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1.. SPDX-License-Identifier: GPL-2.0
2
3.. _kernel_licensing:
4
5Linux kernel licensing rules
6============================
7
8The Linux Kernel is provided under the terms of the GNU General Public
9License version 2 only (GPL-2.0), as provided in LICENSES/preferred/GPL-2.0,
10with an explicit syscall exception described in
11LICENSES/exceptions/Linux-syscall-note, as described in the COPYING file.
12
13This documentation file provides a description of how each source file
14should be annotated to make its license clear and unambiguous.
15It doesn't replace the Kernel's license.
16
17The license described in the COPYING file applies to the kernel source
18as a whole, though individual source files can have a different license
19which is required to be compatible with the GPL-2.0::
20
21 GPL-1.0+ : GNU General Public License v1.0 or later
22 GPL-2.0+ : GNU General Public License v2.0 or later
23 LGPL-2.0 : GNU Library General Public License v2 only
24 LGPL-2.0+ : GNU Library General Public License v2 or later
25 LGPL-2.1 : GNU Lesser General Public License v2.1 only
26 LGPL-2.1+ : GNU Lesser General Public License v2.1 or later
27
28Aside from that, individual files can be provided under a dual license,
29e.g. one of the compatible GPL variants and alternatively under a
30permissive license like BSD, MIT etc.
31
32The User-space API (UAPI) header files, which describe the interface of
33user-space programs to the kernel are a special case. According to the
34note in the kernel COPYING file, the syscall interface is a clear boundary,
35which does not extend the GPL requirements to any software which uses it to
36communicate with the kernel. Because the UAPI headers must be includable
37into any source files which create an executable running on the Linux
38kernel, the exception must be documented by a special license expression.
39
40The common way of expressing the license of a source file is to add the
41matching boilerplate text into the top comment of the file. Due to
42formatting, typos etc. these "boilerplates" are hard to validate for
43tools which are used in the context of license compliance.
44
45An alternative to boilerplate text is the use of Software Package Data
46Exchange (SPDX) license identifiers in each source file. SPDX license
47identifiers are machine parsable and precise shorthands for the license
48under which the content of the file is contributed. SPDX license
49identifiers are managed by the SPDX Workgroup at the Linux Foundation and
50have been agreed on by partners throughout the industry, tool vendors, and
51legal teams. For further information see https://spdx.org/
52
53The Linux kernel requires the precise SPDX identifier in all source files.
54The valid identifiers used in the kernel are explained in the section
55`License identifiers`_ and have been retrieved from the official SPDX
56license list at https://spdx.org/licenses/ along with the license texts.
57
58License identifier syntax
59-------------------------
60
611. Placement:
62
63 The SPDX license identifier in kernel files shall be added at the first
64 possible line in a file which can contain a comment. For the majority
65 of files this is the first line, except for scripts which require the
66 '#!PATH_TO_INTERPRETER' in the first line. For those scripts, the SPDX
67 license identifier goes into the second line.
68
69 The license identifier line can then be followed by one or multiple
70 SPDX-FileCopyrightText lines if desired.
71
72|
73
742. Style:
75
76 The SPDX license identifier is added in form of a comment. The comment
77 style depends on the file type::
78
79 C source: // SPDX-License-Identifier: <SPDX License Expression>
80 C header: /* SPDX-License-Identifier: <SPDX License Expression> */
81 ASM: /* SPDX-License-Identifier: <SPDX License Expression> */
82 scripts: # SPDX-License-Identifier: <SPDX License Expression>
83 .rst: .. SPDX-License-Identifier: <SPDX License Expression>
84 .dts{i}: // SPDX-License-Identifier: <SPDX License Expression>
85
86 If a specific tool cannot handle the standard comment style, then the
87 appropriate comment mechanism which the tool accepts shall be used. This
88 is the reason for having the "/\* \*/" style comment in C header
89 files. There was build breakage observed with generated .lds files where
90 'ld' failed to parse the C++ comment. This has been fixed by now, but
91 there are still older assembler tools which cannot handle C++ style
92 comments.
93
94|
95
963. Syntax:
97
98 A <SPDX License Expression> is either an SPDX short form license
99 identifier found on the SPDX License List, or the combination of two
100 SPDX short form license identifiers separated by "WITH" when a license
101 exception applies. When multiple licenses apply, an expression consists
102 of keywords "AND", "OR" separating sub-expressions and surrounded by
103 "(", ")" .
