random.7: Remove recommendation against consuming large amounts of randomness

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

.\" (C) Copyright 1992-1999 Rickard E. Faith and David A. Wheeler
.\" (faith@cs.unc.edu and dwheeler@ida.org)
.\"
.\" %%%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.\" manual page may be incorrect or out-of-date.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
.\"
.\" 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
.\" 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>
.\" 2007-05-30, mtk: various rewrites and moved much text to new man-pages.7.
.\"
.TH MAN 7 2012-08-05 "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 an.tmac"
macro package (often called the
.B man
macro package).
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.
.PP
For conventions that should be employed when writing man pages
for the Linux \fIman-pages\fP package, see
.BR man-pages (7).
.SS Title line
The first command in a man page (after comment lines,
that is, lines that start with \fB.\\"\fP) should be
.RS
.sp
.B \&.TH
.I "title section date source manual"
.sp
.RE
For details of the arguments that should be supplied to the
.B TH
command, see
.BR man-pages (7).
.PP
Note that BSD mdoc-formatted pages begin with the
.B Dd
command, not the
.B TH
command.
.SS Sections
Sections are started with
.B \&.SH
followed by the heading name.
.\" The following doesn't seem to be required (see Debian bug 411303),
.\" If the name contains spaces and appears
.\" on the same line as
.\" .BR \&.SH ,
.\" then place the heading in double quotes.

The only mandatory 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
item \\- description
.sp
.RE
It is extremely important that this format is followed, and that there is a
backslash before the single dash which follows the item name.
This syntax is used by the
.BR mandb (8)
program to create a database of short descriptions for the
.BR whatis (1)
and
.BR apropos (1)
commands.
(See
.BR lexgrog (1)
for further details on the syntax of the NAME section.)
.PP
For a list of other sections that might appear in a manual page, see
.BR man-pages (7).
.SS Fonts
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.
.SS 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
respecifying the indent value.
A normal (nonindented) 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
.B \&.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 afterward.
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 double quote: \*(lq
.IP \e*(rq
Right angled double quote: \*(rq
.SS 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 \(aqt\(aq or \(aqn\(aq 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 FILES
.IR /usr/share/groff/ [*/] tmac/an.tmac
.br
.I /usr/man/whatis
.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.,
.UR http://www.kernelnotes.org
.UE )
to ensure that tools can automatically find the URLs.
.PP
Tools processing these files should open the file and examine the first
nonwhitespace 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 \fB\'\e"\fP 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 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 lexgrog (1),
.BR man (1),
.BR man2html (1),
.BR whatis (1),
.BR groff_man (7),
.BR groff_www (7),
.BR man-pages (7),
.BR mdoc (7),
.BR mdoc.samples (7)