MAN-PAGES(7)



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)
              Commands that can be executed by the user from within a shell.

       2 System calls
              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 lay-
              out, 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.

   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  au-
                        tomatically  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
           EXAMPLES
           AUTHORS            [Discouraged]
           REPORTING BUGS     [Not used in man-pages]
           COPYRIGHT          [Not used in man-pages]
           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 fol-
              low the .SH NAME command.  All words in this line (including the
              word immediately following the "\-") should be in lowercase, ex-
              cept  where  English or technical terminological convention dic-
              tates otherwise.

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

              For commands, this shows the syntax of the command and its argu-
              ments  (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  inter-
              nals  and implementation details unless they're critical for un-
              derstanding the interface.  Describe the usual case; for  infor-
              mation on command-line options of a program use the OPTIONS sec-
              tion.

              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 val-
              ues the library routine will return to the caller and the condi-
              tions 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 du-
              plicate 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 con-
              figuration 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 signifi-
              cantly 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 ker-
              nel 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 ker-
              nel 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 im-
              plementation 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.

       EXAMPLES
              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 in-
              clude an address for reporting bugs, place this under  the  BUGS
              section.

       REPORTING BUGS
              The  man-pages  project  doesn't use a REPORTING BUGS section in
              manual pages.  Information on reporting bugs is instead supplied
              in  the  script-generated  COLOPHON  section.   However, various
              projects do use a REPORTING BUGS section.  it is recommended  to
              place it near the foot of the page.

       COPYRIGHT
              The  man-pages project doesn't use a COPYRIGHT section in manual
              pages.  Copyright information is instead maintained in the  page
              source.   In  pages  where this section is present, it is recom-
              mended to place it near the foot of the  page,  just  above  SEE
              ALSO.

       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 alphabeti-
              cally 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 em-
              ploy  the  .ad l (don't right justify) and .nh (don't hyphenate)
              directives.  Hyphenation of individual page names  can  be  pre-
              vented 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.)

   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 in-
       cluded 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 ap-
       propriate 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",  "to-
          ward",  and  so  on  rather than the British forms "backwards", "up-
          wards", "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 "un-
                                                     ame -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 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 in-
       dicated 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  de-
       scribed 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 li-
          brary 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).

EXAMPLES
       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 5.07 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                             2020-04-11                      MAN-PAGES(7)

Man(1) output converted with man2html
list of all man pages