1 .\" (C) Copyright 1992-1999 Rickard E. Faith and David A. Wheeler
2 .\" (faith@cs.unc.edu and dwheeler@ida.org)
3 .\" and (C) Copyright 2007 Michael Kerrisk <mtk.manpages@gmail.com>
5 .\" %%%LICENSE_START(VERBATIM)
6 .\" Permission is granted to make and distribute verbatim copies of this
7 .\" manual provided the copyright notice and this permission notice are
8 .\" preserved on all copies.
10 .\" Permission is granted to copy and distribute modified versions of this
11 .\" manual under the conditions for verbatim copying, provided that the
12 .\" entire resulting derived work is distributed under the terms of a
13 .\" permission notice identical to this one.
15 .\" Since the Linux kernel and libraries are constantly changing, this
16 .\" manual page may be incorrect or out-of-date. The author(s) assume no
17 .\" responsibility for errors or omissions, or for damages resulting from
18 .\" the use of the information contained herein. The author(s) may not
19 .\" have taken the same level of care in the production of this manual,
20 .\" which is licensed free of charge, as they might when working
23 .\" Formatted or processed versions of this manual, if unaccompanied by
24 .\" the source, must acknowledge the copyright and authors of this work.
27 .\" 2007-05-30 created by mtk, using text from old man.7 plus
28 .\" rewrites and additional text.
30 .TH MAN-PAGES 7 2013-02-24 "Linux" "Linux Programmer's Manual"
32 man-pages \- conventions for writing Linux man pages
38 This page describes the conventions that should be employed
39 when writing man pages for the Linux \fIman-pages\fP project,
40 which documents the user-space API provided by the Linux kernel
41 and the GNU C library.
42 The project thus provides most of the pages in Section 2,
43 as well as many of the pages that appear
44 in Sections 3, 4, 5, and 7 of the man pages on a Linux system.
45 The conventions described on this page may also be useful
46 for authors writing man pages for other projects.
47 .SS Sections of the manual pages
49 The manual Sections are traditionally defined as follows:
51 .B 1 Commands (Programs)
52 Those commands that can be executed by the user from within
56 Those functions which must be performed by the kernel.
63 .B 4 Special files (devices)
67 .B 5 File formats and conventions
70 and other human-readable files.
74 .B 7 Overview, conventions, and miscellaneous
75 Overviews of various topics, conventions and protocols,
76 character set standards, and miscellaneous other things.
78 .B 8 System management commands
81 many of which only root can execute.
83 .\" .B 9 Kernel routines
84 .\" This is an obsolete manual section.
85 .\" Once it was thought a good idea to document the Linux kernel here,
86 .\" but in fact very little has been documented, and the documentation
87 .\" that exists is outdated already.
88 .\" There are better sources of
89 .\" information for kernel developers.
91 New manual pages should be marked up using the
95 This choice is mainly for consistency: the vast majority of
96 existing Linux manual pages are marked up using these macros.
97 .SS Conventions for source file layout
98 Please limit source code line length to no more than about 75 characters
100 This helps avoid line-wrapping in some mail clients when patches are
103 New sentences should be started on new lines.
104 This makes it easier to see the effect of patches,
105 which often operate at the level of individual sentences.
107 The first command in a man page should be a \fBTH\fP command:
111 .I "title section date source manual"
118 The title of the man page, written in all caps (e.g.,
122 The section number in which the man page should be placed (e.g.,
126 The date of the last revision\(emremember to change this every time a
127 change is made to the man page,
128 since this is the most general way of doing version control.
129 Dates should be written in the form YYYY-MM-DD.
132 The source of the command, function, or system call.
134 For those few \fIman-pages\fP pages in Sections 1 and 8,
135 probably you just want to write
138 For system calls, just write
140 (An earlier practice was to write the version number
141 of the kernel from which the manual page was being written/checked.
142 However, this was never done consistently, and so was
143 probably worse than including no version number.
144 Henceforth, avoid including a version number.)
146 For library calls that are part of glibc or one of the
147 other common GNU libraries, just use
148 .IR "GNU C Library" ", " GNU ,
151 For Section 4 pages, use
154 In cases of doubt, just write
155 .IR Linux ", or " GNU .
158 The title of the manual (e.g., for Section 2 and 3 pages in
159 the \fIman-pages\fP package, use
160 .IR "Linux Programmer's Manual" ).
162 .SS Sections within a manual page
163 The list below shows conventional or suggested sections.
164 Most manual pages should include at least the
167 Arrange a new manual page so that sections
168 are placed in the order shown in the list.
174 CONFIGURATION [Normally only in Section 4]
176 OPTIONS [Normally only in Sections 1, 8]
177 EXIT STATUS [Normally only in Sections 1, 8]
178 RETURN VALUE [Normally only in Sections 2, 3]
179 .\" May 07: Few current man pages have an ERROR HANDLING section,,,
181 ERRORS [Typically only in Sections 2, 3]
182 .\" May 07: Almost no current man pages have a USAGE section,,,
185 .\" May 07: Almost no current man pages have a SECURITY section,,,
189 VERSIONS [Normally only in Sections 2, 3]
194 .\" AUTHORS sections are discouraged
195 .\" AUTHORS [Discouraged]
200 .IR "Where a traditional heading would apply" ", " "please use it" ;
201 this kind of consistency can make the information easier to understand.
