man-pages

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

NAME
       man-pages - conventions for writing Linux man pages

SYNOPSIS
       man [section] title

DESCRIPTION
       This  page describes the conventions that should be employed when writ-
       ing man pages for the Linux  man-pages  project,  which  documents  the
       user-space API provided by the Linux kernel and the GNU C library.  The
       project thus provides most of the pages in Section 2, 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  con-
       ventions  described on this page may also be useful for authors writing
       man pages for other projects.

   Sections of the manual pages
       The manual Sections are traditionally defined as follows:

       1 User commands (Programs)
                 Those commands that can be executed by the user from within a
                 shell.

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

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

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

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

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

       7 Overview, conventions, and miscellaneous
                 Overviews  or descriptions of various topics, conventions and
                 protocols, character set standards, the  standard  filesystem
                 layout, and miscellaneous other things.

       8 System management commands
                 Commands like mount(8), many of which only root can execute.

   Macro package
       New  manual  pages  should be marked up using the groff an.tmac package
       described in man(7).  This choice is mainly for consistency:  the  vast
       majority  of  existing  Linux  manual  pages  are marked up using these
       macros.

   Conventions for source file layout
       Please limit source code line length to no more than about  75  charac-
       ters  wherever  possible.   This helps avoid line-wrapping in some mail
       clients when patches are submitted inline.

       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 individ-
       ual 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 manu-
                        ally update them as part of a patch.)  Dates should be
                        written in the form YYYY-MM-DD.

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

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

                        For system calls, just write Linux.  (An earlier prac-
                        tice  was  to  write  the version number of the kernel
                        from which the manual page was being  written/checked.
                        However,  this was never done consistently, and so was
                        probably  worse  than  including  no  version  number.
                        Henceforth, avoid including a version number.)

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

                        For Section 4 pages, use Linux.

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

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

   Sections within a manual page
       The  list  below shows conventional or suggested sections.  Most manual
       pages should include at least the highlighted sections.  Arrange a  new
       manual page so that sections are placed in the order shown in the list.

           NAME
           SYNOPSIS
           CONFIGURATION      [Normally only in Section 4]
           DESCRIPTION
           OPTIONS            [Normally only in Sections 1, 8]
           EXIT STATUS        [Normally only in Sections 1, 8]
           RETURN VALUE       [Normally only in Sections 2, 3]
           ERRORS             [Typically only in Sections 2, 3]
           ENVIRONMENT
           FILES
           VERSIONS           [Normally only in Sections 2, 3]
           ATTRIBUTES         [Normally only in Sections 2, 3]
           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  sec-
       tions.

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

       NAME          The name of this manual page.

                     See man(7) for important  details  of  the  line(s)  that
                     should  follow  the  .SH NAME command.  All words in this
                     line (including the word immediately following the  "\-")
                     should be in lowercase, except where English or technical
                     terminological convention dictates otherwise.

       SYNOPSIS      A brief summary of the command or function's interface.

                     For commands, this shows the syntax of  the  command  and
                     its  arguments  (including options); boldface is used for
                     as-is text and italics are used to  indicate  replaceable
                     arguments.   Brackets  ([])  surround optional arguments,
                     vertical bars (|) separate choices,  and  ellipses  (...)
                     can  be  repeated.   For functions, it shows any required
                     data declarations or #include directives, followed by the
                     function declaration.

                     Where  a  feature  test macro must be defined in order to
                     obtain the declaration of a function (or a variable) from
                     a header file, then the SYNOPSIS should indicate this, as
                     described in feature_test_macros(7).

       CONFIGURATION Configuration details for a device.

                     This section normally appears only in Section 4 pages.

       DESCRIPTION   An explanation of what the program, function,  or  format
                     does.

                     Discuss  how  it interacts with files and standard input,
                     and what it  produces  on  standard  output  or  standard
                     error.   Omit internals and implementation details unless
                     they're  critical  for   understanding   the   interface.
                     Describe  the usual case; for information on command-line
                     options of a program use the OPTIONS section.

