This manual page explains the
groff tmac.an macro package (often called the
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
mdoc(7)).
Note that NET-2 BSD mdoc man pages can be used with
groff simply by specifying the
-mdoc option instead of the
-man option. Using the
-mandoc option is, however, recommended, since this will automatically detect which
macro package is in use.
The first command in a man page (after comment lines) should be
.THtitle section date source manual,
where:
title
The title of the man page (e.g.,
MAN).
section
The section number the man page should be placed in (e.g.,
7).
date
The date of the last revision—remember to change this every time a
change is made to the man page, since this is the most general way of doing
version control.
source
The source of the command.
For binaries, use something like:
GNU, NET-2, SLS Distribution, MCC Distribution.
For system calls, use the version of the kernel that you are currently
looking at:
Linux 0.99.11.
For library calls, use the source of the function:
GNU, 4.3BSD, Linux DLL 4.4.1.
manual
The title of the manual (e.g.,
Linux Programmer’s Manual).
Note that BSD mdoc-formatted pages begin with the
Dd command, not the
TH command.
The manual sections are traditionally defined as follows:
1 Commands
Those commands that can be executed by the user from within
a shell.
2 System calls
Those functions which must be performed by the kernel.
3 Library calls
Most of the
libc functions, such as
qsort(3).
4 Special files
Files found in
/dev.
5 File formats and conventions
The format for
/etc/passwd and other human-readable files.
6 Games 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.
8 System management commands
Commands like
mount(8),
many of which only root can execute.
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that exists is outdated already.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.
Sections are started with
.SH followed by the heading name. If the name contains spaces and appears
on the same line as
.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:
.SH NAME
chess \- the game of chess
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
makewhatis(8)
program to create a database of short command descriptions for the
whatis(1)
and
apropos(1)
commands.
Some other traditional sections have the following contents:
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
#include directives, followed by the function declaration.
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
OPTIONS section.
If there is some kind of input grammar or complex set of subcommands,
consider describing them in a separate
USAGE section (and just place an overview in the
DESCRIPTION section).
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.
EXIT STATUS
lists the possible exit status values or a program and
the conditions that cause these values to be returned.
OPTIONS
describes the options accepted by the program and how they change
its behavior.
USAGE
describes the grammar of any sublanguage this implements.
EXAMPLES
provides one or more examples describing how this function, file or
command is used.
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
/usr/local, so your base manual page should use
/usr/local as the base.
ENVIRONMENT
lists all environment variables that affect your program or function
and how they affect it.
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.
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
DESCRIPTION or
USAGE section).
However, please include security information somewhere!
CONFORMING TO
describes any standards or conventions this implements.
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:
For functions, 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);
Filenames are always in italics (e.g.,
/usr/include/stdio.h), except in the SYNOPSIS section, where included files are in bold (e.g.,
#include <stdio.h>).
Special macros, which are usually in upper case, are in bold (e.g.,
MAXINT).
When enumerating a list of error codes, the codes are in bold (this list
usually uses the
.TP macro).
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.,
man(7)).
The commands to select the type face are:
.B
Bold
.BI
Bold alternating with italics
(especially useful for function specifications)
.BR
Bold alternating with Roman
(especially useful for referring to other
manual pages)
.I
Italics
.IB
Italics alternating with bold
.IR
Italics alternating with Roman
.RB
Roman alternating with bold
.RI
Roman alternating with italics
.SB
Small alternating with bold
.SM
Small (useful for acronyms)
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
.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.
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 below;
macros may omit
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:
Start relative margin indent: moves the left margin
i to the right (if
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
.RE.
.RE
End relative margin indent and
restores the previous value of the prevailing indent.
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).
.IP x i
Indented paragraph with optional hanging tag.
If the tag
x is omitted, the entire following paragraph is indented by
i. If the tag
x is provided, it is hung at the left margin
before the following indented paragraph
(this is just like
.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 \(bu (bullet) or \(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 i
Begin paragraph with hanging tag. The tag is given on the next line, but
its results are like those of the
.IP command.
(Feature supported with
groff only.)
In order to use hypertext link macros, it is necessary to load the
www.tmac macro package.
Use the request
.mso www.tmac to do this.
.URL url link trailer
Inserts a hypertext link to the URI (URL)
url, with
link as the text of the link.
The
trailer will be printed immediately afterwards.
When generating HTML this should translate into the HTML command
<A HREF="url">link</A>trailer.
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.
It can be useful to define your own
URL macro in manual pages for the benefit of those viewing it with a roff
viewer other than
groff. That way, the URL, link text, and trailer text (if any) are still visible.
Here’s an example:
.de URL
\\$2 \(laURL: \\$1 \(ra\\$3
..
.if \n[.g] .mso www.tmac
.TH
... (later in the page)
This software comes from the
.URL "http://www.gnu.org/" "GNU Project" " of the"
.URL "http://www.fsf.org/" "Free Software Foundation" .
In the above, if
groff is being used, the
www.tmac macro package’s definition of the URL macro will supersede the locally
defined one.
A number of other link macros are available. See
groff_www(7)
for more details.
Although technically
man is a troff macro package, in reality a large number of other tools
process man page files that don’t implement all of troff’s abilities.
Thus, it’s best to avoid some of troff’s more exotic abilities where possible
to permit these other tools to work correctly.
Avoid using the various troff preprocessors
(if you must, go ahead and use
tbl(1),
but try to use the
IP and
TP commands instead for two-column tables).
Avoid using computations; most other tools can’t process them.
Use simple commands that are easy to translate to other formats.
The following troff macros are believed to be safe (though in many cases
they will be ignored by translators):
\,
.,
ad,
bp,
br,
ce,
de,
ds,
el,
ie,
if,
fi,
ft,
hy,
ig,
in,
na,
ne,
nf,
nh,
ps,
so,
sp,
ti,
tr.
You may also use many troff escape sequences (those sequences beginning
with \).
When you need to include the backslash character as normal text,
use \e.
Other sequences you may use, where x or xx are any characters and N
is any digit, include:
\’,
\‘,
\-,
\.,
\,
\%,
\*x,
\*(xx,
\(xx,
\$N,
\nx,
\n(xx,
\fx, and
\f(xx. Avoid using the escape sequences for drawing graphics.
Do not use the optional parameter for
bp (break page).
Use only positive values for
sp (vertical space).
Don’t define a macro
(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
(in) should be paired with a matching negative indent
(although you should be using the
RS and
RE macros instead).
The condition test
(if,ie) should only have ’t’ or ’n’ as the condition.
Only translations
(tr) that can be ignored should be used.
Font changes
(ft and the \f 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).
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.
By all means include full URLs (or URIs) in the text itself;
some tools such as
man2html(1)
can automatically turn them into hypertext links.
You can also use the new
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.
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).
Many man pages begin with ’\" 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
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:
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
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.
