NAME | SYNOPSIS | DESCRIPTION | STYLE GUIDE | EXAMPLE | SEE ALSO | COLOPHON

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

NAME         top

       man-pages - conventions for writing Linux man pages

SYNOPSIS         top

       man [section] title

DESCRIPTION         top

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

       2 System calls
                 Those functions which must be performed by the kernel.

       3 Library calls
                 Most of the libc functions.

       4 Special files (devices)
                 Files found in /dev.

       5 File formats and conventions
                 The format for /etc/passwd and other human-readable files.

       6 Games

       7 Overview, conventions, and miscellaneous
                 Overviews of various topics, conventions and protocols,
                 character set standards, 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.

       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

       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 revision—remember to change
                        this every time a nontrivial change is made to the
                        man page.  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      briefly describes 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   gives 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       describes 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   lists 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.  The error list should be in alphabetical
                     order.

       ENVIRONMENT   lists all environment variables that affect the program
                     or function and how they affect it.

       FILES         lists 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, broken into subsections.  The
                     following subsections are defined:

                     Multithreading (see pthreads(7))
                            This subsection notes attributes relating to
                            multithreaded applications:

                            *  Whether the function is thread-safe.

                            *  Whether the function is a cancellation point.

                            *  Whether the function is async-cancel-safe.

                            Details of these attributes can be found in
                            pthreads(7).

       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 describes 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.)  (See standards(7).)

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

       BUGS          lists limitations, known defects or inconveniences, and
                     other questionable activities.

       EXAMPLE       provides one or more examples describing how this
                     function, file or command is used.  For details on
                     writing example programs, see Example Programs below.

       AUTHORS       lists 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      provides a comma-separated list of related man pages,
                     ordered by section number and then alphabetically by
                     name, possibly followed by other related pages or
                     documents.  Do not terminate this 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 "\%".

STYLE GUIDE         top

       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 bold:

           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.

   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).

   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
                            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
       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.",
       "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.

   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, 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!)

       *  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 susbsection 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         top

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 3.64 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux                            2014-03-16                     MAN-PAGES(7)