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NAME

       man-pages - conventions for writing Linux man pages

SYNOPSIS

       man [section] title

DESCRIPTION

       This  page  describes  the  conventions that should be employed when writing man pages for the Linux man-
       pages project, which documents the user-space API provided by the Linux kernel and  the  GNU  C  library.
       The project thus provides most of the pages in Section 2, many of the pages that appear in Sections 3, 4,
       and 7, and a few of the pages that appear in Sections 1, 5, and 8 of the man pages  on  a  Linux  system.
       The  conventions  described  on  this  page  may  also  be useful for authors writing man pages for other
       projects.

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

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

       2 System calls
                 Those functions which wrap operations performed by the kernel.

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

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

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

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

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

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

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

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

   Title line
       The first command in a man page should be a TH command:

              .TH title section date source manual

       where:

              title     The title of the man page, written in all caps (e.g., MAN-PAGES).

              section   The section number in which the man page should be placed (e.g., 7).

              date      The date of the last nontrivial change that was made to the man page.  (Within the  man-
                        pages  project,  the  necessary updates to these timestamps are handled automatically by
                        scripts, so there is no need to manually update them as part of a patch.)  Dates  should
                        be written in the form YYYY-MM-DD.

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

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

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

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

                        For Section 4 pages, use Linux.

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

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

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

           NAME
           SYNOPSIS
           CONFIGURATION      [Normally only in Section 4]
           DESCRIPTION
           OPTIONS            [Normally only in Sections 1, 8]
           EXIT STATUS        [Normally only in Sections 1, 8]
           RETURN VALUE       [Normally only in Sections 2, 3]
           ERRORS             [Typically only in Sections 2, 3]
           ENVIRONMENT
           FILES
           VERSIONS           [Normally only in Sections 2, 3]
           ATTRIBUTES         [Normally only in Sections 2, 3]
           CONFORMING TO
           NOTES
           BUGS
           EXAMPLE
           SEE ALSO

       Where a traditional heading would apply, please use it; this kind of consistency can make the information
       easier  to  understand.   If  you  must,  you  can create your own headings if they make things easier to
       understand (this can be especially useful for pages in Sections 4 and 5).  However,  before  doing  this,
       consider  whether  you  could  use  the  traditional  headings,  with some subsections (.SS) within those
       sections.

       The following list elaborates on the contents of each of the above sections.

       NAME          The name of this manual page.

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

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

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

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

       CONFIGURATION Configuration details for a device.

                     This section normally appears only in Section 4 pages.

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

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

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

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

                     Including version information is especially useful to users who are  constrained  to  using
                     older kernel or C library versions (which is typical in embedded systems, for example).

       OPTIONS       A  description  of  the  command-line options accepted by a program and how they change its
                     behavior.

                     This section should appear only for Section 1 and 8 manual pages.

       EXIT STATUS   A list of the possible exit status values of a program and the conditions that cause  these
                     values to be returned.

                     This section should appear only for Section 1 and 8 manual pages.

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

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

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

                     The error list should be in alphabetical order.

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

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

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

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

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

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

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

       CONFORMING TO A description of any standards or conventions  that  relate  to  the  function  or  command
                     described by the manual page.

                     The  preferred  terms  to  use  for  the  various  standards  are  listed  as  headings  in
                     standards(7).

                     For a page in Section 2 or 3, this section should note the POSIX.1 version(s) that the call
                     conforms  to,  and  also whether the call is specified in C99.  (Don't worry too much about
                     other standards like SUS, SUSv2, and XPG, or the SVr4 and 4.xBSD implementation  standards,
                     unless  the  call  was  specified  in  those standards, but isn't in the current version of
                     POSIX.1.)

                     If the call is not governed by any standards but commonly exists  on  other  systems,  note
                     them.  If the call is Linux-specific, note this.

                     If  this  section  consists of just a list of standards (which it commonly does), terminate
                     the list with a period ('.').

       NOTES         Miscellaneous notes.

                     For Section 2 and 3 man pages you may find it useful  to  include  subsections  (SS)  named
                     Linux Notes and Glibc Notes.

                     In  Section 2, use the heading C library/kernel differences to mark off notes that describe
                     the differences (if any) between the C library wrapper function for a system call  and  the
                     raw system call interface provided by the kernel.

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

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

                     For details on writing example programs, see Example programs below.

       AUTHORS       A list of authors of the documentation or program.

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

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

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

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

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

STYLE GUIDE

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

   Use of gender-neutral language
       As far as possible, use gender-neutral language in the  text  of  man  pages.   Use  of  "they"  ("them",
       "themself", "their") as a gender-neutral singular pronoun is acceptable.

