Single UNIX Specification Frequently Asked Questions (FAQ Version 1.9)

Last Updated : Oct 28 2004: freq.ques,v 1.9

This is the Frequently Asked Questions file for the Single UNIX Specification. Its maintainer is Andrew Josey (ajosey at The Open Group ). Suggestions and contributions are always welcome.

This document can be found on the world wide web at http://www.opengroup.org/austin/papers/single_unix_faq.html.

UNIX® is a registered trademark of The Open Group in the USA and other countries.

The Open Group holds the definition of what a UNIX system is and its associated trademark in trust for the industry. The official web site for more information is http://www.unix.org.

This article includes answers to the following.

Q0. What is the Single UNIX Specification?
Q1. What is The Open Group Base Working Group ?
Q2. What is the Austin Group?
Q3. What is the latest version of the Single UNIX Specification?
Q4. Where can I read/download the Single UNIX Specification Version 3 from? Is there a book?
Q5. Where can I read/download earlier versions of the Single UNIX Specification from?
Q6. How do I become a participant in the Working Groups?
Q7. What is covered in the Base Definitions Technical Standard (XBD)?
Q8. What is covered in the System Interfaces Technical Standard (XSH)?
Q9. What is covered in the Shell and Utilities Technical Standard (XCU)?
Q10. What is covered in the Rationale Technical Standard (XRAT)
Q11. What is covered in the X/Open Curses Specification (XCURSES)?
Q12. How many APIs are there? Is there a list of APIs?
Q13. What Options are there in the Version 3 Specification?
Q14. What are the required directories and devices?
Q15. What regular expressions are supported?
Q16. How should I compile a conforming program?
Q17. What is the Relationship to the ISO C Standard?
Q18. What happened to the Networking Services Specification (XNS)?
Q19. What System Interfaces are included by Category?
Q20. What is the history of the development of the Single UNIX Specification?
Q21. How does the Single UNIX Specification compare to the Linux Standard Base?
Q22. What are the core technical changes in the latest version of the Single UNIX Specification?
Q23. Does removal of obsolescent utility syntax mean that implementations supporting usages of head -5 file, tail -5 file, tail -l file are no longer allowed?
Q24. Does an operating system have to be derived from AT&T/SCO code to meet the Single UNIX Specification?
Q25. What about UNIX Certification?
Q26. Where can I get a UNIX License Plate from?
Q27. How do I get permission to excerpt materials from the standard for reuse in my product?
Q28. How do I add a question to this FAQ?

Q0. What is the Single UNIX Specification?

The Single UNIX Specification is a set of open, consensus specifications that define the requirements for a conformant UNIX system. The standardized programming environment provides a broad-based functional set of interfaces to support the porting of existing UNIX applications and the development of new applications. The environment also supports a rich set of tools for application development.

The Single UNIX Specification came into being when in 1994 Novell (who had acquired the UNIX systems business of AT&T/USL) decided to get out of that business. Rather than sell the business as a single entity, Novell transferred the rights to the UNIX trademark and the specification (that subsequently became the Single UNIX Specification) to The Open Group (at the time X/Open Company). Subsequently, it sold the source code and the product implementation (UNIXWARE) to SCO. The Open Group also owns the trademark UNIXWARE, transferred to them from SCO more recently.

Q1. What is The Open Group Base Working Group ?

The Open Group's Base Working Group is the group that has and continues to develop the technical specifications that make up the Single UNIX Specification. More information can be found at http://www.opengroup.org/platform/ . The Base Working Group is one of the three parties involved in the Austin Group that maintain the Base Specifications of the Single UNIX Specification Version 3, which are also IEEE Std 1003.1 (POSIX) and ISO/IEC 9945.

Q2. What is the Austin Group?

The Austin Common Standards Revision Group (CSRG) is a joint technical working group established to develop and maintain the core volumes of the Single UNIX Specification, which are also the POSIX 1003.1 standard and ISO/IEC 9945. Anyone wishing to participate in the Austin Group can do so. There are no fees for participation or membership. You may participate as an observer or as a contributor. You do not have to attend face-to-face meetings to participate, electronic participation is most welcome.

See http://www.opengroup.org/austin/ for more information.

See http://www.opengroup.org/austin/faq.html for the Austin Group FAQ.

Q3. What is the latest version of the Single UNIX Specification?

The latest version is the Single UNIX Specification Version 3. The 2004 edition of the Single UNIX Specification was published on April 30th 2004, and updates the 2001 and 2003 editions of the specification to include Technical Corrigendum 1 (TC1) and Technical Corrigendum 2 (TC2). It consists of The Open Group Base Specifications Issue 6 and the X/Open Curses, Issue 4, Version 2 specification.

The Single UNIX Specification uses The Open Group Base Specifications, Issue 6 documentation as its core. The documentation is structured as follows:

Base Definitions, Issue 6 (XBD)
Shell and Utilities, Issue 6 (XCU)
System Interfaces, Issue 6 (XSH)
Rationale (Informative)

New for this version of the Single UNIX Specification is the incorporation of IEEE Std 1003.1 (POSIX) and ISO/IEC 9945 into the document set; The Open Group Base Specifications, Issue 6, ISO/IEC 9945 and IEEE Std 1003.1, 2004 Edition are technically identical. The base document for the joint revision of the documents was The Open Group's Base volumes of its Single UNIX Specification, Version 2. These were selected since they were a superset of the existing POSIX.1 and POSIX.2 specifications and had some organizational aspects that would benefit the audience for the new revision.

Detailed information on the Single UNIX Specification, including accessing the version 3 specification in html is available at http://www.unix.org/version3/

Q4. Where can I read/download the Single UNIX Specification Version 3 from? Is there a book?

The html version of the latest version (which incorporates technical corrigendum 1) is available to read and download from: URL:http://www.unix.org/version3/, you need to register for a copy.

A summary of the changes in Technical Corrigendum 1 is available from: URL:http://www.opengroup.org/austin/docs/austin_155.txt.

The pdf text of just the Technical Corrigendum 1 (changes to the 2001 edition) is available from: URL: http://www.opengroup.org/pubs/catalog/u057.htm .

