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

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