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

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

   Formatting conventions for manual pages describing functions
       For manual pages that describe functions (typically in Sections  2  and  3),  the  arguments  are  always
       specified  using  italics,  even  in the SYNOPSIS section, where the rest of the function is specified in
       bold:

           int myfunction(int argc, char **argv);

       Variable names should, like argument names, be specified in italics.

       Any reference to the subject of the current manual page should be written with the name in bold  followed
       by  a  pair  of parentheses in Roman (normal) font.  For example, in the fcntl(2) man page, references to
       the subject of the page would be written as: fcntl().  The preferred way to write this in the source file
       is:

           .BR fcntl ()

       (Using  this  format,  rather than the use of "\fB...\fP()" makes it easier to write tools that parse man
       page source files.)

   Use semantic newlines
       In the source of a manual page, new sentences should be started on new lines, and long  sentences  should
       split  into  lines  at clause breaks (commas, semicolons, colons, and so on).  This convention, sometimes
       known as "semantic newlines", makes it easier to see the effect of patches, which often  operate  at  the
       level of individual sentences or sentence clauses.

   Formatting conventions (general)
       Paragraphs  should  be  separated  by  suitable  markers  (usually  either  .PP or .IP).  Do not separate
       paragraphs using blank lines, as this  results  in  poor  rendering  in  some  output  formats  (such  as
       PostScript and PDF).

       Filenames  (whether  pathnames,  or  references to header files) are always in italics (e.g., <stdio.h>),
       except in the SYNOPSIS section, where included files  are  in  bold  (e.g.,  #include  <stdio.h>).   When
       referring to a standard header file include, specify the header file surrounded by angle brackets, in the
       usual C way (e.g., <stdio.h>).

       Special macros, which are usually in uppercase, are in bold (e.g., MAXINT).   Exception:  don't  boldface
       NULL.

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

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

           man 7 man-pages

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

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

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

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

       Any reference to another man page should be written with the name in bold, always followed by the section
       number, formatted in Roman (normal) font, without any separating spaces (e.g., intro(2)).  The  preferred
       way to write this in the source file is:

           .BR intro (2)

       (Including the section number in cross references lets tools like man2html(1) create properly hyperlinked
       pages.)

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

   Spelling
       Starting with release 2.59, man-pages follows American spelling  conventions  (previously,  there  was  a
       random  mix of British and American spellings); please write all new pages and patches according to these
       conventions.

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

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

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

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

           .SS Unicode under Linux

   Indentation of structure definitions, shell session logs, and so on
       When structure definitions, shell session logs, and so on are included in running text, indent them by  4
       spaces (i.e., a block enclosed by .in +4n and .in), format them using the .EX and EE macros, and surround
       them with suitable paragraph markers (either .PP or .IP).  For example:

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

   Preferred terms
       The following table lists some preferred terms to use in man pages, mainly to ensure  consistency  across
       pages.

       Term                 Avoid using                    Notes
       ─────────────────────────────────────────────────────────────────────────────────

       bit mask             bitmask
       built-in             builtin
       Epoch                epoch                          For     the    UNIX    Epoch
                                                           (00:00:00, 1 Jan 1970 UTC)
       filename             file name
       filesystem           file system
       hostname             host name
       inode                i-node
       lowercase            lower case, lower-case
       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
                                                           similar
       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.", "cf.", and "a.k.a." should be
       avoided, in favor of suitable full wordings ("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  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, 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 character constants used in code
       examples.

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

       *  Example programs should be written in C.

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

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

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

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

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

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

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

       *  For consistency, all example programs should terminate using either of:

               exit(EXIT_SUCCESS);
               exit(EXIT_FAILURE);

          Avoid using the following forms to terminate a program:

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

       *  If there is extensive explanatory text before the program source code, mark off the source code with a
          subsection heading Program source, as in:

              .SS Program source

          Always do this if the explanatory text includes a shell session log.

       If you include a shell session log demonstrating the use of a program or other system feature:

       *  Place the session log above the source code listing

       *  Indent the session log by four spaces.

       *  Boldface the user input text, to distinguish it from output produced by the system.

       For some examples of what example programs should look like, see wait(2) and pipe(2).

EXAMPLE

       For canonical examples of how man pages in the man-pages package should look, see pipe(2) and fcntl(2).

SEE ALSO

       man(1), man2html(1), attributes(7), groff(7), groff_man(7), man(7), mdoc(7)

COLOPHON

       This page is part of release 5.05 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/.