1.. _applying_patches: 2 3Applying Patches To The Linux Kernel 4++++++++++++++++++++++++++++++++++++ 5 6Original by: 7 Jesper Juhl, August 2005 8 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 note:: 10 11 This document is obsolete.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. 13 14A frequently asked question on the Linux Kernel Mailing List is how to apply 15a patch to the kernel or, more specifically, what base kernel a patch for 16one of the many trees/branches should be applied to. Hopefully this document 17will explain this to you. 18 19In addition to explaining how to apply and revert patches, a brief 20description of the different kernel trees (and examples of how to apply 21their specific patches) is also provided. 22 23 24What is a patch? 25================ 26 27A patch is a small text document containing a delta of changes between two 28different versions of a source tree. Patches are created with the ``diff`` 29program. 30 31To correctly apply a patch you need to know what base it was generated from 32and what new version the patch will change the source tree into. These 33should both be present in the patch file metadata or be possible to deduce 34from the filename. 35 36 37How do I apply or revert a patch? 38================================= 39 40You apply a patch with the ``patch`` program. The patch program reads a diff 41(or patch) file and makes the changes to the source tree described in it. 42 43Patches for the Linux kernel are generated relative to the parent directory 44holding the kernel source dir. 45 46This means that paths to files inside the patch file contain the name of the 47kernel source directories it was generated against (or some other directory 48names like "a/" and "b/"). 49 50Since this is unlikely to match the name of the kernel source dir on your 51local machine (but is often useful info to see what version an otherwise 52unlabeled patch was generated against) you should change into your kernel 53source directory and then strip the first element of the path from filenames 54in the patch file when applying it (the ``-p1`` argument to ``patch`` does 55this). 56 57To revert a previously applied patch, use the -R argument to patch. 58So, if you applied a patch like this:: 59 60 patch -p1 < ../patch-x.y.z 61 62You can revert (undo) it like this:: 63 64 patch -R -p1 < ../patch-x.y.z 65 66 67How do I feed a patch/diff file to ``patch``? 68============================================= 69 70This (as usual with Linux and other UNIX like operating systems) can be 71done in several different ways. 72 73In all the examples below I feed the file (in uncompressed form) to patch 74via stdin using the following syntax:: 75 76 patch -p1 < path/to/patch-x.y.z 77 78If you just want to be able to follow the examples below and don't want to 79know of more than one way to use patch, then you can stop reading this 80section here. 81 82Patch can also get the name of the file to use via the -i argument, like 83this:: 84 85 patch -p1 -i path/to/patch-x.y.z 86 87If your patch file is compressed with gzip or xz and you don't want to 88uncompress it before applying it, then you can feed it to patch like this 89instead:: 90 91 xzcat path/to/patch-x.y.z.xz | patch -p1 92 bzcat path/to/patch-x.y.z.gz | patch -p1 93 94If 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 96gunzip or xz on the file -- like this:: 97 98 gunzip patch-x.y.z.gz 99 xz -d patch-x.y.z.xz 100 101Which will leave you with a plain text patch-x.y.z file that you can feed to 102patch via stdin or the ``-i`` argument, as you prefer. 103 104A few other nice arguments for patch are ``-s`` which causes patch to be silent 105except for errors which is nice to prevent errors from scrolling out of the 106screen too fast, and ``--dry-run`` which causes patch to just print a listing of 107what would happen, but doesn't actually make any changes. Finally ``--verbose`` 108tells patch to print more information about the work being done. 109 110 111Common errors when patching 112=========================== 113 114When patch applies a patch file it attempts to verify the sanity of the 115file in different ways. 116 117Checking that the file looks like a valid patch file and checking the code 118around the bits being modified matches the context provided in the patch are 119just two of the basic sanity checks patch does. 120 121If patch encounters something that doesn't look quite right it has two 122options. It can either refuse to apply the changes and abort or it can try 123to find a way to make the patch apply with a few minor changes. 