Ubuntu Manpage: man-pages - conventions for writing Linux man pages

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:

.TH title section date source manual-section

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.

NAME
LIBRARY [Normally only in Sections 2, 3]
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]
STANDARDS
NOTES
CAVEATS
BUGS
EXAMPLES
AUTHORS [Discouraged]
REPORTING BUGS [Not used in man-pages]
COPYRIGHT [Not used in man-pages]
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.

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 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 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.

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).

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.

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
       .PP) 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:

                int tcsetattr(int fd, int optional_actions,
                              const struct termios *termios_p);

       (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:

                int getopt(int argc, char * const argv[],
                           const char *optstring);
                int getopt_long(int argc, char * const argv[],
                           const char *optstring,
                           const struct option *longopts, int *longindex);

   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(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.)

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 .PP 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 (\[ti])
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.

• 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 .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
nonzero non-zero
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
symbolic link symlink
timestamp time stamp
timezone time zone
uppercase upper case, upper-case
usable useable
user space userspace
username user name
x86-64 x86_64 Except if referring
to result of
"uname -m" or
similar
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 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:

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).

EXAMPLES

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