The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

## 1. Introduction

### 1.1 Scope

IEEE Std 1003.1-2001 defines a standard operating system interface and environment, including a command interpreter (or "shell"), and common utility programs to support applications portability at the source code level. It is intended to be used by both applications developers and system implementors.

IEEE Std 1003.1-2001 comprises four major components (each in an associated volume):

1. General terms, concepts, and interfaces common to all volumes of IEEE Std 1003.1-2001, including utility conventions and C-language header definitions, are included in the Base Definitions volume of IEEE Std 1003.1-2001.

2. Definitions for system service functions and subroutines, language-specific system services for the C programming language, function issues, including portability, error handling, and error recovery, are included in the System Interfaces volume of IEEE Std 1003.1-2001.

3. Definitions for a standard source code-level interface to command interpretation services (a "shell") and common utility programs for application programs are included in the Shell and Utilities volume of IEEE Std 1003.1-2001.

4. Extended rationale that did not fit well into the rest of the document structure, containing historical information concerning the contents of IEEE Std 1003.1-2001 and why features were included or discarded by the standard developers, is included in the Rationale (Informative) volume of IEEE Std 1003.1-2001.

The following areas are outside of the scope of IEEE Std 1003.1-2001:

- Graphics interfaces

- Database management system interfaces

- Record I/O considerations

- Object or binary code portability

- System configuration and resource availability

IEEE Std 1003.1-2001 describes the external characteristics and facilities that are of importance to applications developers, rather than the internal construction techniques employed to achieve these capabilities. Special emphasis is placed on those functions and facilities that are needed in a wide variety of commercial applications.

The facilities provided in IEEE Std 1003.1-2001 are drawn from the following base documents:

- IEEE Std 1003.1-1996 (POSIX-1) (incorporating IEEE Stds 1003.1-1990, 1003.1b-1993, 1003.1c-1995, and 1003.1i-1995)

- The following amendments to the POSIX.1-1990 standard:

  - IEEE P1003.1a draft standard (Additional System Services)

  - IEEE Std 1003.1d-1999 (Additional Realtime Extensions)

  - IEEE Std 1003.1g-2000 (Protocol-Independent Interfaces (PII))

  - IEEE Std 1003.1j-2000 (Advanced Realtime Extensions)

  - IEEE Std 1003.1q-2000 (Tracing)

- IEEE Std 1003.2-1992 (POSIX-2) (includes IEEE Std 1003.2a-1992)

- The following amendments to the ISO POSIX-2:1993 standard:

  - IEEE P1003.2b draft standard (Additional Utilities)

  - IEEE Std 1003.2d-1994 (Batch Environment)

- Open Group Technical Standard, February 1997, System Interface Definitions, Issue 5 (XBD5) (ISBN: 1-85912-186-1, C605)

- Open Group Technical Standard, February 1997, Commands and Utilities, Issue 5 (XCU5) (ISBN: 1-85912-191-8, C604)

- Open Group Technical Standard, February 1997, System Interfaces and Headers, Issue 5 (XSH5) (in 2 Volumes) (ISBN: 1-85912-181-0, C606)

  Note:
    XBD5, XCU5, and XSH5 are collectively referred to as the Base Specifications.

- Open Group Technical Standard, January 2000, Networking Services, Issue 5.2 (XNS5.2) (ISBN: 1-85912-241-8, C808)

- ISO/IEC 9899:1999, Programming Languages - C.

IEEE Std 1003.1-2001 uses the Base Specifications as its organizational basis and adds the following additional functionality to them, drawn from the base documents above:

- Normative text from the ISO POSIX-1:1996 standard and the ISO POSIX-2:1993 standard not included in the Base Specifications

- The amendments to the POSIX.1-1990 standard and the ISO POSIX-2:1993 standard listed above, except for parts of IEEE Std 1003.1g-2000

- Portability Considerations

- Additional rationale and notes

The following features, marked legacy or obsolescent in the base documents, are not carried forward into IEEE Std 1003.1-2001. Other features from the base documents marked legacy or obsolescent are carried forward unless otherwise noted.

