standards(7) — Linux manual page


standards(7)        Miscellaneous Information Manual        standards(7)

NAME         top

       standards - C and UNIX Standards

DESCRIPTION         top

       The STANDARDS 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 (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

       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).

       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 

              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.

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

              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

              IEEE Std 1003.1d-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

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

       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

       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 

       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 ⟨⟩.

              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.

              The POSIX.1-2001 document is broken into four parts:

              XBD: Definitions, terms, and concepts, header file

              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 

              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

              In general, where the STANDARDS 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

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

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

              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         top

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

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