124 125One example of something that's not 'quite right' that patch will attempt to 126fix up is if all the context matches, the lines being changed match, but the 127line numbers are different. This can happen, for example, if the patch makes 128a change in the middle of the file but for some reasons a few lines have 129been added or removed near the beginning of the file. In that case 130everything looks good it has just moved up or down a bit, and patch will 131usually adjust the line numbers and apply the patch. 132 133Whenever patch applies a patch that it had to modify a bit to make it fit 134it'll tell you about it by saying the patch applied with **fuzz**. 135You should be wary of such changes since even though patch probably got it 136right it doesn't /always/ get it right, and the result will sometimes be 137wrong. 138 139When patch encounters a change that it can't fix up with fuzz it rejects it 140outright and leaves a file with a ``.rej`` extension (a reject file). You can 141read this file to see exactly what change couldn't be applied, so you can 142go fix it up by hand if you wish. 143 144If you don't have any third-party patches applied to your kernel source, but 145only patches from kernel.org and you apply the patches in the correct order, 146and have made no modifications yourself to the source files, then you should 147never see a fuzz or reject message from patch. If you do see such messages 148anyway, then there's a high risk that either your local source tree or the 149patch file is corrupted in some way. In that case you should probably try 150re-downloading the patch and if things are still not OK then you'd be advised 151to start with a fresh tree downloaded in full from kernel.org. 152 153Let's look a bit more at some of the messages patch can produce. 154 155If patch stops and presents a ``File to patch:`` prompt, then patch could not 156find a file to be patched. Most likely you forgot to specify -p1 or you are 157in the wrong directory. Less often, you'll find patches that need to be 158applied with ``-p0`` instead of ``-p1`` (reading the patch file should reveal if 159this is the case -- if so, then this is an error by the person who created 160the patch but is not fatal). 161 162If you get ``Hunk #2 succeeded at 1887 with fuzz 2 (offset 7 lines).`` or a 163message similar to that, then it means that patch had to adjust the location 164of the change (in this example it needed to move 7 lines from where it 165expected to make the change to make it fit). 166 167The resulting file may or may not be OK, depending on the reason the file 168was different than expected. 169 170This often happens if you try to apply a patch that was generated against a 171different kernel version than the one you are trying to patch. 172 173If you get a message like ``Hunk #3 FAILED at 2387.``, then it means that the 174patch could not be applied correctly and the patch program was unable to 175fuzz its way through. This will generate a ``.rej`` file with the change that 176caused the patch to fail and also a ``.orig`` file showing you the original 177content that couldn't be changed. 178 179If you get ``Reversed (or previously applied) patch detected! Assume -R? [n]`` 180then patch detected that the change contained in the patch seems to have 181already been made. 182 183If you actually did apply this patch previously and you just re-applied it 184in error, then just say [n]o and abort this patch. If you applied this patch 185previously and actually intended to revert it, but forgot to specify -R, 186then you can say [**y**]es here to make patch revert it for you. 187 188This can also happen if the creator of the patch reversed the source and 189destination directories when creating the patch, and in that case reverting 190the patch will in fact apply it. 191 192A 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 194sense of the file you fed to it. Either your download is broken, you tried to 195feed patch a compressed patch file without uncompressing it first, or the patch 196file that you are using has been mangled by a mail client or mail transfer 197agent along the way somewhere, e.g., by splitting a long line into two lines. 198Often these warnings can easily be fixed by joining (concatenating) the 199two lines that had been split. 200 201As I already mentioned above, these errors should never happen if you apply 202a patch from kernel.org to the correct version of an unmodified source tree. 203So if you get these errors with kernel.org patches then you should probably 204assume that either your patch file or your tree is broken and I'd advise you 205to start over with a fresh download of a full kernel tree and the patch you 206wish to apply. 207 208 209Are there any alternatives to ``patch``? 