From XSH5, the following legacy interfaces, headers, and external variables are not carried forward:

> advance(), brk(), chroot(), compile(), cuserid(), gamma(), getdtablesize(), getpagesize(), getpass(), getw(), putw(), re_comp(), re_exec(), regcmp(), regex(), sbrk(), sigstack(), step(), ttyslot(), valloc(), wait3(), <re_comp.h>, <regexp.h>, <varargs.h>, loc1, __loc1, loc2, locs

From XCU5, the following legacy utilities are not carried forward:

> calendar, cancel, cc, col, cpio, cu, dircmp, dis, egrep, fgrep, line, lint, lpstat, mail, pack, pcat, pg, spell, sum, tar, unpack, uulog, uuname, uupick, uuto

In addition, legacy features within non-legacy reference pages (for example, headers) are not carried forward.

From the ISO POSIX-1:1996 standard, the following obsolescent features are not carried forward:

> Page 112, CLK_TCK
> Page 197 tcgetattr() rate returned option

From the ISO POSIX-2:1993 standard, obsolescent features within the following pages are not carried forward:

> Page 75, zero-length prefix within PATH
> Page 156, 159 set
> Page 178, awk, use of no argument and no parentheses with length
> Page 259, ed
> Page 272, env
> Page 282, find -perm[ -] onum
> Page 295-296, egrep
> Page 299-300, head
> Page 305-306, join
> Page 309-310, kill
> Page 431-433, 435-436, sort
> Page 444-445, tail
> Page 453, 455-456, touch
> Page 464-465, tty
> Page 472, uniq
> Page 515-516, ex
> Page 542-543, expand
> Page 563-565, more
> Page 574-576, newgrp
> Page 578, nice
> Page 594-596, renice
> Page 597-598, split
> Page 600-601, strings
> Page 624-625, vi
> Page 693, lex

The c89 utility (which specified a compiler for the C Language specified by the ISO/IEC 9899:1990 standard) has been replaced by a c99 utility (which specifies a compiler for the C Language specified by the ISO/IEC 9899:1999 standard).

From XSH5, text marked OH (Optional Header) has been reviewed on a case-by-case basis and removed where appropriate. The XCU5 text marked OF (Output Format Incompletely Specified) and UN (Possibly Unsupportable Feature) has been reviewed on a case-by-case basis and removed where appropriate.

For the networking interfaces, the base document is the XNS, Issue 5.2 specification. The following parts of the XNS, Issue 5.2 specification are out of scope and not included in IEEE Std 1003.1-2001:

- Part 3 (XTI)

- Part 4 (Appendixes)

Since there is much duplication between the XNS, Issue 5.2 specification and IEEE Std 1003.1g-2000, material only from the following sections of IEEE Std 1003.1g-2000 has been included:

- General terms related to sockets (Section 2.2.2)

- Socket concepts (Sections 5.1 through 5.3, inclusive)

- The pselect() function (Sections 6.2.2.1 and 6.2.3)

- The sockatmark() function (Section 5.4.13)

- The <sys/select.h> header (Section 6.2)

Emphasis is placed on standardizing existing practice for existing users, with changes and additions limited to correcting deficiencies in the following areas:

- Issues raised by IEEE or ISO/IEC Interpretations against IEEE Std 1003.1 and IEEE Std 1003.2

- Issues raised in corrigenda for the Base Specifications and working group resolutions from The Open Group

- Corrigenda and resolutions passed by The Open Group for the XNS, Issue 5.2 specification

- Changes to make the text self-consistent with the additional material merged

- A reorganization of the options in order to facilitate profiling, both for smaller profiles such as IEEE Std 1003.13, and larger profiles such as the Single UNIX Specification

- Alignment with the ISO/IEC 9899:1999 standard

### 1.2 Conformance

Conformance requirements for IEEE Std 1003.1-2001 are defined in Conformance.

### 1.3 Normative References

The following standards contain provisions which, through references in IEEE Std 1003.1-2001, constitute provisions of IEEE Std 1003.1-2001. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on IEEE Std 1003.1-2001 are encouraged to investigate the possibility of applying the most recent editions of the standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards.

ANS X3.9-1978
  (Reaffirmed 1989) American National Standard for Information Systems: Standard X3.9-1978, Programming Language FORTRAN.1
ISO/IEC 646:1991
  ISO/IEC 646:1991, Information Processing - ISO 7-Bit Coded Character Set for Information Interchange.2
ISO 4217:2001
  ISO 4217:2001, Codes for the Representation of Currencies and Funds.
ISO 8601:2000
  ISO 8601:2000, Data Elements and Interchange Formats - Information Interchange - Representation of Dates and Times.
ISO C (1999)
  ISO/IEC 9899:1999, Programming Languages - C, including Technical Corrigendum 1.
ISO/IEC 10646-1:2000
  ISO/IEC 10646-1:2000, Information Technology - Universal Multiple-Octet Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual Plane.