104
105 License identifiers for licenses like [L]GPL with the 'or later' option
106 are constructed by using a "+" for indicating the 'or later' option.::
107
108 // SPDX-License-Identifier: GPL-2.0+
109 // SPDX-License-Identifier: LGPL-2.1+
110
111 WITH should be used when there is a modifier to a license needed.
112 For example, the linux kernel UAPI files use the expression::
113
114 // SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
115 // SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note
116
117 Other examples using WITH exceptions found in the kernel are::
118
119 // SPDX-License-Identifier: GPL-2.0 WITH mif-exception
120 // SPDX-License-Identifier: GPL-2.0+ WITH GCC-exception-2.0
121
122 Exceptions can only be used with particular License identifiers. The
123 valid License identifiers are listed in the tags of the exception text
124 file. For details see the point `Exceptions`_ in the chapter `License
125 identifiers`_.
126
127 OR should be used if the file is dual licensed and only one license is
128 to be selected. For example, some dtsi files are available under dual
129 licenses::
130
131 // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
132
133 Examples from the kernel for license expressions in dual licensed files::
134
135 // SPDX-License-Identifier: GPL-2.0 OR MIT
136 // SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
137 // SPDX-License-Identifier: GPL-2.0 OR Apache-2.0
138 // SPDX-License-Identifier: GPL-2.0 OR MPL-1.1
139 // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) OR MIT
140 // SPDX-License-Identifier: GPL-1.0+ OR BSD-3-Clause OR OpenSSL
141
142 AND should be used if the file has multiple licenses whose terms all
143 apply to use the file. For example, if code is inherited from another
144 project and permission has been given to put it in the kernel, but the
145 original license terms need to remain in effect::
146
147 // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) AND MIT
148
149 Another other example where both sets of license terms need to be
150 adhered to is::
151
152 // SPDX-License-Identifier: GPL-1.0+ AND LGPL-2.1+
153
154License identifiers
155-------------------
156
157The licenses currently used, as well as the licenses for code added to the
158kernel, can be broken down into:
159
1601. _`Preferred licenses`:
161
162 Whenever possible these licenses should be used as they are known to be
163 fully compatible and widely used. These licenses are available from the
164 directory::
165
166 LICENSES/preferred/
167
168 in the kernel source tree.
169
170 The files in this directory contain the full license text and
171 `Metatags`_. The file names are identical to the SPDX license
172 identifier which shall be used for the license in source files.
173
174 Examples::
175
176 LICENSES/preferred/GPL-2.0
177
178 Contains the GPL version 2 license text and the required metatags::
179
180 LICENSES/preferred/MIT
181
182 Contains the MIT license text and the required metatags
183
184 _`Metatags`:
185
186 The following meta tags must be available in a license file:
187
188 - Valid-License-Identifier:
189
190 One or more lines which declare which License Identifiers are valid
191 inside the project to reference this particular license text. Usually
192 this is a single valid identifier, but e.g. for licenses with the 'or
193 later' options two identifiers are valid.
194
195 - SPDX-URL:
196
197 The URL of the SPDX page which contains additional information related
198 to the license.
199
200 - Usage-Guidance:
201
202 Freeform text for usage advice. The text must include correct examples
203 for the SPDX license identifiers as they should be put into source
204 files according to the `License identifier syntax`_ guidelines.
205
206 - License-Text:
207
208 All text after this tag is treated as the original license text
209
210 File format examples::
211
212 Valid-License-Identifier: GPL-2.0
213 Valid-License-Identifier: GPL-2.0+
214 SPDX-URL: https://spdx.org/licenses/GPL-2.0.html
215 Usage-Guide:
216 To use this license in source code, put one of the following SPDX
217 tag/value pairs into a comment according to the placement
218 guidelines in the licensing rules documentation.
219 For 'GNU General Public License (GPL) version 2 only' use:
220 SPDX-License-Identifier: GPL-2.0
221 For 'GNU General Public License (GPL) version 2 or any later version' use:
222 SPDX-License-Identifier: GPL-2.0+
223 License-Text:
224 Full license text
225
226 ::
227
228 SPDX-License-Identifier: MIT
229 SPDX-URL: https://spdx.org/licenses/MIT.html
230 Usage-Guide:
231 To use this license in source code, put the following SPDX
232 tag/value pair into a comment according to the placement
233 guidelines in the licensing rules documentation.
