man-pages/man7/man.7

.\" (C) Copyright 1992-1999 Rickard E. Faith and David A. Wheeler
.\" (faith@cs.unc.edu and dwheeler@ida.org)
.\"
.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.\" Modified Sun Jul 25 11:06:05 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Sat Jun  8 00:39:52 1996 by aeb
.\" Modified Wed Jun 16 23:00:00 1999 by David A. Wheeler (dwheeler@ida.org)
.\" Modified Thu Jul 15 12:43:28 1999 by aeb
.\"  [todo: split this into man.7 describing the macros
.\"   and manpage.7 describing the Linux man page conventions]
.\" Modified Sun Jan  6 18:26:25 2002 by Martin Schulze <joey@infodrom.org>
.\" Modified Tue Jul 27 20:12:02 2004 by Colin Watson <cjwatson@debian.org>
.\"
.TH MAN 7 2004-07-27 "Linux" "Linux Programmer's Manual"
.SH NAME
man \- macros to format man pages
.SH SYNOPSIS
.B groff \-Tascii \-man
.I file
\&...
.LP
.B groff \-Tps \-man
.I file
\&...
.LP
.B man
.RI [ section ]
.I title
.SH DESCRIPTION
This manual page explains the
.B "groff tmac.an"
macro package (often called the
.B man
macro package) and related conventions for creating manual (man) pages.
This macro package should be used by developers when
writing or porting man pages for Linux.  It is fairly compatible with other
versions of this macro package, so porting man pages should not be a major
problem (exceptions include the NET-2 BSD release, which uses a totally
different macro package called mdoc; see
.BR mdoc (7)).
.PP
Note that NET-2 BSD mdoc man pages can be used with
.B groff
simply by specifying the
.B \-mdoc
option instead of the
.B \-man
option.  Using the
.B \-mandoc
option is, however, recommended, since this will automatically detect which
macro package is in use.
.SH PREAMBLE
The first command in a man page (after comment lines) should be
.RS
.sp
.B \&.TH
.IR "title section date source manual" ,
.sp
.RE
where:
.RS
.TP 10
.I title
The title of the man page (e.g.,
.IR MAN ).
.TP
.I section
The section number the man page should be placed in (e.g.,
.IR 7 ).
.TP
.I date
The date of the last revision\(emremember to change this every time a
change is made to the man page, since this is the most general way of doing
version control.
.TP
.I source
The source of the command.
.sp
For binaries, use something like:
.IR GNU ", " NET-2 ", " "SLS Distribution" ", " "MCC Distribution" .
.sp
For system calls, use the version of the kernel that you are currently
looking at:
.IR "Linux 0.99.11" .
.sp
For library calls, use the source of the function:
.IR GNU ", " "4.3BSD" ", " "Linux DLL 4.4.1" .
.TP
.I manual
The title of the manual (e.g.,
.IR "Linux Programmer's Manual" ).
.RE
.PP
Note that BSD mdoc-formatted pages begin with the
.B Dd
command, not the
.B TH
command.
.PP
The manual sections are traditionally defined as follows:
.RS
.TP 10
.B 1 Commands
Those commands that can be executed by the user from within
a shell.
.TP
.B 2 System calls
Those functions which must be performed by the kernel.
.TP
.B 3 Library calls
Most of the
.I libc
functions, such as
.BR qsort (3).
.TP
.B 4 Special files
Files found in
.IR /dev .
.TP
.B 5 File formats and conventions
The format for
.I /etc/passwd
and other human-readable files.
.TP
.B 6 Games
.TP
.B 7 Conventions and miscellaneous
A description of the standard file system layout, network protocols,
ASCII and other character codes, this man page, and 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. 
.RE
.SH SECTIONS
Sections are started with
.B \&.SH
followed by the heading name.  If the name contains spaces and appears
on the same line as
.BR \&.SH ,
then place the heading in double quotes.  Traditional or suggested
headings include:
NAME, SYNOPSIS, DESCRIPTION, RETURN VALUE,
EXIT STATUS, ERROR HANDLING, ERRORS,
OPTIONS, USAGE, EXAMPLES, FILES, ENVIRONMENT, DIAGNOSTICS, SECURITY,
CONFORMING TO, NOTES, BUGS, AUTHOR, and SEE ALSO.
Where a traditional heading would apply, please use it;
this kind of consistency can make the information easier to understand.
However, feel free to create your own headings if they make things easier
to understand.
The only required heading is NAME, which should be the first section and
be followed on the next line by a one line description of the program:
.RS
.sp
\&.SH NAME
.br
chess \\- the game of chess
.sp
.RE
It is extremely important that this format is followed, and that there is a
backslash before the single dash which follows the command name.  This
syntax is used by the
.BR makewhatis (8)
program to create a database of short command descriptions for the
.BR whatis (1)
and
.BR apropos (1)
commands.
