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2 Applying Patches To The Linux Kernel
3 ------------------------------------
5 Original by: Jesper Juhl, August 2005
6 Last update: 2006-01-05
9 A frequently asked question on the Linux Kernel Mailing List is how to apply
10 a patch to the kernel or, more specifically, what base kernel a patch for
11 one of the many trees/branches should be applied to. Hopefully this document
12 will explain this to you.
14 In addition to explaining how to apply and revert patches, a brief
15 description of the different kernel trees (and examples of how to apply
16 their specific patches) is also provided.
19 What is a patch?
20 ---
21 A patch is a small text document containing a delta of changes between two
22 different versions of a source tree. Patches are created with the `diff'
23 program.
24 To correctly apply a patch you need to know what base it was generated from
25 and what new version the patch will change the source tree into. These
26 should both be present in the patch file metadata or be possible to deduce
27 from the filename.
30 How do I apply or revert a patch?
31 ---
32 You apply a patch with the `patch' program. The patch program reads a diff
33 (or patch) file and makes the changes to the source tree described in it.
35 Patches for the Linux kernel are generated relative to the parent directory
36 holding the kernel source dir.
38 This means that paths to files inside the patch file contain the name of the
39 kernel source directories it was generated against (or some other directory
40 names like "a/" and "b/").
41 Since this is unlikely to match the name of the kernel source dir on your
42 local machine (but is often useful info to see what version an otherwise
43 unlabeled patch was generated against) you should change into your kernel
44 source directory and then strip the first element of the path from filenames
45 in the patch file when applying it (the -p1 argument to `patch' does this).
47 To revert a previously applied patch, use the -R argument to patch.
48 So, if you applied a patch like this:
49 patch -p1 < ../patch-x.y.z
51 You can revert (undo) it like this:
52 patch -R -p1 < ../patch-x.y.z
55 How do I feed a patch/diff file to `patch'?
56 ---
57 This (as usual with Linux and other UNIX like operating systems) can be
58 done in several different ways.
59 In all the examples below I feed the file (in uncompressed form) to patch
60 via stdin using the following syntax:
61 patch -p1 < path/to/patch-x.y.z
63 If you just want to be able to follow the examples below and don't want to
64 know of more than one way to use patch, then you can stop reading this
65 section here.
67 Patch can also get the name of the file to use via the -i argument, like
68 this:
69 patch -p1 -i path/to/patch-x.y.z
71 If your patch file is compressed with gzip or bzip2 and you don't want to
72 uncompress it before applying it, then you can feed it to patch like this
73 instead:
74 zcat path/to/patch-x.y.z.gz | patch -p1
75 bzcat path/to/patch-x.y.z.bz2 | patch -p1
77 If you wish to uncompress the patch file by hand first before applying it
78 (what I assume you've done in the examples below), then you simply run
79 gunzip or bunzip2 on the file -- like this:
80 gunzip patch-x.y.z.gz
81 bunzip2 patch-x.y.z.bz2
83 Which will leave you with a plain text patch-x.y.z file that you can feed to
84 patch via stdin or the -i argument, as you prefer.
86 A few other nice arguments for patch are -s which causes patch to be silent
87 except for errors which is nice to prevent errors from scrolling out of the
88 screen too fast, and --dry-run which causes patch to just print a listing of
89 what would happen, but doesn't actually make any changes. Finally --verbose
90 tells patch to print more information about the work being done.
93 Common errors when patching
94 ---
95 When patch applies a patch file it attempts to verify the sanity of the
96 file in different ways.
97 Checking that the file looks like a valid patch file & checking the code
98 around the bits being modified matches the context provided in the patch are
99 just two of the basic sanity checks patch does.
101 If patch encounters something that doesn't look quite right it has two
102 options. It can either refuse to apply the changes and abort or it can try
103 to find a way to make the patch apply with a few minor changes.
105 One example of something that's not 'quite right' that patch will attempt to
106 fix up is if all the context matches, the lines being changed match, but the
107 line numbers are different. This can happen, for example, if the patch makes
108 a change in the middle of the file but for some reasons a few lines have
109 been added or removed near the beginning of the file. In that case
110 everything looks good it has just moved up or down a bit, and patch will
111 usually adjust the line numbers and apply the patch.
