Based on kernel version 4.9. Page generated on 2016-12-21 14:28 EST.
1 .. _applying_patches: 2 3 Applying Patches To The Linux Kernel 4 ++++++++++++++++++++++++++++++++++++ 5 6 Original by: 7 Jesper Juhl, August 2005 8 9 Last update: 10 2016-09-14 11 12 13 A frequently asked question on the Linux Kernel Mailing List is how to apply 14 a patch to the kernel or, more specifically, what base kernel a patch for 15 one of the many trees/branches should be applied to. Hopefully this document 16 will explain this to you. 17 18 In addition to explaining how to apply and revert patches, a brief 19 description of the different kernel trees (and examples of how to apply 20 their specific patches) is also provided. 21 22 23 What is a patch? 24 ================ 25 26 A patch is a small text document containing a delta of changes between two 27 different versions of a source tree. Patches are created with the ``diff`` 28 program. 29 30 To correctly apply a patch you need to know what base it was generated from 31 and what new version the patch will change the source tree into. These 32 should both be present in the patch file metadata or be possible to deduce 33 from the filename. 34 35 36 How do I apply or revert a patch? 37 ================================= 38 39 You apply a patch with the ``patch`` program. The patch program reads a diff 40 (or patch) file and makes the changes to the source tree described in it. 41 42 Patches for the Linux kernel are generated relative to the parent directory 43 holding the kernel source dir. 44 45 This means that paths to files inside the patch file contain the name of the 46 kernel source directories it was generated against (or some other directory 47 names like "a/" and "b/"). 48 49 Since this is unlikely to match the name of the kernel source dir on your 50 local machine (but is often useful info to see what version an otherwise 51 unlabeled patch was generated against) you should change into your kernel 52 source directory and then strip the first element of the path from filenames 53 in the patch file when applying it (the ``-p1`` argument to ``patch`` does 54 this). 55 56 To revert a previously applied patch, use the -R argument to patch. 57 So, if you applied a patch like this:: 58 59 patch -p1 < ../patch-x.y.z 60 61 You can revert (undo) it like this:: 62 63 patch -R -p1 < ../patch-x.y.z 64 65 66 How do I feed a patch/diff file to ``patch``? 67 ============================================= 68 69 This (as usual with Linux and other UNIX like operating systems) can be 70 done in several different ways. 71 72 In all the examples below I feed the file (in uncompressed form) to patch 73 via stdin using the following syntax:: 74 75 patch -p1 < path/to/patch-x.y.z 76 77 If you just want to be able to follow the examples below and don't want to 78 know of more than one way to use patch, then you can stop reading this 79 section here. 80 81 Patch can also get the name of the file to use via the -i argument, like 82 this:: 83 84 patch -p1 -i path/to/patch-x.y.z 85 86 If your patch file is compressed with gzip or xz and you don't want to 87 uncompress it before applying it, then you can feed it to patch like this 88 instead:: 89 90 xzcat path/to/patch-x.y.z.xz | patch -p1 91 bzcat path/to/patch-x.y.z.gz | patch -p1 92 93 If you wish to uncompress the patch file by hand first before applying it 94 (what I assume you've done in the examples below), then you simply run 95 gunzip or xz on the file -- like this:: 96 97 gunzip patch-x.y.z.gz 98 xz -d patch-x.y.z.xz 99 100 Which will leave you with a plain text patch-x.y.z file that you can feed to 101 patch via stdin or the ``-i`` argument, as you prefer. 102 103 A few other nice arguments for patch are ``-s`` which causes patch to be silent 104 except for errors which is nice to prevent errors from scrolling out of the 105 screen too fast, and ``--dry-run`` which causes patch to just print a listing of 106 what would happen, but doesn't actually make any changes. Finally ``--verbose`` 107 tells patch to print more information about the work being done. 108 109 110 Common errors when patching 111 =========================== 112 113 When patch applies a patch file it attempts to verify the sanity of the 114 file in different ways. 115 116 Checking that the file looks like a valid patch file and checking the code 117 around the bits being modified matches the context provided in the patch are 118 just two of the basic sanity checks patch does. 119 120 If patch encounters something that doesn't look quite right it has two 121 options. It can either refuse to apply the changes and abort or it can try 122 to find a way to make the patch apply with a few minor changes. 