man-pages

       man [section] title

DESCRIPTION
       This  page describes the conventions that should be employed when writ-
       ing 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 User commands (Programs)
                 Those commands that can be executed by the user from within a
                 shell.

       2 System calls
                 Those functions which wrap operations performed by  the  ker-
                 nel.

       3 Library calls
                 All  library  functions  excluding  the  system call wrappers
                 (Most of the libc functions).

       4 Special files (devices)
                 Files found in /dev which allow to access to devices  through
                 the kernel.

       5 File formats and configuration files
                 Describes  various human-readable file formats and configura-
                 tion files.

       6 Games   Games and funny little programs available on the system.

       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.

       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 charac-
       ters wherever possible.  This helps avoid line-wrapping  in  some  mail
       clients when patches are submitted inline.
              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 nontrivial change that was made
                        to the man page.  (Within the man-pages  project,  the
                        necessary  updates  to  these  timestamps  are handled
                        automatically by scripts, so there is no need to manu-
                        ally update them as part of a patch.)  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 prac-
                        tice 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
            VERSIONS           [Normally only in Sections 2, 3]
            ATTRIBUTES         [Normally only in Sections 2, 3]

       tions.

       The following list elaborates on the contents of each of the above sec-
       tions.

       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 otherwise.

       SYNOPSIS      A brief summary of 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.

                     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 feature_test_macros(7).

       CONFIGURATION Configuration details for a device.

                     This section normally appears only in Section 4 pages.

       DESCRIPTION   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 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 .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
                     returned.

                     This  section should appear only for Section 1 and 8 man-
                     ual 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   A list of all environment variables that affect the  pro-
                     gram or function and how they affect it.

       FILES         A list of 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 man-
                     ual page should use /usr/local as the base.

       ATTRIBUTES    A  summary of various attributes of the function(s) docu-
                     mented on  this  page.   See  attributes(7)  for  further
                     details.

       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  writ-
                     ten).   Patches to remedy this are welcome, but, from the
                     perspective of programmers writing new code, this  infor-
                     mation probably matters only in the case of kernel inter-
                     faces 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.

                     the current version of POSIX.1.)

                     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         Miscellaneous notes.

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

                     In  Section  2,  use the heading C library/kernel differ-
                     ences 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.

       BUGS          A  list  of limitations, known defects or inconveniences,
                     and other questionable activities.

       EXAMPLE       One or more examples  demonstrating  how  this  function,
                     file or command is used.

                     For details on writing example programs, see Example Pro-
                     grams below.

       AUTHORS       A list of authors of the documentation or program.

                     Use of an AUTHORS section is strongly discouraged.   Gen-
                     erally,  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      A comma-separated list of  related  man  pages,  possibly
                     followed by other related pages or documents.

                     The  list  should  be  ordered by section number and then
                     alphabetically by name.  Do not terminate this list  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 "\%".

   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.

   Font conventions
       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);

       Variable names should, like argument names, be specified in italics.

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

       Special macros, which are usually in uppercase, are in bold (e.g., MAX-
       INT).  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 an indented line on
       their own, with a blank line before and after the command, 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  com-
       mand.  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 writ-
       ten 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  eas-
       ier to write tools that parse man page source files.)

       Any  reference  to  another man page should be written with the name in

   Spelling
       Starting with release 2.59, man-pages follows American spelling conven-
       tions  (previously,  there  was  a  random  mix of British and American
       spellings); please write all new pages and patches according  to  these
       conventions.

       Aside  from  the well-known spelling differences, there are a few other
       subtleties to watch for:

       *  American English  tends  to  use  the  forms  "backward",  "upward",
          "toward",  and  so  on  rather  than  the British forms "backwards",
          "upwards", "towards", and so on.

   BSD version numbers
       The classical scheme for writing BSD version numbers is  x.yBSD,  where
       x.y is the version number (e.g., 4.2BSD).  Avoid forms such as BSD 4.3.

   Capitalization
       In  subsection  ("SS") headings, capitalize the first word in the head-
       ing, but otherwise use lowercase, except  where  English  usage  (e.g.,
       proper  nouns)  or  programming language requirements (e.g., identifier
       names) dictate otherwise.  For example:

           .SS Unicode under Linux

   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
       .in +4n and .in).

   Preferred terms
       The following table lists some preferred terms to  use  in  man  pages,
       mainly to ensure consistency across pages.

