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609d99a3 | 1 | .. _applying_patches: |
754c7976 | 2 | |
9299c3e9 MCC |
3 | Applying Patches To The Linux Kernel |
4 | ++++++++++++++++++++++++++++++++++++ | |
754c7976 | 5 | |
9299c3e9 MCC |
6 | Original by: |
7 | Jesper Juhl, August 2005 | |
8 | ||
67972a53 JC |
9 | .. note:: |
10 | ||
11 | This document is obsolete. In most cases, rather than using ``patch`` | |
12 | manually, you'll almost certainly want to look at using Git instead. | |
754c7976 JJ |
13 | |
14 | A frequently asked question on the Linux Kernel Mailing List is how to apply | |
15 | a patch to the kernel or, more specifically, what base kernel a patch for | |
16 | one of the many trees/branches should be applied to. Hopefully this document | |
17 | will explain this to you. | |
18 | ||
19 | In addition to explaining how to apply and revert patches, a brief | |
20 | description of the different kernel trees (and examples of how to apply | |
21 | their specific patches) is also provided. | |
22 | ||
23 | ||
24 | What is a patch? | |
9299c3e9 MCC |
25 | ================ |
26 | ||
27 | A patch is a small text document containing a delta of changes between two | |
28 | different versions of a source tree. Patches are created with the ``diff`` | |
754c7976 | 29 | program. |
9299c3e9 | 30 | |
754c7976 JJ |
31 | To correctly apply a patch you need to know what base it was generated from |
32 | and what new version the patch will change the source tree into. These | |
33 | should both be present in the patch file metadata or be possible to deduce | |
34 | from the filename. | |
35 | ||
36 | ||
37 | How do I apply or revert a patch? | |
9299c3e9 MCC |
38 | ================================= |
39 | ||
40 | You apply a patch with the ``patch`` program. The patch program reads a diff | |
754c7976 JJ |
41 | (or patch) file and makes the changes to the source tree described in it. |
42 | ||
43 | Patches for the Linux kernel are generated relative to the parent directory | |
44 | holding the kernel source dir. | |
45 | ||
46 | This means that paths to files inside the patch file contain the name of the | |
47 | kernel source directories it was generated against (or some other directory | |
48 | names like "a/" and "b/"). | |
9299c3e9 | 49 | |
754c7976 JJ |
50 | Since this is unlikely to match the name of the kernel source dir on your |
51 | local machine (but is often useful info to see what version an otherwise | |
52 | unlabeled patch was generated against) you should change into your kernel | |
53 | source directory and then strip the first element of the path from filenames | |
9299c3e9 MCC |
54 | in the patch file when applying it (the ``-p1`` argument to ``patch`` does |
55 | this). | |
754c7976 JJ |
56 | |
57 | To revert a previously applied patch, use the -R argument to patch. | |
1b49ecf2 | 58 | So, if you applied a patch like this:: |
9299c3e9 | 59 | |
754c7976 JJ |
60 | patch -p1 < ../patch-x.y.z |
61 | ||
1b49ecf2 | 62 | You can revert (undo) it like this:: |
9299c3e9 | 63 | |
754c7976 JJ |
64 | patch -R -p1 < ../patch-x.y.z |
65 | ||
66 | ||
9299c3e9 MCC |
67 | How do I feed a patch/diff file to ``patch``? |
68 | ============================================= | |
69 | ||
70 | This (as usual with Linux and other UNIX like operating systems) can be | |
754c7976 | 71 | done in several different ways. |
9299c3e9 | 72 | |
754c7976 | 73 | In all the examples below I feed the file (in uncompressed form) to patch |
1b49ecf2 | 74 | via stdin using the following syntax:: |
9299c3e9 | 75 | |
754c7976 JJ |
76 | patch -p1 < path/to/patch-x.y.z |
77 | ||
78 | If you just want to be able to follow the examples below and don't want to | |
79 | know of more than one way to use patch, then you can stop reading this | |
80 | section here. | |
81 | ||
82 | Patch can also get the name of the file to use via the -i argument, like | |
1b49ecf2 | 83 | this:: |
9299c3e9 | 84 | |
