.\" (C) Copyright 1992-1999 Rickard E. Faith and David A. Wheeler

.\" (faith@cs.unc.edu and dwheeler@ida.org)

.\" and (C) Copyright 2007 Michael Kerrisk <mtk.manpages@gmail.com>

.\"

.\" %%%LICENSE_START(VERBATIM)

.\" Permission is granted to make and distribute verbatim copies of this

.\" manual provided the copyright notice and this permission notice are

.\" preserved on all copies.

.\"

.\" Permission is granted to copy and distribute modified versions of this

.\" manual under the conditions for verbatim copying, provided that the

.\" entire resulting derived work is distributed under the terms of a

.\" permission notice identical to this one.

.\"

.\" Since the Linux kernel and libraries are constantly changing, this

.\" manual page may be incorrect or out-of-date.  The author(s) assume no

.\" responsibility for errors or omissions, or for damages resulting from

.\" the use of the information contained herein.  The author(s) may not

.\" have taken the same level of care in the production of this manual,

.\" which is licensed free of charge, as they might when working

.\" professionally.

.\"

.\" Formatted or processed versions of this manual, if unaccompanied by

.\" the source, must acknowledge the copyright and authors of this work.

.\" %%%LICENSE_END

.\"

.\" 2007-05-30 created by mtk, using text from old man.7 plus

.\" rewrites and additional text.

.\"

.TH MAN-PAGES 7 2018-02-02 "Linux" "Linux Programmer's Manual"

.SH NAME

man-pages \- conventions for writing Linux man pages

.SH SYNOPSIS

.B man

.RI [ section ]

.I title

.SH DESCRIPTION

This page describes the conventions that should be employed

when writing man pages for the Linux \fIman-pages\fP 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.

.SS Sections of the manual pages

.PP

The manual Sections are traditionally defined as follows:

.TP 10

.B 1 User commands (Programs)

Those commands that can be executed by the user from within

a shell.

.TP

.B 2 System calls

Those functions which wrap operations performed by the kernel.

.TP

.B 3 Library calls

All library functions excluding the system call wrappers

(Most of the

.I libc

functions).

.TP

.B 4 Special files (devices)

Files found in

.I /dev

which allow to access to devices through the kernel.

.TP

.B 5 File formats and configuration files

Describes various human-readable file formats and configuration files.

.TP

.B 6 Games

Games and funny little programs available on the system.

.TP

.B 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.

.TP

.B 8 System management commands

Commands like

.BR mount (8),

many of which only root can execute.

.\" .TP

.\" .B 9 Kernel routines

.\" This is an obsolete manual section.

.\" Once it was thought a good idea to document the Linux kernel here,

.\" but in fact very little has been documented, and the documentation

.\" that exists is outdated already.

.\" There are better sources of

.\" information for kernel developers.

.SS Macro package

New manual pages should be marked up using the

.B groff an.tmac

package described in

.BR man (7).

This choice is mainly for consistency: the vast majority of

existing Linux manual pages are marked up using these macros.

.SS 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.

.PP

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.

.SS Title line

The first command in a man page should be a

.B TH

command:

.PP

.RS

.B \&.TH

.I "title section date source manual"

.RE

.PP

where:

.RS

.TP 10

.I title

The title of the man page, written in all caps (e.g.,

.IR MAN-PAGES ).

.TP

.I section

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

.IR 7 ).

.TP

.I date

The date of the last nontrivial change that was made to the man page.

(Within the

.I 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.

.TP

.I source

The source of the command, function, or system call.

.IP

For those few \fIman-pages\fP pages in Sections 1 and 8,

probably you just want to write

.IR GNU .

.IP

For system calls, just write

.IR "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.)

.IP

For library calls that are part of glibc or one of the

other common GNU libraries, just use

.IR "GNU C Library" ", " GNU ,

or an empty string.

.IP

For Section 4 pages, use

.IR "Linux" .

.IP

In cases of doubt, just write

.IR Linux ", or " GNU .

.TP

.I manual

The title of the manual (e.g., for Section 2 and 3 pages in

the \fIman-pages\fP package, use

.IR "Linux Programmer's Manual" ).

.RE

.SS Sections within a manual page

The list below shows conventional or suggested sections.

Most manual pages should include at least the

.B highlighted

sections.

Arrange a new manual page so that sections

are placed in the order shown in the list.