113 Whenever patch applies a patch that it had to modify a bit to make it fit
114 it'll tell you about it by saying the patch applied with 'fuzz'.
115 You should be wary of such changes since even though patch probably got it
116 right it doesn't /always/ get it right, and the result will sometimes be
117 wrong.
119 When patch encounters a change that it can't fix up with fuzz it rejects it
120 outright and leaves a file with a .rej extension (a reject file). You can
121 read this file to see exactly what change couldn't be applied, so you can
122 go fix it up by hand if you wish.
124 If you don't have any third-party patches applied to your kernel source, but
125 only patches from kernel.org and you apply the patches in the correct order,
126 and have made no modifications yourself to the source files, then you should
127 never see a fuzz or reject message from patch. If you do see such messages
128 anyway, then there's a high risk that either your local source tree or the
129 patch file is corrupted in some way. In that case you should probably try
130 re-downloading the patch and if things are still not OK then you'd be advised
131 to start with a fresh tree downloaded in full from kernel.org.
133 Let's look a bit more at some of the messages patch can produce.
135 If patch stops and presents a "File to patch:" prompt, then patch could not
136 find a file to be patched. Most likely you forgot to specify -p1 or you are
137 in the wrong directory. Less often, you'll find patches that need to be
138 applied with -p0 instead of -p1 (reading the patch file should reveal if
139 this is the case -- if so, then this is an error by the person who created
140 the patch but is not fatal).
142 If you get "Hunk #2 succeeded at 1887 with fuzz 2 (offset 7 lines)." or a
143 message similar to that, then it means that patch had to adjust the location
144 of the change (in this example it needed to move 7 lines from where it
145 expected to make the change to make it fit).
146 The resulting file may or may not be OK, depending on the reason the file
147 was different than expected.
148 This often happens if you try to apply a patch that was generated against a
149 different kernel version than the one you are trying to patch.
151 If you get a message like "Hunk #3 FAILED at 2387.", then it means that the
152 patch could not be applied correctly and the patch program was unable to
153 fuzz its way through. This will generate a .rej file with the change that
154 caused the patch to fail and also a .orig file showing you the original
155 content that couldn't be changed.
157 If you get "Reversed (or previously applied) patch detected! Assume -R? [n]"
158 then patch detected that the change contained in the patch seems to have
159 already been made.
160 If you actually did apply this patch previously and you just re-applied it
161 in error, then just say [n]o and abort this patch. If you applied this patch
162 previously and actually intended to revert it, but forgot to specify -R,
163 then you can say [y]es here to make patch revert it for you.
164 This can also happen if the creator of the patch reversed the source and
165 destination directories when creating the patch, and in that case reverting
166 the patch will in fact apply it.
168 A message similar to "patch: **** unexpected end of file in patch" or "patch
169 unexpectedly ends in middle of line" means that patch could make no sense of
170 the file you fed to it. Either your download is broken, you tried to feed
171 patch a compressed patch file without uncompressing it first, or the patch
172 file that you are using has been mangled by a mail client or mail transfer
173 agent along the way somewhere, e.g., by splitting a long line into two lines.
174 Often these warnings can easily be fixed by joining (concatenating) the
175 two lines that had been split.
177 As I already mentioned above, these errors should never happen if you apply
178 a patch from kernel.org to the correct version of an unmodified source tree.
179 So if you get these errors with kernel.org patches then you should probably
180 assume that either your patch file or your tree is broken and I'd advise you
181 to start over with a fresh download of a full kernel tree and the patch you
182 wish to apply.
185 Are there any alternatives to `patch'?
186 ---
187 Yes there are alternatives.
189 You can use the `interdiff' program (http://cyberelk.net/tim/patchutils/) to
190 generate a patch representing the differences between two patches and then
191 apply the result.
192 This will let you move from something like 2.6.12.2 to 2.6.12.3 in a single
193 step. The -z flag to interdiff will even let you feed it patches in gzip or
194 bzip2 compressed form directly without the use of zcat or bzcat or manual
195 decompression.
