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Based on kernel version 3.15.4. Page generated on 2014-07-07 08:59 EST.

1	
2		Applying Patches To The Linux Kernel
3		------------------------------------
4	
5		Original by: Jesper Juhl, August 2005
6		Last update: 2006-01-05
7	
8	
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.
13	
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.
17	
18	
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.
28	
29	
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.
34	
35	Patches for the Linux kernel are generated relative to the parent directory
36	holding the kernel source dir.
37	
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).
46	
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
50	
51	You can revert (undo) it like this:
52		patch -R -p1 < ../patch-x.y.z
53	
54	
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
62	
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.
66	
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
70	
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
76	
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
82	
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.
85	
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.
91	
92	
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.
100	
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.
104	
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.
112	
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.
118	
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.
123	
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.
132	
133	Let's look a bit more at some of the messages patch can produce.
134	
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).
141	
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.
150	
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.
156	
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.
167	
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.
176	
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.
183	
184	
185	Are there any alternatives to `patch'?
186	---
187	 Yes there are alternatives.
188	
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.
196	
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
199	
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.
202	
203	 Another alternative is `ketchup', which is a python script for automatic
204	downloading and applying of patches (http://www.selenic.com/ketchup/).
205	
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.
211	
212	
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.
218	
219	The 2.6.x.y (-stable) and 2.6.x patches live at
220	 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/
221	
222	The -rc patches live at
223	 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/testing/
224	
225	The -git patches live at
226	 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/snapshots/
227	
228	The -mm kernels live at
229	 ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/
230	
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.
236	
237	
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.
242	
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.
247	
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).
252	
253	Here are some examples:
254	
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
260	
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
268	
269	
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.
275	
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.
279	
280	If no 2.6.x.y kernel is available, then the highest numbered 2.6.x kernel is
281	the current stable kernel.
282	
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/
287	
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.
294	
295	Here's a small example:
296	
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
302	
303	
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.
309	
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.
315	
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).
319	
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.
326	
327	Here are 3 examples of how to apply these patches:
328	
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
334	
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
341	
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
348	
349	
350	The -git kernels
351	---
352	 These are daily snapshots of Linus' kernel tree (managed in a git
353	repository, hence the name).
354	
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.
359	
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.
364	
365	Here are some examples of how to apply these patches:
366	
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
372	
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
383	
384	
385	The -mm kernels
386	---
387	 These are experimental kernels released by Andrew Morton.
388	
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.
393	
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).
399	
400	You should generally strive to get your patches into mainline via -mm to
401	ensure maximum testing.
402	
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.
406	
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).
411	
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.
415	
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.
422	
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.
427	
428	Here are some examples of applying the -mm patches:
429	
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
435	
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
445	
446	
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.
450	
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.
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