123 124 One example of something that's not 'quite right' that patch will attempt to 125 fix up is if all the context matches, the lines being changed match, but the 126 line numbers are different. This can happen, for example, if the patch makes 127 a change in the middle of the file but for some reasons a few lines have 128 been added or removed near the beginning of the file. In that case 129 everything looks good it has just moved up or down a bit, and patch will 130 usually adjust the line numbers and apply the patch. 131 132 Whenever patch applies a patch that it had to modify a bit to make it fit 133 it'll tell you about it by saying the patch applied with **fuzz**. 134 You should be wary of such changes since even though patch probably got it 135 right it doesn't /always/ get it right, and the result will sometimes be 136 wrong. 137 138 When patch encounters a change that it can't fix up with fuzz it rejects it 139 outright and leaves a file with a ``.rej`` extension (a reject file). You can 140 read this file to see exactly what change couldn't be applied, so you can 141 go fix it up by hand if you wish. 142 143 If you don't have any third-party patches applied to your kernel source, but 144 only patches from kernel.org and you apply the patches in the correct order, 145 and have made no modifications yourself to the source files, then you should 146 never see a fuzz or reject message from patch. If you do see such messages 147 anyway, then there's a high risk that either your local source tree or the 148 patch file is corrupted in some way. In that case you should probably try 149 re-downloading the patch and if things are still not OK then you'd be advised 150 to start with a fresh tree downloaded in full from kernel.org. 151 152 Let's look a bit more at some of the messages patch can produce. 153 154 If patch stops and presents a ``File to patch:`` prompt, then patch could not 155 find a file to be patched. Most likely you forgot to specify -p1 or you are 156 in the wrong directory. Less often, you'll find patches that need to be 157 applied with ``-p0`` instead of ``-p1`` (reading the patch file should reveal if 158 this is the case -- if so, then this is an error by the person who created 159 the patch but is not fatal). 160 161 If you get ``Hunk #2 succeeded at 1887 with fuzz 2 (offset 7 lines).`` or a 162 message similar to that, then it means that patch had to adjust the location 163 of the change (in this example it needed to move 7 lines from where it 164 expected to make the change to make it fit). 165 166 The resulting file may or may not be OK, depending on the reason the file 167 was different than expected. 168 169 This often happens if you try to apply a patch that was generated against a 170 different kernel version than the one you are trying to patch. 171 172 If you get a message like ``Hunk #3 FAILED at 2387.``, then it means that the 173 patch could not be applied correctly and the patch program was unable to 174 fuzz its way through. This will generate a ``.rej`` file with the change that 175 caused the patch to fail and also a ``.orig`` file showing you the original 176 content that couldn't be changed. 177 178 If you get ``Reversed (or previously applied) patch detected! Assume -R? [n]`` 179 then patch detected that the change contained in the patch seems to have 180 already been made. 181 182 If you actually did apply this patch previously and you just re-applied it 183 in error, then just say [n]o and abort this patch. If you applied this patch 184 previously and actually intended to revert it, but forgot to specify -R, 185 then you can say [**y**]es here to make patch revert it for you. 186 187 This can also happen if the creator of the patch reversed the source and 188 destination directories when creating the patch, and in that case reverting 189 the patch will in fact apply it. 190 191 A message similar to ``patch: **** unexpected end of file in patch`` or 192 ``patch unexpectedly ends in middle of line`` means that patch could make no 193 sense of the file you fed to it. Either your download is broken, you tried to 194 feed patch a compressed patch file without uncompressing it first, or the patch 195 file that you are using has been mangled by a mail client or mail transfer 196 agent along the way somewhere, e.g., by splitting a long line into two lines. 197 Often these warnings can easily be fixed by joining (concatenating) the 198 two lines that had been split. 199 200 As I already mentioned above, these errors should never happen if you apply 201 a patch from kernel.org to the correct version of an unmodified source tree. 202 So if you get these errors with kernel.org patches then you should probably 203 assume that either your patch file or your tree is broken and I'd advise you 204 to start over with a fresh download of a full kernel tree and the patch you 205 wish to apply. 206 207 208 Are there any alternatives to ``patch``? 209 ======================================== 210 211 212 Yes there are alternatives. 