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



NAME
       standards - C and UNIX Standards

DESCRIPTION
       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  stan‐
       dards.

       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 version 2 (SVID 2).

       System V release 4 (SVr4)
              This  was  the  successor  to SVr3, released in 1989.  This version of System V is de‐
              scribed in the "Programmer's Reference Manual: Operating  System  API  (Intel  proces‐
              sors)" (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
              ⟨http://www.sco.com/developers/devspecs/⟩.

       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 occa‐
              sionally 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   ⟨http://www.open-std.org/jtc1/sc22/wg14/www
              /standards⟩.

       C11    This revision of the C  language  standard  was  ratified  by  ISO  in  2011  (ISO/IEC
              9899:2011).

              LFS  The  Large  File Summit specification, completed in 1996.  This specification de‐
              fined mechanisms that allowed 32-bit systems to support the use of large files  (i.e.,
              64-bit file offsets).  See ⟨https://www.opengroup.org/platform/lfs.html⟩.

       POSIX.1-1988
              This  was the first POSIX standard, ratified by IEEE as IEEE Std 1003.1-1988, and sub‐
              sequently adopted (with minor revisions) as an ISO standard in 1990.  The term "POSIX"
              was coined by Richard Stallman.

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

       POSIX.2
              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).

       POSIX.1c  (formerly known as POSIX.4a)
              IEEE Std 1003.1c-1995, which describes the POSIX threads interfaces.

       POSIX.1d
              IEEE Std 1003.1c-1999, which describes additional real-time extensions.

       POSIX.1g
              IEEE Std 1003.1g-2000, which describes networking APIs (including sockets).

       POSIX.1j
              IEEE Std 1003.1j-2000, which describes advanced real-time extensions.

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

       XPG3   Released in 1989, this was the first release of the X/Open  Portability  Guide  to  be
              based on a POSIX standard (POSIX.1-1988).  This multivolume guide was developed by the
              X/Open Group, a multivendor consortium.

       XPG4   A revision of the X/Open Portability Guide, released in 1992.  This revision  incorpo‐
              rated POSIX.2.

       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  stan‐
              dards  (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  (incorrectly)  as
              XPG5.   This  standard  appeared  in 1997.  Systems conforming to this standard can be
              branded UNIX 98.  See also ⟨http://www.unix.org/version2/⟩.)

       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
              ⟨http://www.opengroup.org/austin/⟩.    The   standard   is   available    online    at
              ⟨http://www.unix.org/version3/⟩.

              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  addi‐
              tionally  mandates  a  set of interfaces (the "XSI extension") which are only optional
              for POSIX conformance.  XSI-conformant systems can be branded UNIX 03.

              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
              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 POSIX.1-2001.

              The Single UNIX Specification version 3 (SUSv3) comprises the Base Specifications con‐
              taining XBD, XSH, XCU, and XRAT as above, plus X/Open Curses Issue 4 version 2  as  an
              extra volume that is not in POSIX.1-2001.

              Two  Technical Corrigenda (minor fixes and improvements) of the original 2001 standard
              have occurred: TC1 in 2003 and TC2 in 2004.

       POSIX.1-2008, SUSv4
              Work on the next revision of POSIX.1/SUS was completed  and  ratified  in  2008.   The
              standard is available online at ⟨http://www.unix.org/version4/⟩.

              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 structured in the same way as  its  predecessor.   The  Single
              UNIX Specification version 4 (SUSv4) comprises the Base Specifications containing XBD,
              XSH, XCU, and XRAT, plus X/Open Curses Issue 7 as an  extra  volume  that  is  not  in
              POSIX.1-2008.

              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
              noted.

              Technical  Corrigendum  1 (minor fixes and improvements) of this standard was released
              in 2013.

              Technical Corrigendum 2 of this standard was released in 2016.

              Further   information   can   be   found   on   the    Austin    Group    web    site,
              ⟨http://www.opengroup.org/austin/⟩.

       SUSv4 2016 edition
              This  is equivalent to POSIX.1-2008, with the addition of Technical Corrigenda 1 and 2
              and the XCurses specification.

       POSIX.1-2017
              This revision of POSIX is technically identical to POSIX.1-2008 with Technical  Corri‐
              genda 1 and 2 applied.

       SUSv4 2018 edition
              This is equivalent to POSIX.1-2017, with the addition of the XCurses specification.

       The  interfaces  documented  in  POSIX.1/SUS  are available as manual pages under sections 0p
       (header files), 1p (commands), and 3p (functions); thus one can write "man 3p open".

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

COLOPHON
       This  page  is  part  of  release  5.10 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                                        2020-11-01                                 STANDARDS(7)