The pdf text of just the Technical Corrigendum 2 (changes to both the 2001 and 2003 editions) is available from: URL: http://www.opengroup.org/pubs/catalog/u059.htm .

A summary of the changes in Technical Corrigendum 2 is available from: URL:http://www.opengroup.org/austin/docs/austin_206.txt.

The complete specification in pdf format is available to members of The Open Group from The Open Group publications catalog. If you wish to signup up your organization to become a member of The Open Group and are an active participant in the Austin Group you can sign up for no fee at http://www.opengroup.org/austin/ogmembers/ (note this is for companies and organizations only). If you want to join as an individual, or are working on standardization activities and need a copy to assist you in your work, please contact Andrew Josey directly, he can then add you as an individual affiliate member.

Ongoing draft specifications for future technical corrigenda are available online from the Austin Group web site at http://www.opengroup.org/austin/ . You need to be a member of the Austin Group. Information on how to join the group is on the web site.

URL:http://www.opengroup.org/austin/. (Austin Group Home Page)

Periodically The Open Group does hardcopy runs on the complete 4000 page request.Check the Open Group publications catalog for availability (http://www.opengroup.org/publications/). The Open Group also produces a number of Guide Books, including The Single UNIX Specification Version 3 on CDROM, The Authorized Guide (http://www.unix.org/version3/theguide.html), and the UNIX Internationalization Guide (this is the latest) (http://www.opengroup.org/publications/catalog/g032.htm).

Q5. Where can I read/download earlier version of the Single UNIX Specification from?

The specifications that make up the original Single UNIX Specification (1994) and the Single UNIX Specification Version 2 (1997), and other related specifications can be download in pdf, and html where available, from The Open Group publications catalog at http://www.opengroup.org/publications/catalog/un.htm.

Q6. How do I become a participant in the Working Groups?

To participate in the Austin Group just join the open mailing list. See http://www.opengroup.org/austin/lists.html for more information.

URL:http://www.opengroup.org/austin/lists.html. (How to Join the Austin Group)

If you want to join the Base Working Group please contact Andrew Josey for further information.

Q7. What is covered in the Base Definitions Technical Standard (XBD)?

The XBD document is part of the Base Specifications, Issue 6. XBD provides common definitions for the Base Specifications of the Single UNIX Specification; therefore readers should be familiar with it before using the other parts of the Single UNIX Specification. The presence of this document reduces duplication in the other related parts of the Single UNIX Specification and ensures consistent use of terminology.

This document is structured as follows:

Chapter 1 is an introduction which includes the scope of the Base Specifications, and the scope of the changes made in this revision. Normative references, terminology, and portability codes used throughout the Base Specifications are included in this chapter.
Chapter 2 defines the conformance requirements, both for implementation and application conformance. For implementation conformance, this includes documentation requirements, conformance definitions for the core POSIX subset, conformance definitions for systems conforming to the Single UNIX Specification (denoted as the XSI extension), and option groups (previously known as feature groups).
Chapter 3 contains the general terms and definitions that apply throughout the Base Specifications.
Chapter 4 describes general concepts that apply throughout the Base Specifications.
Chapter 5 describes the notation used to specify file input and output formats in XBD and XCU.
Chapter 6 describes the portable character set and the process of character set definition.
Chapter 7 describes the syntax for defining internationalization locales as well as the POSIX locale provided on all systems.
Chapter 8 describes the use of environment variables for internationalization and other purposes.
Chapter 9 describes the syntax of pattern matching using regular expressions employed by many utilities and matched by the regcomp() and regexec() functions. Both Basic Regular Expressions (BREs) and Extended Regular Expressions (EREs) are described in this chapter.
Chapter 10 describes files and devices found on all systems and their semantics. For example, the device /dev/null is an infinite data source and data sink.
Chapter 11 describes the asynchronous terminal interface for many of the functions in XSH and the stty utility in XCU.
Chapter 12 describes the policies for command line argument construction and parsing. It contains the utility argument syntax used throughout XCU, and also utility syntax guidelines for naming of utilities and the specification of their arguments and option-arguments and operands.
Chapter 13 defines the contents of headers which declare constants, macros, and data structures that are needed by programs using the services provided by the system interfaces defined in XSH. These are in the form of reference pages and are organized alphabetically.

Q8. What is covered in the System Interfaces Technical Standard (XSH)

The XSH document is part of the Base Specifications, Issue 6. XSH describes a set of system interfaces offered to application programs by systems conformant to this part of the Single UNIX Specification. Readers are expected to be experienced C language programmers, and to be familiar with the XBD document.

This document is structured as follows:

Chapter 1 explains the status of this document and its relationship to other formal standards. The scope, conformance, and definitions sections are pointers to the XBD document; the sections are here to meet ISO/IEC rules regarding required sections. The terminology and portability codes are identical to the section in XBD and repeated here for ease of reference.
Chapter 2 contains important concepts, terms, and caveats relating to the rest of this document. This includes information on the compilation environment, the name space, definitions of error numbers, signal concepts, standard I/O streams, STREAMS, XSI IPC, realtime, threads, sockets, tracing, and data types.
Chapter 3 defines the functional interfaces to systems conformant to this part of the Single UNIX Specification. These are in the form of reference pages and are organized alphabetically.

Q9. What is covered in the Shell and Utilities Technical Standard (XCU)?

The XCU¹ document is part of the Base Specifications, Issue 6. XCU describes the shell and utilities that are available to application programs on systems conformant to this part of the Single UNIX Specification. Readers are expected to be familiar with the XBD document.

This document is structured as follows:

Chapter 1 explains the status of this document and its relationship to other formal standards, including the ISO C standard and also the XSH document. It also describes the utility limits, grammar conventions, defaults used by the utility descriptions, considerations for utilities in support of large files, and the list of required built-in utilities. The scope, conformance, and definitions sections are pointers to the XBD document; the sections are here to meet ISO/IEC rules regarding required sections. The terminology and portability codes are identical to the section in XBD and repeated here for ease of reference.
Chapter 2 describes the command language-that is, the shell command language interpreter-used in systems conformant to the Single UNIX Specification.
Chapter 3 describes a set of services and utilities that are implemented on systems supporting the Batch Environment option.
Chapter 4 consists of reference pages for all utilities available on systems conforming to the Single UNIX Specification. These are in the form of reference pages and are organized alphabetically.

