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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/kernel-upgrade.xml,v 1.10 2005/10/06 19:16:11 jkt Exp $ -->
3
4 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
5 <guide link="/doc/en/kernel-upgrade.xml">
6 <title>Gentoo Linux Kernel Upgrade Guide</title>
7 <author title="Author">
8 <mail link="dsd@gentoo.org">Daniel Drake</mail>
9 </author>
10
11 <abstract>
12 This document describes the process of upgrading your kernel from one release
13 to another.
14 </abstract>
15
16 <!-- The content of this document is licensed under the CC-BY-SA license -->
17 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
18 <license/>
19
20 <version>0.1.8</version>
21 <date>2005-10-11</date>
22
23 <chapter>
24 <title>Introduction</title>
25 <section>
26 <body>
27
28 <p>
29 The kernel is one of the few package classes in portage that requires some
30 manual intervention to complete the upgrade. Portage will download and
31 install the kernel source for you, but then it is up to you to step in and
32 compile the new kernel before any changes will take effect.
33 </p>
34
35 <p>
36 Although this guide is targeted at users upgrading from one kernel release
37 to another, it will also be useful for users migrating from one kernel
38 package to another.
39 </p>
40
41 <p>
42 <c>gentoo-sources</c> is used as an example in this document, however, the
43 instructions here also apply to the other packages present in our tree.
44 </p>
45
46 </body>
47 </section>
48 </chapter>
49
50 <chapter>
51 <title>Why upgrade the kernel?</title>
52 <section>
53 <body>
54
55 <p>
56 Generally, upgrading from one minor kernel release to the next won't bring any
57 major differences. There are several reasons to upgrade the kernel. One is to
58 take advantage of a specific new feature or driver; another is to be protected
59 against a security vulnerability, or just to maintain an up-to-date and healthy
60 system.
61 </p>
62
63 <p>
64 Even if you choose not to update to every new kernel revision, it is
65 recommended that you at least upgrade from time to time. It is strongly
66 recommended that you immediately upgrade to a new kernel if that new release
67 solves a security problem.
68 </p>
69
70 </body>
71 </section>
72 </chapter>
73
74 <chapter>
75 <title>Obtaining the newer sources through Portage</title>
76 <section>
77 <body>
78
79 <p>
80 You upgrade the kernel sources like you would upgrade any other package -
81 using the <c>emerge</c> utility. It will probably be the case that you want to
82 upgrade your kernel when you see the upgrade appearing on your world updates
83 list. For example:
84 </p>
85
86 <pre caption="New kernel sources appearing on update list">
87 # <i>emerge -Dup world</i>
88 Calculating dependencies ...done!
89 [ebuild NS ] sys-kernel/gentoo-sources-2.6.9-r2 [2.6.8-r5]
90 </pre>
91
92 <note>
93 The "NS" label in the above output means that the new kernel will be installed
94 in a New Slot, i.e. the sources of your old kernel will be kept around, until
95 you manually remove them.
96 </note>
97
98 <p>
99 You can then go ahead and install the update, e.g.:
100 </p>
101
102 <pre caption="Upgrading your kernel sources">
103 # <i>emerge -u gentoo-sources</i>
104 </pre>
105
106 <p>
107 The kernel sources will then be installed into a subdirectory of
108 <path>/usr/src</path>. In the above example, the new kernel sources will be
109 installed at <path>/usr/src/linux-2.6.9-gentoo-r2</path>.
110 </p>
111
112 </body>
113 </section>
114 </chapter>
115
116 <chapter>
117 <title>Updating the /usr/src/linux symbolic link</title>
118 <section>
119 <body>
120
121 <p>
122 Gentoo requires that the <path>/usr/src/linux</path> symbolic link points to
123 the sources of the kernel you are running.
124 </p>
125
126 <p>
127 Portage can update the symlink automatically when you emerge new kernel
128 sources. All you have to do is add the <c>symlink</c> flag to the USE variable
129 in <path>/etc/make.conf</path>.
