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MAN-PAGES(7)                        Linux Programmer's Manual                        MAN-PAGES(7)



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, as well
       as many of the pages that appear in Sections 3, 4, 5, and 7 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 Commands (Programs)
                 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.

       4 Special files (devices)
                 Files found in /dev.

       5 File formats and conventions
                 The format for /etc/passwd and other human-readable files.

       6 Games

       7 Overview, conventions, and miscellaneous
                 Overviews of various topics, conventions and protocols, character set standards,
                 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 possi-
       ble.  This helps avoid line-wrapping in some  mail  clients  when  patches  are  submitted
       inline.

       New  sentences  should be started on new lines.  This makes it easier to see the effect of
       patches, which often operate at the level of individual sentences.

   Title line
       The first command in a man page should be a TH command:

              .TH title section date source manual

       where:

              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 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.  Dates should be written in the form YYYY-MM-DD.

              source    The source of the command, function, or system call.

                        For those few man-pages pages in Sections 1 and 8, probably you just want
                        to write GNU.

                        For  system  calls,  just write 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.)

                        For  library  calls that are part of glibc or one of the other common GNU
                        libraries, just use GNU C Library, GNU, or an empty string.

                        For Section 4 pages, use Linux.

                        In cases of doubt, just write Linux, or GNU.

              manual    The title of the manual (e.g., for Section 2 and 3 pages in the man-pages
                        package, use Linux Programmer's Manual).

   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
            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
            ATTRIBUTES         [Normally only in Sections 2, 3]
            VERSIONS           [Normally only in Sections 2, 3]
            CONFORMING TO
            NOTES
            BUGS
            EXAMPLE
            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  other-
                     wise.

       SYNOPSIS      briefly  describes  the command or function's interface.  For commands, this
                     shows the syntax of the command and its arguments (including options); bold-
                     face  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 declara-
                     tion 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   gives 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 func-
                     tion, 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 con-
                     strained to using older kernel or C library versions (which  is  typical  in
                     embedded systems, for example).

       OPTIONS       describes 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   lists  the  possible exit status values of a program and the conditions that
                     cause these values to be returned.  This section should appear only for Sec-
                     tion 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.  The error list should be in alphabetical order.

       ENVIRONMENT   lists  all environment variables that affect the program or function and how
                     they affect it.

       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 /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,
                     broken into subsections.  The following subsections are defined:


                     Multithreading (see pthreads(7))
                            This subsection notes attributes relating to  multithreaded  applica-
                            tions:

                            *  Whether the function is thread-safe.

                            *  Whether the function is a cancellation point.

                            *  Whether the function is async-cancel-safe.

                            Details of these attributes can be found in pthreads(7).

       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 ker-
                     nel 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).

                     The syscalls(2) manual page also provides information about kernel  versions
                     in which various system calls first appeared.

       CONFORMING TO describes  any  standards or conventions that relate to the function or com-
                     mand described by the manual page.  For a page in Section 2 or 3, this  sec-
                     tion  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.)  (See standards(7).)

                     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         provides miscellaneous notes.  For Section 2 and 3 man pages you may find it
                     useful to include subsections (SS) named Linux Notes and Glibc Notes.

       BUGS          lists limitations, known defects or inconveniences, and  other  questionable
                     activities.

       EXAMPLE       provides  one or more examples describing how this function, file or command
                     is used.  For details on writing  example  programs,  see  Example  Programs
                     below.

       AUTHORS       lists 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.

       SEE ALSO      provides a comma-separated list of related man  pages,  ordered  by  section
                     number  and  then alphabetically by name, possibly followed by other related
                     pages or documents.  Do not terminate this 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  indi-
                     vidual page names can be prevented by preceding words with the string "\%".

   Font conventions
       For functions, the arguments are always specified using italics, even in the SYNOPSIS sec-
       tion, 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.

       Filenames (whether pathnames, or references to files in the  /usr/include  directory)  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 include  file  under
       /usr/include,  specify  the  header  file surrounded by angle brackets, in the usual C way
       (e.g., <stdio.h>).

       Special macros, which are usually in upper case, 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 in an indented line  on  their  own,  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  ("\ ")
       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.

       Any reference to the subject of the current manual page should be written with the name in
       bold.   If  the subject is a function (i.e., this is a Section 2 or 3 page), then the name
       should be 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.)

       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 prop-
       erly hyperlinked pages.)

   Spelling
       Starting with release 2.59, man-pages follows American spelling conventions; please  write
       all new pages and patches according to these conventions.

   Capitalization
       In  subsection  ("SS")  headings  capitalize  the first word in heading, but otherwise use
       lower case, except where English  usage  (e.g.,  proper  nouns)  or  programming  language
       requirements (e.g., identifier names) dictate otherwise.

   Example programs and shell sessions
       Manual  pages  can  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 pro-
          gram that does nothing other than call an interface usually serves little purpose.

       *  Example programs should be fairly short (preferably less than 100 lines;  ideally  less
          than 50 lines).

       *  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 vary-
          ing their behavior based on inputs (ideally from command-line  arguments,  or  alterna-
          tively, 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!)

       For some examples of what example programs should look like, see wait(2) and pipe(2).

       If you include a shell session demonstrating the use of a program or other system feature,
       boldface the user input text, to distinguish it from output produced by the system.

   Indentation of structure definitions, shell session logs, etc.
       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).

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

SEE ALSO
       man(1), man2html(1), groff(7), groff_man(7), man(7), mdoc(7)

COLOPHON
       This  page  is  part of release 3.53 of the Linux man-pages project.  A description of the
       project,    and    information    about    reporting    bugs,    can    be    found     at
       http://www.kernel.org/doc/man-pages/.



Linux                                       2013-07-24                               MAN-PAGES(7)

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