Footnote

1.: The acronym ``XCU'' derives from the previous version of the specification which was called ``Commands and Utilities''.

Q10. What is covered in the Rationale Technical Standard (XRAT)

The XRAT document is part of the Base Specifications, Issue 6. The XRAT document has been published to assist in the process of review and understanding of the main text. It contains historical information concerning the contents of the Base Specifications, Issue 6 and why features were included or discarded by the standard developers. It also contains notes of interest to application programmers on recommended programming practices, emphasizing the consequences of some aspects that may not be immediately apparent.

This document is organized in parallel to the normative documents of the Base Specification, with a separate part (Parts A, B, and C) for each of the three normative documents. In addition, two additional parts are included: Part D, Portability Considerations and Part E Subprofiling Considerations. The Portability Considerations chapter includes a report on the perceived user requirements for the Base Specification and how the facilities provided satisfy those requirements, together with guidance to writers of profiles on how to use the configurable options, limits, and optional behavior. The Subprofiling Considerations chapter satisfies the requirement that the document address subprofiling. This contains an example set of subprofiling options.

Q11. What is covered in the X/Open Curses Specification (XCURSES)?

XCURSES is not part of the Base Specifications, Issue 6. XCURSES describes a set of interfaces providing a terminal-independent method of updating character screens that are available to application programs on systems conformant to this part of the Single UNIX Specification. This document should be read in conjunction with The Open Group Corrigendum U056.

This document is structured as follows:

Chapter 1 introduces Curses, gives an overview of enhancements that have been made to this version, and lists specific interfaces marked TO BE WITHDRAWN. This chapter also defines the requirements for conformance to this document and shows the generic format followed by interface definitions in Chapter 4.
Chapter 2 describes the relationship between Curses and the C language, the compilation environment, and the X/Open System Interface (XSI) operating system requirements. It also defines the effect of the interface on the name space for identifiers and introduces the major data types that the interfaces use.
Chapter 3 gives an overview of Curses. It discusses the use of some of the key data types and gives general rules for important common concepts such as characters, renditions, and window properties. It contains general rules for the common Curses operations and operating modes. This information is implicitly referenced by the interface definitions in Chapter 4. The chapter explains the system of naming the Curses functions and presents a table of function families. Finally, the chapter contains notes regarding use of macros and restrictions on block-mode terminals.
Chapter 4 defines the Curses functional interfaces.
Chapter 5 defines the contents of headers which declare constants, macros, and data structures that are needed by programs using the services provided by Chapter 4.
Chapter 6 discusses the terminfo database which Curses uses to describe terminals. The chapter specifies the source format of a terminfo entry using a formal grammar, an informal discussion, and an example. Boolean, numeric, and string capabilities are presented in tabular form.
Appendix A discusses the use of these capabilities by the writer of a terminfo entry to describe the characteristics of the terminal in use.
The chapters are followed by a glossary, which contains normative definitions of terms used in the document.

Q12. How many APIs are there? Is there a list of APIs?

There are 1742 APIs, broken down as follows: XSH 1123, XCU 160, XBD 84 and XCURSES 375.

A list of APIs is available at http://www.unix-systems.org/version3/apis.html.

Q13. What Options are there in the Version 3 Specification?

The Version 3 Specification includes a set of profiling options, allowing larger profiles of the options of the Base standard. In earlier versions of the Single UNIX Specification these were formerly known as Feature Groups. The Option Groups within the Single UNIX Specification are defined within XBD, Section 2.1.5.2, XSI Option Groups.

The Single UNIX Specification Version 3 contains the following Option Groups:

Encryption, covering the functions crypt(), encrypt( ), and setkey.()
Realtime, covering the functions from the IEEE Std 1003.1b-1993 Realtime extension.
Realtime Threads, covering the functions from the IEEE Std 1003.1c-1995 Threads extension that are related to realtime functionality.
Advanced Realtime, covering some of the non-threads-related functions from IEEE Std 1003.1d-1999 and IEEE Std 1003.1j-2000.
Advanced Realtime Threads, covering some of the threads-related functions from IEEE Std 1003.1d-1999 and IEEE Std 1003.1j-2000.
Tracing, covering the functionality from IEEE Std 1003.1q-2000.
XSI STREAMS, covering the functionality and interfaces related to STREAMS, a uniform mechanism for implementing networking services and other character-based I/O as described in XSH, Section 2.6, STREAMS. This was mandatory in previous versions of the Single UNIX Specification, but is now optional in this version.
Legacy, covering the functionality and interfaces which were mandatory in previous versions of the Single UNIX Specification, but are optional in this version.

Q14. What are the required directories and devices?

The Single UNIX Specification describes an applications portability environment, and as such defines a certain minimal set of directories and devices that applications regularly use.

The following directories are defined:

/ The root directory of the file system.
/dev Contains the devices /dev/console, /dev/null, and /dev/tty.
/tmp A directory where applications can create temporary files.

The directory structure does not cross into such system management issues as where user accounts are organized or software packages are installed. Refer to XBD, Section 10.1, Directory Structure and Files for more information. XBD, Chapter 10, Directory Structure and Devices also defines the mapping of control character sequences to real character values, and describes the actions an implementation must take when it cannot support certain terminal behavior.

Q15. What regular expressions are supported?

Both Basic Regular Expressions (BREs) and Extended Regular Expressions (EREs) are supported and are described in XBD, Chapter 9, Regular Expressions and all of the utilities and interfaces that use regular expressions refer back to this definition.

Basic regular expressions: csplit, ctags, ed, ex, expr, grep, more, nl, pax, pg, sed, vi

Extended regular expressions: awk, egrep, grep -E, lex

The functions regcomp() and regexec() in XSH, Chapter 3, System Interfaces implement regular expressions as defined in the Single UNIX Specification.

Q16. How should I compile a conforming program?

XCU defines c99 as the interface to the C compilation environment. The c99 interface is new to this version of the specification and an interface to the standard C compiler. The c89 and cc utilities are no longer defined in this version of the Single UNIX Specification although implementations may additionally support them for backwards-compatibility.