130 </p>
131
132 <pre caption="Example of USE variable in /etc/make.conf">
133 <comment>(Add the symlink keyword)</comment>
134 USE="<i>symlink</i> x86 3dnow 3dnowex X aac aalib adns alsa apache2"
135 </pre>
136
137 <p>
138 If you really want to do it yourself, the following example shows you how to
139 make the link point to <path>linux-2.6.9-gentoo-r2</path>:
140 </p>
141
142 <pre caption="Updating the /usr/src/linux softlink manually">
143 # <i>cd /usr/src</i>
144 # <i>ln -sfn linux-2.6.9-gentoo-r2 linux</i>
145 </pre>
146
147 </body>
148 </section>
149 </chapter>
150
151 <chapter id="install">
152 <title>Configuring, compiling and installing the new kernel</title>
153 <section>
154 <body>
155
156 <p>
157 For either of these options, you should refer to the instructions given in the
158 <uri link="/doc/en/handbook/index.xml">Gentoo
159 Handbook</uri> relating to <e>Configuring the Kernel</e> and <e>Configuring
160 the Bootloader</e>. Below is an outline of the required actions:
161 </p>
162
163 </body>
164 </section>
165 <section>
166 <title>Option 1: Automatic kernel setup with Genkernel</title>
167 <body>
168
169 <p>
170 If you are a genkernel user, you just need to repeat the stages you went
171 through when installing your kernel for the first time.
172 </p>
173
174 <p>
175 Simply run genkernel in the normal way:
176 </p>
177
178 <pre caption="Invoking genkernel">
179 <comment>(For 2.4 kernels:)</comment>
180 # <i>genkernel all</i>
181
182 <comment>(For 2.6 kernels:)</comment>
183 # <i>genkernel --udev all</i>
184 </pre>
185
186 <p>
187 You can also use extra parameters for other genkernel functionality. For
188 example, if you wish to configure some extra kernel options using
189 <c>menuconfig</c> and you wish genkernel to automatically update your grub
190 boot loader configuration, then invoke genkernel as follows:
191 </p>
192
193 <pre caption="Invoking genkernel with some common arguments">
194 # <i>genkernel --menuconfig --bootloader=grub all</i>
195 </pre>
196
197 <p>
198 For more info, follow the
199 <uri link="/doc/en/genkernel.xml">Gentoo Linux Genkernel
200 Guide</uri>, or refer to the <uri link="/doc/en/handbook/index.xml">Gentoo
201 Handbook</uri>. Many of the options can be set in the configuration file for
202 <c>genkernel</c>, <path>/etc/genkernel.conf</path>.
203 </p>
204
205 </body>
206 </section>
207 <section>
208 <title>Option 2: Manual configuration</title>
209 <body>
210
211 <p>
212 To begin, open the <c>menuconfig</c> utility in the kernel source tree:
213 </p>
214
215 <pre caption="Invoking menuconfig">
216 # <i>cd /usr/src/linux</i>
217 # <i>make menuconfig</i>
218 </pre>
219
220 <p>
221 Select the options required for your hardware and operating environment. For
222 additional information on kernel configuration, refer to the chapter entitled
223 <e>Configuring the Kernel</e> of the <uri
224 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
225 </p>
226
227 <p>
228 Next, compile your kernel and copy it over to your boot partition. Again,
229 follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
230 instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
231 <path>/boot</path> is a separate partition, ensure it is mounted before copying
232 the compiled kernel to this directory! Failing to do so would keep you from
233 booting the system with your new kernel.
234 </p>
235
236 <pre caption="Compiling and installing the new kernel">
237 # <i>make &amp;&amp; make modules_install</i>
238 # <i>mount /boot</i>
239 # <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.9-gentoo-r2</i>
240 </pre>
241
242 <p>
243 Finally, you should update your boot loader configuration, adding an entry for
244 the new kernel (don't delete the old one just yet!) and unmount the
245 <path>/boot</path> partition. Again, refer to the
246 <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
247 for detailed instructions on this procedure.
248 </p>
249
250 </body>
251 </section>
252 </chapter>
253
254 <chapter>
255 <title>Reinstalling external modules</title>
256 <section>
257 <body>
258
259 <p>
260 If you use any kernel modules that are not included in the kernel source tree
261 but are provided elsewhere in portage (e.g. NVIDIA or ATI graphics drivers),
262 then you must reinstall these after upgrading the kernel. This is as simple as
263 re-merging the packages involved. For more information, refer to the chapter on
264 <e>Configuring the Kernel</e> in the <uri
265 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
266 To ensure these packages will build against the source tree at
267 <path>/usr/src/linux</path>, first uninstall the packages, then re-emerge them.
268 If old sources for these packages are kept by portage, this uninstall/re-emerge
269 procedure will make sure that they are rebuilt to work with the new kernel.
270 </p>
271
272 <p>
273 We provide you with an easy tool (<c>sys-kernel/module-rebuild</c>) which
274 rebuilds all the kernel modules you have installed using separate ebuilds.
275 </p>
276
277 </body>
278 </section>
279 </chapter>
280
281 <chapter>
282 <title>Rebooting into the new kernel</title>
283 <section>
284 <body>
285
286 <p>
287 Next, close all applications and reboot your system. If you followed the above
288 instructions correctly, the boot loader menu should include an entry for the
289 new kernel. Select the new kernel and let the system boot.
