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STANDARDS(7) Linux Programmer's Manual STANDARDS(7)


     standards - C and UNIX Standards


     The  CONFORMING TO section that appears in many manual pages identifies
     various standards to which the documented interface conforms.  The fol-
     lowing list briefly describes these standards.
     V7     Version  7  (also  known  as  Seventh Edition) UNIX, released by
            AT&T/Bell Labs in 1979.  After this point, UNIX systems diverged
            into two main dialects: BSD and System V.
     4.2BSD This is an implementation standard defined by the 4.2 release of
            the Berkeley Software Distribution, released by  the  University
            of  California at Berkeley.  This was the first Berkeley release
            that contained a TCP/IP stack and the sockets API.   4.2BSD  was
            released in 1983.
            Earlier  major  BSD  releases included 3BSD (1980), 4BSD (1980),
            and 4.1BSD (1981).
     4.3BSD The successor to 4.2BSD, released in 1986.
     4.4BSD The successor to 4.3BSD, released in 1993.  This  was  the  last
            major Berkeley release.
     System V
            This  is  an implementation standard defined by AT&T's milestone
            1983 release of its commercial System  V  (five)  release.   The
            previous major AT&T release was System III, released in 1981.
     System V release 2 (SVr2)
            This  was the next System V release, made in 1985.  The SVr2 was
            formally described in the System V Interface Definition  version
            1 (SVID 1) published in 1985.
     System V release 3 (SVr3)
            This  was the successor to SVr2, released in 1986.  This release
            was formally described in the System V Interface Definition ver-
            sion 2 (SVID 2).
     System V release 4 (SVr4)
            This  was the successor to SVr3, released in 1989.  This version
            of System V is described in the "Programmer's Reference  Manual:
            Operating  System  API  (Intel processors)" (Prentice-Hall 1992,
            ISBN 0-13-951294-2) This release was formally described  in  the
            System V Interface Definition version 3 (SVID 3), and is consid-
            ered the definitive System V release.
     SVID 4 System V Interface Definition version 4, issued in 1995.  Avail-
            able online at
     C89    This was the first C language standard, ratified by ANSI (Ameri-
            can National Standards Institute) in 1989 (X3.159-1989).   Some-
            times  this  is  known  as ANSI C, but since C99 is also an ANSI
            standard, this term is ambiguous.  This standard was also  rati-
            fied  by  ISO  (International  Standards  Organization)  in 1990
            (ISO/IEC 9899:1990), and is thus occasionally referred to as ISO
     C99    This  revision of the C language standard was ratified by ISO in
            1999 (ISO/IEC 9899:1999).  Available online at
     C11    This revision of the C language standard was ratified by ISO  in
            2011 (ISO/IEC 9899:2011).
            "Portable  Operating  System  Interface  for  Computing Environ-
            ments".  IEEE 1003.1-1990  part  1,  ratified  by  ISO  in  1990
            (ISO/IEC  9945-1:1990).   The term "POSIX" was coined by Richard
            IEEE Std 1003.2-1992, describing commands and  utilities,  rati-
            fied by ISO in 1993 (ISO/IEC 9945-2:1993).
     POSIX.1b (formerly known as POSIX.4)
            IEEE  Std 1003.1b-1993, describing real-time facilities for por-
            table operating  systems,  ratified  by  ISO  in  1996  (ISO/IEC
            IEEE  Std 1003.1c-1995, which describes the POSIX threads inter-
            IEEE Std  1003.1c-1999,  which  describes  additional  real-time
            IEEE  Std 1003.1g-2000, which describes networking APIs (includ-
            ing sockets).
            IEEE Std 1003.1j-2000, which describes advanced real-time exten-
            A  1996  revision  of  POSIX.1  which  incorporated POSIX.1b and
     XPG3   Released in 1989, this was the first significant release of  the
            X/Open Portability Guide, produced by the X/Open Company, a mul-
            tivendor consortium.  This multivolume guide was  based  on  the