There are a number of tasks that must be done to effectively make the interface environment available to a program. A number of C-language macros, referred to as feature test macros, must be defined before any headers are included. These macros might more accurately be referred to as header configuration macros, as they control what symbols and prototypes will be exposed by the headers. The macro _XOPEN_SOURCE must be defined to a value of 600 to make available the functionality of the Single UNIX Specification, Version 3. With respect to POSIX functionality covered by the Single UNIX Specification, this is equivalent to defining the POSIX macro {_POSIX_C_SOURCE} to be 200112L.

Use of the {_XOPEN_SOURCE} macro should not be confused with the other feature test macros associated with Feature Groups and functionality, such as {_XOPEN_UNIX}. These feature test macros are the implementation's way of announcing functionality to the application.

Q17. What is the Relationship to the ISO C Standard?

The most recent revision to the ISO C standard occurred in 1999. The ISO C standard is itself independent of any operating system in so much as it may be implemented in many environments including hosted environments.

The Single UNIX Specification has a long history of building on the ISO C standard and deferring to it where applicable. Whereas revisions of POSIX.1 prior to the Austin Group specification built upon the ISO C standard by reference only, and also allowed support for traditional C as an alternative. The Single UNIX Specification in contrast, has always included manual pages for the ISO C interfaces.

The Version 3 Specification takes the latter approach. The standard developers believed it essential for a programmer to have a single complete reference place. They also recognized that deference to the formal standard had to be addressed for the duplicate interface definitions which occur in both the ISO C standard and their document.

It was agreed that where an interface has a version in the ISO C standard, the DESCRIPTION section should describe the relationship to the ISO C standard and markings added as appropriate within the manual page to show where the ISO C standard has been extended.

A block of text was added to the start of each affected reference page stating whether the page is aligned with the ISO C standard or extended. Each page was parsed for additions beyond the ISO C standard and these extensions are marked as CX extensions (for C Extensions).

Q18. What happened to the Networking Services Specification (XNS)?

Unlike previous versions of the Single UNIX Specification, for Version 3 the Networking Services have now been integrated into the Base Specifications. This includes sockets and IP address resolution interfaces. The X/Open Transport Interface (XTI) is no longer a requirement in Version 3 of the Single UNIX Specification. As with other functions in XSH, the application developer needs to define {_XOPEN_SOURCE} to be 600 prior to the inclusion of any Single UNIX Specification headers. The c99 compiler utilities recognize the additional -l operand for the xnet library.

Q19. What System Interfaces are included by Category?

The system interfaces in the Version 3 specification categorized by functional grouping are as follows:

Jump Interfaces: longjmp(), setjmp()
Maths Library Interfaces: acos(), acosf(), acosh(), acoshf(), acoshl(), acosl(), asin(), asinf(), asinh(), asinhf(), asinhl(), asinl(), atan(), atan2(), atan2f(), atan2l(), atanf(), atanh(), atanhf(), atanhl(), atanl(), cabs(), cabsf(), cabsl(), cacos(), cacosf(), cacosh(), cacoshf(), cacoshl(), cacosl(), carg(), cargf(), cargl(), casin(), casinf(), casinh(), casinhf(), casinhl(), casinl(), catan(), catanf(), catanh(), catanhf(), catanhl(), catanl(), cbrt(), cbrtf(), cbrtl(), ccos(), ccosf(), ccosh(), ccoshf(), ccoshl(), ccosl(), ceil(), ceilf(), ceill(), cexp(), cexpf(), cexpl(), cimag(), cimagf(), cimagl(), clog(), clogf(), clogl(), conj(), conjf(), conjl(), copysign(), copysignf(), copysignl(), cos(), cosf(), cosh(), coshf(), coshl(), cosl(), cpow(), cpowf(), cpowl(), cproj(), cprojf(), cprojl(), creal(), crealf(), creall(), csin(), csinf(), csinh(), csinhf(), csinhl(), csinl(), csqrt(), csqrtf(), csqrtl(), ctan(), ctanf(), ctanh(), ctanhf(), ctanhl(), ctanl(), erf(), erfc(), erfcf(), erfcl(), erff(), erfl(), exp(), exp2(), exp2f(), exp2l(), expf(), expl(), expm1(), expm1f(), expm1l(), fabs(), fabsf(), fabsl(), fdim(), fdimf(), fdiml(), floor(), floorf(), floorl(), fma(), fmaf(), fmal(), fmax(), fmaxf(), fmaxl(), fmin(), fminf(), fminl(), fmod(), fmodf(), fmodl(), fpclassify(), frexp(), frexpf(), frexpl(), hypot(), hypotf(), hypotl(), ilogb(), ilogbf(), ilogbl(), isfinite(), isgreater(), isgreaterequal(), isinf(), isless(), islessequal(), islessgreater(), isnan(), isnormal(), isunordered(), ldexp(), ldexpf(), ldexpl(), lgamma(), lgammaf(), lgammal(), llrint(), llrintf(), llrintl(), llround(), llroundf(), llroundl(), log(), log10(), log10f(), log10l(), log1p(), log1pf(), log1pl(), log2(), log2f(), log2l(), logb(), logbf(), logbl(), logf(), logl(), lrint(), lrintf(), lrintl(), lround(), lroundf(), lroundl(), modf(), modff(), modfl(), nan(), nanf(), nanl(), nearbyint(), nearbyintf(), nearbyintl(), nextafter(), nextafterf(), nextafterl(), nexttoward(), nexttowardf(), nexttowardl(), pow(), powf(), powl(), remainder(), remainderf(), remainderl(), remquo(), remquof(), remquol(), rint(), rintf(), rintl(), round(), roundf(), roundl(), scalbln(), scalblnf(), scalblnl(), scalbn(), scalbnf(), scalbnl(), signbit(), sin(), sinf(), sinh(), sinhf(), sinhl(), sinl(), sqrt(), sqrtf(), sqrtl(), tan(), tanf(), tanh(), tanhf(), tanhl(), tanl(), tgamma(), tgammaf(), tgammal(), trunc(), truncf(), truncl()
General ISO C Library Interfaces: abs(), asctime(), atof(), atoi(), atol(), atoll(), bsearch(), calloc(), ctime(), difftime(), div(), feclearexcept(), fegetenv(), fegetexceptflag(), fegetround(), feholdexcept(), feraiseexcept(), fesetenv(), fesetexceptflag(), fesetround(), fetestexcept(), feupdateenv(), free(), gmtime(), imaxabs(), imaxdiv(), isalnum(), isalpha(), isblank(), iscntrl(), isdigit(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), isxdigit(), labs(), ldiv(), llabs(), lldiv(), localeconv(), localtime(), malloc(), memchr(), memcmp(), memcpy(), memmove(), memset(), mktime(), qsort(), rand(), realloc(), setlocale(), snprintf(), sprintf(), srand(), sscanf(), strcat(), strchr(), strcmp(), strcoll(), strcpy(), strcspn(), strerror(), strftime(), strlen(), strncat(), strncmp(), strncpy(), strpbrk(), strrchr(), strspn(), strstr(), strtod(), strtof(), strtoimax(), strtok(), strtol(), strtold(), strtoll(), strtoul(), strtoull(), strtoumax(), strxfrm(), time(), tolower(), toupper(), tzname, tzset(), va_arg(), va_copy(), va_end(), va_start(), vsnprintf(), vsprintf(), vsscanf()
Thread-Safe General ISO C Library Interfaces: asctime_r(), ctime_r(), gmtime_r(), localtime_r(), rand_r(), strerror_r(), strtok_r()
Wide-Character ISO C Library Interfaces: btowc(), iswalnum(), iswalpha(), iswblank(), iswcntrl(), iswctype(), iswdigit(), iswgraph(), iswlower(), iswprint(), iswpunct(), iswspace(), iswupper(), iswxdigit(), mblen(), mbrlen(), mbrtowc(), mbsinit(), mbsrtowcs(), mbstowcs(), mbtowc(), swprintf(), swscanf(), towctrans(), towlower(), towupper(), vswprintf(), vswscanf(), wcrtomb(), wcscat(), wcschr(), wcscmp(), wcscoll(), wcscpy(), wcscspn(), wcsftime(), wcslen(), wcsncat(), wcsncmp(), wcsncpy(), wcspbrk(), wcsrchr(), wcsrtombs(), wcsspn(), wcsstr(), wcstod(), wcstof(), wcstoimax(), wcstok(), wcstol(), wcstold(), wcstoll(), wcstombs(), wcstoul(), wcstoull(), wcstoumax(), wcsxfrm(), wctob(), wctomb(), wctrans(), wctype(), wmemchr(), wmemcmp(), wmemcpy(), wmemmove(), wmemset()
General C Library Extension Interfaces: fnmatch(), getopt(), optarg, opterr, optind, optopt
Device Input and Output Interfaces: FD_CLR(), FD_ISSET(), FD_SET(), FD_ZERO(), clearerr(), close(), fclose(), fdopen(), feof(), ferror(), fflush(), fgetc(), fgets(), fileno(), fopen(), fprintf(), fputc(), fputs(), fread(), freopen(), fscanf(), fwrite(), getc(), getchar(), gets(), open(), perror(), printf(), pselect(), putc(), putchar(), puts(), read(), scanf(), select(), setbuf(), setvbuf(), stderr, stdin, stdout, ungetc(), vfprintf(), vfscanf(), vprintf(), vscanf(), write()
General Terminal Interfaces: cfgetispeed(), cfgetospeed(), cfsetispeed(), cfsetospeed(), ctermid(), isatty(), tcdrain(), tcflow(), tcflush(), tcgetattr(), tcsendbreak(), tcsetattr(), ttyname()
Thread-Safe General Terminal Interfaces: ttyname_r()
File Descriptor Management Interfaces: dup(), dup2(), fcntl(), fgetpos(), fseek(), fseeko(), fsetpos(), ftell(), ftello(), ftruncate(), lseek(), rewind()
FIFO Interfaces: mkfifo()
File Attributes Interfaces: chmod(), chown(), fchmod(), fchown(), umask()
Thread-Safe Stdio Locking Interfaces: flockfile(), ftrylockfile(), funlockfile(), getc_unlocked(), getchar_unlocked(), putc_unlocked(), putchar_unlocked()
File System Interfaces: access(), chdir(), closedir(), creat(), fpathconf(), fstat(), getcwd(), link(), mkdir(), opendir(), pathconf(), readdir(), remove(), rename(), rewinddir(), rmdir(), stat(), tmpfile(), tmpnam(), unlink(), utime()
File System Extensions Interfaces: glob(), globfree()
Thread-Safe File System Interfaces: readdir_r()
Job Control Interfaces: setpgid(), tcgetpgrp(), tcsetpgrp()
Multiple Processes Interfaces: _Exit(), _exit(), assert(), atexit(), clock(), execl(), execle(), execlp(), execv(), execve(), execvp(), exit(), fork(), getpgrp(), getpid(), getppid(), setsid(), sleep(), times(), wait(), waitpid()
Networking Interfaces: accept(), bind(), connect(), endhostent(), endnetent(), endprotoent(), endservent(), freeaddrinfo(), gai_strerror(), getaddrinfo(), gethostbyaddr(), gethostbyname(), gethostent(), gethostname(), getnameinfo(), getnetbyaddr(), getnetbyname(), getnetent(), getpeername(), getprotobyname(), getprotobynumber(), getprotoent(), getservbyname(), getservbyport(), getservent(), getsockname(), getsockopt(), h_errno, htonl(), htons(), if_freenameindex(), if_indextoname(), if_nameindex(), if_nametoindex(), inet_addr(), inet_ntoa(), inet_ntop(), inet_pton(), listen(), ntohl(), ntohs(), recv(), recvfrom(), recvmsg(), send(), sendmsg(), sendto(), sethostent(), setnetent(), setprotoent(), setservent(), setsockopt(), shutdown(), socket(), sockatmark(), socketpair()
Pipe Interfaces: pipe()
Regular Expressions Interfaces: regcomp(), regerror(), regexec(), regfree()
Shell and Utilities Interfaces: pclose(), popen(), system(), wordexp(), wordfree()
Signal Interfaces: abort(), alarm(), kill(), pause(), raise(), sigaction(), sigaddset(), sigdelset(), sigemptyset(), sigfillset(), sigismember(), signal(), sigpending(), sigprocmask(), sigsuspend(), sigwait()
Signal Jump Functions Interfaces: siglongjmp(), sigsetjmp()
Single Process Interfaces: confstr(), environ, errno, getenv(), setenv(), sysconf(), uname(), unsetenv()
Symbolic Links Interfaces: lstat(), readlink(), symlink()
System Database Interfaces: getgrgid(), getgrnam(), getpwnam(), getpwuid()
Thread-Safe System Database Interfaces: getgrgid_r(), getgrnam_r(), getpwnam_r(), getpwuid_r()