.PP
Some other traditional sections have the following contents:
.TP 14
.B SYNOPSIS
briefly describes 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
.B #include
directives, followed by the function declaration.
.TP
.B DESCRIPTION
gives an explanation of what the command, 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 options 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).
.TP
.B RETURN VALUE
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 EXIT STATUS
lists the possible exit status values or a program and
the conditions that cause these values to be returned.
.TP
.B OPTIONS
describes the options accepted by the program and how they change
its behavior.
.TP
.B USAGE
describes the grammar of any sublanguage this implements.
.TP
.B EXAMPLES
provides one or more examples describing how this function, file or
command is used.
.TP
.B FILES
lists 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
.IR /usr/local ,
so your base manual page should use
.I /usr/local
as the base.
.TP
.B ENVIRONMENT
lists all environment variables that affect your program or function
and how they affect it.
.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 your program.
.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 CONFORMING TO
describes any standards or conventions this implements.
.TP
.B NOTES
provides miscellaneous notes.
.TP
.B BUGS
lists limitations, known defects or inconveniences,
and other questionable activities.
.TP
.B AUTHOR
lists authors of the documentation or program so you can mail in bug
reports.
.TP
.B SEE ALSO
lists related man pages in alphabetical order, possibly followed by
other related pages or documents.
Conventionally this is the last section.
.SH FONTS
Although there are many arbitrary conventions for man pages in the UNIX
world, the existence of several hundred Linux-specific man pages defines our
font standards:
.IP
For functions, the arguments are always specified using italics,
.IR "even in the SYNOPSIS section" ,
where the rest of the function is specified in bold:
.RS
.BI "int myfunction(int " argc ", char **" argv );
.RE
.IP
Filenames are always in italics (e.g.,
.IR "/usr/include/stdio.h" ),
except in the SYNOPSIS section, where included files are in bold (e.g.,
.BR "#include <stdio.h>" ).
.IP
Special macros, which are usually in upper case, are in bold (e.g.,
.BR MAXINT ).
.IP
When enumerating a list of error codes, the codes are in bold (this list
usually uses the
.B \&.TP
macro).
.IP
Any reference to another man page (or to the subject of the current man
page) is in bold.  If the manual section number is given, it is given in
Roman (normal) font, without any spaces (e.g.,
.BR man (7)).
.LP
The commands to select the type face are:
.TP 4
.B \&.B
Bold
.TP
.B \&.BI
Bold alternating with italics
(especially useful for function specifications)
.TP
.B \&.BR
Bold alternating with Roman
(especially useful for referring to other
manual pages)
.TP
.B \&.I
Italics
.TP
.B \&.IB
Italics alternating with bold
.TP
.B \&.IR
Italics alternating with Roman
.TP
.B \&.RB
Roman alternating with bold
.TP
.B \&.RI
Roman alternating with italics
.TP
.B \&.SB
Small alternating with bold
.TP
.B \&.SM
Small (useful for acronyms)
.LP
Traditionally, each command can have up to six arguments, but the GNU
implementation removes this limitation (you might still want to limit
yourself to 6 arguments for portability's sake).
Arguments are delimited by
spaces.  Double quotes can be used to specify an argument which contains
spaces.  All of the arguments will be printed next to each other without
intervening spaces, so that the
.B \&.BR
command can be used to specify a word in bold followed by a mark of
punctuation in Roman.
If no arguments are given, the command is applied to the following line
of text.
.SH "OTHER MACROS AND STRINGS"
.PP
Below are other relevant macros and predefined strings.
Unless noted otherwise, all macros
cause a break (end the current line of text).
Many of these macros set or use the "prevailing indent."
The "prevailing indent" value is set by any macro with the parameter
.I i
below;
macros may omit
.I i
in which case the current prevailing indent will be used.
As a result, successive indented paragraphs can use the same indent without
re-specifying the indent value.
A normal (non-indented) paragraph resets the prevailing indent value
to its default value (0.5 inches).
By default a given indent is measured in ens; 
try to use ens or ems as units for
indents, since these will automatically adjust to font size changes.
The other key macro definitions are:
.SS "Normal Paragraphs"
.TP 9m
.B \&.LP
Same as
.B \&.PP
(begin a new paragraph).
.TP
.B \&.P
Same as
.B \&.PP
(begin a new paragraph).
.TP
.B \&.PP
Begin a new paragraph and reset prevailing indent.
.SS "Relative Margin Indent"
.TP 9m
.BI \&.RS " i"
Start relative margin indent: moves the left margin
.I i
to the right (if
.I i
is omitted, the prevailing indent value is used).