754c7976 JJ |
85 | patch -p1 -i path/to/patch-x.y.z |
86 | ||
330ae7e9 | 87 | If your patch file is compressed with gzip or xz and you don't want to |
754c7976 | 88 | uncompress it before applying it, then you can feed it to patch like this |
1b49ecf2 | 89 | instead:: |
9299c3e9 | 90 | |
330ae7e9 MCC |
91 | xzcat path/to/patch-x.y.z.xz | patch -p1 |
92 | bzcat path/to/patch-x.y.z.gz | patch -p1 | |
754c7976 JJ |
93 | |
94 | If you wish to uncompress the patch file by hand first before applying it | |
95 | (what I assume you've done in the examples below), then you simply run | |
1b49ecf2 | 96 | gunzip or xz on the file -- like this:: |
9299c3e9 | 97 | |
754c7976 | 98 | gunzip patch-x.y.z.gz |
330ae7e9 | 99 | xz -d patch-x.y.z.xz |
754c7976 JJ |
100 | |
101 | Which will leave you with a plain text patch-x.y.z file that you can feed to | |
9299c3e9 | 102 | patch via stdin or the ``-i`` argument, as you prefer. |
754c7976 | 103 | |
9299c3e9 | 104 | A few other nice arguments for patch are ``-s`` which causes patch to be silent |
754c7976 | 105 | except for errors which is nice to prevent errors from scrolling out of the |
9299c3e9 MCC |
106 | screen too fast, and ``--dry-run`` which causes patch to just print a listing of |
107 | what would happen, but doesn't actually make any changes. Finally ``--verbose`` | |
754c7976 JJ |
108 | tells patch to print more information about the work being done. |
109 | ||
110 | ||
111 | Common errors when patching | |
9299c3e9 MCC |
112 | =========================== |
113 | ||
114 | When patch applies a patch file it attempts to verify the sanity of the | |
754c7976 | 115 | file in different ways. |
9299c3e9 | 116 | |
2d69049a | 117 | Checking that the file looks like a valid patch file and checking the code |
754c7976 JJ |
118 | around the bits being modified matches the context provided in the patch are |
119 | just two of the basic sanity checks patch does. | |
120 | ||
121 | If patch encounters something that doesn't look quite right it has two | |
122 | options. It can either refuse to apply the changes and abort or it can try | |
123 | to find a way to make the patch apply with a few minor changes. | |
124 | ||
125 | One example of something that's not 'quite right' that patch will attempt to | |
126 | fix up is if all the context matches, the lines being changed match, but the | |
127 | line numbers are different. This can happen, for example, if the patch makes | |
128 | a change in the middle of the file but for some reasons a few lines have | |
129 | been added or removed near the beginning of the file. In that case | |
130 | everything looks good it has just moved up or down a bit, and patch will | |
131 | usually adjust the line numbers and apply the patch. | |
132 | ||
133 | Whenever patch applies a patch that it had to modify a bit to make it fit | |
9299c3e9 | 134 | it'll tell you about it by saying the patch applied with **fuzz**. |
754c7976 JJ |
135 | You should be wary of such changes since even though patch probably got it |
136 | right it doesn't /always/ get it right, and the result will sometimes be | |
137 | wrong. | |
138 | ||
139 | When patch encounters a change that it can't fix up with fuzz it rejects it | |
9299c3e9 | 140 | outright and leaves a file with a ``.rej`` extension (a reject file). You can |
90f2447d | 141 | read this file to see exactly what change couldn't be applied, so you can |
754c7976 JJ |
142 | go fix it up by hand if you wish. |
143 | ||
c594a50d | 144 | If you don't have any third-party patches applied to your kernel source, but |
754c7976 JJ |
145 | only patches from kernel.org and you apply the patches in the correct order, |
146 | and have made no modifications yourself to the source files, then you should | |
147 | never see a fuzz or reject message from patch. If you do see such messages | |
148 | anyway, then there's a high risk that either your local source tree or the | |
