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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 nontrivial change that  was  made
                        to  the  man page.  (Within the man-pages project, the
                        necessary  updates  to  these  timetamps  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.

                     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, 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 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 ABI
                     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  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 "\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 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 '\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!)

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

COLOPHON

       This page is part of release 3.74 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/.