213 214 You can use the ``interdiff`` program (http://cyberelk.net/tim/patchutils/) to 215 generate a patch representing the differences between two patches and then 216 apply the result. 217 218 This will let you move from something like 4.7.2 to 4.7.3 in a single 219 step. The -z flag to interdiff will even let you feed it patches in gzip or 220 bzip2 compressed form directly without the use of zcat or bzcat or manual 221 decompression. 222 223 Here's how you'd go from 4.7.2 to 4.7.3 in a single step:: 224 225 interdiff -z ../patch-4.7.2.gz ../patch-4.7.3.gz | patch -p1 226 227 Although interdiff may save you a step or two you are generally advised to 228 do the additional steps since interdiff can get things wrong in some cases. 229 230 Another alternative is ``ketchup``, which is a python script for automatic 231 downloading and applying of patches (http://www.selenic.com/ketchup/). 232 233 Other nice tools are diffstat, which shows a summary of changes made by a 234 patch; lsdiff, which displays a short listing of affected files in a patch 235 file, along with (optionally) the line numbers of the start of each patch; 236 and grepdiff, which displays a list of the files modified by a patch where 237 the patch contains a given regular expression. 238 239 240 Where can I download the patches? 241 ================================= 242 243 The patches are available at http://kernel.org/ 244 Most recent patches are linked from the front page, but they also have 245 specific homes. 246 247 The 4.x.y (-stable) and 4.x patches live at 248 249 ftp://ftp.kernel.org/pub/linux/kernel/v4.x/ 250 251 The -rc patches live at 252 253 ftp://ftp.kernel.org/pub/linux/kernel/v4.x/testing/ 254 255 In place of ``ftp.kernel.org`` you can use ``ftp.cc.kernel.org``, where cc is a 256 country code. This way you'll be downloading from a mirror site that's most 257 likely geographically closer to you, resulting in faster downloads for you, 258 less bandwidth used globally and less load on the main kernel.org servers -- 259 these are good things, so do use mirrors when possible. 260 261 262 The 4.x kernels 263 =============== 264 265 These are the base stable releases released by Linus. The highest numbered 266 release is the most recent. 267 268 If regressions or other serious flaws are found, then a -stable fix patch 269 will be released (see below) on top of this base. Once a new 4.x base 270 kernel is released, a patch is made available that is a delta between the 271 previous 4.x kernel and the new one. 272 273 To apply a patch moving from 4.6 to 4.7, you'd do the following (note 274 that such patches do **NOT** apply on top of 4.x.y kernels but on top of the 275 base 4.x kernel -- if you need to move from 4.x.y to 4.x+1 you need to 276 first revert the 4.x.y patch). 277 278 Here are some examples:: 279 280 # moving from 4.6 to 4.7 281 282 $ cd ~/linux-4.6 # change to kernel source dir 283 $ patch -p1 < ../patch-4.7 # apply the 4.7 patch 284 $ cd .. 285 $ mv linux-4.6 linux-4.7 # rename source dir 286 287 # moving from 4.6.1 to 4.7 288 289 $ cd ~/linux-4.6.1 # change to kernel source dir 290 $ patch -p1 -R < ../patch-4.6.1 # revert the 4.6.1 patch 291 # source dir is now 4.6 292 $ patch -p1 < ../patch-4.7 # apply new 4.7 patch 293 $ cd .. 294 $ mv linux-4.6.1 linux-4.7 # rename source dir 295 296 297 The 4.x.y kernels 298 ================= 299 300 Kernels with 3-digit versions are -stable kernels. They contain small(ish) 301 critical fixes for security problems or significant regressions discovered 302 in a given 4.x kernel. 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. 307 308 If no 4.x.y kernel is available, then the highest numbered 4.x kernel is 309 the current stable kernel. 310 311 .. note:: 312 313 The -stable team usually do make incremental patches available as well 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 316 ftp://ftp.kernel.org/pub/linux/kernel/v4.x/incr/ 317 318 These patches are not incremental, meaning that for example the 4.7.3 319 patch does not apply on top of the 4.7.2 kernel source, but rather on top 320 of the base 4.7 kernel source. 321 322 So, in order to apply the 4.7.3 patch to your existing 4.7.2 kernel 323 source you have to first back out the 4.7.2 patch (so you are left with a 324 base 4.7 kernel source) and then apply the new 4.7.3 patch. 325 326 Here's a small example:: 327 328 $ cd ~/linux-4.7.2 # change to the kernel source dir 329 $ patch -p1 -R < ../patch-4.7.2 # revert the 4.7.2 patch 330 $ patch -p1 < ../patch-4.7.3 # apply the new 4.7.3 patch 331 $ cd .. 332 $ mv linux-4.7.2 linux-4.7.3 # rename the kernel source dir 333 334 The -rc kernels 335 =============== 336 337 These are release-candidate kernels. These are development kernels released 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 349 stuff (such people should see the sections about -git and -mm kernels below). 