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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 1.5 2005/05/23 18:40:25 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>0.1.4</version>
21 <date>2005-05-23</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 # <i>genkernel all</i>
170 </pre>
171
172 <p>
173 You can also use extra parameters for other genkernel functionality. For
174 example, if you wish to configure some extra kernel options using
175 <c>menuconfig</c> and you wish genkernel to automatically update your grub
176 boot loader configuration, then invoke genkernel as follows:
177 </p>
178
179 <pre caption="Invoking genkernel with some common arguments">
180 # <i>genkernel --menuconfig --bootloader=grub all</i>
181 </pre>
182
183 <p>
184 For more info, follow the
185 <uri link="/doc/en/genkernel.xml">Gentoo Linux Genkernel
186 Guide</uri>, or refer to the <uri link="/doc/en/handbook/index.xml">Gentoo
187 Handbook</uri>. Many of the options can be set in the configuration file for
188 <c>genkernel</c>, <path>/etc/genkernel.conf</path>.
189 </p>
190
191 </body>
192 </section>
193 <section>
194 <title>Option 2: Manual configuration</title>
195 <body>
196
197 <p>
198 To begin, open the <c>menuconfig</c> utility in the kernel source tree:
199 </p>
200
201 <pre caption="Invoking menuconfig">
202 # <i>cd /usr/src/linux</i>
203 # <i>make menuconfig</i>
204 </pre>
205
206 <p>
207 Select the options required for your hardware and operating environment. For
208 additional information on kernel configuration, refer to the chapter entitled
209 <e>Configuring the Kernel</e> of the <uri
210 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
211 </p>
212
213 <p>
214 Next, compile your kernel and copy it over to your boot partition. Again,
215 follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
216 instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
217 <path>/boot</path> is a separate partition, ensure it is mounted before copying
218 the compiled kernel to this directory! Failing to do so would keep you from
219 booting the system with your new kernel.
220 </p>
221
222 <pre caption="Compiling and installing the new kernel">
223 # <i>make &amp;&amp; make modules_install</i>
224 # <i>mount /boot</i>
225 # <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.9-gentoo-r2</i>
226 # <i>cp System.map /boot/System.map-2.6.9-gentoo-r2</i>
227 </pre>
228
229 <p>
230 Finally, you should update your boot loader configuration, adding an entry for
231 the new kernel (don't delete the old one just yet!) and unmount the
232 <path>/boot</path> partition. Again, refer to the
233 <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
234 for detailed instructions on this procedure.
235 </p>
236
237 </body>
238 </section>
239 </chapter>
240
241 <chapter>
242 <title>Reinstalling external modules</title>
243 <section>
244 <body>
245
246 <p>
247 If you use any kernel modules that are not included in the kernel source tree
248 but are provided elsewhere in portage (e.g. NVIDIA or ATI graphics drivers),
249 then you must reinstall these after upgrading the kernel. This is as simple as
250 re-merging the packages involved. For more information, refer to the chapter on
251 <e>Configuring the Kernel</e> in the <uri
252 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
253 To ensure these packages will build against the source tree at
254 <path>/usr/src/linux</path>, first uninstall the packages, then re-emerge them.
255 If old sources for these packages are kept by portage, this uninstall/re-emerge
256 procedure will make sure that they are rebuilt to work with the new kernel.
257 </p>
258
259 </body>
260 </section>
261 </chapter>
262
263 <chapter>
264 <title>Rebooting into the new kernel</title>
265 <section>
266 <body>
267
268 <p>
269 Next, close all applications and reboot your system. If you followed the above
270 instructions correctly, the boot loader menu should include an entry for the
271 new kernel. Select the new kernel and let the system boot.
272 </p>
273
274 <p>
275 Hopefully, your system successfully boots with the new kernel, and you can log
276 in to resume whatever you were doing. If this is the case, then the upgrade is
277 complete.
