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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 1.6 2005/05/23 19:15:46 swift 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/2.0 -->
18 <license/>
19
20 <version>0.1.5</version>
21 <date>2005-05-25</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 you to maintain a symbolic link, located at
123 <path>/usr/src/linux</path>. This should point to the sources of the
124 kernel you are running.
125 </p>
126
127 <p>
128 In any case, we need to update the symbolic link to point at the kernel
129 sources that we are about to upgrade to. Continuing our example:
130 </p>
131
132 <pre caption="Updating the /usr/src/linux softlink">
133 # <i>cd /usr/src</i>
134 # <i>ln -sfn linux-2.6.9-gentoo-r2 linux</i>
135 </pre>
136
137 </body>
138 </section>
139 </chapter>
140
141 <chapter id="install">
142 <title>Configuring, compiling and installing the new kernel</title>
143 <section>
144 <body>
145
146 <p>
147 For either of these options, you should refer to the instructions given in the
148 <uri link="/doc/en/handbook/index.xml">Gentoo
149 Handbook</uri> relating to <e>Configuring the Kernel</e> and <e>Configuring
150 the Bootloader</e>. Below is an outline of the required actions:
151 </p>
152
153 </body>
154 </section>
155 <section>
156 <title>Option 1: Automatic kernel setup with Genkernel</title>
157 <body>
158
159 <p>
160 If you are a genkernel user, you just need to repeat the stages you went
161 through when installing your kernel for the first time.
162 </p>
163
164 <p>
165 Simply run genkernel in the normal way:
166 </p>
167
168 <pre caption="Invoking genkernel">
169 <comment>(For 2.4 kernels:)</comment>
170 # <i>genkernel all</i>
171
172 <comment>(For 2.6 kernels:)</comment>
173 # <i>genkernel --udev all</i>
174 </pre>
175
176 <p>
177 You can also use extra parameters for other genkernel functionality. For
178 example, if you wish to configure some extra kernel options using
179 <c>menuconfig</c> and you wish genkernel to automatically update your grub
180 boot loader configuration, then invoke genkernel as follows:
181 </p>
182
183 <pre caption="Invoking genkernel with some common arguments">
184 # <i>genkernel --menuconfig --bootloader=grub all</i>
185 </pre>
186
187 <p>
188 For more info, follow the
189 <uri link="/doc/en/genkernel.xml">Gentoo Linux Genkernel
190 Guide</uri>, or refer to the <uri link="/doc/en/handbook/index.xml">Gentoo
191 Handbook</uri>. Many of the options can be set in the configuration file for
192 <c>genkernel</c>, <path>/etc/genkernel.conf</path>.
193 </p>
194
195 </body>
196 </section>
197 <section>
198 <title>Option 2: Manual configuration</title>
199 <body>
200
201 <p>
202 To begin, open the <c>menuconfig</c> utility in the kernel source tree:
203 </p>
204
205 <pre caption="Invoking menuconfig">
206 # <i>cd /usr/src/linux</i>
207 # <i>make menuconfig</i>
208 </pre>
209
210 <p>
211 Select the options required for your hardware and operating environment. For
212 additional information on kernel configuration, refer to the chapter entitled
213 <e>Configuring the Kernel</e> of the <uri
214 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
215 </p>
216
217 <p>
218 Next, compile your kernel and copy it over to your boot partition. Again,
219 follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
220 instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
221 <path>/boot</path> is a separate partition, ensure it is mounted before copying
222 the compiled kernel to this directory! Failing to do so would keep you from
223 booting the system with your new kernel.
224 </p>
225
226 <pre caption="Compiling and installing the new kernel">
227 # <i>make &amp;&amp; make modules_install</i>
228 # <i>mount /boot</i>
229 # <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.9-gentoo-r2</i>
230 # <i>cp System.map /boot/System.map-2.6.9-gentoo-r2</i>
231 </pre>
232
233 <p>
234 Finally, you should update your boot loader configuration, adding an entry for
235 the new kernel (don't delete the old one just yet!) and unmount the
236 <path>/boot</path> partition. Again, refer to the
237 <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
238 for detailed instructions on this procedure.
239 </p>
240
241 </body>
242 </section>
243 </chapter>
244
245 <chapter>
246 <title>Reinstalling external modules</title>
247 <section>
248 <body>
249
250 <p>
251 If you use any kernel modules that are not included in the kernel source tree
252 but are provided elsewhere in portage (e.g. NVIDIA or ATI graphics drivers),
253 then you must reinstall these after upgrading the kernel. This is as simple as
254 re-merging the packages involved. For more information, refer to the chapter on
255 <e>Configuring the Kernel</e> in the <uri
256 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
257 To ensure these packages will build against the source tree at
258 <path>/usr/src/linux</path>, first uninstall the packages, then re-emerge them.
259 If old sources for these packages are kept by portage, this uninstall/re-emerge
260 procedure will make sure that they are rebuilt to work with the new kernel.