149 | patch file is corrupted in some way. In that case you should probably try | |
90f2447d | 150 | re-downloading the patch and if things are still not OK then you'd be advised |
754c7976 JJ |
151 | to start with a fresh tree downloaded in full from kernel.org. |
152 | ||
153 | Let's look a bit more at some of the messages patch can produce. | |
154 | ||
9299c3e9 | 155 | If patch stops and presents a ``File to patch:`` prompt, then patch could not |
754c7976 JJ |
156 | find a file to be patched. Most likely you forgot to specify -p1 or you are |
157 | in the wrong directory. Less often, you'll find patches that need to be | |
9299c3e9 | 158 | applied with ``-p0`` instead of ``-p1`` (reading the patch file should reveal if |
c594a50d | 159 | this is the case -- if so, then this is an error by the person who created |
754c7976 JJ |
160 | the patch but is not fatal). |
161 | ||
9299c3e9 | 162 | If you get ``Hunk #2 succeeded at 1887 with fuzz 2 (offset 7 lines).`` or a |
754c7976 JJ |
163 | message similar to that, then it means that patch had to adjust the location |
164 | of the change (in this example it needed to move 7 lines from where it | |
165 | expected to make the change to make it fit). | |
9299c3e9 | 166 | |
754c7976 JJ |
167 | The resulting file may or may not be OK, depending on the reason the file |
168 | was different than expected. | |
9299c3e9 | 169 | |
754c7976 JJ |
170 | This often happens if you try to apply a patch that was generated against a |
171 | different kernel version than the one you are trying to patch. | |
172 | ||
9299c3e9 | 173 | If you get a message like ``Hunk #3 FAILED at 2387.``, then it means that the |
754c7976 | 174 | patch could not be applied correctly and the patch program was unable to |
9299c3e9 MCC |
175 | fuzz its way through. This will generate a ``.rej`` file with the change that |
176 | caused the patch to fail and also a ``.orig`` file showing you the original | |
754c7976 JJ |
177 | content that couldn't be changed. |
178 | ||
9299c3e9 | 179 | If you get ``Reversed (or previously applied) patch detected! Assume -R? [n]`` |
754c7976 JJ |
180 | then patch detected that the change contained in the patch seems to have |
181 | already been made. | |
9299c3e9 | 182 | |
754c7976 JJ |
183 | If you actually did apply this patch previously and you just re-applied it |
184 | in error, then just say [n]o and abort this patch. If you applied this patch | |
185 | previously and actually intended to revert it, but forgot to specify -R, | |
9299c3e9 MCC |
186 | then you can say [**y**]es here to make patch revert it for you. |
187 | ||
754c7976 JJ |
188 | This can also happen if the creator of the patch reversed the source and |
189 | destination directories when creating the patch, and in that case reverting | |
190 | the patch will in fact apply it. | |
191 | ||
9299c3e9 MCC |
192 | A message similar to ``patch: **** unexpected end of file in patch`` or |
193 | ``patch unexpectedly ends in middle of line`` means that patch could make no | |
194 | sense of the file you fed to it. Either your download is broken, you tried to | |
195 | feed patch a compressed patch file without uncompressing it first, or the patch | |
c594a50d RD |
196 | file that you are using has been mangled by a mail client or mail transfer |
197 | agent along the way somewhere, e.g., by splitting a long line into two lines. | |
198 | Often these warnings can easily be fixed by joining (concatenating) the | |
199 | two lines that had been split. | |
754c7976 JJ |
200 | |
201 | As I already mentioned above, these errors should never happen if you apply | |
202 | a patch from kernel.org to the correct version of an unmodified source tree. | |
203 | So if you get these errors with kernel.org patches then you should probably | |
c594a50d | 204 | assume that either your patch file or your tree is broken and I'd advise you |
754c7976 JJ |
205 | to start over with a fresh download of a full kernel tree and the patch you |
