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       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 following list  briefly  describes  these

       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

       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 version 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
              considered the definitive System V release.

       SVID 4 System V Interface Definition version 4,  issued  in  1995.   Available  online  at

       C89    This  was  the  first  C  language  standard,  ratified  by ANSI (American National
              Standards Institute) in 1989 (X3.159-1989).  Sometimes this is known as ANSI C, but
              since C99 is also an ANSI standard, this term is ambiguous.  This standard was also
              ratified by ISO (International Standards Organization) in 1990 (ISO/IEC 9899:1990),
              and is thus occasionally referred to as ISO C90.

       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

              "Portable Operating System Interface for Computing Environments".  IEEE 1003.1-1990
              part 1, ratified by ISO in 1990 (ISO/IEC 9945-1:1990).  The term "POSIX" was coined
              by Richard Stallman.

              IEEE Std 1003.2-1992, describing commands and utilities, ratified 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 portable operating
              systems, ratified by ISO in 1996 (ISO/IEC 9945-1:1996).

              IEEE Std 1003.1c-1995, which describes the POSIX threads interfaces.

              IEEE Std 1003.1c-1999, which describes additional real-time extensions.

              IEEE Std 1003.1g-2000, which describes networking APIs (including sockets).

              IEEE Std 1003.1j-2000, which describes advanced real-time extensions.

              A 1996 revision of POSIX.1 which incorporated POSIX.1b and POSIX.1c.

       XPG3   Released in 1989, this was the first significant release of the X/Open  Portability
              Guide,  produced by the X/Open Company, a multivendor 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 standard.

       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  available  in  the Linux manual pages package under sections 1p and 3p (e.g.,
              "man 3p open").

              The standard defines two levels of  conformance:  POSIX  conformance,  which  is  a
              baseline  set  of  interfaces required of a conforming 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 specifications.

              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

              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 POSIX.1-2001.

              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 ratified 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  standard.   A  few
              interfaces that are present in POSIX.1-2001 are marked as obsolete in POSIX.1-2008,
              or removed from the standard altogether.

              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 specification.

              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

              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

              Further    information   can   be   found   on   the   Austin   Group   web   site,


       getconf(1), confstr(3), pathconf(3),  sysconf(3),  attributes(7),  feature_test_macros(7),
       libc(7), posixoptions(7)


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