man-pages(7)

NAME#

man-pages - conventions for writing Linux man pages

SYNOPSIS#

man [section] title

DESCRIPTION#

This page describes the conventions that should be employed when writing man pages for the Linux man-pages project, which documents the user-space API provided by the Linux kernel and the GNU C library. The project thus provides most of the pages in Section 2, many of the pages that appear in Sections 3, 4, and 7, and a few of the pages that appear in Sections 1, 5, and 8 of the man pages on a Linux system. The conventions described on this page may also be useful for authors writing man pages for other projects.

Sections of the manual pages#

The manual Sections are traditionally defined as follows:

1 User commands (Programs)

Commands that can be executed by the user from within a shell.

2 System calls

Functions which wrap operations performed by the kernel.

3 Library calls

All library functions excluding the system call wrappers (Most of the libc functions).

4 Special files (devices)

Files found in /dev which allow to access to devices through the kernel.

5 File formats and configuration files

Describes various human-readable file formats and configuration files.

6 Games

Games and funny little programs available on the system.

7 Overview, conventions, and miscellaneous

Overviews or descriptions of various topics, conventions, and protocols, character set standards, the standard filesystem layout, and miscellaneous other things.

8 System management commands

Commands like mount(8), many of which only root can execute.

Macro package#

New manual pages should be marked up using the groff an.tmac package described in man(7). This choice is mainly for consistency: the vast majority of existing Linux manual pages are marked up using these macros.

Conventions for source file layout#

Please limit source code line length to no more than about 75 characters wherever possible. This helps avoid line-wrapping in some mail clients when patches are submitted inline.

Title line#

The first command in a man page should be a TH command:

The arguments of the command are as follows:

title

The title of the man page, written in all caps (e.g., MAN-PAGES).

section

The section number in which the man page should be placed (e.g., 7).

date

The date of the last nontrivial change that was made to the man page. (Within the man-pages project, the necessary updates to these timestamps are handled automatically by scripts, so there is no need to manually update them as part of a patch.) Dates should be written in the form YYYY-MM-DD.

source

The name and version of the project that provides the manual page (not necessarily the package that provides the functionality).

manual-section

Normally, this should be empty, since the default value will be good.

Sections within a manual page#

The list below shows conventional or suggested sections. Most manual pages should include at least the highlighted sections. Arrange a new manual page so that sections are placed in the order shown in the list.

Where a traditional heading would apply, please use it; this kind of consistency can make the information easier to understand. If you must, you can create your own headings if they make things easier to understand (this can be especially useful for pages in Sections 4 and 5). However, before doing this, consider whether you could use the traditional headings, with some subsections (.SS) within those sections.

The following list elaborates on the contents of each of the above sections.

NAME

The name of this manual page.

See man(7) for important details of the line(s) that should follow the .SH NAME command. All words in this line (including the word immediately following the "\-") should be in lowercase, except where English or technical terminological convention dictates otherwise.

LIBRARY

The library providing a symbol.

It shows the common name of the library, and in parentheses, the name of the library file and, if needed, the linker flag needed to link a program against it: (libfoo[, -lfoo]).

SYNOPSIS

A brief summary of the command or function's interface.

For commands, this shows the syntax of the command and its arguments (including options); boldface is used for as-is text and italics are used to indicate replaceable arguments. Brackets ([]) surround optional arguments, vertical bars (|) separate choices, and ellipses (...) can be repeated. For functions, it shows any required data declarations or #include directives, followed by the function declaration.

Where a feature test macro must be defined in order to obtain the declaration of a function (or a variable) from a header file, then the SYNOPSIS should indicate this, as described in feature_test_macros(7).

CONFIGURATION

Configuration details for a device.

This section normally appears only in Section 4 pages.

DESCRIPTION

An explanation of what the program, function, or format does.

Discuss how it interacts with files and standard input, and what it produces on standard output or standard error. Omit internals and implementation details unless they're critical for understanding the interface. Describe the usual case; for information on command-line options of a program use the OPTIONS section.

