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 (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
⟨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 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 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, 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 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".
