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       man-pages - conventions for writing Linux man pages


       man [section] title


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

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

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

       2 System calls
                 Those  functions  which  wrap  operations  performed  by  the

       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

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

       New  sentences should be started on new lines.  This makes it easier to
       see the effect  of  patches,  which  often  operate  at  the  level  of
       individual sentences.

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

              .TH title section date source manual


              title     The  title of the man page, written in all caps (e.g.,

              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

   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.

            CONFIGURATION      [Normally only in Section 4]
            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]
            VERSIONS           [Normally only in Sections 2, 3]
            ATTRIBUTES         [Normally only in Sections 2, 3]
            CONFORMING TO
            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

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

       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

                     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

                     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

       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

                     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

       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

       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

                     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.


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

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

   Font conventions
       For functions, the arguments are always specified using  italics,  even
       in the SYNOPSIS section, where the rest of the function is specified in

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

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

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

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

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

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

           man 7 man-pages

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

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

       Any reference to the subject of  the  current  manual  page  should  be
       written  with  the  name  in bold.  If the subject is a function (i.e.,
       this is a Section 2 or 3 page), then the name should be followed  by  a
       pair  of  parentheses  in  Roman  (normal)  font.   For example, in the
       fcntl(2) man page, references to the  subject  of  the  page  would  be
       written  as:  fcntl().   The  preferred way to write this in the source
       file is:

           .BR fcntl ()

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

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

           .BR intro (2)

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

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

       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

       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.

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

           .SS Unicode under Linux

   Indentation of structure definitions, shell session logs, and so on
       When structure definitions, shell session logs, and so on are  included
       in  running  text,  indent  them by 4 spaces (i.e., a block enclosed by
       .in +4n and .in).

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

       Term                 Avoid using              Notes

       bit mask             bitmask
       built-in             builtin
       Epoch                epoch                    For  the UNIX Epoch
                                                     (00:00:00,  1   Jan
                                                     1970 UTC)
       filename             file name
       filesystem           file system
       hostname             host name
       inode                i-node
       lowercase            lower case, lower-case
       pathname             path name
       pseudoterminal       pseudo-terminal
       privileged port      reserved  port, system
       real-time            realtime, real time
       run time             runtime
       saved set-group-ID   saved group ID,  saved

       saved set-user-ID    saved  user  ID, saved
       set-group-ID         set-GID, setgid
       set-user-ID          set-UID, setuid
       superuser            super user, super-user
       superblock           super  block,   super-
       timestamp            time stamp
       timezone             time zone
       uppercase            upper case, upper-case
       usable               useable
       user space           userspace
       username             user name
       zeros                zeroes

       See also the discussion Hyphenation of attributive compounds below.

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

       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
       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

       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:


   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".

       For hyperlinks, use the .UR/.UE macro pair  (see  groff_man(7)).   This
       produces  proper  hyperlinks  that  can  be used in a web browser, when
       rendering a page with, say:

            BROWSER=firefox man -H pagename

   Use of e.g., i.e., etc., a.k.a., and similar
       In general, the use of abbreviations such as  "e.g.",  "i.e.",  "etc.",
       "a.k.a."   should  be avoided, in favor of suitable full wordings ("for
       example", "that is", "and so on", "also known as").

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

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

       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:


       Hyphens  should  be  retained when the prefixes are used in nonstandard
       English words, with trademarks, proper  nouns,  acronyms,  or  compound
       terms.  Some examples:


       Finally,  note that "re-create" and "recreate" are two different verbs,
       and the former is probably what you want.

   Real minus character
       Where a real minus character is required (e.g., for numbers such as -1,
       or  when  writing  options that have a leading dash, such as in ls -l),
       use the following form in the man page source:


       This guideline applies also to code examples.

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


       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

       *  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


          Avoid using the following forms to terminate a program:

              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).


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


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


       This  page  is  part of release 4.04 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