When describing new behavior or new flags for a system call or library function, be careful to note the kernel or C library version that introduced the change. The preferred method of noting this information for flags is as part of a .TP list, in the following form (here, for a new system call flag):

XYZ_FLAG (since Linux 3.7)

Description of flag...

Including version information is especially useful to users who are constrained to using older kernel or C library versions (which is typical in embedded systems, for example).

OPTIONS

A description of the command-line options accepted by a program and how they change its behavior.

This section should appear only for Section 1 and 8 manual pages.

EXIT STATUS

A list of the possible exit status values of a program and the conditions that cause these values to be returned.

This section should appear only for Section 1 and 8 manual pages.

RETURN VALUE

For Section 2 and 3 pages, this section gives a list of the values the library routine will return to the caller and the conditions that cause these values to be returned.

ERRORS

For Section 2 and 3 manual pages, this is a list of the values that may be placed in errno in the event of an error, along with information about the cause of the errors.

Where several different conditions produce the same error, the preferred approach is to create separate list entries (with duplicate error names) for each of the conditions. This makes the separate conditions clear, may make the list easier to read, and allows metainformation (e.g., kernel version number where the condition first became applicable) to be more easily marked for each condition.

The error list should be in alphabetical order.

ENVIRONMENT

A list of all environment variables that affect the program or function and how they affect it.

FILES

A list of the files the program or function uses, such as configuration files, startup files, and files the program directly operates on.

Give the full pathname of these files, and use the installation process to modify the directory part to match user preferences. For many programs, the default installation location is in /usr/local, so your base manual page should use /usr/local as the base.

ATTRIBUTES

A summary of various attributes of the function(s) documented on this page. See attributes(7) for further details.

VERSIONS

A summary of systems where the API performs differently, or where there's a similar API.

STANDARDS

A description of any standards or conventions that relate to the function or command described by the manual page.

The preferred terms to use for the various standards are listed as headings in standards(7).

This section should note the current standards to which the API conforms to.

If the API is not governed by any standards but commonly exists on other systems, note them. If the call is Linux-specific or GNU-specific, note this. If it's available in the BSDs, note that.

If this section consists of just a list of standards (which it commonly does), terminate the list with a period ('.').

HISTORY

A brief summary of the Linux kernel or glibc versions where a system call or library function appeared, or changed significantly in its operation.

As a general rule, every new interface should include a HISTORY section in its manual page. Unfortunately, many existing manual pages don't include this information (since there was no policy to do so when they were written). Patches to remedy this are welcome, but, from the perspective of programmers writing new code, this information probably matters only in the case of kernel interfaces that have been added in Linux 2.4 or later (i.e., changes since Linux 2.2), and library functions that have been added to glibc since glibc 2.1 (i.e., changes since glibc 2.0).

The syscalls(2) manual page also provides information about kernel versions in which various system calls first appeared.

Old versions of standards should be mentioned here, rather than in STANDARDS, for example, SUS, SUSv2, and XPG, or the SVr4 and 4.xBSD implementation standards.

NOTES

Miscellaneous notes.

For Section 2 and 3 man pages you may find it useful to include subsections (SS) named Linux Notes and glibc Notes.

In Section 2, use the heading C library/kernel differences to mark off notes that describe the differences (if any) between the C library wrapper function for a system call and the raw system call interface provided by the kernel.

CAVEATS

Warnings about typical user misuse of an API, that don't constitute an API bug or design defect.

BUGS

A list of limitations, known defects or inconveniences, and other questionable activities.

EXAMPLES

One or more examples demonstrating how this function, file, or command is used.

For details on writing example programs, see Example programs below.

AUTHORS

A list of authors of the documentation or program.

Use of an AUTHORS section is strongly discouraged. Generally, it is better not to clutter every page with a list of (over time potentially numerous) authors; if you write or significantly amend a page, add a copyright notice as a comment in the source file. If you are the author of a device driver and want to include an address for reporting bugs, place this under the BUGS section.