206 | wish to apply. | |
207 | ||
208 | ||
9299c3e9 MCC |
209 | Are there any alternatives to ``patch``? |
210 | ======================================== | |
90f2447d | 211 | |
9299c3e9 MCC |
212 | |
213 | Yes there are alternatives. | |
214 | ||
215 | You can use the ``interdiff`` program (http://cyberelk.net/tim/patchutils/) to | |
90f2447d JJ |
216 | generate a patch representing the differences between two patches and then |
217 | apply the result. | |
9299c3e9 | 218 | |
0358affb | 219 | This will let you move from something like 5.7.2 to 5.7.3 in a single |
754c7976 JJ |
220 | step. The -z flag to interdiff will even let you feed it patches in gzip or |
221 | bzip2 compressed form directly without the use of zcat or bzcat or manual | |
222 | decompression. | |
223 | ||
0358affb | 224 | Here's how you'd go from 5.7.2 to 5.7.3 in a single step:: |
9299c3e9 | 225 | |
0358affb | 226 | interdiff -z ../patch-5.7.2.gz ../patch-5.7.3.gz | patch -p1 |
754c7976 JJ |
227 | |
228 | Although interdiff may save you a step or two you are generally advised to | |
229 | do the additional steps since interdiff can get things wrong in some cases. | |
230 | ||
9299c3e9 | 231 | Another alternative is ``ketchup``, which is a python script for automatic |
93431e06 | 232 | downloading and applying of patches (https://www.selenic.com/ketchup/). |
754c7976 | 233 | |
9299c3e9 | 234 | Other nice tools are diffstat, which shows a summary of changes made by a |
c594a50d RD |
235 | patch; lsdiff, which displays a short listing of affected files in a patch |
236 | file, along with (optionally) the line numbers of the start of each patch; | |
237 | and grepdiff, which displays a list of the files modified by a patch where | |
754c7976 JJ |
238 | the patch contains a given regular expression. |
239 | ||
240 | ||
241 | Where can I download the patches? | |
9299c3e9 MCC |
242 | ================================= |
243 | ||
93431e06 | 244 | The patches are available at https://kernel.org/ |
754c7976 JJ |
245 | Most recent patches are linked from the front page, but they also have |
246 | specific homes. | |
247 | ||
0358affb | 248 | The 5.x.y (-stable) and 5.x patches live at |
9299c3e9 | 249 | |
0358affb | 250 | https://www.kernel.org/pub/linux/kernel/v5.x/ |
754c7976 | 251 | |
0358affb AB |
252 | The -rc patches are not stored on the webserver but are generated on |
253 | demand from git tags such as | |
9299c3e9 | 254 | |
0358affb | 255 | https://git.kernel.org/torvalds/p/v5.1-rc1/v5.0 |
754c7976 | 256 | |
0358affb | 257 | The stable -rc patches live at |
754c7976 | 258 | |
0358affb AB |
259 | https://www.kernel.org/pub/linux/kernel/v5.x/stable-review/ |
260 | ||
261 | ||
262 | The 5.x kernels | |
330ae7e9 | 263 | =============== |
9299c3e9 MCC |
264 | |
265 | These are the base stable releases released by Linus. The highest numbered | |
754c7976 JJ |
266 | release is the most recent. |
267 | ||
c594a50d | 268 | If regressions or other serious flaws are found, then a -stable fix patch |
0358affb | 269 | will be released (see below) on top of this base. Once a new 5.x base |
754c7976 | 270 | kernel is released, a patch is made available that is a delta between the |
0358affb | 271 | previous 5.x kernel and the new one. |
754c7976 | 272 | |
0358affb AB |
273 | To apply a patch moving from 5.6 to 5.7, you'd do the following (note |
274 | that such patches do **NOT** apply on top of 5.x.y kernels but on top of the | |
275 | base 5.x kernel -- if you need to move from 5.x.y to 5.x+1 you need to | |
276 | first revert the 5.x.y patch). | |
754c7976 | 277 | |
1b49ecf2 | 278 | Here are some examples:: |
9299c3e9 | 279 | |
0358affb | 280 | # moving from 5.6 to 5.7 |
330ae7e9 | 281 | |
0358affb AB |
282 | $ cd ~/linux-5.6 # change to kernel source dir |
283 | $ patch -p1 < ../patch-5.7 # apply the 5.7 patch | |
9299c3e9 | 284 | $ cd .. |
0358affb | 285 | $ mv linux-5.6 linux-5.7 # rename source dir |