A new prevailing indent is set to 0.5 inches.
As a result, all following paragraph(s) will be
indented until the corresponding
.BR \&.RE .
.TP
.B \&.RE
End relative margin indent and
restores the previous value of the prevailing indent.
.SS "Indented Paragraph Macros"
.TP 9m
.BI \&.HP " i"
Begin paragraph with a hanging indent
(the first line of the paragraph is at the left margin of
normal paragraphs, and the rest of the paragraph's lines are indented).
.TP
.BI \&.IP " x i"
Indented paragraph with optional hanging tag.
If the tag
.I x
is omitted, the entire following paragraph is indented by
.IR i .
If the tag
.I x
is provided, it is hung at the left margin
before the following indented paragraph
(this is just like
.BR \&.TP
except the tag is included with the command instead of being on the
following line).
If the tag is too long, the text after the tag will be moved down to the
next line (text will not be lost or garbled).
For bulleted lists, use this macro with \e(bu (bullet) or \e(em (em dash)
as the tag, and for numbered lists, use the number or letter followed by
a period as the tag;
this simplifies translation to other formats.
.TP
.BI \&.TP " i"
Begin paragraph with hanging tag.  The tag is given on the next line, but
its results are like those of the
.B \&.IP
command.
.SS "Hypertext Link Macros"
(Feature supported with
.B groff
only.)
In order to use hypertext link macros, it is necessary to load the
.B www.tmac
macro package.
Use the request
.B .mso www.tmac
to do this.
.TP 9m
.BI \&.URL " url link trailer"
Inserts a hypertext link to the URI (URL)
.IR url ,
with
.I link
as the text of the link.
The
.I trailer
will be printed immediately afterwards.
When generating HTML this should translate into the HTML command
\fB<A HREF="\fP\fIurl\fP\fB">\fIlink\fP\fB</A>\fP\fItrailer\fP.
.\" The following is a kludge to get a paragraph into the listing.
.TP
.B " "
This and other related macros are new, and
many tools won't do anything with them, but
since many tools (including troff) will simply ignore undefined macros
(or at worst insert their text) these are safe to insert.
.\" The following is a kludge to get a paragraph into the listing.
.TP
.B " "
It can be useful to define your own
.B URL
macro in manual pages for the benefit of those viewing it with a roff
viewer other than
.BR groff .
That way, the URL, link text, and trailer text (if any) are still visible.
.\" The following is a kludge to get a paragraph into the listing.
.TP
.B " "
Here's an example:
.RS 1.5i
\&.de URL
.br
\\\\$2 \\(laURL: \\\\$1 \\(ra\\\\$3
.br
\&..
.br
\&.if \\n[.g] .mso www.tmac
.br
\&.TH
.I ...
.br
.I (later in the page)
.br
This software comes from the
.br
\&.URL "http://www.gnu.org/" "GNU Project" " of the"
.br
\&.URL "http://www.fsf.org/" "Free Software Foundation" .
.RE
.\" The following is a kludge to get a paragraph into the listing.
.TP
.B " "
In the above, if
.B groff
is being used, the
.B www.tmac
macro package's definition of the URL macro will supersede the locally
defined one.
.PP
A number of other link macros are available.  See
.BR groff_www (7)
for more details.
.SS "Miscellaneous Macros"
.TP 9m
.B \&.DT
Reset tabs to default tab values (every 0.5 inches);
does not cause a break.
.TP
.BI \&.PD " d"
Set inter-paragraph vertical distance to d
(if omitted, d=0.4v);
does not cause a break.
.TP
.BI \&.SS " t"
Subheading
.I t
(like
.BR \&.SH ,
but used for a subsection inside a section).
.SS "Predefined Strings"
The
.B man
package has the following predefined strings:
.IP \e*R
Registration Symbol: \*R
.IP \e*S
Change to default font size
.IP \e*(Tm
Trademark Symbol: \*(Tm
.IP \e*(lq
Left angled doublequote: \*(lq
.IP \e*(rq
Right angled doublequote: \*(rq
.SH "SAFE SUBSET"
Although technically
.B man
is a troff macro package, in reality a large number of other tools
process man page files that don't implement all of troff's abilities.
Thus, it's best to avoid some of troff's more exotic abilities where possible
to permit these other tools to work correctly.
Avoid using the various troff preprocessors
(if you must, go ahead and use
.BR tbl (1),
but try to use the
.B IP
and 
.B TP
commands instead for two-column tables).
Avoid using computations; most other tools can't process them.
Use simple commands that are easy to translate to other formats.