210======================================== 211 212 213Yes there are alternatives. 214 215You can use the ``interdiff`` program (http://cyberelk.net/tim/patchutils/) to 216generate a patch representing the differences between two patches and then 217apply the result. 218 219This will let you move from something like 5.7.2 to 5.7.3 in a single 220step. The -z flag to interdiff will even let you feed it patches in gzip or 221bzip2 compressed form directly without the use of zcat or bzcat or manual 222decompression. 223 224Here's how you'd go from 5.7.2 to 5.7.3 in a single step:: 225 226 interdiff -z ../patch-5.7.2.gz ../patch-5.7.3.gz | patch -p1 227 228Although interdiff may save you a step or two you are generally advised to 229do the additional steps since interdiff can get things wrong in some cases. 230 231Another alternative is ``ketchup``, which is a python script for automatic 232downloading and applying of patches (https://www.selenic.com/ketchup/). 233 234Other nice tools are diffstat, which shows a summary of changes made by a 235patch; lsdiff, which displays a short listing of affected files in a patch 236file, along with (optionally) the line numbers of the start of each patch; 237and grepdiff, which displays a list of the files modified by a patch where 238the patch contains a given regular expression. 239 240 241Where can I download the patches? 242================================= 243 244The patches are available at https://kernel.org/ 245Most recent patches are linked from the front page, but they also have 246specific homes. 247 248The 5.x.y (-stable) and 5.x patches live at 249 250 https://www.kernel.org/pub/linux/kernel/v5.x/ 251 252The 5.x.y incremental patches live at 253 254 https://www.kernel.org/pub/linux/kernel/v5.x/incr/ 255 256The -rc patches are not stored on the webserver but are generated on 257demand from git tags such as 258 259 https://git.kernel.org/torvalds/p/v5.1-rc1/v5.0 260 261The stable -rc patches live at 262 263 https://www.kernel.org/pub/linux/kernel/v5.x/stable-review/ 264 265 266The 5.x kernels 267=============== 268 269These are the base stable releases released by Linus. The highest numbered 270release is the most recent. 271 272If regressions or other serious flaws are found, then a -stable fix patch 273will be released (see below) on top of this base. Once a new 5.x base 274kernel is released, a patch is made available that is a delta between the 275previous 5.x kernel and the new one. 276 277To apply a patch moving from 5.6 to 5.7, you'd do the following (note 278that such patches do **NOT** apply on top of 5.x.y kernels but on top of the 279base 5.x kernel -- if you need to move from 5.x.y to 5.x+1 you need to 280first revert the 5.x.y patch). 281 282Here are some examples:: 283 284 # moving from 5.6 to 5.7 285 286 $ cd ~/linux-5.6 # change to kernel source dir 287 $ patch -p1 < ../patch-5.7 # apply the 5.7 patch 288 $ cd .. 289 $ mv linux-5.6 linux-5.7 # rename source dir 290 291 # moving from 5.6.1 to 5.7 292 293 $ cd ~/linux-5.6.1 # change to kernel source dir 294 $ patch -p1 -R < ../patch-5.6.1 # revert the 5.6.1 patch 295 # source dir is now 5.6 296 $ patch -p1 < ../patch-5.7 # apply new 5.7 patch 297 $ cd .. 298 $ mv linux-5.6.1 linux-5.7 # rename source dir 299 300 301The 5.x.y kernels 302================= 303 304Kernels with 3-digit versions are -stable kernels. They contain small(ish) 305critical fixes for security problems or significant regressions discovered 306in a given 5.x kernel. 307 308This is the recommended branch for users who want the most recent stable 309kernel and are not interested in helping test development/experimental 310versions. 311 312If no 5.x.y kernel is available, then the highest numbered 5.x kernel is 313the current stable kernel. 314 315The -stable team provides normal as well as incremental patches. Below is 316how to apply these patches. 317 318Normal patches 319~~~~~~~~~~~~~~ 320 321These patches are not incremental, meaning that for example the 5.7.3 322patch does not apply on top of the 5.7.2 kernel source, but rather on top 323of the base 5.7 kernel source. 324 325So, in order to apply the 5.7.3 patch to your existing 5.7.2 kernel 326source you have to first back out the 5.7.2 patch (so you are left with a 327base 5.7 kernel source) and then apply the new 5.7.3 patch. 328 329Here's a small example:: 330 331 $ cd ~/linux-5.7.2 # change to the kernel source dir 332 $ patch -p1 -R < ../patch-5.7.2 # revert the 5.7.2 patch 333 $ patch -p1 < ../patch-5.7.3 # apply the new 5.7.3 patch 334 $ cd .. 335 $ mv linux-5.7.2 linux-5.7.3 # rename the kernel source dir 336 337Incremental patches 338~~~~~~~~~~~~~~~~~~~ 339 340Incremental patches are different: instead of being applied on top 341of base 5.x kernel, they are applied on top of previous stable kernel 342(5.x.y-1). 