standards(7)

🌸 standards(7) — Miscellaneous Information Manual 🌸

okay so bestie, buckle up 💖 this is the page for standards(7), and it's literally the lore bible of C and UNIX standards. every time a man page hits you with "STANDARDS" and a bunch of cryptic acronyms, this is the page that tells you what those acronyms actually are. grab a snack, it's a long one 🍓

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💜 NAME 💜

standards — C and UNIX Standards. that's it, that's the name, iconic.

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✨ DESCRIPTION ✨

so the STANDARDS section shows up in so many man pages, right? and it's just listing a bunch of standards that the documented interface conforms to, no explanation, like it expects you to already know. rude. this page is the fix 🫶

the following list briefly describes these standards. lowkey essential reading, ngl.

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🌈 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. this is the moment the family tree forked, the main character origin story fr fr 🌳

🦋 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. it 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. sockets?? networking?? the blueprint 💅
  • 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.
• 4.4BSD — the successor to 4.3BSD, released in 1993. this was the last major Berkeley release. sources are available online. end of an era 😭

🧚 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. the lost sibling, we never met them 🙈
• 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).
• 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), and is considered the definitive System V release. the final boss 👑
• 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]. the original text, the holy scripture 📖
• 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.
  • the rationale for the C89 standard is also available online.
  • 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 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.
  • the primary change in C95 was support for international character sets. 🌍
• C96 — Technical Corrigendum 2 of C90 was ratified by ISO/IEC in 1996 (ISO/IEC 9899:1990/Cor2:1996). a draft is available online.
• C99 — this revision of the C language standard was ratified by ISO/IEC in 1999 (ISO/IEC 9899:1999).
  • Technical Corrigendum 1 of C99 was ratified by ISO/IEC in 2001 (ISO/IEC 9899:1999/Cor1:2001).
  • Technical Corrigendum 2 of C99 was ratified by ISO/IEC in 2004 (ISO/IEC 9899:1999/Cor2:2004).
  • Technical Corrigendum 3 of C99 was ratified by ISO/IEC in 2007 (ISO/IEC 9899:1999/Cor3:2007). a draft is available online.
  • the rationale for the C99 standard is also available online.
• C11 — this revision of the C language standard was ratified by ISO/IEC in 2011 (ISO/IEC 9899:2011). a draft is available online.
  • Technical Corrigendum 1 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.
• C23 — this revision of the C language standard was ratified by ISO/IEC in 2024 (ISO/IEC 9899:2024). a draft is available online. the newest baby, fresh out the box 🎀

🫶 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.
• 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.
• 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). threads, bestie 🧵
• 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.
  • 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.
  • 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.

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okay that's not even the end bestie, there's MORE, don't go anywhere 💖

quick note before we keep going bestie — if the STANDARDS section of a man page lists POSIX.1-2001, you can basically assume the interface also conforms to POSIX.1-2008, unless it literally says otherwise. 💅

Wanna dig deeper? The Austin Group web site has the receipts: http://www.opengroup.org/austin/. ✨

POSIX.1-2008 2013 edition 🎀

Technical Corrigendum 1 of POSIX.1-2008 got ratified by IEEE in 2013 (IEEE Std 1003.1-2008/Cor1-2013). It's available online. 🌐

People informally call this one POSIX.1-2013. iykyk. 😌

POSIX.1-2008 2016 edition 🦋

Technical Corrigendum 2 of POSIX.1-2008 got ratified by IEEE in 2016 (IEEE Std 1003.1-2008/Cor2-2016). Also available online. 🌸

SUSv4 2016 edition ✨

This one is equivalent to POSIX.1-2008 2016 edition, but with the XCurses specification added on top. so basically the deluxe version 💅

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). Available online, ofc. 🌈

SUSv4 2018 edition 🍓

Equivalent to POSIX.1-2017, with the XCurses specification added. same energy as before but newer 🫶

POSIX.1-2024 / SUSv5 🔥

Work on the next revision of POSIX.1/SUS got completed and ratified by IEEE in 2024 (IEEE Std 1003.1-2024). It is available online. 🎉

POSIX.1-2024 is aligned with C17, which means every library function standardized in C17 is also standardized in POSIX.1-2024. iconic behavior honestly 😭💖

Further information can be found on the Austin Group web site. 🌐

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The interfaces documented in POSIX.1/SUS are available as manual pages under:

• section 0p — header files 📄
• section 1p — commands ⌨️
• section 3p — functions 🧚

so yes bestie, you can literally write:

man 3p open

and the universe provides. 💫

Other standards 🌸

• LFS — the Large File Summit specification, completed in 1996. This spec defined mechanisms that let 32-bit systems support large files (i.e., 64-bit file offsets). See https://www.opengroup.org/platform/lfs.html. 💾

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SEE ALSO 👀

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

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go read them, no cap — they're the supporting cast and they ate 💅

and that's a wrap on this Linux man-pages 6.20 page, dated 2026-08-03 — she's giving standards, she's giving lore, she's giving everything. mwah, go touch some header files bestie 🎀✨🦋