ioctl_tty.2: TIOCGSID is equivalent to tcgetsid()

[man-pages.git] / man7 / man-pages.7

.\" (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.\" manual page may be incorrect or out-of-date.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 2021-03-22 "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
The manual Sections are traditionally defined as follows:
.TP
.B 1 User commands (Programs)
Commands that can be executed by the user from within
a shell.
.TP
.B 2 System calls
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.
.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
The arguments of the command are as follows:
.TP
.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" ).
.\"
.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
.RS
.TS
l l.
\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
EXAMPLES
.\" AUTHORS sections are discouraged
AUTHORS [Discouraged]
REPORTING BUGS  [Not used in man-pages]
COPYRIGHT       [Not used in man-pages]
\fBSEE ALSO\fP
.TE
.RE
.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
.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 "\e\-") 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 16
.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 EXAMPLES
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 REPORTING BUGS
The
.IR 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.
.TP
.B COPYRIGHT
The
.IR 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.
.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 "\e%".
.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 FORMATTING AND WORDING CONVENTIONS
The following subsections note some details for preferred formatting and
wording conventions in various sections of the pages in the
.IR man-pages
project.
.SS SYNOPSIS
Wrap the function prototype(s) in a
.IR .nf / .fi
pair to prevent filling.
.PP
In general, where more than one function prototype is shown in the SYNOPSIS,
the prototypes should
.I not
be separated by blank lines.
However, blank lines (achieved using
.IR .PP )
may be added in the following cases:
.IP * 3
to separate long lists of function prototypes into related groups
(see for example
.BR list (3));
.IP *
in other cases that may improve readability.
.PP
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:
.IP 1. 3
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:
.PP
.RS
.nf
.BI "int tcsetattr(int " fd ", int " optional_actions ,
.BI "              const struct termios *" termios_p );
.fi
.RE
.IP 2. 3
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:
.PP
.RS
.nf
.BI "int getopt(int " argc ", char * const " argv[] ,
.BI "           const char *" optstring );
.BI "int getopt_long(int " argc ", char * const " argv[] ,
.BI "           const char *" optstring ,
.BI "           const struct option *" longopts ", int *" longindex );
.fi
.RE
.SS RETURN VALUE
The preferred wording to describe how
.I errno
is set is
.RI \(dq errno
is set to indicate the error"
or similar.
.\" Before man-pages 5.11, many different wordings were used, which
.\" was confusing, and potentially made scripted edits more difficult.
This wording is consistent with the wording used in both POSIX.1 and FreeBSD.
.SS ATTRIBUTES
.\" See man-pages commit c466875ecd64ed3d3cd3e578406851b7dfb397bf
Note the following:
.IP * 3
Wrap the table in this section in a
.IR ".ad\ l" / .ad
pair to disable text filling and a
.IR .nh / .hy
pair to disable hyphenation.
.IP *
Ensure that the table occupies the full page width through the use of an
.I 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).
.IP *
Make free use of
.IR 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).
.PP
For examples of all of the above, see the source code of various pages.
.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
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 "\efB...\efP()"
makes it easier to write tools that parse man page source files.)
.\"
.SS Use semantic newlines
In the source of a manual page,
new sentences should be started on new lines,
and long sentences should be split into lines at clause breaks
(commas, semicolons, colons, and so on).
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 or sentence clauses.
.\"
.SS Formatting conventions (general)
Paragraphs should be separated by suitable markers (usually either
.I .PP
or
.IR .IP ).
Do
.I not
separate paragraphs using blank lines, as this results in poor rendering
in some output formats (such as PostScript and PDF).
.PP
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
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 \(haX .
.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.
.IP *
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".
.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.
.ad l
.TS
l l l
---
l l ll.
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.
.ad l
.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
.ad
.\"
.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 byte
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", "and so on", "compare to", "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 "\e(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 Generating optimal glyphs
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
    \e\-
.PP
This guideline applies also to code examples.
.PP
The use of real minus signs serves the following purposes:
.\" https://lore.kernel.org/linux-man/20210121061158.5ul7226fgbrmodbt@localhost.localdomain/
.IP * 3
To provide better renderings on various targets other than
ASCII terminals,
notably in PDF and on Unicode/UTF\-8-capable terminals.
.IP *
To generate glyphs that when copied from rendered pages will
produce real minus signs when pasted into a terminal.
.PP
To produce unslanted single quotes that render well in ASCII, UTF-8, and PDF,
use "\e(aq" ("apostrophe quote"); for example
.PP
    \e(aqC\e(aq
.PP
where
.I C
is the quoted character.
This guideline applies also to character constants used in code examples.
.PP
Where a proper caret (\(ha) 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.
.PP
Using a naked "\(ti" 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.
.\"
.SS 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:
.IP * 3
Example programs should be written in C.
.IP *
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.
.IP *
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.
.IP *
Expressive code is appreciated.
.IP *
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.
.IP *
Example programs should do error checking after system calls and
library function calls.
.IP *
Example programs should be complete, and compile without
warnings when compiled with \fIcc\ \-Wall\fP.
.IP *
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).
.IP *
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:
.IP
    indent \-npro \-kr \-i4 \-ts4 \-sob \-l72 \-ss \-nut \-psl prog.c
.IP *
For consistency, all example programs should terminate using either of:
.IP
     exit(EXIT_SUCCESS);
     exit(EXIT_FAILURE);
.IP
Avoid using the following forms to terminate a program:
.IP
    exit(0);
    exit(1);
    return n;
.IP *
If there is extensive explanatory text before the
program source code, mark off the source code
with a subsection heading
.IR "Program source" ,
as in:
.IP
    .SS Program source
.IP
Always do this if the explanatory text includes a shell session log.
.PP
If you include a shell session log demonstrating the use of a program
or other system feature:
.IP * 3
Place the session log above the source code listing
.IP *
Indent the session log by four spaces.
.IP *
Boldface the user input text,
to distinguish it from output produced by the system.
.PP
For some examples of what example programs should look like, see
.BR wait (2)
and
.BR pipe (2).
.SH EXAMPLES
For canonical examples of how man pages in the
.I man-pages
package should look, see
.BR pipe (2)
and
.BR fcntl (2).
.SH SEE ALSO
.BR man (1),
.BR man2html (1),
.BR attributes (7),
.BR groff (7),
.BR groff_man (7),
.BR man (7),
.BR mdoc (7)