REPORTING BUGS

The man-pages project doesn't use a REPORTING BUGS section in manual pages. Information on reporting bugs is instead supplied in the script-generated COLOPHON section. However, various projects do use a REPORTING BUGS section. It is recommended to place it near the foot of the page.

COPYRIGHT

The man-pages project doesn't use a COPYRIGHT section in manual pages. Copyright information is instead maintained in the page source. In pages where this section is present, it is recommended to place it near the foot of the page, just above SEE ALSO.

SEE ALSO

A comma-separated list of related man pages, possibly followed by other related pages or documents.

The list should be ordered by section number and then alphabetically by name. Do not terminate this list with a period.

Where the SEE ALSO list contains many long manual page names, to improve the visual result of the output, it may be useful to employ the .ad l (don't right justify) and .nh (don't hyphenate) directives. Hyphenation of individual page names can be prevented by preceding words with the string "\%".

Given the distributed, autonomous nature of FOSS projects and their documentation, it is sometimes necessary—and in many cases desirable—that the SEE ALSO section includes references to manual pages provided by other projects.

FORMATTING AND WORDING CONVENTIONS#

The following subsections note some details for preferred formatting and wording conventions in various sections of the pages in the man-pages project.

SYNOPSIS#

Wrap the function prototype(s) in a .nf/.fi pair to prevent filling.

In general, where more than one function prototype is shown in the SYNOPSIS, the prototypes should not be separated by blank lines. However, blank lines (achieved using .P) may be added in the following cases:

•

to separate long lists of function prototypes into related groups (see for example list(3));

•

in other cases that may improve readability.

In the SYNOPSIS, a long function prototype may need to be continued over to the next line. The continuation line is indented according to the following rules:

(1)

If there is a single such prototype that needs to be continued, then align the continuation line so that when the page is rendered on a fixed-width font device (e.g., on an xterm) the continuation line starts just below the start of the argument list in the line above. (Exception: the indentation may be adjusted if necessary to prevent a very long continuation line or a further continuation line where the function prototype is very long.) As an example:

bash

int tcsetattr(int \nfd\n, int \noptional_actions\n,\n
\n              const struct termios *\ntermios_p\n);

(2)

But, where multiple functions in the SYNOPSIS require continuation lines, and the function names have different lengths, then align all continuation lines to start in the same column. This provides a nicer rendering in PDF output (because the SYNOPSIS uses a variable width font where spaces render narrower than most characters). As an example:

bash

int getopt(int \nargc\n, char * const \nargv[]\n,\n
\n           const char *\noptstring\n);\n
\nint getopt_long(int \nargc\n, char * const \nargv[]\n,\n
\n           const char *\noptstring\n,\n
\n           const struct option *\nlongopts\n, int *\nlongindex\n);

RETURN VALUE#

The preferred wording to describe how errno is set is "errno is set to indicate the error" or similar. This wording is consistent with the wording used in both POSIX.1 and FreeBSD.

ATTRIBUTES#

Note the following:

•

Wrap the table in this section in a .ad l/.ad pair to disable text filling and a .nh/.hy pair to disable hyphenation.

•

Ensure that the table occupies the full page width through the use of an lbx description for one of the columns (usually the first column, though in some cases the last column if it contains a lot of text).

•

Make free use of T{/T} macro pairs to allow table cells to be broken over multiple lines (also bearing in mind that pages may sometimes be rendered to a width of less than 80 columns).

For examples of all of the above, see the source code of various pages.

STYLE GUIDE#

The following subsections describe the preferred style for the man-pages project. For details not covered below, the Chicago Manual of Style is usually a good source; try also grepping for preexisting usage in the project source tree.

Use of gender-neutral language#

As far as possible, use gender-neutral language in the text of man pages. Use of "they" ("them", "themself", "their") as a gender-neutral singular pronoun is acceptable.