197 Here's how you'd go from 2.6.12.2 to 2.6.12.3 in a single step:
198 interdiff -z ../patch-2.6.12.2.bz2 ../patch-2.6.12.3.gz | patch -p1
200 Although interdiff may save you a step or two you are generally advised to
201 do the additional steps since interdiff can get things wrong in some cases.
203 Another alternative is `ketchup', which is a python script for automatic
204 downloading and applying of patches (http://www.selenic.com/ketchup/).
206 Other nice tools are diffstat, which shows a summary of changes made by a
207 patch; lsdiff, which displays a short listing of affected files in a patch
208 file, along with (optionally) the line numbers of the start of each patch;
209 and grepdiff, which displays a list of the files modified by a patch where
210 the patch contains a given regular expression.
213 Where can I download the patches?
214 ---
215 The patches are available at http://kernel.org/
216 Most recent patches are linked from the front page, but they also have
217 specific homes.
219 The 2.6.x.y (-stable) and 2.6.x patches live at
220 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/
222 The -rc patches live at
223 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/testing/
225 The -git patches live at
226 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/snapshots/
228 The -mm kernels live at
229 ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/
231 In place of ftp.kernel.org you can use ftp.cc.kernel.org, where cc is a
232 country code. This way you'll be downloading from a mirror site that's most
233 likely geographically closer to you, resulting in faster downloads for you,
234 less bandwidth used globally and less load on the main kernel.org servers --
235 these are good things, so do use mirrors when possible.
238 The 2.6.x kernels
239 ---
240 These are the base stable releases released by Linus. The highest numbered
241 release is the most recent.
243 If regressions or other serious flaws are found, then a -stable fix patch
244 will be released (see below) on top of this base. Once a new 2.6.x base
245 kernel is released, a patch is made available that is a delta between the
246 previous 2.6.x kernel and the new one.
248 To apply a patch moving from 2.6.11 to 2.6.12, you'd do the following (note
249 that such patches do *NOT* apply on top of 2.6.x.y kernels but on top of the
250 base 2.6.x kernel -- if you need to move from 2.6.x.y to 2.6.x+1 you need to
251 first revert the 2.6.x.y patch).
253 Here are some examples:
255 # moving from 2.6.11 to 2.6.12
256 $ cd ~/linux-2.6.11 # change to kernel source dir
257 $ patch -p1 < ../patch-2.6.12 # apply the 2.6.12 patch
258 $ cd ..
259 $ mv linux-2.6.11 linux-2.6.12 # rename source dir
261 # moving from 2.6.11.1 to 2.6.12
262 $ cd ~/linux-2.6.11.1 # change to kernel source dir
263 $ patch -p1 -R < ../patch-2.6.11.1 # revert the 2.6.11.1 patch
264 # source dir is now 2.6.11
265 $ patch -p1 < ../patch-2.6.12 # apply new 2.6.12 patch
266 $ cd ..
267 $ mv linux-2.6.11.1 linux-2.6.12 # rename source dir
270 The 2.6.x.y kernels
271 ---
272 Kernels with 4-digit versions are -stable kernels. They contain small(ish)
273 critical fixes for security problems or significant regressions discovered
274 in a given 2.6.x kernel.
276 This is the recommended branch for users who want the most recent stable
277 kernel and are not interested in helping test development/experimental
278 versions.
280 If no 2.6.x.y kernel is available, then the highest numbered 2.6.x kernel is
281 the current stable kernel.
283 note: the -stable team usually do make incremental patches available as well
284 as patches against the latest mainline release, but I only cover the
285 non-incremental ones below. The incremental ones can be found at
286 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/incr/
288 These patches are not incremental, meaning that for example the 2.6.12.3
289 patch does not apply on top of the 2.6.12.2 kernel source, but rather on top
290 of the base 2.6.12 kernel source .
291 So, in order to apply the 2.6.12.3 patch to your existing 2.6.12.2 kernel
292 source you have to first back out the 2.6.12.2 patch (so you are left with a
293 base 2.6.12 kernel source) and then apply the new 2.6.12.3 patch.