754c7976 | 286 | |
0358affb | 287 | # moving from 5.6.1 to 5.7 |
330ae7e9 | 288 | |
0358affb AB |
289 | $ cd ~/linux-5.6.1 # change to kernel source dir |
290 | $ patch -p1 -R < ../patch-5.6.1 # revert the 5.6.1 patch | |
291 | # source dir is now 5.6 | |
292 | $ patch -p1 < ../patch-5.7 # apply new 5.7 patch | |
9299c3e9 | 293 | $ cd .. |
0358affb | 294 | $ mv linux-5.6.1 linux-5.7 # rename source dir |
754c7976 JJ |
295 | |
296 | ||
0358affb | 297 | The 5.x.y kernels |
330ae7e9 | 298 | ================= |
9299c3e9 | 299 | |
330ae7e9 | 300 | Kernels with 3-digit versions are -stable kernels. They contain small(ish) |
754c7976 | 301 | critical fixes for security problems or significant regressions discovered |
0358affb | 302 | in a given 5.x kernel. |
754c7976 JJ |
303 | |
304 | This is the recommended branch for users who want the most recent stable | |
305 | kernel and are not interested in helping test development/experimental | |
306 | versions. | |
307 | ||
0358affb | 308 | If no 5.x.y kernel is available, then the highest numbered 5.x kernel is |
754c7976 JJ |
309 | the current stable kernel. |
310 | ||
9299c3e9 MCC |
311 | .. note:: |
312 | ||
313 | The -stable team usually do make incremental patches available as well | |
c594a50d RD |
314 | as patches against the latest mainline release, but I only cover the |
315 | non-incremental ones below. The incremental ones can be found at | |
0358affb | 316 | https://www.kernel.org/pub/linux/kernel/v5.x/incr/ |
c594a50d | 317 | |
0358affb AB |
318 | These patches are not incremental, meaning that for example the 5.7.3 |
319 | patch does not apply on top of the 5.7.2 kernel source, but rather on top | |
320 | of the base 5.7 kernel source. | |
9299c3e9 | 321 | |
0358affb AB |
322 | So, in order to apply the 5.7.3 patch to your existing 5.7.2 kernel |
323 | source you have to first back out the 5.7.2 patch (so you are left with a | |
324 | base 5.7 kernel source) and then apply the new 5.7.3 patch. | |
754c7976 | 325 | |
1b49ecf2 | 326 | Here's a small example:: |
754c7976 | 327 | |
0358affb AB |
328 | $ cd ~/linux-5.7.2 # change to the kernel source dir |
329 | $ patch -p1 -R < ../patch-5.7.2 # revert the 5.7.2 patch | |
330 | $ patch -p1 < ../patch-5.7.3 # apply the new 5.7.3 patch | |
9299c3e9 | 331 | $ cd .. |
0358affb | 332 | $ mv linux-5.7.2 linux-5.7.3 # rename the kernel source dir |
754c7976 JJ |
333 | |
334 | The -rc kernels | |
9299c3e9 MCC |
335 | =============== |
336 | ||
337 | These are release-candidate kernels. These are development kernels released | |
754c7976 JJ |
338 | by Linus whenever he deems the current git (the kernel's source management |
339 | tool) tree to be in a reasonably sane state adequate for testing. | |
340 | ||
341 | These kernels are not stable and you should expect occasional breakage if | |
342 | you intend to run them. This is however the most stable of the main | |
343 | development branches and is also what will eventually turn into the next | |
344 | stable kernel, so it is important that it be tested by as many people as | |
345 | possible. | |
346 | ||
347 | This is a good branch to run for people who want to help out testing | |
348 | development kernels but do not want to run some of the really experimental | |
f7a6dd84 | 349 | stuff (such people should see the sections about -next and -mm kernels below). |
754c7976 | 350 | |
0358affb AB |
351 | The -rc patches are not incremental, they apply to a base 5.x kernel, just |
352 | like the 5.x.y patches described above. The kernel version before the -rcN | |
754c7976 JJ |
353 | suffix denotes the version of the kernel that this -rc kernel will eventually |
354 | turn into. | |
9299c3e9 | 355 | |
0358affb AB |
356 | So, 5.8-rc5 means that this is the fifth release candidate for the 5.8 |
357 | kernel and the patch should be applied on top of the 5.7 kernel source. | |
754c7976 | 358 | |