Formatting conventions for manual pages describing commands#

For manual pages that describe a command (typically in Sections 1 and 8), the arguments are always specified using italics, even in the SYNOPSIS section.

The name of the command, and its options, should always be formatted in bold.

Formatting conventions for manual pages describing functions#

For manual pages that describe functions (typically in Sections 2 and 3), the arguments are always specified using italics, even in the SYNOPSIS section, where the rest of the function is specified in bold:

int myfunction(intargc, char **argv);

Variable names should, like argument names, be specified in italics.

Any reference to the subject of the current manual page should be written with the name in bold followed by a pair of parentheses in Roman (normal) font. For example, in the fcntl(2) man page, references to the subject of the page would be written as: fcntl(). The preferred way to write this in the source file is:

\n
    .BR fcntl ()

(Using this format, rather than the use of "\fB...\fP()" makes it easier to write tools that parse man page source files.)

Use semantic newlines#

In the source of a manual page, new sentences should be started on new lines, long sentences should be split into lines at clause breaks (commas, semicolons, colons, and so on), and long clauses should be split at phrase boundaries. This convention, sometimes known as "semantic newlines", makes it easier to see the effect of patches, which often operate at the level of individual sentences, clauses, or phrases.

Lists#

There are different kinds of lists:

Tagged paragraphs

These are used for a list of tags and their descriptions. When the tags are constants (either macros or numbers) they are in bold. Use the .TP macro.

An example is this "Tagged paragraphs" subsection is itself.

Ordered lists

Elements are preceded by a number in parentheses (1), (2). These represent a set of steps that have an order.

When there are substeps, they will be numbered like (4.2).

Positional lists

Elements are preceded by a number (index) in square brackets [4], [5]. These represent fields in a set. The first index will be:

0

When it represents fields of a C data structure, to be consistent with arrays.

1

When it represents fields of a file, to be consistent with tools like cut(1).

Alternatives list

Elements are preceded by a letter in parentheses (a), (b). These represent a set of (normally) exclusive alternatives.

Bullet lists

Elements are preceded by bullet symbols (\[bu]). Anything that doesn't fit elsewhere is usually covered by this type of list.

Numbered notes

Not really a list, but the syntax is identical to "positional lists".

There should always be exactly 2 spaces between the list symbol and the elements. This doesn't apply to "tagged paragraphs", which use the default indentation rules.

Formatting conventions (general)#

Paragraphs should be separated by suitable markers (usually either .P or .IP). Do not separate paragraphs using blank lines, as this results in poor rendering in some output formats (such as PostScript and PDF).

Filenames (whether pathnames, or references to header files) are always in italics (e.g., <stdio.h>), except in the SYNOPSIS section, where included files are in bold (e.g., #include <stdio.h>). When referring to a standard header file include, specify the header file surrounded by angle brackets, in the usual C way (e.g., <stdio.h>).

Special macros, which are usually in uppercase, are in bold (e.g., MAXINT). Exception: don't boldface NULL.

When enumerating a list of error codes, the codes are in bold (this list usually uses the .TP macro).

Complete commands should, if long, be written as an indented line on their own, with a blank line before and after the command, for example

man 7 man-pages

If the command is short, then it can be included inline in the text, in italic format, for example, man 7 man-pages. In this case, it may be worth using nonbreaking spaces (\~) at suitable places in the command. Command options should be written in italics (e.g., -l).

Expressions, if not written on a separate indented line, should be specified in italics. Again, the use of nonbreaking spaces may be appropriate if the expression is inlined with normal text.

When showing example shell sessions, user input should be formatted in bold, for example

$ \ndate\n
Thu Jul  7 13:01:27 CEST 2016

Any reference to another man page should be written with the name in bold, always followed by the section number, formatted in Roman (normal) font, without any separating spaces (e.g., intro(2)). The preferred way to write this in the source file is:

\n
    .BR intro (2)

(Including the section number in cross references lets tools like man2html(1) create properly hyperlinked pages.)

Control characters should be written in bold face, with no quotes; for example, ^X.