### 1.4 Terminology

For the purposes of IEEE Std 1003.1-2001, the following terminology definitions apply:

#### can

Describes a permissible optional feature or behavior available to the user or application. The feature or behavior is mandatory for an implementation that conforms to IEEE Std 1003.1-2001. An application can rely on the existence of the feature or behavior.

#### implementation-defined

Describes a value or behavior that is not defined by IEEE Std 1003.1-2001 but is selected by an implementor. The value or behavior may vary among implementations that conform to IEEE Std 1003.1-2001. An application should not rely on the existence of the value or behavior. An application that relies on such a value or behavior cannot be assured to be portable across conforming implementations.

The implementor shall document such a value or behavior so that it can be used correctly by an application.

#### legacy

Describes a feature or behavior that is being retained for compatibility with older applications, but which has limitations which make it inappropriate for developing portable applications. New applications should use alternative means of obtaining equivalent functionality.

#### may

Describes a feature or behavior that is optional for an implementation that conforms to IEEE Std 1003.1-2001. An application should not rely on the existence of the feature or behavior. An application that relies on such a feature or behavior cannot be assured to be portable across conforming implementations.

To avoid ambiguity, the opposite of may is expressed as need not, instead of may not.

#### shall

For an implementation that conforms to IEEE Std 1003.1-2001, describes a feature or behavior that is mandatory. An application can rely on the existence of the feature or behavior.

For an application or user, describes a behavior that is mandatory.

#### should

For an implementation that conforms to IEEE Std 1003.1-2001, describes a feature or behavior that is recommended but not mandatory. An application should not rely on the existence of the feature or behavior. An application that relies on such a feature or behavior cannot be assured to be portable across conforming implementations.

For an application, describes a feature or behavior that is recommended programming practice for optimum portability.

#### undefined

Describes the nature of a value or behavior not defined by IEEE Std 1003.1-2001 which results from use of an invalid program construct or invalid data input.

The value or behavior may vary among implementations that conform to IEEE Std 1003.1-2001. An application should not rely on the existence or validity of the value or behavior. An application that relies on any particular value or behavior cannot be assured to be portable across conforming implementations.

#### unspecified

Describes the nature of a value or behavior not specified by IEEE Std 1003.1-2001 which results from use of a valid program construct or valid data input.

The value or behavior may vary among implementations that conform to IEEE Std 1003.1-2001. An application should not rely on the existence or validity of the value or behavior. An application that relies on any particular value or behavior cannot be assured to be portable across conforming implementations.

### 1.5 Portability

Some of the utilities in the Shell and Utilities volume of IEEE Std 1003.1-2001 and functions in the System Interfaces volume of IEEE Std 1003.1-2001 describe functionality that might not be fully portable to systems meeting the requirements for POSIX conformance (see the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 2, Conformance).

Where optional, enhanced, or reduced functionality is specified, the text is shaded and a code in the margin identifies the nature of the option, extension, or warning (see Codes). For maximum portability, an application should avoid such functionality.

Unless the primary task of a utility is to produce textual material on its standard output, application developers should not rely on the format or content of any such material that may be produced. Where the primary task is to provide such material, but the output format is incompletely specified, the description is marked with the OF margin code and shading. Application developers are warned not to expect that the output of such an interface on one system is any guide to its behavior on another system.

#### 1.5.1 Codes

The codes and their meanings are as follows. See also Margin Code Notation.

[ADV] Advisory Information
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the ADV margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the ADV margin legend.

[AIO] Asynchronous Input and Output
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the AIO margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the AIO margin legend.

[BAR] Barriers
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the BAR margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the BAR margin legend.

[BE] Batch Environment Services and Utilities
The functionality described is optional.

Where applicable, utilities are marked with the BE margin legend in the SYNOPSIS section. Where additional semantics apply to a utility, the material is identified by use of the BE margin legend.

[CD] C-Language Development Utilities
The functionality described is optional.

Where applicable, utilities are marked with the CD margin legend in the SYNOPSIS section. Where additional semantics apply to a utility, the material is identified by use of the CD margin legend.

[CPT] Process CPU-Time Clocks
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the CPT margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the CPT margin legend.