202 If you must, you can create your own
203 headings if they make things easier to understand (this can
204 be especially useful for pages in Sections 4 and 5).
205 However, before doing this, consider whether you could use the
206 traditional headings, with some subsections (\fI.SS\fP) within
209 The following list elaborates on the contents of each of
213 The name of this manual page.
216 for important details of the line(s) that should follow the
217 \fB.SH NAME\fP command.
218 All words in this line (including the word immediately
219 following the "\\\-") should be in lowercase,
220 except where English or technical terminological convention
224 briefly describes the command or function's interface.
225 For commands, this shows the syntax of the command and its arguments
227 boldface is used for as-is text and italics are used to
228 indicate replaceable arguments.
229 Brackets ([]) surround optional arguments, vertical bars (|)
230 separate choices, and ellipses (\&...) can be repeated.
231 For functions, it shows any required data declarations or
233 directives, followed by the function declaration.
235 Where a feature test macro must be defined in order to obtain
236 the declaration of a function (or a variable) from a header file,
237 then the SYNOPSIS should indicate this, as described in
238 .BR feature_test_macros (7).
239 .\" FIXME . Say something here about compiler options
242 Configuration details for a device.
243 This section normally only appears in Section 4 pages.
246 gives an explanation of what the program, function, or format does.
247 Discuss how it interacts with files and standard input, and what it
248 produces on standard output or standard error.
249 Omit internals and implementation details unless they're critical for
250 understanding the interface.
251 Describe the usual case;
252 for information on command-line options of a program use the
255 .\" If there is some kind of input grammar or complex set of subcommands,
256 .\" consider describing them in a separate
258 .\" section (and just place an overview in the
263 describes the command-line options accepted by a
264 program and how they change its behavior.
265 This section should only appear for Section 1 and 8 manual pages.
268 .\" describes the grammar of any sublanguage this implements.
271 lists the possible exit status values of a program and
272 the conditions that cause these values to be returned.
273 This section should only appear for Section 1 and 8 manual pages.
276 For Section 2 and 3 pages, this section gives a
277 list of the values the library routine will return to the caller
278 and the conditions that cause these values to be returned.
281 For Section 2 and 3 manual pages, this is a list of the
282 values that may be placed in
284 in the event of an error, along with information about the cause
286 .IR "The error list should be in alphabetical order" .
289 lists all environment variables that affect the program or function
290 and how they affect it.
293 lists the files the program or function uses, such as
294 configuration files, startup files,
295 and files the program directly operates on.
296 Give the full pathname of these files, and use the installation
297 process to modify the directory part to match user preferences.
298 For many programs, the default installation location is in
300 so your base manual page should use
303 .\" May 07: Almost no current man pages have a DIAGNOSTICS section;
304 .\" "RETURN VALUE" or "EXIT STATUS" is preferred.
307 .\" gives an overview of the most common error messages and how to
309 .\" You don't need to explain system error messages
310 .\" or fatal signals that can appear during execution of any program
311 .\" unless they're special in some way to the program.
313 .\" May 07: Almost no current man pages have a SECURITY section.
316 .\"discusses security issues and implications.
317 .\"Warn about configurations or environments that should be avoided,
318 .\"commands that may have security implications, and so on, especially
319 .\"if they aren't obvious.
320 .\"Discussing security in a separate section isn't necessary;
321 .\"if it's easier to understand, place security information in the
322 .\"other sections (such as the
327 .\" However, please include security information somewhere!
330 A brief summary of the Linux kernel or glibc versions where a
331 system call or library function appeared,
332 or changed significantly in its operation.
333 As a general rule, every new interface should
334 include a VERSIONS section in its manual page.
336 many existing manual pages don't include this information
337 (since there was no policy to do so when they were written).
338 Patches to remedy this are welcome,
339 but, from the perspective of programmers writing new code,
340 this information probably only matters in the case of kernel
341 interfaces that have been added in Linux 2.4 or later
342 (i.e., changes since kernel 2.2),
343 and library functions that have been added to glibc since version 2.1
344 (i.e., changes since glibc 2.0).
348 manual page also provides information about kernel versions
349 in which various system calls first appeared.
352 describes any standards or conventions that relate to the function
353 or command described by the manual page.
354 For a page in Section 2 or 3,
355 this section should note the POSIX.1
356 version(s) that the call conforms to,
357 and also whether the call is specified in C99.
358 (Don't worry too much about other standards like SUS, SUSv2, and XPG,
359 or the SVr4 and 4.xBSD implementation standards,
360 unless the call was specified in those standards,
361 but isn't in the current version of POSIX.1.)
365 If the call is not governed by any standards but commonly
366 exists on other systems, note them.
