbooting</e>.
728 </p>
730 <pre caption="Configuring a 2.6.x series kernel to support DHCP">
731 Device Drivers --->
732 Networking Support --->
733 Networking options
734 [*] TCP/IP networking--->
735 [*] IP: kernel level autoconfiguration
736 [*] IP: DHCP support
737 <comment>(These options tell the kernel to send a DHCP request at bootup.)</comment>
738 </pre>
740 <p>
741 Additionally, you should enable SquashFS because most modern Gentoo
742 Installation CDs require it. Support for SquashFS is not included with the
743 generic kernel source tree. To enable SquashFS, apply the necessary patches to
744 the generic kernel source or install <c>gentoo-sources</c>.
745 </p>
747 <pre caption="Configuring the kernel to support SquashFS">
748 File systems--->
749 Miscellaneous filesystems --->
750 [*] SquashFS 2.X - Squashed file system support
751 </pre>
753 <p>
754 Once the compilation process is completed, create a compressed <e>tarball</e>
755 (tar.gz) that contains the kernel's modules. This step is only necessary if
756 your kernel version does not match the kernel image version on the Installation
757 CD.
758 </p>
760 <pre caption="Creating a compressed tarball containing the kernel modules">
761 <comment># Create a tar.gz containing all the modules</comment>
762 cd /
763 tar -cf /tmp/modules-X.Y.Z.tar.gz /lib/modules/X.Y.Z/
764 </pre>
766 <p>
767 Depending on your network boot mechanism, you will need to do some of the
768 following steps:
769 </p>
771 <pre caption="Creating a boot image">
772 <comment># Create a etherboot image</comment>
773 emerge mknbi
774 cd /boot
775 mkelf-linux -params="root=/dev/ram0 init=/linuxrc ip=dhcp" kernel... initrd... > etherboot.img
777 <comment># Create a OpenBoot / SPARC64 TFTP image</comment>
778 emerge sparc-utils
779 cd /boot
780 elftoaout kernel... -o kernel.aout
781 piggyback64 kernel.aout System.map-... initrd-...
782 mv kernel.aout openboot.img <comment># This is the boot image</comment>
784 <comment># PXE does not need any more steps, the kernel and initrd can be used as is</comment>
785 </pre>
787 <p>
788 Finally, copy this kernel to your TFTP server. The details are
789 architecture-dependent and are beyond the scope of this guide. Please refer to
790 the documentation for your platform.
791 </p>
793 </body>
794 </section>
796 <section>
797 <title>NFS Setup</title>
798 <body>
800 <p>
801 To setup a NFS share that contains the Installation CD, use the loop device to
802 mount the ISO image and then copy the contents of the CD into the NFS share. As
803 a nice extra, genkernel's initrd scripts will extract all tar.gz files located
804 in the <path>/nfs/livecd/add/</path> directory. All you have to do here is copy
805 the <c>modules-X.Y.Z.tar.gz</c> archive to the <path>/nfs/livecd/add/</path>
806 directory.
807 </p>
809 <pre caption="Preparing the NFS share">
810 <comment># This assumes that /nfs/livecd is a exported NFS share</comment>
811 mount /mnt/cdrom /tmp/gentoo-livecd.iso -o loop
812 cp -p /mnt/cdrom /nfs/livecd
813 umount /mnt/cdrom
815 <comment># Copy the modules.tar.gz into /add</comment>
816 mkdir /nfs/livecd/add
817 cp /tmp/modules-X.Y.Z.tar.gz /nfs/livecd/add
818 </pre>
820 </body>
821 </section>
823 <section>
824 <title>DHCP Setup</title>
825 <body>
827 <p>
828 The netboot images will ask your DHCP server for an IP as well as a
829 root-path parameter. Both can be specified per host using a MAC
830 address to identify machines:
831 </p>
833 <pre caption="Sample client dhcpd.conf setup">
834 ...
836 host netbootableMachine {
837 hardware ethernet 11:22:33:44:55:66;
838 fixed-address;
839 option root-path "";
840 }
841 <comment># Here, is the NFS server
842 # While will be the IP address of the netbooted machine</comment>
843 ...
844 </pre>
846 </body>
847 </section>
849 <section>
850 <title>Netbooting Instructions</title>
851 <body>
853 <p>
854 Netbooting itself is again very platform-specific. The important part
855 is to specify the <c>ip=dhcp</c> and <c>init=/linuxrc</c> parameters
856 on the kernel command line, as this will bring up the
857 network interface and tell the initrd scripts to mount the Installation CD via
858 NFS. Here are some platform-specific tips:
859 </p>
861 <pre caption="Netbooting Instructions">
862 <comment># Etherboot - insert the etherboot disk into the drive and reboot
863 # The kernel command line was specified when the image was constructed</comment>
865 <comment># Sparc64 - Hit Stop-A at the boot prompt </comment>
866 ok boot net ip=dhcp init=/linuxrc
868 <comment># PXE - Setup pxelinux (part of syslinux), then create a pxelinux.cfg/default along the lines of:</comment>
870 DEFAULT gentoo
871 TIMEOUT 40
872 PROMPT 1
874 LABEL gentoo
875 KERNEL kernel-X.Y.Z
876 APPEND initrd=initrd-X.Y.Z root=/dev/ram0 init=/linuxrc ip=dhcp
877 </pre>
879 </body>
880 </section>
882 </chapter>
884 <chapter>
885 <title>Conclusion</title>
887 <section>
888 <title>To Automate or not to Automate?</title>
889 <body>
891 <p>
892 The purpose of genkernel is to provide an (easier) alternative to the
893 time-tested approach to kernel compilation. As always, you are free to decide
894 on whether or not you want to automate the kernel compilation process.
895 </p>
897 </body>
898 </section>
900 </chapter>
902 </guide>

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