[CS] Clock Selection
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the CS margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the CS margin legend.

[CX] Extension to the ISO C standard
The functionality described is an extension to the ISO C standard. Application writers may make use of an extension as it is supported on all IEEE Std 1003.1-2001-conforming systems.

With each function or header from the ISO C standard, a statement to the effect that "any conflict is unintentional" is included. That is intended to refer to a direct conflict. IEEE Std 1003.1-2001 acts in part as a profile of the ISO C standard, and it may choose to further constrain behaviors allowed to vary by the ISO C standard. Such limitations are not considered conflicts.

Where additional semantics apply to a function or header, the material is identified by use of the CX margin legend.

[FD] FORTRAN Development Utilities
The functionality described is optional.

Where applicable, utilities are marked with the FD margin legend in the SYNOPSIS section. Where additional semantics apply to a utility, the material is identified by use of the FD margin legend.

[FR] FORTRAN Runtime Utilities
The functionality described is optional.

Where applicable, utilities are marked with the FR margin legend in the SYNOPSIS section. Where additional semantics apply to a utility, the material is identified by use of the FR margin legend.

[FSC] File Synchronization
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the FSC margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the FSC margin legend.

[IP6] IPV6
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the IP6 margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the IP6 margin legend.

[MC1] Advisory Information and either Memory Mapped Files or Shared Memory Objects
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

This is a shorthand notation for combinations of multiple option codes.

Where applicable, functions are marked with the MC1 margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MC1 margin legend.

Refer to Margin Code Notation.

[MC2] Memory Mapped Files, Shared Memory Objects, or Memory Protection
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

This is a shorthand notation for combinations of multiple option codes.

Where applicable, functions are marked with the MC2 margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MC2 margin legend.

Refer to Margin Code Notation.

[MC3] Memory Mapped Files, Shared Memory Objects, or Typed Memory Objects
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

This is a shorthand notation for combinations of multiple option codes.

Where applicable, functions are marked with the MC3 margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MC3 margin legend.

Refer to Margin Code Notation.

[MF] Memory Mapped Files
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the MF margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MF margin legend.

[ML] Process Memory Locking
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the ML margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the ML margin legend.

[MR] Range Memory Locking
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the MLR margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MLR margin legend.

[MON] Monotonic Clock
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the MON margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MON margin legend.

[MPR] Memory Protection
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the MPR margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MPR margin legend.

[MSG] Message Passing
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the MSG margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MSG margin legend.

[MX] IEC 60559 Floating-Point Option
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the MX margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the MX margin legend.

[OB] Obsolescent
The functionality described may be withdrawn in a future version of this volume of IEEE Std 1003.1-2001. Strictly Conforming POSIX Applications and Strictly Conforming XSI Applications shall not use obsolescent features.

Where applicable, the material is identified by use of the OB margin legend.

[OF] Output Format Incompletely Specified
The functionality described is an XSI extension. The format of the output produced by the utility is not fully specified. It is therefore not possible to post-process this output in a consistent fashion. Typical problems include unknown length of strings and unspecified field delimiters.

Where applicable, the material is identified by use of the OF margin legend.

[OH] Optional Header
In the SYNOPSIS section of some interfaces in the System Interfaces volume of IEEE Std 1003.1-2001 an included header is marked as in the following example:

    [OH]
    #include <sys/types.h>

    #include <grp.h>
    struct group *getgrnam(const char *name);

The OH margin legend indicates that the marked header is not required on XSI-conformant systems.

[PIO] Prioritized Input and Output
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the PIO margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the PIO margin legend.

[PS] Process Scheduling
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the PS margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the PS margin legend.

[RS] Raw Sockets
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the RS margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the RS margin legend.

[RTS] Realtime Signals Extension
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the RTS margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the RTS margin legend.

[SD] Software Development Utilities
The functionality described is optional.

Where applicable, utilities are marked with the SD margin legend in the SYNOPSIS section. Where additional semantics apply to a utility, the material is identified by use of the SD margin legend.

[SEM] Semaphores
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the SEM margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the SEM margin legend.

[SHM] Shared Memory Objects
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the SHM margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the SHM margin legend.

[SIO] Synchronized Input and Output
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the SIO margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the SIO margin legend.

[SPI] Spin Locks
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the SPI margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the SPI margin legend.

