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 ============================= ============================================= 488 489 490 491