278 </p>
279
280 <p>
281 If you made a mistake and the system fails to boot with the new kernel, reboot
282 the system and select the entry from the boot loader that corresponds to the
283 last known working kernel. You can then restart from the <uri link="#install">
284 Configuring, compiling, and installing the new kernel</uri> stage -- making
285 the appropriate changes to correct your mistake. In some cases, you might not
286 even need to reboot to do this (e.g. you missed a driver for an audio device,
287 Ethernet adapter, etc.)
288 </p>
289
290 </body>
291 </section>
292 </chapter>
293
294 <chapter>
295 <title>Running multiple kernels</title>
296 <section>
297 <body>
298
299 <p>
300 You may have noticed, that when installing the sources for your newer kernel,
301 the sources for your existing kernel were not removed. This is by design -- it
302 allows you to easily switch between running different kernels.
303 </p>
304
305 <p>
306 Switching between multiple kernels is as simple as leaving the kernel sources
307 under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on
308 your <path>/boot</path> partition (referenced by entries in your boot loader
309 configuration). Every time you boot up, you will be presented with a choice of
310 which kernel to boot into.
311 </p>
312
313 </body>
314 </section>
315 </chapter>
316
317 <chapter>
318 <title>Removing older kernels</title>
319 <section>
320 <body>
321
322 <p>
323 Continuing on from the last section, you may be happy with your new kernel and
324 not have any need to keep older kernel versions around. To easily remove all
325 sources for a particular kernel except for the newest one, you can take
326 advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
327 the example using <c>gentoo-sources</c>:
328 </p>
329
330 <pre caption="Pruning old versions">
331 # <i>emerge -P gentoo-sources</i>
332 </pre>
333
334 <p>
335 In most cases, temporary files used during compilation will still remain under
336 the appropriate source directory under <path>/usr/src</path>. It is safe to
337 remove these using <c>rm</c>.
338 </p>
339
340 <p>
341 You can also safely delete any modules that were used by this kernel. This can
342 be done by removing the appropriate directories under <path>/lib/modules/</path>
343 that relate to the kernel versions you are removing. Be careful not to delete
344 modules belonging to kernels that you still use!
345 </p>
346
347 <p>
348 Finally, you can mount your <path>/boot</path> partition and remove the
349 <path>bzImage</path> and <path>System.map</path> files for the kernel(s)
350 you are pruning. You should also edit your boot loader configuration so that it
351 no longer references such kernel(s).
352 </p>
353
354 </body>
355 </section>
356 </chapter>
357
358 <chapter>
359 <title>Advanced: Using your old kernel .config to configure a new one</title>
360 <section>
361 <body>
362
363 <p>
364 It is sometimes possible to save time by re-using the configuration file from
365 your old kernel when configuring the new one. Note that this is generally
366 unsafe -- too many changes between every kernel release for this to be a
367 reliable upgrade path.
368 </p>
369
370 <p>
371 The only situation where this is appropriate is when upgrading from one Gentoo
372 kernel revision to another. For example, the changes made between
373 <c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
374 small, so it is usually OK to use the following method. However, it is not
375 appropriate to use it in the example used throughout this document: upgrading
376 from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
377 method described below does not display enough context to the user, often
378 resulting in the user running into problems because they disabled options that
379 they really didn't want to.
380 </p>
381
382 <p>
383 To reuse your old <path>.config</path>, you simply need to copy it over and then
384 run <c>make oldconfig</c>. In the following example, we take the configuration
385 from <c>gentoo-sources-2.6.9-r1</c> and import it into
386 <c>gentoo-sources-2.6.9-r2</c>.
387 </p>
388
389 <pre caption="Reusing your old config">
390 # <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
391 # <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
392 # <i>make oldconfig</i>
393 </pre>
394
395 <p>
396 At this point, you may be asked to produce answers for configuration options
397 which have changed between the two versions. Once you have done that, you can
398 compile and install your kernel as normal, without having to go through the
399 <c>menuconfig</c> configuration process.
400 </p>
401
402 </body>
403 </section>
404 </chapter>
405
406 <chapter>
407 <title>Problems after a kernel upgrade?</title>
408 <section>
409 <body>
410
411 <p>
412 With the rapid development of the Linux kernel, it is inevitable that some
413 changes made from one kernel release to another may cause some problems. If you
414 have any issues with the latest versions of <uri
415 link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
416 please do report the issues to us.
417 </p>
418
419 </body>
420 </section>
421 </chapter>
422
423 </guide>

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