295 Here's a small example:
297 $ cd ~/linux-2.6.12.2 # change into the kernel source dir
298 $ patch -p1 -R < ../patch-2.6.12.2 # revert the 2.6.12.2 patch
299 $ patch -p1 < ../patch-2.6.12.3 # apply the new 2.6.12.3 patch
300 $ cd ..
301 $ mv linux-2.6.12.2 linux-2.6.12.3 # rename the kernel source dir
304 The -rc kernels
305 ---
306 These are release-candidate kernels. These are development kernels released
307 by Linus whenever he deems the current git (the kernel's source management
308 tool) tree to be in a reasonably sane state adequate for testing.
310 These kernels are not stable and you should expect occasional breakage if
311 you intend to run them. This is however the most stable of the main
312 development branches and is also what will eventually turn into the next
313 stable kernel, so it is important that it be tested by as many people as
314 possible.
316 This is a good branch to run for people who want to help out testing
317 development kernels but do not want to run some of the really experimental
318 stuff (such people should see the sections about -git and -mm kernels below).
320 The -rc patches are not incremental, they apply to a base 2.6.x kernel, just
321 like the 2.6.x.y patches described above. The kernel version before the -rcN
322 suffix denotes the version of the kernel that this -rc kernel will eventually
323 turn into.
324 So, 2.6.13-rc5 means that this is the fifth release candidate for the 2.6.13
325 kernel and the patch should be applied on top of the 2.6.12 kernel source.
327 Here are 3 examples of how to apply these patches:
329 # first an example of moving from 2.6.12 to 2.6.13-rc3
330 $ cd ~/linux-2.6.12 # change into the 2.6.12 source dir
331 $ patch -p1 < ../patch-2.6.13-rc3 # apply the 2.6.13-rc3 patch
332 $ cd ..
333 $ mv linux-2.6.12 linux-2.6.13-rc3 # rename the source dir
335 # now let's move from 2.6.13-rc3 to 2.6.13-rc5
336 $ cd ~/linux-2.6.13-rc3 # change into the 2.6.13-rc3 dir
337 $ patch -p1 -R < ../patch-2.6.13-rc3 # revert the 2.6.13-rc3 patch
338 $ patch -p1 < ../patch-2.6.13-rc5 # apply the new 2.6.13-rc5 patch
339 $ cd ..
340 $ mv linux-2.6.13-rc3 linux-2.6.13-rc5 # rename the source dir
342 # finally let's try and move from 2.6.12.3 to 2.6.13-rc5
343 $ cd ~/linux-2.6.12.3 # change to the kernel source dir
344 $ patch -p1 -R < ../patch-2.6.12.3 # revert the 2.6.12.3 patch
345 $ patch -p1 < ../patch-2.6.13-rc5 # apply new 2.6.13-rc5 patch
346 $ cd ..
347 $ mv linux-2.6.12.3 linux-2.6.13-rc5 # rename the kernel source dir
350 The -git kernels
351 ---
352 These are daily snapshots of Linus' kernel tree (managed in a git
353 repository, hence the name).
355 These patches are usually released daily and represent the current state of
356 Linus's tree. They are more experimental than -rc kernels since they are
357 generated automatically without even a cursory glance to see if they are
358 sane.
360 -git patches are not incremental and apply either to a base 2.6.x kernel or
361 a base 2.6.x-rc kernel -- you can see which from their name.
362 A patch named 2.6.12-git1 applies to the 2.6.12 kernel source and a patch
363 named 2.6.13-rc3-git2 applies to the source of the 2.6.13-rc3 kernel.
365 Here are some examples of how to apply these patches:
367 # moving from 2.6.12 to 2.6.12-git1
368 $ cd ~/linux-2.6.12 # change to the kernel source dir
369 $ patch -p1 < ../patch-2.6.12-git1 # apply the 2.6.12-git1 patch
370 $ cd ..
