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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, many of
       the pages that appear in Sections 3, 4, and 7, and a few  of  the  pages  that  appear  in
       Sections  1,  5,  and  8 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 kernel.

       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 configuration 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 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 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  manually
                        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 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      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  users  who  are
                     constrained to using older kernel or C library versions (which is typical in
                     embedded systems, for example).

       OPTIONS       A description of 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   A list of 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.

                     Where  several  different  conditions  produce the same error, the preferred
                     approach is to create separate list entries (with duplicate error names) for
                     each  of the conditions.  This makes the separate conditions clear, may make
                     the list easier to read, and allows metainformation  (e.g.,  kernel  version
                     number where the condition first became applicable) to be more easily marked
                     for each condition.

                     The error list should be in alphabetical order.

       ENVIRONMENT   A list of all environment variables that affect the program 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  manual  page
                     should use /usr/local as the base.

       ATTRIBUTES    A  summary of various attributes of the function(s) documented 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
                     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 A description of 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.)

                     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 differences 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 Programs below.

       AUTHORS       A list of 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      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
                     individual  page  names  can be prevented by preceding words with the string
                     "\%".

                     Given  the  distributed,  autonomous  nature  of  FOSS  projects  and  their
                     documentation,  it  is  sometimes necessary—and in many cases desirable—that
                     the SEE ALSO section includes references to manual pages provided  by  other
                     projects.

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.

   Formatting conventions for manual pages describing commands
       For manual pages that describe a command (typically in Sections 1 and  8),  the  arguments
       are always specified using italics, even in the SYNOPSIS section.

       The name of the command, and its options, should always be formatted in bold.

   Formatting conventions for manual pages describing functions
       For  manual  pages  that describe functions (typically in Sections 2 and 3), 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.

       Any reference to the subject of the current manual page should be written with the name in
       bold 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.)

   Formatting conventions (general)
       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.

       When showing example shell sessions, user input should be formatted in bold, for example

           $ date
           Thu Jul  7 13:01:27 CEST 2016

       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), format them using the
       .EX and EE macros, and surround them with suitable paragraph markers (either .PP or  .IP).
       For example:

               .PP
               .in +4n
               .EX
               int
               main(int argc, char *argv[])
               {
                   return 0;
               }
               .EE
               .in
               .PP

   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 '\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", 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!)  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 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 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 4.13 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 https://www.kernel.org/doc/man-pages/.