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SPDX-License-Identifier: GPL-2.02 3.. _kernel_licensing:4 5Linux kernel licensing rules6============================7 8The Linux Kernel is provided under the terms of the GNU General Public9License version 2 only (GPL-2.0), as provided in LICENSES/preferred/GPL-2.0,10with an explicit syscall exception described in11LICENSES/exceptions/Linux-syscall-note, as described in the COPYING file.12 13This documentation file provides a description of how each source file14should 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 source18as a whole, though individual source files can have a different license19which is required to be compatible with the GPL-2.0::20 21 GPL-1.0+ : GNU General Public License v1.0 or later22 GPL-2.0+ : GNU General Public License v2.0 or later23 LGPL-2.0 : GNU Library General Public License v2 only24 LGPL-2.0+ : GNU Library General Public License v2 or later25 LGPL-2.1 : GNU Lesser General Public License v2.1 only26 LGPL-2.1+ : GNU Lesser General Public License v2.1 or later27 28Aside from that, individual files can be provided under a dual license,29e.g. one of the compatible GPL variants and alternatively under a30permissive license like BSD, MIT etc.31 32The User-space API (UAPI) header files, which describe the interface of33user-space programs to the kernel are a special case. According to the34note 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 to36communicate with the kernel. Because the UAPI headers must be includable37into any source files which create an executable running on the Linux38kernel, 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 the41matching boilerplate text into the top comment of the file. Due to42formatting, typos etc. these "boilerplates" are hard to validate for43tools which are used in the context of license compliance.44 45An alternative to boilerplate text is the use of Software Package Data46Exchange (SPDX) license identifiers in each source file. SPDX license47identifiers are machine parsable and precise shorthands for the license48under which the content of the file is contributed. SPDX license49identifiers are managed by the SPDX Workgroup at the Linux Foundation and50have been agreed on by partners throughout the industry, tool vendors, and51legal 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 section55`License identifiers`_ and have been retrieved from the official SPDX56license list at https://spdx.org/licenses/ along with the license texts.57 58License identifier syntax59-------------------------60 611. Placement:62 63 The SPDX license identifier in kernel files shall be added at the first64 possible line in a file which can contain a comment. For the majority65 of files this is the first line, except for scripts which require the66 '#!PATH_TO_INTERPRETER' in the first line. For those scripts the SPDX67 identifier goes into the second line.68 69|70 712. Style:72 73 The SPDX license identifier is added in form of a comment. The comment74 style depends on the file type::75 76 C source: // SPDX-License-Identifier: <SPDX License Expression>77 C header: /* SPDX-License-Identifier: <SPDX License Expression> */78 ASM: /* SPDX-License-Identifier: <SPDX License Expression> */79 scripts: # SPDX-License-Identifier: <SPDX License Expression>80 .rst: .. SPDX-License-Identifier: <SPDX License Expression>81 .dts{i}: // SPDX-License-Identifier: <SPDX License Expression>82 83 If a specific tool cannot handle the standard comment style, then the84 appropriate comment mechanism which the tool accepts shall be used. This85 is the reason for having the "/\* \*/" style comment in C header86 files. There was build breakage observed with generated .lds files where87 'ld' failed to parse the C++ comment. This has been fixed by now, but88 there are still older assembler tools which cannot handle C++ style89 comments.90 91|92 933. Syntax:94 95 A <SPDX License Expression> is either an SPDX short form license96 identifier found on the SPDX License List, or the combination of two97 SPDX short form license identifiers separated by "WITH" when a license98 exception applies. When multiple licenses apply, an expression consists99 of keywords "AND", "OR" separating sub-expressions and surrounded by100 "(", ")" .101 102 License identifiers for licenses like [L]GPL with the 'or later' option103 are constructed by using a "+" for indicating