371 $ mv linux-2.6.12 linux-2.6.12-git1 # rename the kernel source dir
373 # moving from 2.6.12-git1 to 2.6.13-rc2-git3
374 $ cd ~/linux-2.6.12-git1 # change to the kernel source dir
375 $ patch -p1 -R < ../patch-2.6.12-git1 # revert the 2.6.12-git1 patch
376 # we now have a 2.6.12 kernel
377 $ patch -p1 < ../patch-2.6.13-rc2 # apply the 2.6.13-rc2 patch
378 # the kernel is now 2.6.13-rc2
379 $ patch -p1 < ../patch-2.6.13-rc2-git3 # apply the 2.6.13-rc2-git3 patch
380 # the kernel is now 2.6.13-rc2-git3
381 $ cd ..
382 $ mv linux-2.6.12-git1 linux-2.6.13-rc2-git3 # rename source dir
385 The -mm kernels
386 ---
387 These are experimental kernels released by Andrew Morton.
389 The -mm tree serves as a sort of proving ground for new features and other
390 experimental patches.
391 Once a patch has proved its worth in -mm for a while Andrew pushes it on to
392 Linus for inclusion in mainline.
394 Although it's encouraged that patches flow to Linus via the -mm tree, this
395 is not always enforced.
396 Subsystem maintainers (or individuals) sometimes push their patches directly
397 to Linus, even though (or after) they have been merged and tested in -mm (or
398 sometimes even without prior testing in -mm).
400 You should generally strive to get your patches into mainline via -mm to
401 ensure maximum testing.
403 This branch is in constant flux and contains many experimental features, a
404 lot of debugging patches not appropriate for mainline etc., and is the most
405 experimental of the branches described in this document.
407 These kernels are not appropriate for use on systems that are supposed to be
408 stable and they are more risky to run than any of the other branches (make
409 sure you have up-to-date backups -- that goes for any experimental kernel but
410 even more so for -mm kernels).
412 These kernels in addition to all the other experimental patches they contain
413 usually also contain any changes in the mainline -git kernels available at
414 the time of release.
416 Testing of -mm kernels is greatly appreciated since the whole point of the
417 tree is to weed out regressions, crashes, data corruption bugs, build
418 breakage (and any other bug in general) before changes are merged into the
419 more stable mainline Linus tree.
420 But testers of -mm should be aware that breakage in this tree is more common
421 than in any other tree.
423 The -mm kernels are not released on a fixed schedule, but usually a few -mm
424 kernels are released in between each -rc kernel (1 to 3 is common).
425 The -mm kernels apply to either a base 2.6.x kernel (when no -rc kernels
426 have been released yet) or to a Linus -rc kernel.
428 Here are some examples of applying the -mm patches:
430 # moving from 2.6.12 to 2.6.12-mm1
431 $ cd ~/linux-2.6.12 # change to the 2.6.12 source dir
432 $ patch -p1 < ../2.6.12-mm1 # apply the 2.6.12-mm1 patch
433 $ cd ..
434 $ mv linux-2.6.12 linux-2.6.12-mm1 # rename the source appropriately
436 # moving from 2.6.12-mm1 to 2.6.13-rc3-mm3
437 $ cd ~/linux-2.6.12-mm1
438 $ patch -p1 -R < ../2.6.12-mm1 # revert the 2.6.12-mm1 patch
439 # we now have a 2.6.12 source
440 $ patch -p1 < ../patch-2.6.13-rc3 # apply the 2.6.13-rc3 patch
441 # we now have a 2.6.13-rc3 source
442 $ patch -p1 < ../2.6.13-rc3-mm3 # apply the 2.6.13-rc3-mm3 patch
443 $ cd ..
444 $ mv linux-2.6.12-mm1 linux-2.6.13-rc3-mm3 # rename the source dir
447 This concludes this list of explanations of the various kernel trees.
448 I hope you are now clear on how to apply the various patches and help testing
449 the kernel.
451 Thank you's to Randy Dunlap, Rolf Eike Beer, Linus Torvalds, Bodo Eggert,
452 Johannes Stezenbach, Grant Coady, Pavel Machek and others that I may have
453 forgotten for their reviews and contributions to this document.