.PP

.in +4n

.nf

\fBNAME\fP

\fBSYNOPSIS\fP

CONFIGURATION      [Normally only in Section 4]

\fBDESCRIPTION\fP

OPTIONS            [Normally only in Sections 1, 8]

EXIT STATUS        [Normally only in Sections 1, 8]

RETURN VALUE       [Normally only in Sections 2, 3]

.\" May 07: Few current man pages have an ERROR HANDLING section,,,

.\" ERROR HANDLING,

ERRORS             [Typically only in Sections 2, 3]

.\" May 07: Almost no current man pages have a USAGE section,,,

.\" USAGE,

.\" DIAGNOSTICS,

.\" May 07: Almost no current man pages have a SECURITY section,,,

.\" SECURITY,

ENVIRONMENT

FILES

VERSIONS           [Normally only in Sections 2, 3]

ATTRIBUTES         [Normally only in Sections 2, 3]

CONFORMING TO

NOTES

BUGS

EXAMPLE

.\" AUTHORS sections are discouraged

.\" AUTHORS             [Discouraged]

\fBSEE ALSO\fP

.fi

.in

.PP

.IR "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 (\fI.SS\fP) within

those sections.

.PP

The following list elaborates on the contents of each of

the above sections.

.TP 14

.B NAME

The name of this manual page.

.IP

See

.BR man (7)

for important details of the line(s) that should follow the

\fB.SH NAME\fP 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.

.TP

.B SYNOPSIS

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

.IP

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

.B #include

directives, followed by the function declaration.

.IP

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

.BR feature_test_macros (7).

.\" FIXME . Say something here about compiler options

.TP

.B CONFIGURATION

Configuration details for a device.

.IP

This section normally appears only in Section 4 pages.

.TP

.B DESCRIPTION

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

.IP

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

.B OPTIONS

section.

.\" If there is some kind of input grammar or complex set of subcommands,

.\" consider describing them in a separate

.\" .B USAGE

.\" section (and just place an overview in the

.\" .B DESCRIPTION

.\" section).

.IP

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

.B .TP

list, in the following form (here, for a new system call flag):

.RS 22

.TP

.BR XYZ_FLAG " (since Linux 3.7)"

Description of flag...

.RE

.IP

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).

.TP

.B OPTIONS

A description of the command-line options accepted by a

program and how they change its behavior.

.IP

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

.\" .TP

.\" .B USAGE

.\" describes the grammar of any sublanguage this implements.

.TP

.B EXIT STATUS

A list of the possible exit status values of a program and

the conditions that cause these values to be returned.

.IP

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

.TP

.B 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.

.TP

.B ERRORS

For Section 2 and 3 manual pages, this is a list of the

values that may be placed in

.I errno

in the event of an error, along with information about the cause

of the errors.

.IP

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.

.IP

.IR "The error list should be in alphabetical order" .

.TP

.B ENVIRONMENT

A list of all environment variables that affect the program or function

and how they affect it.

.TP

.B FILES

A list of the files the program or function uses, such as

configuration files, startup files,

and files the program directly operates on.

.IP

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

.IR /usr/local ,

so your base manual page should use

.I /usr/local

as the base.

.\" May 07: Almost no current man pages have a DIAGNOSTICS section;

.\"         "RETURN VALUE" or "EXIT STATUS" is preferred.

.\" .TP

.\" .B DIAGNOSTICS

.\" gives an overview of the most common error messages and how to

.\" cope with them.

.\" You don't need to explain system error messages

.\" or fatal signals that can appear during execution of any program

.\" unless they're special in some way to the program.

.\"

.\" May 07: Almost no current man pages have a SECURITY section.

.\".TP

.\".B SECURITY

.\"discusses security issues and implications.

.\"Warn about configurations or environments that should be avoided,

.\"commands that may have security implications, and so on, especially

.\"if they aren't obvious.

.\"Discussing security in a separate section isn't necessary;

.\"if it's easier to understand, place security information in the

.\"other sections (such as the

.\" .B DESCRIPTION

.\" or

.\" .B USAGE

.\" section).

.\" However, please include security information somewhere!

.TP

.B ATTRIBUTES

A summary of various attributes of the function(s) documented on this page.

See

.BR attributes (7)

for further details.

.TP

.B 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.

.IP

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).

.IP

The

.BR syscalls (2)

manual page also provides information about kernel versions

in which various system calls first appeared.

.TP

.B CONFORMING TO

A description of any standards or conventions that relate to the function

or command described by the manual page.

.IP

The preferred terms to use for the various standards are listed as

headings in

.BR standards (7).

.IP

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.)