the 'or later' option.::104 105 // SPDX-License-Identifier: GPL-2.0+106 // SPDX-License-Identifier: LGPL-2.1+107 108 WITH should be used when there is a modifier to a license needed.109 For example, the linux kernel UAPI files use the expression::110 111 // SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note112 // SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note113 114 Other examples using WITH exceptions found in the kernel are::115 116 // SPDX-License-Identifier: GPL-2.0 WITH mif-exception117 // SPDX-License-Identifier: GPL-2.0+ WITH GCC-exception-2.0118 119 Exceptions can only be used with particular License identifiers. The120 valid License identifiers are listed in the tags of the exception text121 file. For details see the point `Exceptions`_ in the chapter `License122 identifiers`_.123 124 OR should be used if the file is dual licensed and only one license is125 to be selected. For example, some dtsi files are available under dual126 licenses::127 128 // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause129 130 Examples from the kernel for license expressions in dual licensed files::131 132 // SPDX-License-Identifier: GPL-2.0 OR MIT133 // SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause134 // SPDX-License-Identifier: GPL-2.0 OR Apache-2.0135 // SPDX-License-Identifier: GPL-2.0 OR MPL-1.1136 // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) OR MIT137 // SPDX-License-Identifier: GPL-1.0+ OR BSD-3-Clause OR OpenSSL138 139 AND should be used if the file has multiple licenses whose terms all140 apply to use the file. For example, if code is inherited from another141 project and permission has been given to put it in the kernel, but the142 original license terms need to remain in effect::143 144 // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) AND MIT145 146 Another other example where both sets of license terms need to be147 adhered to is::148 149 // SPDX-License-Identifier: GPL-1.0+ AND LGPL-2.1+150 151License identifiers152-------------------153 154The licenses currently used, as well as the licenses for code added to the155kernel, can be broken down into:156 1571. _`Preferred licenses`:158 159 Whenever possible these licenses should be used as they are known to be160 fully compatible and widely used. These licenses are available from the161 directory::162 163 LICENSES/preferred/164 165 in the kernel source tree.166 167 The files in this directory contain the full license text and168 `Metatags`_. The file names are identical to the SPDX license169 identifier which shall be used for the license in source files.170 171 Examples::172 173 LICENSES/preferred/GPL-2.0174 175 Contains the GPL version 2 license text and the required metatags::176 177 LICENSES/preferred/MIT178 179 Contains the MIT license text and the required metatags180 181 _`Metatags`:182 183 The following meta tags must be available in a license file:184 185 - Valid-License-Identifier:186 187 One or more lines which declare which License Identifiers are valid188 inside the project to reference this particular license text. Usually189 this is a single valid identifier, but e.g. for licenses with the 'or190 later' options two identifiers are valid.191 192 - SPDX-URL:193 194 The URL of the SPDX page which contains additional information related195 to the license.196 197 - Usage-Guidance:198 199 Freeform text for usage advice. The text must include correct examples200 for the SPDX license identifiers as they should be put into source201 files according to the `License identifier syntax`_ guidelines.202 203 - License-Text:204 205 All text after this tag is treated as the original license text206 207 File format examples::208 209 Valid-License-Identifier: GPL-2.0210 Valid-License-Identifier: GPL-2.0+211 SPDX-URL: https://spdx.org/licenses/GPL-2.0.html212 Usage-Guide:213 To use this license in source code, put one of the following SPDX214 tag/value pairs into a comment according to the placement215 guidelines in the licensing rules documentation.216 For 'GNU General Public License (GPL) version 2 only' use:217 SPDX-License-Identifier: GPL-2.0218 For 'GNU General Public License (GPL) version 2 or any later version' use:219 SPDX-License-Identifier: GPL-2.0+220 License-Text:221 Full license text222 223 ::224 225 SPDX-License-Identifier: MIT226 SPDX-URL: https://spdx.org/licenses/MIT.html227 Usage-Guide:228 To use this license