234 SPDX-License-Identifier: MIT
235 License-Text:
236 Full license text
237
238|
239
2402. Deprecated licenses:
241
242 These licenses should only be used for existing code or for importing
243 code from a different project. These licenses are available from the
244 directory::
245
246 LICENSES/deprecated/
247
248 in the kernel source tree.
249
250 The files in this directory contain the full license text and
251 `Metatags`_. The file names are identical to the SPDX license
252 identifier which shall be used for the license in source files.
253
254 Examples::
255
256 LICENSES/deprecated/ISC
257
258 Contains the Internet Systems Consortium license text and the required
259 metatags::
260
261 LICENSES/deprecated/GPL-1.0
262
263 Contains the GPL version 1 license text and the required metatags.
264
265 Metatags:
266
267 The metatag requirements for 'other' licenses are identical to the
268 requirements of the `Preferred licenses`_.
269
270 File format example::
271
272 Valid-License-Identifier: ISC
273 SPDX-URL: https://spdx.org/licenses/ISC.html
274 Usage-Guide:
275 Usage of this license in the kernel for new code is discouraged
276 and it should solely be used for importing code from an already
277 existing project.
278 To use this license in source code, put the following SPDX
279 tag/value pair into a comment according to the placement
280 guidelines in the licensing rules documentation.
281 SPDX-License-Identifier: ISC
282 License-Text:
283 Full license text
284
285|
286
2873. Dual Licensing Only
288
289 These licenses should only be used to dual license code with another
290 license in addition to a preferred license. These licenses are available
291 from the directory::
292
293 LICENSES/dual/
294
295 in the kernel source tree.
296
297 The files in this directory contain the full license text and
298 `Metatags`_. The file names are identical to the SPDX license
299 identifier which shall be used for the license in source files.
300
301 Examples::
302
303 LICENSES/dual/MPL-1.1
304
305 Contains the Mozilla Public License version 1.1 license text and the
306 required metatags::
307
308 LICENSES/dual/Apache-2.0
309
310 Contains the Apache License version 2.0 license text and the required
311 metatags.
312
313 Metatags:
314
315 The metatag requirements for 'other' licenses are identical to the
316 requirements of the `Preferred licenses`_.
317
318 File format example::
319
320 Valid-License-Identifier: MPL-1.1
321 SPDX-URL: https://spdx.org/licenses/MPL-1.1.html
322 Usage-Guide:
323 Do NOT use. The MPL-1.1 is not GPL2 compatible. It may only be used for
324 dual-licensed files where the other license is GPL2 compatible.
325 If you end up using this it MUST be used together with a GPL2 compatible
326 license using "OR".
327 To use the Mozilla Public License version 1.1 put the following SPDX
328 tag/value pair into a comment according to the placement guidelines in
329 the licensing rules documentation:
330 SPDX-License-Identifier: MPL-1.1
331 License-Text:
332 Full license text
333
334|
335
3364. _`Exceptions`:
337
338 Some licenses can be amended with exceptions which grant certain rights
339 which the original license does not. These exceptions are available
340 from the directory::
341
342 LICENSES/exceptions/
343
344 in the kernel source tree. The files in this directory contain the full
345 exception text and the required `Exception Metatags`_.
346
347 Examples::
348
349 LICENSES/exceptions/Linux-syscall-note
350
351 Contains the Linux syscall exception as documented in the COPYING
352 file of the Linux kernel, which is used for UAPI header files.
353 e.g. /\* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note \*/::
354
355 LICENSES/exceptions/GCC-exception-2.0
356
357 Contains the GCC 'linking exception' which allows to link any binary
358 independent of its license against the compiled version of a file marked
359 with this exception. This is required for creating runnable executables
360 from source code which is not compatible with the GPL.
361
362 _`Exception Metatags`:
363
364 The following meta tags must be available in an exception file:
365
366 - SPDX-Exception-Identifier:
367
368 One exception identifier which can be used with SPDX license
369 identifiers.
370
371 - SPDX-URL:
372
373 The URL of the SPDX page which contains additional information related
374 to the exception.
375
376 - SPDX-Licenses:
377
378 A comma separated list of SPDX license identifiers for which the
379 exception can be used.