.IP

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.

.IP

If this section consists of just a list of standards

(which it commonly does),

terminate the list with a period (\(aq.\(aq).

.TP

.B NOTES

Miscellaneous notes.

.IP

For Section 2 and 3 man pages you may find it useful to include

subsections (\fBSS\fP) named \fILinux Notes\fP and \fIGlibc Notes\fP.

.IP

In Section 2, use the heading

.I "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.

.TP

.B BUGS

A list of limitations, known defects or inconveniences,

and other questionable activities.

.TP

.B EXAMPLE

One or more examples demonstrating how this function, file or

command is used.

.IP

For details on writing example programs,

see \fIExample Programs\fP below.

.TP

.B AUTHORS

A list of authors of the documentation or program.

.IP

\fBUse of an AUTHORS section is strongly discouraged\fP.

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.

.TP

.B SEE ALSO

A comma-separated list of related man pages, possibly followed by

other related pages or documents.

.IP

The list should be ordered by section number and

then alphabetically by name.

Do not terminate this list with a period.

.IP

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

.I .ad l

(don't right justify)

and

.I .nh

(don't hyphenate)

directives.

Hyphenation of individual page names can be prevented

by preceding words with the string "\\%".

.IP

Given the distributed, autonomous nature of FOSS projects

and their documentation, it is sometimes necessary\(emand in many cases

desirable\(emthat the SEE ALSO section includes references to

manual pages provided by other projects.

.SH STYLE GUIDE

The following subsections describe the preferred style for the

.IR 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.

.SS 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.

.\"

.SS Formatting conventions for manual pages describing commands

.PP

For manual pages that describe a command (typically in Sections 1 and 8),

the arguments are always specified using italics,

.IR "even in the SYNOPSIS section" .

.PP

The name of the command, and its options, should

always be formatted in bold.

.\"

.SS 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,

.IR "even in the SYNOPSIS section" ,

where the rest of the function is specified in bold:

.PP

.BI "    int myfunction(int " argc ", char **" argv );

.PP

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

.PP

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

.BR fcntl (2)

man page, references to the subject of the page would be written as:

.BR fcntl ().

The preferred way to write this in the source file is:

.PP

.EX

    .BR fcntl ()

.EE

.PP

(Using this format, rather than the use of "\\fB...\\fP()"

makes it easier to write tools that parse man page source files.)

.\"

.SS Formatting conventions (general)

Filenames (whether pathnames, or references to header files)

are always in italics (e.g.,

.IR <stdio.h> ),

except in the SYNOPSIS section, where included files are in bold (e.g.,

.BR "#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.,

.IR <stdio.h> ).

.PP

Special macros, which are usually in uppercase, are in bold (e.g.,

.BR MAXINT ).

Exception: don't boldface NULL.

.PP

When enumerating a list of error codes, the codes are in bold (this list

usually uses the

.B \&.TP

macro).

.PP

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

.PP

.in +4n

.EX

man 7 man-pages

.EE

.in

.PP

If the command is short, then it can be included inline in the text,

in italic format, for example,

.IR "man 7 man-pages" .

In this case, it may be worth using nonbreaking spaces

("\e\ ") at suitable places in the command.

Command options should be written in italics (e.g.,

.IR \-l ).

.PP

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.

.PP

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

.PP

.in +4n

.EX

$ \fBdate\fP

Thu Jul  7 13:01:27 CEST 2016

.EE

.in

.PP

.PP

Any reference to another man page

should be written with the name in bold,

.I always

followed by the section number,

formatted in Roman (normal) font, without any

separating spaces (e.g.,

.BR intro (2)).

The preferred way to write this in the source file is:

.PP

.EX

    .BR intro (2)

.EE

.PP

(Including the section number in cross references lets tools like

.BR man2html (1)

create properly hyperlinked pages.)

.PP

Control characters should be written in bold face,

with no quotes; for example,

.BR ^X .

.SS Spelling

Starting with release 2.59,

.I 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.

.PP

Aside from the well-known spelling differences,

there are a few other subtleties to watch for:

.IP * 3

American English tends to use the forms "backward", "upward", "toward",

and so on

rather than the British forms "backwards", "upwards", "towards", and so on.

.SS BSD version numbers

The classical scheme for writing BSD version numbers is

.IR x.yBSD ,

where

.I x.y

is the version number (e.g., 4.2BSD).

Avoid forms such as

.IR "BSD 4.3" .