Threads Interfaces: pthread_addr_setstacksize(), pthread_atfork(), pthread_attr_destroy(), pthread_attr_getdetachstate(), pthread_attr_getstackaddr(), pthread_attr_getstacksize(), pthread_attr_init(), pthread_attr_setdetachstate(), pthread_attr_setschedparam(), pthread_attr_setstackaddr(), pthread_barrierattr_destroy(), pthread_barrierattr_getpshared(), pthread_barrierattr_init(), pthread_barrierattr_setpshared(), pthread_barrier_destroy(), pthread_barrier_init(), pthread_barrier_wait(), pthread_cancel(), pthread_cleanup_pop(), pthread_cleanup_push(), pthread_cond_broadcast(), pthread_cond_destroy(), pthread_cond_init(), pthread_cond_signal(), pthread_cond_timedwait(), pthread_cond_wait(), pthread_condattr_destroy(), pthread_condattr_getpshared(), pthread_condattr_init(), pthread_condattr_setpshared(), pthread_create(), pthread_detach(), pthread_equal(), pthread_exit(), pthread_getschedparam(), pthread_getspecific(), pthread_join(), pthread_key_create(), pthread_key_delete(), pthread_kill(), pthread_mutex_destroy(), pthread_mutex_init(), pthread_mutex_lock(), pthread_mutex_timedlock(), pthread_mutex_trylock(), pthread_mutex_unlock(), pthread_mutexattr_destroy(), pthread_mutexattr_getpshared(), pthread_mutexattr_init(), pthread_mutexattr_setpshared(), pthread_once(), pthread_rwlockattr_destroy(), pthread_rwlockattr_getpshared(), pthread_rwlockattr_init(), pthread_rwlockattr_setpshared(), pthread_rwlock_destroy(), pthread_rwlock_init(), pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), pthread_rwlock_timedwrlock(), pthread_rwlock_tryrdlock(), pthread_rwlock_trywrlock(), pthread_rwlock_unlock(), pthread_rwlock_wrlock(), pthread_self(), pthread_setcancelstate(), pthread_setcanceltype(), pthread_setspecific(), pthread_sigmask(), pthread_spin_destroy(), pthread_spin_init(), pthread_spin_lock(), pthread_spin_trylock(), pthread_spin_unlock(), pthread_testcancel()
Realtime Threads Interfaces: pthread_attr_getinheritsched(), pthread_attr_getschedpolicy(), pthread_attr_getscope(), pthread_attr_setinheritsched(), pthread_attr_setschedpolicy(), pthread_attr_setscope(), pthread_getschedparam(), pthread_mutex_getprioceiling(), pthread_mutex_setprioceiling(), pthread_mutexattr_getprioceiling(), pthread_mutexattr_getprotocol(), pthread_mutexattr_setprioceiling(), pthread_mutexattr_setprotocol(), pthread_setschedparam()
Realtime Interfaces: aio_cancel(), aio_error(), aio_fsync(), aio_read(), aio_return(), aio_suspend(), aio_write(), clock_getres(), clock_gettime(), clock_settime(), fdatasync(), lio_listio(), mlock(), mlockall(), mq_close(), mq_getattr(), mq_notify(), mq_open(), mq_receive(), mq_send(), mq_setattr(), mq_timedreceive(), mq_timedsend(), mq_unlink(), munlock(), munlockall(), nanosleep(), sched_get_priority_max(), sched_get_priority_min(), sched_getparam(), sched_getscheduler(), sched_rr_get_interval(), sched_setparam(), sched_setscheduler(), sched_yield(), sem_close(), sem_destroy(), sem_getvalue(), sem_init(), sem_open(), sem_post(), sem_timedwait(), sem_trywait(), sem_unlink(), sem_wait(), shm_open(), shm_unlink(), sigqueue(), sigtimedwait(), sigwaitinfo(), timer_create(), timer_delete(), timer_getoverrun(), timer_gettime(), timer_settime()
Tracing Interfaces: posix_trace_attr_destroy(), posix_trace_attr_getclockres(), posix_trace_attr_getcreatetime(), posix_trace_attr_getgenversion(), posix_trace_attr_getinherited(), posix_trace_attr_getlogfullpolicy(), posix_trace_attr_getlogsize(), posix_trace_attr_getmaxdatasize(), posix_trace_attr_getmaxsystemeventsize(), posix_trace_attr_getmaxusereventsize(), posix_trace_attr_getname(), posix_trace_attr_getstreamfullpolicy(), posix_trace_attr_getstreamsize(), posix_trace_attr_init(), posix_trace_attr_setinherited(), posix_trace_attr_setlogfullpolicy(), posix_trace_attr_setlogsize(), posix_trace_attr_setmaxdatasize(), posix_trace_attr_setname(), posix_trace_attr_setstreamfullpolicy(), posix_trace_attr_setstreamsize(), posix_trace_clear(), posix_trace_close(), posix_trace_create(), posix_trace_create_withlog(), posix_trace_event(), posix_trace_eventid_equal(), posix_trace_eventid_get_name(), posix_trace_eventid_open(), posix_trace_eventset_add(), posix_trace_eventset_del(), posix_trace_eventset_empty(), posix_trace_eventset_fill(), posix_trace_eventset_ismember(), posix_trace_eventtypelist_getnext_id(), posix_trace_eventtypelist_rewind(), posix_trace_flush(), posix_trace_get_attr(), posix_trace_get_filter(), posix_trace_getnext_event(), posix_trace_get_status(), posix_trace_open(), posix_trace_rewind(), posix_trace_set_filter(), posix_trace_shutdown(), posix_trace_start(), posix_trace_stop(), posix_trace_timedgetnext_event(), posix_trace_trid_eventid_open(), posix_trace_trygetnext_event()
Advisory Interfaces Interfaces: posix_fadvise(), posix_fallocate(), posix_madvise()
Typed Memory Interfaces Interfaces: posix_mem_offset(), posix_typed_mem_get_info(), posix_typed_mem_open()
User and Group Interfaces: getegid(), geteuid(), getgid(), getgroups(), getlogin(), getuid(), setegid(), seteuid(), setgid(), setuid()
Thread-Safe User and Group Interfaces: getlogin_r()
Wide Character Device Input and Output Interfaces: fgetwc(), fgetws(), fputwc(), fputws(), fwide(), fwprintf(), fwscanf(), getwc(), getwchar(), putwc(), putwchar(), ungetwc(), vfwprintf(), vfwscanf(), vwprintf(), vwscanf(), wprintf(), wscanf()
XSI General C Library Interfaces: _tolower(), _toupper(), a64l(), daylight(), drand48(), erand48(), ffs(), getcontext(), getdate(), getsubopt(), hcreate(), hdestroy(), hsearch(), iconv(), iconv_close(), iconv_open(), initstate(), insque(), isascii(), jrand48(), l64a(), lcong48(), lfind(), lrand48(), lsearch(), makecontext(), memccpy(), mrand48(), nrand48(), random(), remque(), seed48(), setcontext(), setstate(), signgam, srand48(), srandom(), strcasecmp(), strdup(), strfmon(), strncasecmp(), strptime(), swab(), swapcontext(), tdelete(), tfind(), timezone(), toascii(), tsearch(), twalk()
XSI Encryption Interfaces: crypt(), encrypt(), setkey()
XSI Database Management Interfaces: dbm_clearerr(), dbm_close(), dbm_delete(), dbm_error(), dbm_fetch(), dbm_firstkey(), dbm_nextkey(), dbm_open(), dbm_store()
XSI Device Input and Output Interfaces: fmtmsg(), poll(), pread(), pwrite(), readv(), writev()
XSI General Terminal Interfaces: grantpt(), posix_openpt(), ptsname(), unlockpt()
XSI Dynamic Linking Interfaces: dlclose(), dlerror(), dlopen(), dlsym()
XSI File Descriptor Management Interfaces: truncate()
XSI File System Interfaces: basename(), dirname(), fchdir(), fstatvfs(), ftw(), lchown(), lockf(), mknod(), mkstemp(), nftw(), realpath(), seekdir(), statvfs(), sync(), telldir(), tempnam()
XSI Internationalization Interfaces: catclose(), catgets(), catopen(), nl_langinfo()
XSI Interprocess Communication Interfaces: ftok(), msgctl(), msgget(), msgrcv(), msgsnd(), semctl(), semget(), semop(), shmat(), shmctl(), shmdt(), shmget()
XSI Job Control Interfaces: tcgetsid()
XSI Jump Functions Interfaces: _longjmp(), _setjmp()
XSI Maths Library Interfaces: j0(), j1(), jn(), scalb(), y0(), y1(), yn()
XSI Multiple Process Interfaces: getpgid(), getpriority(), getrlimit(), getrusage(), getsid(), nice(), setpgrp(), setpriority(), setrlimit(), ulimit(), usleep(), vfork(), waitid()
XSI Signal Interfaces: bsd_signal(), killpg(), sigaltstack(), sighold(), sigignore(), siginterrupt(), sigpause(), sigrelse(), sigset(), ualarm()
XSI Single Process Interfaces: gethostid(), gettimeofday(), putenv()
XSI System Database Interfaces: endpwent(), getpwent(), setpwent()
XSI System Logging Interfaces: closelog(), openlog(), setlogmask(), syslog()
XSI Thread Mutex Extensions Interfaces: pthread_mutexattr_gettype(), pthread_mutexattr_settype()
XSI Threads Extensions Interfaces: pthread_attr_getguardsize(), pthread_attr_setguardsize(), pthread_getconcurrency(), pthread_setconcurrency()
XSI Timers Interfaces: getitimer(), setitimer()
XSI User and Group Interfaces: endgrent(), endutxent(), getgrent(), getutxent(), getutxid(), getutxline(), pututxline(), setgrent(), setregid(), setreuid(), setutxent()
XSI Wide-Character Library Interfaces: wcswidth(), wcwidth()
XSI Legacy Interfaces: bcmp(), bcopy(), bzero(), ecvt(), fcvt(), ftime(), gcvt(), getwd(), index(), mktemp(), rindex(), utimes(), wcswcs()