                     When describing new behavior or new flags  for  a  system
                     call  or  library function, be careful to note the kernel
                     or C library version that  introduced  the  change.   The
                     preferred  method of noting this information for flags is
                     as part of a .TP list, in the following form (here, for a
                     new system call flag):

                             XYZ_FLAG (since Linux 3.7)
                                    Description of flag...

                     Including  version  information  is  especially useful to
                     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 man-
                     ual 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  man-
                     ual pages.

       RETURN VALUE  For  Section  2 and 3 pages, this section gives a list of
                     the values the library routine will return to the  caller
                     and   the  conditions  that  cause  these  values  to  be
                     returned.

       ERRORS        For Section 2 and 3 manual pages, this is a list  of  the
                     values  that  may  be  placed in errno in the event of an
                     error, along with information  about  the  cause  of  the
                     errors.

                     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 con-
                     ditions.  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 con-
                     dition.

                     The error list should be in alphabetical order.

       ENVIRONMENT   A list of all environment variables that affect the  pro-
                     gram or function and how they affect it.

       FILES         A list of the files the program or function uses, such as
                     configuration files, startup files, and files the program
                     directly operates on.

                     Give  the  full  pathname  of  these  files,  and use the
                     installation process to  modify  the  directory  part  to
                     match  user  preferences.  For many programs, the default
                     installation location is in /usr/local, so your base man-
                     ual page should use /usr/local as the base.

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

       VERSIONS      A  brief  summary  of  the Linux kernel or glibc versions
                     where a system call  or  library  function  appeared,  or
                     changed significantly in its operation.

                     As  a  general rule, every new interface should include a
                     VERSIONS section in its manual page.  Unfortunately, many
                     existing  manual  pages  don't  include  this information
                     (since there was no policy to do so when they were  writ-
                     ten).   Patches to remedy this are welcome, but, from the
                     perspective of programmers writing new code, this  infor-
                     mation probably matters only in the case of kernel inter-
                     faces that have been added in Linux 2.4 or  later  (i.e.,
                     changes  since  kernel  2.2),  and library functions that
                     have been added to glibc since version 2.1 (i.e., changes
                     since glibc 2.0).

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

       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 differ-
                     ences to mark off notes that describe the differences (if
                     any)  between the C library wrapper function for a system
                     call and the raw system call interface  provided  by  the
                     kernel.

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

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

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

       AUTHORS       A list of authors of the documentation or program.

                     Use of an AUTHORS section is strongly discouraged.   Gen-
                     erally,  it  is  better  not to clutter every page with a
                     list of (over time potentially numerous) authors; if  you
                     write  or  significantly  amend  a  page, add a copyright
                     notice as a comment in the source file.  If you  are  the
                     author  of a device driver and want to include an address
                     for reporting bugs, place this under the BUGS section.

       SEE ALSO      A comma-separated list of  related  man  pages,  possibly
                     followed by other related pages or documents.

                     The  list  should  be  ordered by section number and then
                     alphabetically by name.  Do not terminate this list  with
                     a period.

                     Where  the  SEE  ALSO list contains many long manual page
                     names, to improve the visual result of the output, it may
                     be  useful  to employ the .ad l (don't right justify) and
                     .nh (don't hyphenate) directives.  Hyphenation  of  indi-
                     vidual  page  names  can  be prevented by preceding words
                     with the string "\%".

                     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  SYN-
       OPSIS 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 SYN-
       OPSIS 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 writ-
       ten  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  eas-
       ier 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., MAX-
       INT).  Exception: don't boldface NULL.

       When enumerating a list of error codes, the codes  are  in  bold  (this
       list usually uses the .TP macro).

       Complete  commands  should,  if long, be written as an indented line on
       their own, with a blank line before and after the command, for example

           man 7 man-pages

       If the command is short, then it can be included inline in the text, in
       italic  format,  for example, man 7 man-pages.  In this case, it may be
       worth using nonbreaking spaces ("\ ") at suitable places  in  the  com-
       mand.  Command options should be written in italics (e.g., -l).

