man-pages(7) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | STYLE GUIDE | EXAMPLES | 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,
       many of the pages that appear in Sections 3, 4, and 7, and a few of
       the pages that appear in Sections 1, 5, and 8 of the man pages on a
       Linux system.  The conventions described on this page may also be
       useful for authors writing man pages for other projects.

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

       1 User commands (Programs)
              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
              layout, and miscellaneous other things.

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

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

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

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

              .TH title section date source manual

       The arguments of the command are as follows:

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

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

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

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

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

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

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

              For Section 4 pages, use Linux.

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

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

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

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

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

       NAME   The name of this manual page.

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

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

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

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

       CONFIGURATION
              Configuration details for a device.

              This section normally appears only in Section 4 pages.

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

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

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

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

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

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

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

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

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

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

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

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

              The error list should be in alphabetical order.

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

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

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

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

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

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

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

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

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

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

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

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

       NOTES  Miscellaneous notes.

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

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

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

       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 include 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 recommended 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
              alphabetically by name.  Do not terminate this list with a
              period.

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

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

STYLE GUIDE         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.

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

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

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

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

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

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

           .BR fcntl ()

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

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

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

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

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

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

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

           man 7 man-pages

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

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

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

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

       Any reference to another man page should be written with the name in
       bold, always followed by the section number, formatted in Roman (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 con‐
       ventions (previously, there was a random mix of British and American
       spellings); please write all new pages and patches according to these
       conventions.

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

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

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

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

           .SS Unicode under Linux

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

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

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

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

       bit mask             bitmask
       built-in             builtin
       Epoch                epoch                    For the UNIX Epoch
                                                     (00:00:00, 1 Jan
                                                     1970 UTC)
       filename             file name
       filesystem           file system
       hostname             host name
       inode                i-node
       lowercase            lower case, lower-case
       nonzero              non-zero
       pathname             path name
       pseudoterminal       pseudo-terminal
       privileged port      reserved port, system
                            port
       real-time            realtime, real time
       run time             runtime
       saved set-group-ID   saved group ID, saved
                            set-GID
       saved set-user-ID    saved user ID, saved
                            set-UID
       set-group-ID         set-GID, setgid
       set-user-ID          set-UID, setuid
       superuser            super user, super-user
       superblock           super block, super-
                            block
       timestamp            time stamp
       timezone             time zone
       uppercase            upper case, upper-case
       usable               useable
       user space           userspace

       username             user name
       x86-64               x86_64                   Except if referring
                                                     to result of
                                                     "uname -m" or simi‐
                                                     lar
       zeros                zeroes

       See also the discussion Hyphenation of attributive compounds below.

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

       Avoid             Use instead         Notes
       ──────────────────────────────────────────────────────────

       32bit             32-bit              same for 8-bit,
                                             16-bit, etc.
       current process   calling process     A common mistake
                                             made by kernel pro‐
                                             grammers when writ‐
                                             ing man pages
       manpage           man page, manual
                         page
       minus infinity    negative infinity
       non-root          unprivileged user
       non-superuser     unprivileged user
       nonprivileged     unprivileged
       OS                operating system
       plus infinity     positive infinity
       pty               pseudoterminal
       tty               terminal
       Unices            UNIX systems
       Unixes            UNIX systems

   Trademarks
       Use the correct spelling and case for trademarks.  The following is a
       list of the correct spellings of various relevant trademarks that are
       sometimes misspelled:

            DG/UX
            HP-UX
            UNIX
            UnixWare

   NULL, NUL, null pointer, and null character
       A null pointer is a pointer that points to nothing, and is normally
       indicated by the constant NULL.  On the other hand, NUL is the null
       byte, a byte with the value 0, represented in C via the character
       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-ter‐
       minated".

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

            BROWSER=firefox man -H pagename

   Use of e.g., i.e., etc., a.k.a., and similar
       In general, the use of abbreviations such as "e.g.", "i.e.", "etc.",
       "cf.", and "a.k.a." should be avoided, in favor of suitable full
       wordings ("for example", "that is", "and so on", "compare to", "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 ter‐
       minal, 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 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.

   Generating optimal glyphs
       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 follow‐
       ing form in the man page source:

           \-

       This guideline applies also to code examples.

       To produce unslanted single quotes that render well in ASCII, UTF-8,
       and PDF, use "\(aq" ("apostrophe quote"); for example

           \(aqC\(aq

       where C is the quoted character.  This guideline applies also to
       character constants used in code examples.

       Where a proper caret (^) that renders well in both a terminal and PDF
       is required, use "\(ha".  This is especially necessary in code sam‐
       ples, to get a nicely rendered caret when rendering to PDF.

       Using a naked "~" character results in a poor rendering in PDF.
       Instead use "\(ti".  This is especially necessary in code samples, to
       get a nicely rendered tilde when rendering to PDF.

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

       *  Example programs should be written in C.

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

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

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

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

       *  Where possible and appropriate, example programs should allow
          experimentation, by varying their behavior based on inputs (ide‐
          ally 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 char‐
          acters in source code!)  The following command can be used to for‐
          mat 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 pro‐
          duced by the system.

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

EXAMPLES         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), attributes(7), groff(7), groff_man(7), man(7),
       mdoc(7)

COLOPHON         top

       This page is part of release 5.08 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                            2020-08-13                     MAN-PAGES(7)

Pages that refer to this page: intro(1)groff_filenames(5)glibc(7)libc(7)man(7)