       Term                 Avoid using              Notes
       ------------------------------------------------------------------

       bit mask             bitmask
       built-in             builtin
       Epoch                epoch                    For  the UNIX Epoch
                                                     (00:00:00,  1   Jan
                                                     1970 UTC)
       filename             file name
       filesystem           file system
       hostname             host name
       inode                i-node
       lowercase            lower case, lower-case
       pathname             path name
       pseudoterminal       pseudo-terminal
       privileged port      reserved  port, system
                            port
       real-time            realtime, real time
       run time             runtime
       saved set-group-ID   saved group ID,  saved
       usable               useable
       user space           userspace
       username             user name
       zeros                zeroes

       See also the discussion Hyphenation of attributive compounds below.

   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.

       Avoid             Use instead           Notes
       ------------------------------------------------------------

       32bit             32-bit                same   for   8-bit,
                                               16-bit, etc.
       current process   calling process       A  common   mistake
                                               made by kernel pro-
                                               grammers when writ-
                                               ing man pages
       manpage           man   page,  manual
                         page
       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

   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:

            DG/UX
            HP-UX
            UNIX
            UnixWare

   NULL, NUL, null pointer, and null character
       A null pointer is a pointer that points to  nothing,  and  is  normally
       indicated  by  the  constant  NULL.  On the other hand, NUL is the null
       byte, a byte with the value 0, represented in C via the character  con-
       stant '\0'.

       The  preferred term for the pointer is "null pointer" or simply "NULL";
       avoid writing "NULL pointer".

       The preferred term for the byte is "null byte".  Avoid  writing  "NUL",

   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.",
       "a.k.a."   should  be avoided, in favor of suitable full wordings ("for
       example", "that is", "and so on", "also known as").

       The only place where such abbreviations may be acceptable is  in  short
       parenthetical asides (e.g., like this one).

       Always  include periods in such abbreviations, as shown here.  In addi-
       tion, "e.g." and "i.e." should always be followed by a comma.

   Em-dashes
       The way to write an em-dash--the glyph that appears at  either  end  of
       this subphrase--in *roff is with the macro "\(em".  (On an ASCII termi-
       nal, an em-dash typically renders as two hyphens, but  in  other  typo-
       graphical  contexts  it  renders  as a long dash.)  Em-dashes should be
       written without surrounding spaces.

   Hyphenation of attributive compounds
       Compound terms should be hyphenated when used attributively  (i.e.,  to
       qualify a following noun). Some examples:

           32-bit value
           command-line argument
           floating-point number
           run-time check
           user-space function
           wide-character string

   Hyphenation with multi, non, pre, re, sub, and so on
       The  general  tendency in modern English is not to hyphenate after pre-
       fixes 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:

           interprocess
           multithreaded
           multiprocess
           nonblocking
           nondefault
           nonempty
           noninteractive
           nonnegative
           nonportable
           nonzero
           preallocated
           precreate
           prerecorded
           reestablished
           reinitialize
           rearm
           reread
           subcomponent

       Finally,  note that "re-create" and "recreate" are two different verbs,
       and the former is probably what you want.

   Real minus character
       Where a real minus character is required (e.g., for numbers such as -1,
       or  when  writing  options that have a leading dash, such as in ls -l),
       use the following form in the man page source:

           \-

       This guideline applies also to code examples.

   Character constants
       To produce single quotes that render well in both ASCII and UTF-8,  use
       the following form for character constants in the man page source:

           \(aqC\(aq

       where  C is the quoted character.  This guideline applies also to char-
       acter constants used in code examples.

   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:

       *  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  descrip-
          tion  of  the interface.  An example program 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 exper-
          imentation, by varying their behavior based on inputs (ideally  from
          command-line arguments, or alternatively, via input read by the pro-
          gram).

       *  Example programs should be  laid  out  according  to  Kernighan  and
          Ritchie  style, with 4-space indents.  (Avoid the use of TAB charac-
          ters in source code!)  The following command can be used  to  format
          your source code to something close to the preferred style:

              indent -npro -kr -i4 -ts4 -sob -l72 -ss -nut -psl prog.c

       *  For  consistency, all example programs should terminate using either
          code,  mark  off  the  source code with a subsection heading Program
          source, as in:

              .SS Program source

          Always do this if the explanatory text includes a shell session log.

       If you include a shell session log demonstrating the use of  a  program
       or other system feature:

       *  Place the session log above the source code listing

       *  Indent the session log by four spaces.

       *  Boldface the user input text, to distinguish it from output produced
          by the system.

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

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),  attributes(7),  groff(7),  groff_man(7),  man(7),
       mdoc(7)

COLOPHON
       This  page  is  part of release 4.04 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux                             2015-07-23                      MAN-PAGES(7)
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