Spelling#

Starting with release 2.59, man-pages follows American spelling conventions (previously, there was a random mix of British and American spellings); please write all new pages and patches according to these conventions.

Aside from the well-known spelling differences, there are a few other subtleties to watch for:

•

American English tends to use the forms "backward", "upward", "toward", and so on rather than the British forms "backwards", "upwards", "towards", and so on.

•

Opinions are divided on "acknowledgement" vs "acknowledgment". The latter is predominant, but not universal usage in American English. POSIX and the BSD license use the former spelling. In the Linux man-pages project, we use "acknowledgement".

BSD version numbers#

The classical scheme for writing BSD version numbers is x.yBSD, where x.y is the version number (e.g., 4.2BSD). Avoid forms such as BSD 4.3.

Capitalization#

In subsection ("SS") headings, capitalize the first word in the heading, but otherwise use lowercase, except where English usage (e.g., proper nouns) or programming language requirements (e.g., identifier names) dictate otherwise. For example:

.SS Unicode under Linux

Indentation of structure definitions, shell session logs, and so on#

When structure definitions, shell session logs, and so on are included in running text, indent them by 4 spaces (i.e., a block enclosed by .in +4n and .in), format them using the .EX and .EE macros, and surround them with suitable paragraph markers (either .P or .IP). For example:

.P
.in +4n
.EX
int
main(int argc, char *argv[])
{
\n
    return 0;
}
.EE
.in
.P

Preferred terms#

The following table lists some preferred terms to use in man pages, mainly to ensure consistency across pages.

See also the discussion Hyphenation of attributive compounds below.

Terms to avoid#

The following table lists some terms to avoid using in man pages, along with some suggested alternatives, mainly to ensure consistency across pages.

Trademarks#

Use the correct spelling and case for trademarks. The following is a list of the correct spellings of various relevant trademarks that are sometimes misspelled:

DG/UX
HP-UX
UNIX
UnixWare

NULL, NUL, null pointer, and null byte#

A null pointer is a pointer that points to nothing, and is normally indicated by the constant NULL. On the other hand, NUL is the null byte, a byte with the value 0, represented in C via the character constant '\0'.

The preferred term for the pointer is "null pointer" or simply "NULL"; avoid writing "NULL pointer".

The preferred term for the byte is "null byte". Avoid writing "NUL", since it is too easily confused with "NULL". Avoid also the terms "zero byte" and "null character". The byte that terminates a C string should be described as "the terminating null byte"; strings may be described as "null-terminated", but avoid the use of "NUL-terminated".

Hyperlinks#

For hyperlinks, use the .UR/.UE macro pair (see groff_man(7)). This produces proper hyperlinks that can be used in a web browser, when rendering a page with, say:

BROWSER=firefox man -H pagename

Use of e.g., i.e., etc., a.k.a., and similar#

In general, the use of abbreviations such as "e.g.", "i.e.", "etc.", "cf.", and "a.k.a." should be avoided, in favor of suitable full wordings ("for example", "that is", "and so on", "compare to", "also known as").

The only place where such abbreviations may be acceptable is in short parenthetical asides (e.g., like this one).

Always include periods in such abbreviations, as shown here. In addition, "e.g." and "i.e." should always be followed by a comma.

Em-dashes#

The way to write an em-dash—the glyph that appears at either end of this subphrase—in *roff is with the macro "\[em]". (On an ASCII terminal, an em-dash typically renders as two hyphens, but in other typographical contexts it renders as a long dash.) Em-dashes should be written without surrounding spaces.

