--- name: "standards" section: "7" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/standards" --- # standards(7) C and UNIX Standards ## NAME standards - C and UNIX Standards ## DESCRIPTION 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. ### Research Unix - **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. Sources are available online ⟨https:\\://www.tuhs.org/\\:cgi\\-bin/\\:utree.pl?file=V7⟩. ### BSD - **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. Sources are available online ⟨https:\\://www.tuhs.org/\\:cgi\\-bin/\\:utree.pl?file=4.2BSD⟩. - Earlier major BSD releases included *3BSD* (1980), *4BSD* (1980), and *4.1BSD* (1981). - **4.3BSD** The successor to 4.2BSD, released in 1986. Sources are available online ⟨https:\\://www.tuhs.org/\\:cgi\\-bin/\\:utree.pl?file=4.3BSD⟩. - **4.4BSD** The successor to 4.3BSD, released in 1993. This was the last major Berkeley release. Sources are available online ⟨https:\\://www.tuhs.org/\\:cgi\\-bin/\\:utree.pl?file=4.4BSD⟩. ### Unix/TS - **Unix/TS 4** This was an internal release of Unix that was never released to the public (in which case it would have been called System IV). The previous major AT&T release was *System III*, released in 1981. - **System V (SVr1)** This is an implementation standard defined by AT&T's milestone 1983 release of its commercial System V (five) release. - **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 Issue 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 Issue 2* (*SVID 2*) ⟨https:\\://bitsavers.org/\\:pdf/\\:att/\\:unix/\\:SVID/\\:System\_V\_Interface\_Definition\_Issue\_2\_Volume\_1\_1986.pdf⟩. - **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 Third Edition* (*SVID 3*) ⟨https:\\://archive.org/\\:details/\\:systemvinterface0001unse/⟩, 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/⟩. ### Standard C - **K&R** This refers to the C language as specified in *“The C Programming Language”* \[Brian W. Kernighan and Dennis M. Ritchie; Prentice Hall; 1st Ed., 1978\]. - **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. It is available online ⟨https:\\://nvlpubs.nist.gov/\\:nistpubs/\\:Legacy/\\:FIPS/\\:fipspub160.pdf⟩. - The rationale for the C89 standard is also available online ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:C89Rationale.pdf⟩. - This standard was also ratified by ISO (International Standards Organization) and IEC (International Electrotechnical Commision) in 1990 (*ISO/IEC 9899:1990*), and is thus occasionally referred to as *ISO C90*. - **C94** Technical Corrigendum 1 ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:tc1.htm⟩ of C90 was ratified by ISO/IEC in 1994 (*ISO/IEC 9899:1990/Cor1:1994*). - **C95** This amendment of the C language standard was ratified by ISO/IEC in 1995 (*ISO/IEC 9899:1990/Amd1:1995*). A draft is available online ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:n412.pdf⟩. - The primary change in C95 was support for international character sets. - **C96** Technical Corrigendum 2 ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:tc2.htm⟩ of C90 was ratified by ISO/IEC in 1996 (*ISO/IEC 9899:1990/Cor2:1996*). A draft is available online ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:n457.pdf⟩. - **C99** This revision of the C language standard was ratified by ISO/IEC in 1999 (*ISO/IEC 9899:1999*). - Technical Corrigendum 1 ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:9899tc1/\\:n32071.PDF⟩ of C99 was ratified by ISO/IEC in 2001 (*ISO/IEC 9899:1999/Cor1:2001*). - Technical Corrigendum 2 ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:9899\\-1999\_cor\_2\\-2004.pdf⟩ of C99 was ratified by ISO/IEC in 2004 (*ISO/IEC 9899:1999/Cor2:2004*). - Technical Corrigendum 3 ⟨https:\\://www.open\\-std.org/\\:JTC1/\\:SC22/\\:WG14/\\:www/\\:docs/\\:n1235.pdf⟩ of C99 was ratified by ISO/IEC in 2007 (*ISO/IEC 9899:1999/Cor3:2007*). A draft is available online ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:n1256.pdf⟩. - The rationale for the C99 standard is also available online ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:C99RationaleV5.10.pdf⟩. - **C11** This revision of the C language standard was ratified by ISO/IEC in 2011 (*ISO/IEC 9899:2011*). A draft is available online ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:n1570.pdf⟩. - Technical Corrigendum 1 ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:n1606.pdf⟩ of C11 was ratified by ISO/IEC in 2012 (*ISO/IEC 9899:2011/Cor1:2012*). - **C17** This revision of the C language standard was ratified by ISO/IEC in 2018 (*ISO/IEC 9899:2018*). A draft is available online ⟨https:\\://web.archive.org/\\:web/\\:20181230041359if\_/\\:http:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:abq/\\:c17\_updated\_proposed\_fdis.pdf⟩. - **C23** This revision of the C language standard