in source code, put the following SPDX229 tag/value pair into a comment according to the placement230 guidelines in the licensing rules documentation.231 SPDX-License-Identifier: MIT232 License-Text:233 Full license text234 235|236 2372. Deprecated licenses:238 239 These licenses should only be used for existing code or for importing240 code from a different project. These licenses are available from the241 directory::242 243 LICENSES/deprecated/244 245 in the kernel source tree.246 247 The files in this directory contain the full license text and248 `Metatags`_. The file names are identical to the SPDX license249 identifier which shall be used for the license in source files.250 251 Examples::252 253 LICENSES/deprecated/ISC254 255 Contains the Internet Systems Consortium license text and the required256 metatags::257 258 LICENSES/deprecated/GPL-1.0259 260 Contains the GPL version 1 license text and the required metatags.261 262 Metatags:263 264 The metatag requirements for 'other' licenses are identical to the265 requirements of the `Preferred licenses`_.266 267 File format example::268 269 Valid-License-Identifier: ISC270 SPDX-URL: https://spdx.org/licenses/ISC.html271 Usage-Guide:272 Usage of this license in the kernel for new code is discouraged273 and it should solely be used for importing code from an already274 existing project.275 To use this license in source code, put the following SPDX276 tag/value pair into a comment according to the placement277 guidelines in the licensing rules documentation.278 SPDX-License-Identifier: ISC279 License-Text:280 Full license text281 282|283 2843. Dual Licensing Only285 286 These licenses should only be used to dual license code with another287 license in addition to a preferred license. These licenses are available288 from the directory::289 290 LICENSES/dual/291 292 in the kernel source tree.293 294 The files in this directory contain the full license text and295 `Metatags`_. The file names are identical to the SPDX license296 identifier which shall be used for the license in source files.297 298 Examples::299 300 LICENSES/dual/MPL-1.1301 302 Contains the Mozilla Public License version 1.1 license text and the303 required metatags::304 305 LICENSES/dual/Apache-2.0306 307 Contains the Apache License version 2.0 license text and the required308 metatags.309 310 Metatags:311 312 The metatag requirements for 'other' licenses are identical to the313 requirements of the `Preferred licenses`_.314 315 File format example::316 317 Valid-License-Identifier: MPL-1.1318 SPDX-URL: https://spdx.org/licenses/MPL-1.1.html319 Usage-Guide:320 Do NOT use. The MPL-1.1 is not GPL2 compatible. It may only be used for321 dual-licensed files where the other license is GPL2 compatible.322 If you end up using this it MUST be used together with a GPL2 compatible323 license using "OR".324 To use the Mozilla Public License version 1.1 put the following SPDX325 tag/value pair into a comment according to the placement guidelines in326 the licensing rules documentation:327 SPDX-License-Identifier: MPL-1.1328 License-Text:329 Full license text330 331|332 3334. _`Exceptions`:334 335 Some licenses can be amended with exceptions which grant certain rights336 which the original license does not. These exceptions are available337 from the directory::338 339 LICENSES/exceptions/340 341 in the kernel source tree. The files in this directory contain the full342 exception text and the required `Exception Metatags`_.343 344 Examples::345 346 LICENSES/exceptions/Linux-syscall-note347 348 Contains the Linux syscall exception as documented in the COPYING349 file of the Linux kernel, which is used for UAPI header files.350 e.g. /\* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note \*/::351 352 LICENSES/exceptions/GCC-exception-2.0353 354 Contains the GCC 'linking exception' which allows to link any binary355 independent of its license against the compiled version of a file marked356 with this exception. This is required for creating runnable executables357 from source code which is not compatible with the GPL.358 359 _`Exception Metatags`:360 361 The following meta tags must be available in an exception file:362 363 - SPDX-Exception-Identifier:364 365 One exception identifier which can be used with SPDX license366 identifiers.367 368 - SPDX-URL:369 370 The URL of the SPDX page which contains additional information