380
381 - Usage-Guidance:
382
383 Freeform text for usage advice. The text must be followed by correct
384 examples for the SPDX license identifiers as they should be put into
385 source files according to the `License identifier syntax`_ guidelines.
386
387 - Exception-Text:
388
389 All text after this tag is treated as the original exception text
390
391 File format examples::
392
393 SPDX-Exception-Identifier: Linux-syscall-note
394 SPDX-URL: https://spdx.org/licenses/Linux-syscall-note.html
395 SPDX-Licenses: GPL-2.0, GPL-2.0+, GPL-1.0+, LGPL-2.0, LGPL-2.0+, LGPL-2.1, LGPL-2.1+
396 Usage-Guidance:
397 This exception is used together with one of the above SPDX-Licenses
398 to mark user-space API (uapi) header files so they can be included
399 into non GPL compliant user-space application code.
400 To use this exception add it with the keyword WITH to one of the
401 identifiers in the SPDX-Licenses tag:
402 SPDX-License-Identifier: <SPDX-License> WITH Linux-syscall-note
403 Exception-Text:
404 Full exception text
405
406 ::
407
408 SPDX-Exception-Identifier: GCC-exception-2.0
409 SPDX-URL: https://spdx.org/licenses/GCC-exception-2.0.html
410 SPDX-Licenses: GPL-2.0, GPL-2.0+
411 Usage-Guidance:
412 The "GCC Runtime Library exception 2.0" is used together with one
413 of the above SPDX-Licenses for code imported from the GCC runtime
414 library.
415 To use this exception add it with the keyword WITH to one of the
416 identifiers in the SPDX-Licenses tag:
417 SPDX-License-Identifier: <SPDX-License> WITH GCC-exception-2.0
418 Exception-Text:
419 Full exception text
420
421
422All SPDX license identifiers and exceptions must have a corresponding file
423in the LICENSES subdirectories. This is required to allow tool
424verification (e.g. checkpatch.pl) and to have the licenses ready to read
425and extract right from the source, which is recommended by various FOSS
426organizations, e.g. the `FSFE REUSE initiative <https://reuse.software/>`_.
427
428_`MODULE_LICENSE`
429-----------------
430
431 Loadable kernel modules also require a MODULE_LICENSE() tag. This tag is
432 neither a replacement for proper source code license information
433 (SPDX-License-Identifier) nor in any way relevant for expressing or
434 determining the exact license under which the source code of the module
435 is provided.
436
437 The sole purpose of this tag is to provide sufficient information
438 whether the module is free software or proprietary for the kernel
439 module loader and for user space tools.
440
441 The valid license strings for MODULE_LICENSE() are:
442
443 ============================= =============================================
444 "GPL" Module is licensed under GPL version 2. This
445 does not express any distinction between
446 GPL-2.0-only or GPL-2.0-or-later. The exact
447 license information can only be determined
448 via the license information in the
449 corresponding source files.
450
451 "GPL v2" Same as "GPL". It exists for historic
452 reasons.
453
454 "GPL and additional rights" Historical variant of expressing that the
455 module source is dual licensed under a
456 GPL v2 variant and MIT license. Please do
457 not use in new code.
458
459 "Dual MIT/GPL" The correct way of expressing that the
460 module is dual licensed under a GPL v2
461 variant or MIT license choice.
462
463 "Dual BSD/GPL" The module is dual licensed under a GPL v2
464 variant or BSD license choice. The exact
465 variant of the BSD license can only be
466 determined via the license information
467 in the corresponding source files.
468
469 "Dual MPL/GPL" The module is dual licensed under a GPL v2
470 variant or Mozilla Public License (MPL)
471 choice. The exact variant of the MPL
472 license can only be determined via the
473 license information in the corresponding
474 source files.
475
476 "Proprietary" The module is under a proprietary license.
477 "Proprietary" is to be understood only as
478 "The license is not compatible to GPLv2".
479 This string is solely for non-GPL2 compatible
480 third party modules and cannot be used for
481 modules which have their source code in the
482 kernel tree. Modules tagged that way are
483 tainting the kernel with the 'P' flag when
484 loaded and the kernel module loader refuses
485 to link such modules against symbols which
486 are exported with EXPORT_SYMBOL_GPL().
487 ============================= =============================================
488
489
490