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)
Those commands that can be executed by the user from within a
shell.
2 System calls
Those 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.
New sentences should be started on new lines. This makes it easier to
see the effect of patches, which often operate at the level of
individual sentences.
Title line
The first command in a man page should be a TH command:
.TH title section date source manual
where:
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 source of the command, function, or system call.
For those few man-pages pages in Sections 1 and 8,
probably you just want to write GNU.
For system calls, just write Linux. (An earlier
practice was to write the version number of the kernel
from which the manual page was being written/checked.
However, this was never done consistently, and so was
probably worse than including no version number.
Henceforth, avoid including a version number.)
For library calls that are part of glibc or one of the
other common GNU libraries, just use GNU C Library,
GNU, or an empty string.
For Section 4 pages, use Linux.
In cases of doubt, just write Linux, or GNU.
manual The title of the manual (e.g., for Section 2 and 3
pages in the man-pages package, use Linux Programmer's
Manual).
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.
NAME
SYNOPSIS
CONFIGURATION [Normally only in Section 4]
DESCRIPTION
OPTIONS [Normally only in Sections 1, 8]
EXIT STATUS [Normally only in Sections 1, 8]
RETURN VALUE [Normally only in Sections 2, 3]
ERRORS [Typically only in Sections 2, 3]
ENVIRONMENT
FILES
VERSIONS [Normally only in Sections 2, 3]
ATTRIBUTES [Normally only in Sections 2, 3]
CONFORMING TO
NOTES
BUGS
EXAMPLE
SEE ALSO
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.
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.
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 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
VERSIONS 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 kernel 2.2), and library functions
that have been added to glibc since version 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.
CONFORMING TO 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).
For a page in Section 2 or 3, this section should note
the POSIX.1 version(s) that the call conforms to, and
also whether the call is specified in C99. (Don't worry
too much about other standards like SUS, SUSv2, and XPG,
or the SVr4 and 4.xBSD implementation standards, unless
the call was specified in those standards, but isn't in
the current version of POSIX.1.)
If the call is not governed by any standards but commonly
exists on other systems, note them. If the call is
Linux-specific, note this.
If this section consists of just a list of standards
(which it commonly does), terminate the list with a
period ('.').
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.
BUGS A list of limitations, known defects or inconveniences,
and other questionable activities.
EXAMPLE 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.
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.
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 functions
For manual pages that describe 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(int argc, 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:
.BR fcntl ()
(Using this format, rather than the use of "\fB...\fP()" makes it
easier to write tools that parse man page source files.)
Formatting conventions (general)
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
$ date
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:
.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.
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).
Preferred terms
The following table lists some preferred terms to use in man pages,
mainly to ensure consistency across pages.
Term Avoid using Notes
bit mask bitmask
built-in builtin
Epoch epoch For the UNIX Epoch
(00:00:00, 1 Jan
1970 UTC)
filename file name
filesystem file system
hostname host name
inode i-node
lowercase lower case, lower-case
pathname path name
pseudoterminal pseudo-terminal
privileged port reserved port, system
port
real-time realtime, real time
run time runtime
saved set-group-ID saved group ID, saved
set-GID
saved set-user-ID saved user ID, saved
set-UID
set-group-ID set-GID, setgid
set-user-ID set-UID, setuid
superuser super user, super-user
superblock super block, super-
block
timestamp time stamp
timezone time zone
uppercase upper case, upper-case
usable useable
user space userspace
username user name
zeros zeroes
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.
Avoid Use instead Notes
32bit 32-bit same for 8-bit,
16-bit, etc.
current process calling process A common mistake
made by kernel
programmers when
writing man pages
manpage man page, manual
page
minus infinity negative infinity
non-root unprivileged user
non-superuser unprivileged user
nonprivileged unprivileged
OS operating system
plus infinity positive infinity
pty pseudoterminal
tty terminal
Unices UNIX systems
Unixes UNIX systems
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 character
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.",
"a.k.a." should be avoided, in favor of suitable full wordings ("for
example", "that is", "and so on", "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.
Real minus character
Where a real minus character is required (e.g., for numbers such as -1,
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.
Character constants
To produce single quotes that render well in both ASCII and UTF-8, use
the following form for character constants in the man page source:
\(aqC\(aq
where C is the quoted character. This guideline applies also to
character constants used in code examples.
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 be fairly short (preferably less than 100
lines; ideally less than 50 lines).
* 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:
indent -npro -kr -i4 -ts4 -sob -l72 -ss -nut -psl prog.c
* For consistency, all example programs should terminate using either
of:
exit(EXIT_SUCCESS);
exit(EXIT_FAILURE);
Avoid using the following forms to terminate a program:
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:
.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).
EXAMPLE
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)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
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