Q20. What is the history of the development of the Single UNIX Specification?

The Open Group has been the custodian of the specification for the UNIX system and the trademark since 1994. This is a source level API specification which has traditionally built upon the formal IEEE POSIX standards. It is vendor neutral and not tied to any particular implementation.

The project that led to the creation of the Single UNIX Specification started when several vendors (Sun Microsystems, IBM, Hewlett-Packard, Novell/USL, and OSF) joined together to provide a single unified specification of the UNIX system services. By implementing a single common definition of the UNIX system services, third-party independent software vendors (ISVs) would be able to more easily deliver strategic applications on all of these vendors' platforms at once.

A two-pronged approach was used to develop the Single UNIX Specification. First, a set of formal industry specifications was chosen to form the overall base for the work. This would provide stability, vendor neutrality, and lay a well charted course for future application development, taking advantage of the careful work that has gone into developing these specifications. It would also preserve the portability of existing applications already developed to these core models.

The XPG4 Base (1992) was chosen as the stable functional base from which to start. XPG4 Base supports the POSIX.1 system interface and the ISO C standards at its core. It also provided a rich set of 174 commands and utilities.

To this base was added the traditional UNIX System V Interface Definition, (SVID) Edition 3, Level 1 calls, and the OSF Application Environment Specification Full Use interface definitions. This represented the stable central core of the latter two specifications.

The second part of the approach was to incorporate interfaces that were acknowledged common practice but had not yet been incorporated into any formal specification or standard. The intent was to ensure existing applications running on UNIX systems would port with relative ease to a platform supporting the Single UNIX Specification. A survey of real world applications was used to determine what additional interfaces would be required in the specification.