350 351 The -rc patches are not incremental, they apply to a base 4.x kernel, just 352 like the 4.x.y patches described above. The kernel version before the -rcN 353 suffix denotes the version of the kernel that this -rc kernel will eventually 354 turn into. 355 356 So, 4.8-rc5 means that this is the fifth release candidate for the 4.8 357 kernel and the patch should be applied on top of the 4.7 kernel source. 358 359 Here are 3 examples of how to apply these patches:: 360 361 # first an example of moving from 4.7 to 4.8-rc3 362 363 $ cd ~/linux-4.7 # change to the 4.7 source dir 364 $ patch -p1 < ../patch-4.8-rc3 # apply the 4.8-rc3 patch 365 $ cd .. 366 $ mv linux-4.7 linux-4.8-rc3 # rename the source dir 367 368 # now let's move from 4.8-rc3 to 4.8-rc5 369 370 $ cd ~/linux-4.8-rc3 # change to the 4.8-rc3 dir 371 $ patch -p1 -R < ../patch-4.8-rc3 # revert the 4.8-rc3 patch 372 $ patch -p1 < ../patch-4.8-rc5 # apply the new 4.8-rc5 patch 373 $ cd .. 374 $ mv linux-4.8-rc3 linux-4.8-rc5 # rename the source dir 375 376 # finally let's try and move from 4.7.3 to 4.8-rc5 377 378 $ cd ~/linux-4.7.3 # change to the kernel source dir 379 $ patch -p1 -R < ../patch-4.7.3 # revert the 4.7.3 patch 380 $ patch -p1 < ../patch-4.8-rc5 # apply new 4.8-rc5 patch 381 $ cd .. 382 $ mv linux-4.7.3 linux-4.8-rc5 # rename the kernel source dir 383 384 385 The -git kernels 386 ================ 387 388 These are daily snapshots of Linus' kernel tree (managed in a git 389 repository, hence the name). 390 391 These patches are usually released daily and represent the current state of 392 Linus's tree. They are more experimental than -rc kernels since they are 393 generated automatically without even a cursory glance to see if they are 394 sane. 395 396 -git patches are not incremental and apply either to a base 4.x kernel or 397 a base 4.x-rc kernel -- you can see which from their name. 398 A patch named 4.7-git1 applies to the 4.7 kernel source and a patch 399 named 4.8-rc3-git2 applies to the source of the 4.8-rc3 kernel. 400 401 Here are some examples of how to apply these patches:: 402 403 # moving from 4.7 to 4.7-git1 404 405 $ cd ~/linux-4.7 # change to the kernel source dir 406 $ patch -p1 < ../patch-4.7-git1 # apply the 4.7-git1 patch 407 $ cd .. 408 $ mv linux-4.7 linux-4.7-git1 # rename the kernel source dir 409 410 # moving from 4.7-git1 to 4.8-rc2-git3 411 412 $ cd ~/linux-4.7-git1 # change to the kernel source dir 413 $ patch -p1 -R < ../patch-4.7-git1 # revert the 4.7-git1 patch 414 # we now have a 4.7 kernel 415 $ patch -p1 < ../patch-4.8-rc2 # apply the 4.8-rc2 patch 416 # the kernel is now 4.8-rc2 417 $ patch -p1 < ../patch-4.8-rc2-git3 # apply the 4.8-rc2-git3 patch 418 # the kernel is now 4.8-rc2-git3 419 $ cd .. 420 $ mv linux-4.7-git1 linux-4.8-rc2-git3 # rename source dir 421 422 423 The -mm patches and the linux-next tree 424 ======================================= 425 426 The -mm patches are experimental patches released by Andrew Morton. 427 428 In the past, -mm tree were used to also test subsystem patches, but this 429 function is now done via the 430 :ref:`linux-next <https://www.kernel.org/doc/man-pages/linux-next.html>` 431 tree. The Subsystem maintainers push their patches first to linux-next, 432 and, during the merge window, sends them directly to Linus. 433 434 The -mm patches serve as a sort of proving ground for new features and other 435 experimental patches that aren't merged via a subsystem tree. 436 Once such patches has proved its worth in -mm for a while Andrew pushes 437 it on to Linus for inclusion in mainline. 438 439 The linux-next tree is daily updated, and includes the -mm patches. 440 Both are in constant flux and contains many experimental features, a 441 lot of debugging patches not appropriate for mainline etc., and is the most 442 experimental of the branches described in this document. 443 444 These patches are not appropriate for use on systems that are supposed to be 445 stable and they are more risky to run than any of the other branches (make 446 sure you have up-to-date backups -- that goes for any experimental kernel but 447 even more so for -mm patches or using a Kernel from the linux-next tree). 448 449 Testing of -mm patches and linux-next is greatly appreciated since the whole 450 point of those are to weed out regressions, crashes, data corruption bugs, 451 build breakage (and any other bug in general) before changes are merged into 452 the more stable mainline Linus tree. 453 454 But testers of -mm and linux-next should be aware that breakages are 455 more common than in any other tree. 456 457 458 This concludes this list of explanations of the various kernel trees. 459 I hope you are now clear on how to apply the various patches and help testing 460 the kernel. 461 462 Thank you's to Randy Dunlap, Rolf Eike Beer, Linus Torvalds, Bodo Eggert, 463 Johannes Stezenbach, Grant Coady, Pavel Machek and others that I may have 464 forgotten for their reviews and contributions to this document.