367 If the call is Linux-specific, note this.
369 If this section consists of just a list of standards
370 (which it commonly does),
371 terminate the list with a period (\(aq.\(aq).
374 provides miscellaneous notes.
375 For Section 2 and 3 man pages you may find it useful to include
376 subsections (\fBSS\fP) named \fILinux Notes\fP and \fIGlibc Notes\fP.
379 lists limitations, known defects or inconveniences,
380 and other questionable activities.
383 provides one or more examples describing how this function, file or
385 For details on writing example programs,
386 see \fIExample Programs\fP below.
389 lists authors of the documentation or program.
390 \fBUse of an AUTHORS section is strongly discouraged\fP.
391 Generally, it is better not to clutter every page with a list
392 of (over time potentially numerous) authors;
393 if you write or significantly amend a page,
394 add a copyright notice as a comment in the source file.
395 If you are the author of a device driver and want to include
396 an address for reporting bugs, place this under the BUGS section.
399 provides a comma-separated list of related man pages,
400 ordered by section number and
401 then alphabetically by name, possibly followed by
402 other related pages or documents.
403 Do not terminate this with a period.
405 Where the SEE ALSO list contains many long manual page names,
406 to improve the visual result of the output, it may be useful to employ the
408 (don't right justify)
413 Hyphenation of individual page names can be prevented
414 by preceding words with the string "\\%".
417 For functions, the arguments are always specified using italics,
418 .IR "even in the SYNOPSIS section" ,
419 where the rest of the function is specified in bold:
421 .BI " int myfunction(int " argc ", char **" argv );
423 Variable names should, like argument names, be specified in italics.
425 Filenames (whether pathnames, or references to files in the
428 are always in italics (e.g.,
430 except in the SYNOPSIS section, where included files are in bold (e.g.,
431 .BR "#include <stdio.h>" ).
432 When referring to a standard include file under
434 specify the header file surrounded by angle brackets,
435 in the usual C way (e.g.,
438 Special macros, which are usually in upper case, are in bold (e.g.,
440 Exception: don't boldface NULL.
442 When enumerating a list of error codes, the codes are in bold (this list
447 Complete commands should, if long,
448 be written as in an indented line on their own, for example
456 If the command is short, then it can be included inline in the text,
457 in italic format, for example,
458 .IR "man 7 man-pages" .
459 In this case, it may be worth using nonbreaking spaces
460 ("\e\ ") at suitable places in the command.
461 Command options should be written in italics, e.g.,
464 Expressions, if not written on a separate indented line, should
465 be specified in italics.
466 Again, the use of nonbreaking spaces may be appropriate
467 if the expression is inlined with normal text.
469 Any reference to the subject of the current manual page
470 should be written with the name in bold.
471 If the subject is a function (i.e., this is a Section 2 or 3 page),
472 then the name should be followed by a pair of parentheses
473 in Roman (normal) font.
476 man page, references to the subject of the page would be written as:
478 The preferred way to write this in the source file is:
484 (Using this format, rather than the use of "\\fB...\\fP()"
485 makes it easier to write tools that parse man page source files.)
487 Any reference to another man page
488 should be written with the name in bold,
489 \fIalways\fP followed by the section number,
490 formatted in Roman (normal) font, without any
491 separating spaces (e.g.,
493 The preferred way to write this in the source file is:
499 (Including the section number in cross references lets tools like
501 create properly hyperlinked pages.)
503 Starting with release 2.59,
505 follows American spelling conventions;
506 please write all new pages and patches according to these conventions.
508 In subsection ("SS") headings
509 capitalize the first word in heading, but otherwise use lower case,
510 except where English usage (e.g., proper nouns) or programming
511 language requirements (e.g., identifier names) dictate otherwise.
512 .SS Example programs and shell sessions
513 Manual pages can include example programs demonstrating how to
514 use a system call or library function.
515 However, note the following:
518 Example programs should be written in C.
521 An example program is only necessary and useful if it demonstrates
522 something beyond what can easily be provided in a textual
523 description of the interface.
524 An example program that does nothing
525 other than call an interface usually serves little purpose.
528 Example programs should be fairly short (preferably less than 100 lines;
529 ideally less than 50 lines).
532 Example programs should do error checking after system calls and
533 library function calls.
536 Example programs should be complete, and compile without
537 warnings when compiled with \fIcc\ \-Wall\fP.
540 Where possible and appropriate, example programs should allow
541 experimentation, by varying their behavior based on inputs
542 (ideally from command-line arguments, or alternatively, via
543 input read by the program).
546 Example programs should be laid out according to Kernighan and
547 Ritchie style, with 4-space indents.
548 (Avoid the use of TAB characters in source code!)
550 For some examples of what example programs should look like, see
555 If you include a shell session demonstrating the use of a program
556 or other system feature, boldface the user input text,
557 to distinguish it from output produced by the system.
558 .SS Indentation of structure definitions, shell session logs, etc.
559 When structure definitions, shell session logs, and so on are included
560 in running text, indent them by 4 spaces (i.e., a block enclosed by
565 For canonical examples of how man pages in the
567 package should look, see
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