343 344Here's the example to apply these:: 345 346 $ cd ~/linux-5.7.2 # change to the kernel source dir 347 $ patch -p1 < ../patch-5.7.2-3 # apply the new 5.7.3 patch 348 $ cd .. 349 $ mv linux-5.7.2 linux-5.7.3 # rename the kernel source dir 350 351 352The -rc kernels 353=============== 354 355These are release-candidate kernels. These are development kernels released 356by Linus whenever he deems the current git (the kernel's source management 357tool) tree to be in a reasonably sane state adequate for testing. 358 359These kernels are not stable and you should expect occasional breakage if 360you intend to run them. This is however the most stable of the main 361development branches and is also what will eventually turn into the next 362stable kernel, so it is important that it be tested by as many people as 363possible. 364 365This is a good branch to run for people who want to help out testing 366development kernels but do not want to run some of the really experimental 367stuff (such people should see the sections about -next and -mm kernels below). 368 369The -rc patches are not incremental, they apply to a base 5.x kernel, just 370like the 5.x.y patches described above. The kernel version before the -rcN 371suffix denotes the version of the kernel that this -rc kernel will eventually 372turn into. 373 374So, 5.8-rc5 means that this is the fifth release candidate for the 5.8 375kernel and the patch should be applied on top of the 5.7 kernel source. 376 377Here are 3 examples of how to apply these patches:: 378 379 # first an example of moving from 5.7 to 5.8-rc3 380 381 $ cd ~/linux-5.7 # change to the 5.7 source dir 382 $ patch -p1 < ../patch-5.8-rc3 # apply the 5.8-rc3 patch 383 $ cd .. 384 $ mv linux-5.7 linux-5.8-rc3 # rename the source dir 385 386 # now let's move from 5.8-rc3 to 5.8-rc5 387 388 $ cd ~/linux-5.8-rc3 # change to the 5.8-rc3 dir 389 $ patch -p1 -R < ../patch-5.8-rc3 # revert the 5.8-rc3 patch 390 $ patch -p1 < ../patch-5.8-rc5 # apply the new 5.8-rc5 patch 391 $ cd .. 392 $ mv linux-5.8-rc3 linux-5.8-rc5 # rename the source dir 393 394 # finally let's try and move from 5.7.3 to 5.8-rc5 395 396 $ cd ~/linux-5.7.3 # change to the kernel source dir 397 $ patch -p1 -R < ../patch-5.7.3 # revert the 5.7.3 patch 398 $ patch -p1 < ../patch-5.8-rc5 # apply new 5.8-rc5 patch 399 $ cd .. 400 $ mv linux-5.7.3 linux-5.8-rc5 # rename the kernel source dir 401 402 403The -mm patches and the linux-next tree 404======================================= 405 406The -mm patches are experimental patches released by Andrew Morton. 407 408In the past, -mm tree were used to also test subsystem patches, but this 409function is now done via the 410`linux-next` (https://www.kernel.org/doc/man-pages/linux-next.html) 411tree. The Subsystem maintainers push their patches first to linux-next, 412and, during the merge window, sends them directly to Linus. 413 414The -mm patches serve as a sort of proving ground for new features and other 415experimental patches that aren't merged via a subsystem tree. 416Once such patches has proved its worth in -mm for a while Andrew pushes 417it on to Linus for inclusion in mainline. 418 419The linux-next tree is daily updated, and includes the -mm patches. 420Both are in constant flux and contains many experimental features, a 421lot of debugging patches not appropriate for mainline etc., and is the most 422experimental of the branches described in this document. 423 424These patches are not appropriate for use on systems that are supposed to be 425stable and they are more risky to run than any of the other branches (make 426sure you have up-to-date backups -- that goes for any experimental kernel but 427even more so for -mm patches or using a Kernel from the linux-next tree). 428 429Testing of -mm patches and linux-next is greatly appreciated since the whole 430point of those are to weed out regressions, crashes, data corruption bugs, 431build breakage (and any other bug in general) before changes are merged into 432the more stable mainline Linus tree. 433 434But testers of -mm and linux-next should be aware that breakages are 435more common than in any other tree. 436 437 438This concludes this list of explanations of the various kernel trees. 439I hope you are now clear on how to apply the various patches and help testing 440the kernel. 441 442Thank you's to Randy Dunlap, Rolf Eike Beer, Linus Torvalds, Bodo Eggert, 443Johannes Stezenbach, Grant Coady, Pavel Machek and others that I may have 444forgotten for their reviews and contributions to this document. 445