.SS 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:

.PP

.EX

    .SS Unicode under Linux

.EE

.\"

.SS 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

.I ".in\ +4n"

and

.IR ".in" ),

format them using the

.I .EX

and

.I EE

macros, and surround them with suitable paragraph markers (either

.I .PP

or

.IR .IP ).

For example:

.PP

.in +4n

.EX

    .PP

    .in +4n

    .EX

    int

    main(int argc, char *argv[])

    {

        return 0;

    }

    .EE

    .in

    .PP

.EE

.in

.SS Preferred terms

The following table lists some preferred terms to use in man pages,

mainly to ensure consistency across pages.

.TS

l l l

---

l l l.

Term	Avoid using	Notes

bit mask	bitmask

built-in	builtin

Epoch	epoch	T{

For the UNIX Epoch (00:00:00, 1 Jan 1970 UTC)

T}

filename	file name

filesystem	file system

hostname	host name

inode	i-node

lowercase	lower case, lower-case

nonzero	non-zero

pathname	path name

pseudoterminal	pseudo-terminal

privileged port	T{

reserved port,

system port

T}

real-time	T{

realtime,

real time

T}

run time	runtime

saved set-group-ID	T{

saved group ID,

saved set-GID

T}

saved set-user-ID	T{

saved user ID,

saved set-UID

T}

set-group-ID	set-GID, setgid

set-user-ID	set-UID, setuid

superuser	T{

super user,

super-user

T}

superblock	T{

super block,

super-block

T}

timestamp	time stamp

timezone	time zone

uppercase	upper case, upper-case

usable	useable

user space	userspace

username	user name

x86-64	x86_64	T{

Except if referring to result of "uname\ \-m" or similar

T}

zeros	zeroes

.TE

.PP

See also the discussion

.IR "Hyphenation of attributive compounds"

below.

.SS 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.

.TS

l l l

---

l l l.

Avoid	Use instead	Notes

32bit	32-bit	T{

same for 8-bit, 16-bit, etc.

T}

current process	calling process	T{

A common mistake made by kernel programmers when writing man pages

T}

manpage	T{

man page, manual page

T}

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

.TE

.SS 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:

.PP

     DG/UX

     HP-UX

     UNIX

     UnixWare

.SS NULL, NUL, null pointer, and null character

A

.IR "null pointer"

is a pointer that points to nothing,

and is normally indicated by the constant

.IR NULL .

On the other hand,

.I NUL

is the

.IR "null byte",

a byte with the value 0, represented in C via the character constant

.IR \(aq\e0\(aq .

.PP

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

avoid writing "NULL pointer".

.PP

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".

.SS Hyperlinks

For hyperlinks, use the

.IR .UR / .UE

macro pair

(see

.BR groff_man (7)).

This produces proper hyperlinks that can be used in a web browser,

when rendering a page with, say:

.PP

     BROWSER=firefox man -H pagename

.SS 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", "compare to", "and so on", "also known as").

.PP

The only place where such abbreviations may be acceptable is in

.I short

parenthetical asides (e.g., like this one).

.PP

Always include periods in such abbreviations, as shown here.

In addition, "e.g." and "i.e." should always be followed by a comma.

.SS Em-dashes

The way to write an em-dash\(emthe glyph that appears

at either end of this subphrase\(emin *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

.I without

surrounding spaces.

.SS Hyphenation of attributive compounds

Compound terms should be hyphenated when used attributively

(i.e., to qualify a following noun). Some examples:

.PP

    32-bit value

    command-line argument

    floating-point number

    run-time check

    user-space function

    wide-character string

.SS 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:

.PP

    interprocess

    multithreaded

    multiprocess

    nonblocking

    nondefault

    nonempty

    noninteractive

    nonnegative

    nonportable

    nonzero

    preallocated

    precreate

    prerecorded

    reestablished

    reinitialize

    rearm

    reread

    subcomponent

    subdirectory

    subsystem

.PP

Hyphens should be retained when the prefixes are used in nonstandard

English words, with trademarks, proper nouns, acronyms, or compound terms.

Some examples:

.PP

    non-ASCII

    non-English

    non-NULL

    non-real-time

.PP

Finally, note that "re-create" and "recreate" are two different verbs,

and the former is probably what you want.

.SS Real minus character

Where a real minus character is required (e.g., for numbers such as \-1,

for man page cross references such as

.BR utf\-8 (7),

or when writing options that have a leading dash, such as in

.IR "ls\ \-l"),

use the following form in the man page source:

.PP

    \\\-

.PP