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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  possible.  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  nontrivial  change  is made to the man
                        page.  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
            VERSIONS           [Normally only in Sections 2, 3]
            ATTRIBUTES         [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 otherwise.

       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 #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   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 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
                     users  who  are  constrained  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  Section 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 applications:

                            *  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 kernel 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 command described by the  manual  page.   The
                     preferred  terms  to  use  for  the various standards are
                     listed as  headings  in  standards(7).   For  a  page  in
                     Section  2  or  3,  this  section 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
                     individual page names can be prevented by preceding words
                     with the string "\%".

STYLE GUIDE

       The  following  subsections  describe  the preferred style for the man-
       pages project.  For details not covered below, the  Chicago  Manual  of
       Style is usually a good source; try also grepping for preexisting usage
       in the project source tree.

   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.,
       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 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
       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  "B...P()"  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 properly hyperlinked pages.)

       Control  characters should be written in bold face, with no quotes; for
       example, ^X.

   Spelling
       Starting  with  release  2.59,  man-pages  follows  American   spelling
       conventions (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
       heading, 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
                            set-GID
       saved set-user-ID    saved  user  ID, saved
                            set-UID
       set-group-ID         set-GID, setgid
       set-user-ID          set-UID, setuid
       superuser            super user, super-user
       superblock           super  block,   super-
                            block
       timestamp            time stamp
       timezone             time zone
       uppercase            upper case, upper-case
       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
                                               programmers    when
                                               writing 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
       constant ''.

       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",
       since  it  is  too  easily  confused with "NULL".  Avoid also the terms
       "zero byte" and "null character".  The byte that terminates a C  string
       should  be  described  as  "the  terminating null byte"; strings may be
       described as "null-terminated", but avoid the use of "NUL-terminated".

   Hyperlinks
       For hyperlinks, use the .UR/.UE macro pair  (see  groff_man(7)).   This
       produces  proper  hyperlinks  that  can  be used in a web browser, when
       rendering a page with, say:

            BROWSER=firefox man -H pagename

   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
       addition, "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
       terminal, an em-dash typically renders as two  hyphens,  but  in  other
       typographical 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
       prefixes 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
           subdirectory
           subsystem

       Hyphens  should  be  retained when the prefixes are used in nonstandard
       English words, with trademarks, proper  nouns,  acronyms,  or  compound
       terms.  Some examples:

           non-ASCII
           non-English
           non-NULL
           non-real-time

       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
       character 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
          description  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
          experimentation, by varying their behavior based on inputs  (ideally
          from command-line arguments, or alternatively, 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 consistency, all example programs should terminate using  either
          of:

               exit(EXIT_SUCCESS);
               exit(EXIT_FAILURE);

          Avoid using the following forms to terminate a program:

              exit(0);
              exit(1);
              return n;

       *  If  there  is  extensive  explanatory text before the program source
          code, mark off the source code with a  susbsection  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), groff(7), groff_man(7), man(7), mdoc(7)

COLOPHON

       This  page  is  part of release 3.65 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/.



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