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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 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 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  (In‐
              tel 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 ⟨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 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 ⟨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 defined 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 subsequently 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 incorporated 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 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 (incorrectly) as XPG5.  This standard appeared in 1997.  Systems conforming to this stan‐
              dard 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 Confor‐
              mance, 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.

              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 containing 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,  un‐
              less 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 Corrigenda 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)

Linux                                                                          2020-11-01                                                                   STANDARDS(7)