[SPN] Spawn
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the SPN margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the SPN margin legend.

[SS] Process Sporadic Server
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the SS margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the SS margin legend.

[TCT] Thread CPU-Time Clocks
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TCT margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TCT margin legend.

[TEF] Trace Event Filter
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TEF margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TEF margin legend.

[THR] Threads
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the THR margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the THR margin legend.

[TMO] Timeouts
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TMO margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TMO margin legend.

[TMR] Timers
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TMR margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TMR margin legend.

[TPI] Thread Priority Inheritance
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TPI margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TPI margin legend.

[TPP] Thread Priority Protection
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TPP margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TPP margin legend.

[TPS] Thread Execution Scheduling
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TPS margin legend for the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TPS margin legend.

[TRC] Trace
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TRC margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TRC margin legend.

[TRI] Trace Inherit
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TRI margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TRI margin legend.

[TRL] Trace Log
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TRL margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TRL margin legend.

[TSA] Thread Stack Address Attribute
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TSA margin legend for the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TSA margin legend.

[TSF] Thread-Safe Functions
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TSF margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TSF margin legend.

[TSH] Thread Process-Shared Synchronization
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TSH margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TSH margin legend.

[TSP] Thread Sporadic Server
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TSP margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TSP margin legend.

[TSS] Thread Stack Size Attribute
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TSS margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TSS margin legend.

[TYM] Typed Memory Objects
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the TYM margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the TYM margin legend.

[UP] User Portability Utilities
The functionality described is optional.

Where applicable, utilities are marked with the UP margin legend in the SYNOPSIS section. Where additional semantics apply to a utility, the material is identified by use of the UP margin legend.

[XSI] Extension
The functionality described is an XSI extension. Functionality marked XSI is also an extension to the ISO C standard. Application writers may confidently make use of an extension on all systems supporting the X/Open System Interfaces Extension.

If an entire SYNOPSIS section is shaded and marked XSI, all the functionality described in that reference page is an extension. See XSI Conformance.

[XSR] XSI STREAMS
The functionality described is optional. The functionality described is also an extension to the ISO C standard.

Where applicable, functions are marked with the XSR margin legend in the SYNOPSIS section. Where additional semantics apply to a function, the material is identified by use of the XSR margin legend.

#### 1.5.2 Margin Code Notation

Some of the functionality described in IEEE Std 1003.1-2001 depends on support of more than one option, or independently may depend on several options. The following notation for margin codes is used to denote the following cases.

##### A Feature Dependent on One or Two Options

In this case, margin codes have a <space> separator; for example:

[MF] This feature requires support for only the Memory Mapped Files option.

[MF SHM] This feature requires support for both the Memory Mapped Files and the Shared Memory Objects options; that is, an application which uses this feature is portable only between implementations that provide both options.

##### A Feature Dependent on Either of the Options Denoted

In this case, margin codes have a `'|'` separator to denote the logical OR; for example:

[MF|SHM] This feature is dependent on support for either the Memory Mapped Files option or the Shared Memory Objects option; that is, an application which uses this feature is portable between implementations that provide any (or all) of the options.

##### A Feature Dependent on More than Two Options

The following shorthand notations are used:

[MC1] The MC1 margin code is shorthand for ADV (MF|SHM). Features which are shaded with this margin code require support of the Advisory Information option and either the Memory Mapped Files or Shared Memory Objects option.

[MC2] The MC2 margin code is shorthand for MF|SHM|MPR. Features which are shaded with this margin code require support of either the Memory Mapped Files, Shared Memory Objects, or Memory Protection options.

[MC3] The MC3 margin code is shorthand for MF|SHM|TYM. Features which are shaded with this margin code require support of either the Memory Mapped Files, Shared Memory Objects, or Typed Memory Objects options.

##### Large Sections Dependent on an Option

Where large sections of text are dependent on support for an option, a lead-in text block is provided and shaded accordingly; for example:

[TRC] This section describes extensions to support tracing of user applications. This functionality is dependent on support of the Trace option (and the rest of this section is not further marked for this option).

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#### Footnotes

1.
  ANSI documents can be obtained from the Sales Department, American National Standards Institute, 1430 Broadway, New York, NY 10018, U.S.A.
2.
  ISO/IEC documents can be obtained from the ISO office: 1 Rue de Varembé, Case Postale 56, CH-1211, Genève 20, Switzerland/Suisse