was ratified by ISO/IEC in 2024 (*ISO/IEC 9899:2024*). A draft is available online ⟨https:\\://www.open\\-std.org/\\:jtc1/\\:sc22/\\:wg14/\\:www/\\:docs/\\:n3220.pdf⟩. ### POSIX and SUS - **POSIX.1-1988** This was the first POSIX standard, ratified by IEEE in 1998 (*IEEE Std 1003.1-1988*). The term "POSIX" was coined by Richard Stallman. It is available online ⟨https:\\://nvlpubs.nist.gov/\\:nistpubs/\\:Legacy/\\:FIPS/\\:fipspub151\\-1.pdf⟩. - **POSIX.1-1990** Part 1, "Portable Operating System Interface for Computing Environments". Ratified by IEEE in 1990, (*IEEE Std 1003.1-1990*), and ratified by ISO/IEC in 1990 (*ISO/IEC 9945-1:1990*). It is available online ⟨https:\\://nvlpubs.nist.gov/\\:nistpubs/\\:Legacy/\\:FIPS/\\:fipspub151\\-2.pdf⟩. - **POSIX.2** Part 2, which describes commands and utilities. Ratified by IEEE in 1992 (*IEEE Std 1003.2-1992*), and ratified by ISO/IEC in 1993 (*ISO/IEC 9945-2:1993*). - **POSIX.1b** (formerly known as *POSIX.4*) Part 1b, which describes real-time facilities for portable operating systems. Ratified by IEEE in 1993 (*IEEE Std 1003.1b-1993*). - **POSIX.1c** (formerly known as *POSIX.4a*) Part 1c, which describes the POSIX threads interfaces. Ratified by IEEE in 1995 (*IEEE Std 1003.1c-1995*). - **POSIX.1d** Part 1d, which describes additional real-time extensions. Ratified by IEEE in 1999 (*IEEE Std 1003.1d-1999*). - **POSIX.1g** Part 1g, which describes networking APIs (including sockets). Ratified by IEEE in 2000 (*IEEE Std 1003.1g-2000*). - **POSIX.1j** Part 1j, which describes advanced real-time extensions. Ratified by IEEE in 2000 (*IEEE Std 1003.1j-2000*). - **POSIX.1-1996** A revision of POSIX.1 which incorporated POSIX.1b and POSIX.1c. Ratified by ISO/IEC in 1996 (*ISO/IEC 9945-1:1996*). - **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). It is also known as *Issue 3*. 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. It is also known as *Issue 4*. 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 as *Issue 5*. 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. - **POSIX.1-2001 2002 edition** Technical Corrigendum 1 of POSIX.1-2001 was ratified by IEEE in 2002 (*IEEE Std 1003.1-2001/Cor1-2002*). - This is informally known as *POSIX.1-2002*. - **POSIX.1-2001 2004 edition** Technical Corrigendum 2 of POSIX.1-2001 was ratified by IEEE in 2004 (*IEEE Std 1003.1-2001/Cor2-2004*). It is available online ⟨https:\\://pubs.opengroup.org/\\:onlinepubs/\\:009695399/⟩. - This is informally known as *POSIX.1-2004*. - **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/⟩, and also here ⟨https:\\://pubs.opengroup.org/\\:onlinepubs/\\:9699919799.2008edition/⟩. - 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 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. - Further information can be found on the Austin Group web site, ⟨http:\\://www.opengroup.org\\:/austin/⟩. - **POSIX.1-2008 2013 edition** Technical Corrigendum 1 of POSIX.1-2008 was ratified by IEEE in 2013 (*IEEE Std 1003.1-2008/Cor1-2013*). It is available online ⟨https:\\://pubs.opengroup.org/\\:onlinepubs/\\:9699919799.2013edition/⟩. - This is informally known as *POSIX.1-2013*. - **POSIX.1-2008 2016 edition** Technical Corrigendum 2 of POSIX.1-2008 was ratified by IEEE in 2016 (*IEEE Std 1003.1-2008/Cor2-2016*). It is available online ⟨https:\\://pubs.opengroup.org/\\:onlinepubs/\\:9699919799.2016edition/⟩. - **SUSv4 2016 edition** This is equivalent to POSIX.1-2008 2016 edition, with the addition of the XCurses specification. - **POSIX.1-2017** This revision of POSIX is technically identical to POSIX.1-2008 2016 edition. Ratified by IEEE in 2017 (*IEEE Std 1003.1-2017*). It is available online ⟨https:\\://pubs.opengroup.org/\\:onlinepubs/\\:9699919799/⟩. - **SUSv4 2018 edition** This is equivalent to POSIX.1-2017, with the addition of the XCurses specification. - **POSIX.1-2024** **SUSv5** Work on the next revision of POSIX.1/SUS was completed and ratified by IEEE in 2024 (*IEEE Std 1003.1-2024*). It is available online ⟨https:\\://pubs.opengroup.org/\\:onlinepubs/\\:9799919799/⟩. - POSIX.1-2024 is aligned with C17, so that all of the library functions standardized in C17 are also standardized in POSIX.1-2024. - Further information can be found on the Austin Group web site ⟨http:\\://www.opengroup.org/\\:austin/⟩. 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*. ### Other standards - **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⟩. ## SEE ALSO [**getconf**(1)](/getconf/1.md), [**confstr**(3)](/confstr/3.md), [**pathconf**(3)](/pathconf/3.md), [**sysconf**(3)](/sysconf/3.md), [**attributes**(7)](/attributes/7.md), [**feature\_test\_macros**(7)](/feature_test_macros/7.md), [**libc**(7)](/libc/7.md), [**posixoptions**(7)](/posixoptions/7.md), [**system\_data\_types**(7)](/system_data_types/7.md)