            POSIX standards.
     XPG4   A revision of the X/Open Portability Guide, released in 1992.
     XPG4v2 A 1994 revision of XPG4.  This is also referred to as Spec 1170,
            where 1170 referred to the number of interfaces defined by  this
     SUS (SUSv1)
            Single UNIX Specification.  This was a repackaging of XPG4v2 and
            other X/Open standards (X/Open Curses Issue 4 version 2,  X/Open
            Networking  Service  (XNS) Issue 4).  Systems conforming to this
            standard can be branded UNIX 95.
     SUSv2  Single UNIX Specification version 2.  Sometimes also referred to
            as XPG5.  This standard appeared in 1997.  Systems conforming to
            this standard can be branded UNIX 98.  See also
     POSIX.1-2001, SUSv3
            This was a 2001  revision  and  consolidation  of  the  POSIX.1,
            POSIX.2,  and  SUS  standards  into a single document, conducted
            under the auspices of the Austin Group The standard is available
            online  at  and the interfaces that it describes are also avail-
            able in the Linux manual pages package under sections 1p and  3p
            (e.g., "man 3p open").
            The  standard  defines  two levels of conformance: POSIX confor-
            mance, which is a baseline set of interfaces required of a  con-
            forming system; and XSI Conformance, which additionally mandates
            a set  of  interfaces  (the  "XSI  extension")  which  are  only
            optional  for  POSIX conformance.  XSI-conformant systems can be
            branded UNIX 03.  (XSI conformance constitutes the  Single  UNIX
            Specification version 3 (SUSv3).)
            The POSIX.1-2001 document is broken into four parts:
            XBD:  Definitions,  terms  and  concepts, header file specifica-
            XSH: Specifications of functions (i.e., system calls and library
            functions in actual implementations).
            XCU:  Specifications  of  commands and utilities (i.e., the area
            formerly described by POSIX.2).
            XRAT: Informative text on the other parts of the standard.
            POSIX.1-2001 is aligned with C99, so that  all  of  the  library
            functions   standardized   in   C99  are  also  standardized  in
            Two Technical Corrigenda (minor fixes and improvements)  of  the
            original 2001 standard have occurred: TC1 in 2003 (also known as
            POSIX.1-2003), and TC2 in 2004 (also known as POSIX.1-2004).
     POSIX.1-2008, SUSv4
            Work on the next revision of POSIX.1/SUS was completed and rati-
            fied in 2008.
            The  changes  in  this  revision  are not as large as those that
            occurred for POSIX.1-2001/SUSv3, but a number of new  interfaces
            are  added  and  various  details of existing specifications are
            modified.   Many  of  the  interfaces  that  were  optional   in
            POSIX.1-2001  become mandatory in the 2008 revision of the stan-
            dard.  A few interfaces that are  present  in  POSIX.1-2001  are
            marked as obsolete in POSIX.1-2008, or removed from the standard
            The revised standard is broken  into  the  same  four  parts  as
            POSIX.1-2001, and again there are two levels of conformance: the
            baseline POSIX Conformance, and XSI Conformance, which  mandates
            an  additional set of interfaces beyond those in the base speci-
            In general, where the CONFORMING TO section  of  a  manual  page
            lists  POSIX.1-2001,  it  can be assumed that the interface also
            conforms to POSIX.1-2008, unless otherwise noted.
            Technical Corrigendum 1 (minor fixes and improvements)  of  this
            standard was released in 2013 (also known as POSIX.1-2013).
            Technical  Corrigendum  2  of this standard was released in 2016
            (also known as POSIX.1-2016).
            Further information can be found on the Austin Group web site,


     getconf(1), confstr(3), pathconf(3),  sysconf(3),  attributes(7),  fea-
     ture_test_macros(7), libc(7), posixoptions(7)


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Linux 2017-11-26 STANDARDS(7)

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