       Expressions,  if  not  written  on  a separate indented line, should be
       specified in italics.  Again, the use  of  nonbreaking  spaces  may  be
       appropriate if the expression is inlined with normal text.

       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 (nor-
       mal) font, without any separating spaces (e.g.,  intro(2)).   The  pre-
       ferred 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 conven-
       tions (previously, there was a  random  mix  of  British  and  American
       spellings);  please  write all new pages and patches according to these
       conventions.

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

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

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

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

           .SS Unicode under Linux

   Indentation of structure definitions, shell session logs, and so on
       When  structure definitions, shell session logs, and so on are included
       in running text, indent them by 4 spaces (i.e.,  a  block  enclosed  by
       .in +4n and .in), 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
       nonzero              non-zero
       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
       x86-64               x86_64                   Except if referring
                                                     to    result     of
                                                     "uname -m" or simi-
                                                     lar
       zeros                zeroes

       See also the discussion Hyphenation of attributive compounds below.

   Terms to avoid
       The following table lists some terms to avoid using in man pages, along
       with  some  suggested alternatives, mainly to ensure consistency across
       pages.

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

       32bit             32-bit                same   for   8-bit,
                                               16-bit, etc.
       current process   calling process       A   common  mistake
                                               made by kernel pro-
                                               grammers when writ-
                                               ing man pages
       manpage           man  page,   manual
                         page
       minus infinity    negative infinity
       non-root          unprivileged user
       non-superuser     unprivileged user
       nonprivileged     unprivileged
       OS                operating system
       plus infinity     positive infinity
       pty               pseudoterminal
       tty               terminal
       Unices            UNIX systems
       Unixes            UNIX systems

   Trademarks
       Use  the  correct spelling and case for trademarks.  The following is a
       list of the correct spellings of various relevant trademarks  that  are
       sometimes misspelled:

            DG/UX
            HP-UX
            UNIX
            UnixWare

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

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

       The  preferred  term for the byte is "null byte".  Avoid writing "NUL",
       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 ren-
       dering 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.",
       "cf.", and "a.k.a." should be avoided, in favor of suitable full  word-
       ings  ("for example", "that is", "compare to", "and so on", "also known
       as").

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

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

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

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

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

   Hyphenation with multi, non, pre, re, sub, and so on
       The  general  tendency in modern English is not to hyphenate after pre-
       fixes such as "multi", "non", "pre", "re", "sub", and  so  on.   Manual
       pages should generally follow this rule when these prefixes are used in
       natural English constructions with simple suffixes.  The following list
       gives some examples of the preferred forms:

           interprocess
           multithreaded
           multiprocess
           nonblocking
           nondefault
           nonempty
           noninteractive
           nonnegative
           nonportable
           nonzero
           preallocated
           precreate
           prerecorded
           reestablished
           reinitialize
           rearm
           reread
           subcomponent
           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,
       for man page cross references such as utf-8(7), or when writing options
       that have a leading dash, such as in ls -l), use the following form  in
       the man page source:

           \-

       This guideline applies also to code examples.

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

           \(aqC\(aq

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

   Example programs and shell sessions
       Manual  pages  may  include example programs demonstrating how to use a
       system call or library function.  However, note the following:

       *  Example programs should be written in C.

       *  An example program is necessary and useful only if  it  demonstrates
          something  beyond  what can easily be provided in a textual descrip-
          tion of the interface.  An example program that does  nothing  other
          than call an interface usually serves little purpose.

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

       *  Example programs should do error checking  after  system  calls  and
          library function calls.

       *  Example  programs  should  be complete, and compile without warnings
          when compiled with cc -Wall.

       *  Where possible and appropriate, example programs should allow exper-
          imentation,  by varying their behavior based on inputs (ideally from
          command-line arguments, or alternatively, via input read by the pro-
          gram).

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

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

       *  For consistency, all example programs should terminate using  either
          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 4.15 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/.

Linux                             2018-02-02                      MAN-PAGES(7)
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