290 </p>
291
292 <p>
293 Hopefully, your system successfully boots with the new kernel, and you can log
294 in to resume whatever you were doing. If this is the case, then the upgrade is
295 complete.
296 </p>
297
298 <p>
299 If you made a mistake and the system fails to boot with the new kernel, reboot
300 the system and select the entry from the boot loader that corresponds to the
301 last known working kernel. You can then restart from the <uri link="#install">
302 Configuring, compiling, and installing the new kernel</uri> stage -- making
303 the appropriate changes to correct your mistake. In some cases, you might not
304 even need to reboot to do this (e.g. you missed a driver for an audio device,
305 Ethernet adapter, etc.)
306 </p>
307
308 </body>
309 </section>
310 </chapter>
311
312 <chapter>
313 <title>Running multiple kernels</title>
314 <section>
315 <body>
316
317 <p>
318 You may have noticed, that when installing the sources for your newer kernel,
319 the sources for your existing kernel were not removed. This is by design -- it
320 allows you to easily switch between running different kernels.
321 </p>
322
323 <p>
324 Switching between multiple kernels is as simple as leaving the kernel sources
325 under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on
326 your <path>/boot</path> partition (referenced by entries in your boot loader
327 configuration). Every time you boot up, you will be presented with a choice of
328 which kernel to boot into.
329 </p>
330
331 </body>
332 </section>
333 </chapter>
334
335 <chapter>
336 <title>Removing older kernels</title>
337 <section>
338 <body>
339
340 <p>
341 Continuing on from the last section, you may be happy with your new kernel and
342 not have any need to keep older kernel versions around. To easily remove all
343 sources for a particular kernel except for the newest one, you can take
344 advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
345 the example using <c>gentoo-sources</c>:
346 </p>
347
348 <pre caption="Pruning old versions">
349 # <i>emerge -P gentoo-sources</i>
350 </pre>
351
352 <p>
353 In most cases, temporary files used during compilation will still remain under
354 the appropriate source directory under <path>/usr/src</path>. It is safe to
355 remove these using <c>rm</c>.
356 </p>
357
358 <p>
359 You can also safely delete any modules that were used by this kernel. This can
360 be done by removing the appropriate directories under <path>/lib/modules/</path>
361 that relate to the kernel versions you are removing. Be careful not to delete
362 modules belonging to kernels that you still use!
363 </p>
364
365 <p>
366 Finally, you can mount your <path>/boot</path> partition and remove the
367 <path>bzImage</path> file(s) for the kernel(s) you are pruning. You should also
368 edit your boot loader configuration so that it no longer references such
369 kernel(s).
370 </p>
371
372 </body>
373 </section>
374 </chapter>
375
376 <chapter>
377 <title>Advanced: Using your old kernel .config to configure a new one</title>
378 <section>
379 <body>
380
381 <p>
382 It is sometimes possible to save time by re-using the configuration file from
383 your old kernel when configuring the new one. Note that this is generally
384 unsafe -- too many changes between every kernel release for this to be a
385 reliable upgrade path.
386 </p>
387
388 <p>
389 The only situation where this is appropriate is when upgrading from one Gentoo
390 kernel revision to another. For example, the changes made between
391 <c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
392 small, so it is usually OK to use the following method. However, it is not
393 appropriate to use it in the example used throughout this document: upgrading
394 from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
395 method described below does not display enough context to the user, often
396 resulting in the user running into problems because they disabled options that
397 they really didn't want to.
398 </p>
399
400 <p>
401 To reuse your old <path>.config</path>, you simply need to copy it over and then
402 run <c>make oldconfig</c>. In the following example, we take the configuration
403 from <c>gentoo-sources-2.6.9-r1</c> and import it into
404 <c>gentoo-sources-2.6.9-r2</c>.
405 </p>
406
407 <pre caption="Reusing your old config">
408 # <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
409 # <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
410 # <i>make oldconfig</i>
411 </pre>
412
413 <p>
414 At this point, you may be asked to produce answers for configuration options
415 which have changed between the two versions. Once you have done that, you can
416 compile and install your kernel as normal, without having to go through the
417 <c>menuconfig</c> configuration process.
418 </p>
419
420 </body>
421 </section>
422 </chapter>
423
424 <chapter>
425 <title>Problems after a kernel upgrade?</title>
426 <section>
427 <body>
428
429 <p>
430 With the rapid development of the Linux kernel, it is inevitable that some
431 changes made from one kernel release to another may cause some problems. If you
432 have any issues with the latest versions of <uri
433 link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
434 please do report the issues to us.
435 </p>
436
437 </body>
438 </section>
439 </chapter>
440
441 </guide>

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