MAN-PAGES
Section: Linux Programmer's Manual (7)
Updated: 2017-09-15
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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.
-
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 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 (aq.aq).
- 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 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(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),
format them using the
.EX
and
EE
macros, and surround them with suitable paragraph markers (either
.PP
or
.IP).
For example:
.PP
.in +4n
.EX
int
main(int argc, char *argv[])
{
return 0;
}
.EE
.in
.PP
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
aq\0aq.
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 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- Sections of the manual pages
-
- Macro package
-
- Conventions for source file layout
-
- Title line
-
- Sections within a manual page
-
- STYLE GUIDE
-
- Use of gender-neutral language
-
- Formatting conventions for manual pages describing commands
-
- Formatting conventions for manual pages describing functions
-
- Formatting conventions (general)
-
- Spelling
-
- BSD version numbers
-
- Capitalization
-
- Indentation of structure definitions, shell session logs, and so on
-
- Preferred terms
-
- Terms to avoid
-
- Trademarks
-
- NULL, NUL, null pointer, and null character
-
- Hyperlinks
-
- Use of e.g., i.e., etc., a.k.a., and similar
-
- Em-dashes
-
- Hyphenation of attributive compounds
-
- Hyphenation with multi, non, pre, re, sub, and so on
-
- Real minus character
-
- Character constants
-
- Example programs and shell sessions
-
- EXAMPLE
-
- SEE ALSO
-
- COLOPHON
-
|
|
- Running on 
-
:
: 