261 </p>
262
263 </body>
264 </section>
265 </chapter>
266
267 <chapter>
268 <title>Rebooting into the new kernel</title>
269 <section>
270 <body>
271
272 <p>
273 Next, close all applications and reboot your system. If you followed the above
274 instructions correctly, the boot loader menu should include an entry for the
275 new kernel. Select the new kernel and let the system boot.
276 </p>
277
278 <p>
279 Hopefully, your system successfully boots with the new kernel, and you can log
280 in to resume whatever you were doing. If this is the case, then the upgrade is
281 complete.
282 </p>
283
284 <p>
285 If you made a mistake and the system fails to boot with the new kernel, reboot
286 the system and select the entry from the boot loader that corresponds to the
287 last known working kernel. You can then restart from the <uri link="#install">
288 Configuring, compiling, and installing the new kernel</uri> stage -- making
289 the appropriate changes to correct your mistake. In some cases, you might not
290 even need to reboot to do this (e.g. you missed a driver for an audio device,
291 Ethernet adapter, etc.)
292 </p>
293
294 </body>
295 </section>
296 </chapter>
297
298 <chapter>
299 <title>Running multiple kernels</title>
300 <section>
301 <body>
302
303 <p>
304 You may have noticed, that when installing the sources for your newer kernel,
305 the sources for your existing kernel were not removed. This is by design -- it
306 allows you to easily switch between running different kernels.
307 </p>
308
309 <p>
310 Switching between multiple kernels is as simple as leaving the kernel sources
311 under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on
312 your <path>/boot</path> partition (referenced by entries in your boot loader
313 configuration). Every time you boot up, you will be presented with a choice of
314 which kernel to boot into.
315 </p>
316
317 </body>
318 </section>
319 </chapter>
320
321 <chapter>
322 <title>Removing older kernels</title>
323 <section>
324 <body>
325
326 <p>
327 Continuing on from the last section, you may be happy with your new kernel and
328 not have any need to keep older kernel versions around. To easily remove all
329 sources for a particular kernel except for the newest one, you can take
330 advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
331 the example using <c>gentoo-sources</c>:
332 </p>
333
334 <pre caption="Pruning old versions">
335 # <i>emerge -P gentoo-sources</i>
336 </pre>
337
338 <p>
339 In most cases, temporary files used during compilation will still remain under
340 the appropriate source directory under <path>/usr/src</path>. It is safe to
341 remove these using <c>rm</c>.
342 </p>
343
344 <p>
345 You can also safely delete any modules that were used by this kernel. This can
346 be done by removing the appropriate directories under <path>/lib/modules/</path>
347 that relate to the kernel versions you are removing. Be careful not to delete
348 modules belonging to kernels that you still use!
349 </p>
350
351 <p>
352 Finally, you can mount your <path>/boot</path> partition and remove the
353 <path>bzImage</path> and <path>System.map</path> files for the kernel(s)
354 you are pruning. You should also edit your boot loader configuration so that it
355 no longer references such kernel(s).
356 </p>
357
358 </body>
359 </section>
360 </chapter>
361
362 <chapter>
363 <title>Advanced: Using your old kernel .config to configure a new one</title>
364 <section>
365 <body>
366
367 <p>
368 It is sometimes possible to save time by re-using the configuration file from
369 your old kernel when configuring the new one. Note that this is generally
370 unsafe -- too many changes between every kernel release for this to be a
371 reliable upgrade path.
372 </p>
373
374 <p>
375 The only situation where this is appropriate is when upgrading from one Gentoo
376 kernel revision to another. For example, the changes made between
377 <c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
378 small, so it is usually OK to use the following method. However, it is not
379 appropriate to use it in the example used throughout this document: upgrading
380 from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
381 method described below does not display enough context to the user, often
382 resulting in the user running into problems because they disabled options that
383 they really didn't want to.
384 </p>
385
386 <p>
387 To reuse your old <path>.config</path>, you simply need to copy it over and then
388 run <c>make oldconfig</c>. In the following example, we take the configuration
389 from <c>gentoo-sources-2.6.9-r1</c> and import it into
390 <c>gentoo-sources-2.6.9-r2</c>.
391 </p>
392
393 <pre caption="Reusing your old config">
394 # <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
395 # <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
396 # <i>make oldconfig</i>
397 </pre>
398
399 <p>
400 At this point, you may be asked to produce answers for configuration options
401 which have changed between the two versions. Once you have done that, you can
402 compile and install your kernel as normal, without having to go through the
403 <c>menuconfig</c> configuration process.
404 </p>
405
406 </body>
407 </section>
408 </chapter>
409
410 <chapter>
411 <title>Problems after a kernel upgrade?</title>
412 <section>
413 <body>
414
415 <p>
416 With the rapid development of the Linux kernel, it is inevitable that some
417 changes made from one kernel release to another may cause some problems. If you
418 have any issues with the latest versions of <uri
419 link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
420 please do report the issues to us.
421 </p>
422
423 </body>
424 </section>
425 </chapter>
426
427 </guide>

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