related371 to the exception.372 373 - SPDX-Licenses:374 375 A comma separated list of SPDX license identifiers for which the376 exception can be used.377 378 - Usage-Guidance:379 380 Freeform text for usage advice. The text must be followed by correct381 examples for the SPDX license identifiers as they should be put into382 source files according to the `License identifier syntax`_ guidelines.383 384 - Exception-Text:385 386 All text after this tag is treated as the original exception text387 388 File format examples::389 390 SPDX-Exception-Identifier: Linux-syscall-note391 SPDX-URL: https://spdx.org/licenses/Linux-syscall-note.html392 SPDX-Licenses: GPL-2.0, GPL-2.0+, GPL-1.0+, LGPL-2.0, LGPL-2.0+, LGPL-2.1, LGPL-2.1+393 Usage-Guidance:394 This exception is used together with one of the above SPDX-Licenses395 to mark user-space API (uapi) header files so they can be included396 into non GPL compliant user-space application code.397 To use this exception add it with the keyword WITH to one of the398 identifiers in the SPDX-Licenses tag:399 SPDX-License-Identifier: <SPDX-License> WITH Linux-syscall-note400 Exception-Text:401 Full exception text402 403 ::404 405 SPDX-Exception-Identifier: GCC-exception-2.0406 SPDX-URL: https://spdx.org/licenses/GCC-exception-2.0.html407 SPDX-Licenses: GPL-2.0, GPL-2.0+408 Usage-Guidance:409 The "GCC Runtime Library exception 2.0" is used together with one410 of the above SPDX-Licenses for code imported from the GCC runtime411 library.412 To use this exception add it with the keyword WITH to one of the413 identifiers in the SPDX-Licenses tag:414 SPDX-License-Identifier: <SPDX-License> WITH GCC-exception-2.0415 Exception-Text:416 Full exception text417 418 419All SPDX license identifiers and exceptions must have a corresponding file420in the LICENSES subdirectories. This is required to allow tool421verification (e.g. checkpatch.pl) and to have the licenses ready to read422and extract right from the source, which is recommended by various FOSS423organizations, e.g. the `FSFE REUSE initiative <https://reuse.software/>`_.424 425_`MODULE_LICENSE`426-----------------427 428 Loadable kernel modules also require a MODULE_LICENSE() tag. This tag is429 neither a replacement for proper source code license information430 (SPDX-License-Identifier) nor in any way relevant for expressing or431 determining the exact license under which the source code of the module432 is provided.433 434 The sole purpose of this tag is to provide sufficient information435 whether the module is free software or proprietary for the kernel436 module loader and for user space tools.437 438 The valid license strings for MODULE_LICENSE() are:439 440 ============================= =============================================441 "GPL" Module is licensed under GPL version 2. This442 does not express any distinction between443 GPL-2.0-only or GPL-2.0-or-later. The exact444 license information can only be determined445 via the license information in the446 corresponding source files.447 448 "GPL v2" Same as "GPL". It exists for historic449 reasons.450 451 "GPL and additional rights" Historical variant of expressing that the452 module source is dual licensed under a453 GPL v2 variant and MIT license. Please do454 not use in new code.455 456 "Dual MIT/GPL" The correct way of expressing that the457 module is dual licensed under a GPL v2458 variant or MIT license choice.459 460 "Dual BSD/GPL" The module is dual licensed under a GPL v2461 variant or BSD license choice. The exact462 variant of the BSD license can only be463 determined via the license information464 in the corresponding source files.465 466 "Dual MPL/GPL" The module is dual licensed under a GPL v2467 variant or Mozilla Public License (MPL)468 choice. The exact variant of the MPL469 license can only be determined via the470 license information in the corresponding471 source files.472 473 "Proprietary" The module is under a proprietary license.474 This string is solely for proprietary third475 party modules and cannot be used for modules476 which have their source code in the kernel477 tree. Modules tagged that way are tainting478 the kernel with the 'P' flag when loaded and479 the kernel module loader refuses to link such480 modules against symbols which are exported481 with EXPORT_SYMBOL_GPL().482 ============================= =============================================483 484 485 486