standards(7) - phpMan
STANDARDS(7) Linux Programmer's Manual STANDARDS(7)
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 Soft‐
ware 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
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 pro‐
cessors)" (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 consid‐
ered 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 Stan‐
dards 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
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
POSIX.1b (formerly known as POSIX.4)
IEEE Std 1003.1b-1993, describing real-time facilities for portable operating sys‐
tems, 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.
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 as XPG5. This
standard appeared in 1997. Systems conforming to this standard can be branded UNIX
98. See also ⟨http://www.UNIX-systems.org/version2/⟩.)
This was a 2001 revision and consolidation of the POSIX.1, POSIX.2, and SUS stan‐
dards 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-systems.org/version3/⟩, 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 base‐
line 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
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 stan‐
dard have occurred: TC1 in 2003 (referred to as POSIX.1-2003), and TC2 in 2004
(referred to as POSIX.1-2004).
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 inter‐
faces 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 Con‐
formance, which mandates an additional set of interfaces beyond those in the base
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 (referred to as POSIX.1-2013).
Further information can be found on the Austin group web site,
feature_test_macros(7), libc(7), posixoptions(7)
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Linux 2014-01-15 STANDARDS(7)