Fifty successful application packages were chosen to be analyzed using the following criteria:

- Ranked in International Data Corp's. 1992, 'Survey of Leading UNIX Applications',

- The application's domain of applicability was checked to ensure that no single application type (for example, databases) was overly represented,

- The application had to be available for analysis either as source code, or as a shared or dynamic linked library.

From the group of fifty, the top ten were selected carefully, ensuring that no more than two representative application packages in a particular problem space were chosen. The ten chosen applications were:

AutoCAD; Cadence; FrameMaker; Informix; Island Write/Paint; Lotus 1-2-3; SAS (4GL); Sybase; Teamwork; WordPerfect

APIs used by the applications that were not part of the base specifications were analyzed:

- If an API was used by any of the top ten applications, it was considered for inclusion.

- If an API was not used by one of the top ten, but was used by any three of the remaining 40 applications, it was considered for inclusion.

- While the investigation of these 50 applications was representative of large complex applications, it still was not considered as a broad enough survey, so an additional 3500 modules were scanned. If an API was used at least seven times in modules that came from at least two platforms (to screen out vendor specific libraries), then the interface was considered for inclusion.

When the survey was complete, there were 130 interfaces that did not already appear in the base specification. These interfaces were predominantly BSD interfaces that had never been covered in XPG4 Base, the SVID, or the AES, but did represent common practice in UNIX system applications developed originally on BSD-derived platforms. Such things as sockets and the 4.3BSD memory management calls were commonly used in many applications.

The goal was to ensure that APIs in common use were included, even if they were not in the formal specifications that made up the base. Making the Single UNIX Specification a superset of existing base specifications ensured any existing applications should work unmodified.

The Single UNIX Specification has evolved through several iterations; Version 2 in 1997 incorporated updates to the formal standards, as well as industry driven additions such as large file handling, dynamic linking, datasize neutrality and extended threads functionality. Version 3 in 2001 merges with the IEEE POSIX standard.

A list of the interfaces in Version 3 of the Single UNIX Specification together with comparative information on the presence of the interface in other specifications is available at http://www.unix.org/v3-apis.html

A wall poster with the history and timeline of the Single UNIX Specification is available at http://www.unix.org/Posters/

Q21. How does the Single UNIX Specification compare to the Linux Standard Base?

The Single UNIX Specification specifies application programming interfaces (APIs) at the source level, and is about application source code portability. Its neither a code implementation nor an operating system, but a stable definition of a programming interface that those systems supporting the specification guarantee to provide to the application programmer. Efforts such as the Linux Standard Base, and similarly the iBCS2 for x86 implementations of System V, are about binary portability and define a specific binary implementation of an interface to operating system services.

The LSB draws on the Single UNIX Specification for many of its interfaces although does not formally defer to it preferring to document any differences where they exist, such as where certain aspects of Linux cannot currently conform to the industry standards. Some interfaces are not included in the LSB, since they are outside the remit of a binary runtime environment, typically these are development interfaces or user level tools. Likewise there are some areas in the LSB that are outside the scope of the Single UNIX Specification (for example system administration interfaces).

Two white papers with further information on this topic are at: http://www.opengroup.org/platform/single_unix_specification/doc.tpl?gdid=6075, http://www.opengroup.org/platform/single_unix_specification/doc.tpl?gdid=5992.

Q22. What are the core technical changes in the latest version of the Single UNIX Specification?

The main changes are as follows: alignment with ISO/IEC 9899:1999 (ISO C), integration of the Networking Services volume (apart from XTI), support for IPv6, integration of recent POSIX realtime amendments ( 1003.1d, 1003.1j, 1003.1q), amendments to the core POSIX functionality from the 1003.2b and 1003.1a amendments, application of technical corrigendum from The Open Group and IEEE interpretations, revision of options , removal of obsolescent and legacy interfaces.

Q23. Does removal of obsolescent utility syntax mean that implementations supporting usages of head -5 file, tail -5 file, tail -l file are no longer allowed?

No, in general the intent of removing the obsolescent forms of the utility synopses was not to disallow them to be supported by implementations but to downgrade the status of their use in applications from conforming application using an obsolescent feature to non-conforming application. In general it is allowed for utilities to have extensions that violate the utility syntax guidelines so long as the forms defined in the standard that are required to follow the utility syntax guidelines do so. The cases cited fit the case. The Austin Group has more general cases under review at the present time.

Q24. Does an operating system have to be derived from AT&T/SCO code to meet the Single UNIX Specification?

No. As the owner of the UNIX trademark, The Open Group has separated the UNIX trademark from any actual code stream itself, thus allowing multiple implementations. Since the introduction of the Single UNIX Specification, there has been a single, open, consensus specification that defines the requirements for a conformant UNIX system.

Q25. What about UNIX Certification?

There is a mark, or brand, that is used to identify those products that have been certified as conforming to the Single UNIX Specification, initially UNIX 93, followed subsequently by UNIX 95, UNIX 98 and now UNIX 03. Information on the UNIX certification program which operates under The Open Group's Open Brand, can be found at http://www.opengroup.org/certification/idx/unix.html

The UNIX 03 Certification Guide is available at http://www.opengroup.org/openbrand/docs/UNIX03_Certification_Guide.html.

The Practical Guide to the Open Brand is available at http://www.opengroup.org/openbrand/Certification_Guide/

The register of Certified Products is available at http://www.opengroup.org/openbrand/register/

Q26. Where can I get a UNIX License Plate from?

The classic "Live Free or Die" license plates can be ordered from The Open Group's publications catalog at: http://www.opengroup.org/publications/catalog/n900.htm.

A wall poster with the story of the history of the license plate can be downloaded from http://www.unix.org/Posters/

Q27. How do I get permission to excerpt materials from the standard for reuse in my product?

All queries regarding permission to reproduce sections of the standard should be sent to austin-group-permissions at Open Group . Permission needs to be granted by both copyright holders, The IEEE and The Open Group.

Q28. How do I add a question to this FAQ?

Send the question (preferably with a proposed answer) to Andrew Josey.