Hyphenation of attributive compounds#

Compound terms should be hyphenated when used attributively (i.e., to qualify a following noun). Some examples:

32-bit value
command-line argument
floating-point number
run-time check
user-space function
wide-character string

Hyphenation with multi, non, pre, re, sub, and so on#

The general tendency in modern English is not to hyphenate after prefixes such as "multi", "non", "pre", "re", "sub", and so on. Manual pages should generally follow this rule when these prefixes are used in natural English constructions with simple suffixes. The following list gives some examples of the preferred forms:

interprocess
multithreaded
multiprocess
nonblocking
nondefault
nonempty
noninteractive
nonnegative
nonportable
nonzero
preallocated
precreate
prerecorded
reestablished
reinitialize
rearm
reread
subcomponent
subdirectory
subsystem

Hyphens should be retained when the prefixes are used in nonstandard English words, with trademarks, proper nouns, acronyms, or compound terms. Some examples:

non-ASCII
non-English
non-NULL
non-real-time

Finally, note that "re-create" and "recreate" are two different verbs, and the former is probably what you want.

Generating optimal glyphs#

Where a real minus character is required (e.g., for numbers such as -1, for man page cross references such as utf-8(7), or when writing options that have a leading dash, such as in ls -l), use the following form in the man page source:

\-

This guideline applies also to code examples.

The use of real minus signs serves the following purposes:

•

To provide better renderings on various targets other than ASCII terminals, notably in PDF and on Unicode/UTF-8-capable terminals.

•

To generate glyphs that when copied from rendered pages will produce real minus signs when pasted into a terminal.

To produce unslanted single quotes that render well in ASCII, UTF-8, and PDF, use "\[aq]" ("apostrophe quote"); for example

\[aq]C\[aq]

where C is the quoted character. This guideline applies also to character constants used in code examples.

Where a proper caret (^) that renders well in both a terminal and PDF is required, use "\[ha]". This is especially necessary in code samples, to get a nicely rendered caret when rendering to PDF.

Using a naked "~" character results in a poor rendering in PDF. Instead use "\[ti]". This is especially necessary in code samples, to get a nicely rendered tilde when rendering to PDF.

Example programs and shell sessions#

Manual pages may include example programs demonstrating how to use a system call or library function. However, note the following:

•

Example programs should be written in C.

•

An example program is necessary and useful only if it demonstrates something beyond what can easily be provided in a textual description of the interface. An example program that does nothing other than call an interface usually serves little purpose.

•

Example programs should ideally be short (e.g., a good example can often be provided in less than 100 lines of code), though in some cases longer programs may be necessary to properly illustrate the use of an API.

•

Expressive code is appreciated.

•

Comments should included where helpful. Complete sentences in free-standing comments should be terminated by a period. Periods should generally be omitted in "tag" comments (i.e., comments that are placed on the same line of code); such comments are in any case typically brief phrases rather than complete sentences.

•

Example programs should do error checking after system calls and library function calls.

•

Example programs should be complete, and compile without warnings when compiled with cc -Wall.

•

Where possible and appropriate, example programs should allow experimentation, by varying their behavior based on inputs (ideally from command-line arguments, or alternatively, via input read by the program).

•

Example programs should be laid out according to Kernighan and Ritchie style, with 4-space indents. (Avoid the use of TAB characters in source code!) The following command can be used to format your source code to something close to the preferred style:

bash

indent -npro -kr -i4 -ts4 -sob -l72 -ss -nut -psl prog.c

•

For consistency, all example programs should terminate using either of:

bash

exit(EXIT_SUCCESS);
exit(EXIT_FAILURE);

Avoid using the following forms to terminate a program:

bash

exit(0);
exit(1);
return n;

•

If there is extensive explanatory text before the program source code, mark off the source code with a subsection heading Program source, as in:

bash

.SS Program source

Always do this if the explanatory text includes a shell session log.

If you include a shell session log demonstrating the use of a program or other system feature:

•

Place the session log above the source code listing.

•

Indent the session log by four spaces.

•

Boldface the user input text, to distinguish it from output produced by the system.

For some examples of what example programs should look like, see wait(2) and pipe(2).

EXAMPLES#

For canonical examples of how man pages in the man-pages package should look, see pipe(2) and fcntl(2).

SEE ALSO#

man(1), man2html(1), attributes(7), groff(7), groff_man(7), man(7), mdoc(7)