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man: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 4.16 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/.

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