The following troff macros are believed to be safe (though in many cases
they will be ignored by translators):
.BR \e" ,
.BR . ,
.BR ad ,
.BR bp ,
.BR br ,
.BR ce ,
.BR de ,
.BR ds ,
.BR el ,
.BR ie ,
.BR if ,
.BR fi ,
.BR ft ,
.BR hy ,
.BR ig ,
.BR in ,
.BR na ,
.BR ne ,
.BR nf ,
.BR nh ,
.BR ps ,
.BR so ,
.BR sp ,
.BR ti ,
.BR tr .
.PP
You may also use many troff escape sequences (those sequences beginning
with \e).
When you need to include the backslash character as normal text,
use \ee.
Other sequences you may use, where x or xx are any characters and N
is any digit, include:
.BR \e' ,
.BR \e` ,
.BR \e- ,
.BR \e. ,
.BR \e" ,
.BR \e% ,
.BR \e*x ,
.BR \e*(xx ,
.BR \e(xx ,
.BR \e$N ,
.BR \enx ,
.BR \en(xx ,
.BR \efx ,
and
.BR \ef(xx .
Avoid using the escape sequences for drawing graphics.
.PP
Do not use the optional parameter for
.B bp
(break page).
Use only positive values for
.B sp
(vertical space).
Don't define a macro
.RB ( de )
with the same name as a macro in this or the
mdoc macro package with a different meaning; it's likely that
such redefinitions will be ignored.
Every positive indent
.RB ( in )
should be paired with a matching negative indent
(although you should be using the
.B RS
and
.B RE
macros instead).
The condition test
.RB ( if,ie )
should only have 't' or 'n' as the condition.
Only translations 
.RB ( tr )
that can be ignored should be used.
Font changes
.RB ( ft
and the \fB\ef\fP escape sequence)
should only have the values 1, 2, 3, 4, R, I, B, P, or CW
(the ft command may also have no parameters).
.PP
If you use capabilities beyond these, check the
results carefully on several tools.
Once you've confirmed that the additional capability is safe,
let the maintainer of this
document know about the safe command or sequence
that should be added to this list.
.SH NOTES
.PP
By all means include full URLs (or URIs) in the text itself;
some tools such as
.BR man2html (1)
can automatically turn them into hypertext links.
You can also use the new
.B URL
macro to identify links to related information.
If you include URLs, use the full URL
(e.g., <http://www.kernelnotes.org>) to ensure that tools
can automatically find the URLs.
.PP
Tools processing these files should open the file and examine the first
non-whitespace character. A period (.) or single quote (')
at the beginning of a line indicates a troff-based file (such as man or mdoc).
A left angle bracket (<) indicates an SGML/XML-based
file (such as HTML or Docbook). Anything else suggests simple ASCII
text (e.g., a "catman" result).
.PP
Many man pages begin with '\e" followed by a space and a list of characters,
indicating how the page is to be preprocessed.
For portability's sake to non-troff translators we recommend that you avoid
using anything other than
.BR tbl (1),
and Linux can detect that automatically.
However, you might want to include this information so your man page
can be handled by other (less capable) systems.
Here are the definitions of the preprocessors invoked by these characters:
.TP 3
.B e
eqn(1)
.TP
.B g
grap(1)
.TP
.B p
pic(1)
.TP
.B r
refer(1)
.TP
.B t
tbl(1)
.TP
.B v
vgrind(1)
.SH FILES
.IR /usr/share/groff/ [*/] tmac/tmac.an
.br
.I /usr/man/whatis
.SH BUGS
.PP
Most of the macros describe formatting (e.g., font type and spacing) instead
of marking semantic content (e.g., this text is a reference to another page),
compared to formats like mdoc and DocBook (even HTML has more semantic
markings).
This situation makes it harder to vary the
.B man
format for different media,
to make the formatting consistent for a given media, and to automatically
insert cross-references.
By sticking to the safe subset described above, it should be easier to
automate transitioning to a different reference page format in the future.
.LP
The Sun macro
.B TX
is not implemented.
.SH AUTHORS
.IP \(em 3m
James Clark (jjc@jclark.com) wrote the implementation of the macro package.
.IP \(em
Rickard E. Faith (faith@cs.unc.edu) wrote the initial version of
this manual page.
.IP \(em
Jens Schweikhardt (schweikh@noc.fdn.de) wrote the Linux Man-Page Mini-HOWTO
(which influenced this manual page).
.IP \(em
David A. Wheeler (dwheeler@ida.org) heavily modified this
manual page, such as adding detailed information on sections and macros.
.SH "SEE ALSO"
.BR apropos (1),
.BR groff (1),
.BR man (1),
.BR man2html (1),
.BR mdoc (7),
.BR mdoc.samples (7),
.BR groff_man (7),
.BR groff_www (7),
.BR whatis (1)