1b49ecf2 | 359 | Here are 3 examples of how to apply these patches:: |
9299c3e9 | 360 | |
0358affb | 361 | # first an example of moving from 5.7 to 5.8-rc3 |
330ae7e9 | 362 | |
0358affb AB |
363 | $ cd ~/linux-5.7 # change to the 5.7 source dir |
364 | $ patch -p1 < ../patch-5.8-rc3 # apply the 5.8-rc3 patch | |
9299c3e9 | 365 | $ cd .. |
0358affb | 366 | $ mv linux-5.7 linux-5.8-rc3 # rename the source dir |
754c7976 | 367 | |
0358affb | 368 | # now let's move from 5.8-rc3 to 5.8-rc5 |
330ae7e9 | 369 | |
0358affb AB |
370 | $ cd ~/linux-5.8-rc3 # change to the 5.8-rc3 dir |
371 | $ patch -p1 -R < ../patch-5.8-rc3 # revert the 5.8-rc3 patch | |
372 | $ patch -p1 < ../patch-5.8-rc5 # apply the new 5.8-rc5 patch | |
9299c3e9 | 373 | $ cd .. |
0358affb | 374 | $ mv linux-5.8-rc3 linux-5.8-rc5 # rename the source dir |
330ae7e9 | 375 | |
0358affb | 376 | # finally let's try and move from 5.7.3 to 5.8-rc5 |
754c7976 | 377 | |
0358affb AB |
378 | $ cd ~/linux-5.7.3 # change to the kernel source dir |
379 | $ patch -p1 -R < ../patch-5.7.3 # revert the 5.7.3 patch | |
380 | $ patch -p1 < ../patch-5.8-rc5 # apply new 5.8-rc5 patch | |
9299c3e9 | 381 | $ cd .. |
0358affb | 382 | $ mv linux-5.7.3 linux-5.8-rc5 # rename the kernel source dir |
754c7976 JJ |
383 | |
384 | ||
330ae7e9 MCC |
385 | The -mm patches and the linux-next tree |
386 | ======================================= | |
754c7976 | 387 | |
330ae7e9 | 388 | The -mm patches are experimental patches released by Andrew Morton. |
9299c3e9 | 389 | |
330ae7e9 MCC |
390 | In the past, -mm tree were used to also test subsystem patches, but this |
391 | function is now done via the | |
d44f571f | 392 | `linux-next` (https://www.kernel.org/doc/man-pages/linux-next.html) |
330ae7e9 MCC |
393 | tree. The Subsystem maintainers push their patches first to linux-next, |
394 | and, during the merge window, sends them directly to Linus. | |
754c7976 | 395 | |
330ae7e9 MCC |
396 | The -mm patches serve as a sort of proving ground for new features and other |
397 | experimental patches that aren't merged via a subsystem tree. | |
398 | Once such patches has proved its worth in -mm for a while Andrew pushes | |
399 | it on to Linus for inclusion in mainline. | |
754c7976 | 400 | |
330ae7e9 MCC |
401 | The linux-next tree is daily updated, and includes the -mm patches. |
402 | Both are in constant flux and contains many experimental features, a | |
c594a50d | 403 | lot of debugging patches not appropriate for mainline etc., and is the most |
754c7976 JJ |
404 | experimental of the branches described in this document. |
405 | ||
330ae7e9 | 406 | These patches are not appropriate for use on systems that are supposed to be |
754c7976 | 407 | stable and they are more risky to run than any of the other branches (make |
c594a50d | 408 | sure you have up-to-date backups -- that goes for any experimental kernel but |
330ae7e9 | 409 | even more so for -mm patches or using a Kernel from the linux-next tree). |
754c7976 | 410 | |
330ae7e9 MCC |
411 | Testing of -mm patches and linux-next is greatly appreciated since the whole |
412 | point of those are to weed out regressions, crashes, data corruption bugs, | |
413 | build breakage (and any other bug in general) before changes are merged into | |
414 | the more stable mainline Linus tree. | |
9299c3e9 | 415 | |
330ae7e9 MCC |
416 | But testers of -mm and linux-next should be aware that breakages are |
417 | more common than in any other tree. | |
754c7976 JJ |
418 | |
419 | ||
90f2447d JJ |
420 | This concludes this list of explanations of the various kernel trees. |
421 | I hope you are now clear on how to apply the various patches and help testing | |
422 | the kernel. | |
423 | ||
424 | Thank you's to Randy Dunlap, Rolf Eike Beer, Linus Torvalds, Bodo Eggert, | |
425 | Johannes Stezenbach, Grant Coady, Pavel Machek and others that I may have | |
426 | forgotten for their reviews and contributions to this document. |