The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group

#### NAME

> unistd.h - standard symbolic constants and types

#### SYNOPSIS

> `#include <unistd.h>`

#### DESCRIPTION

> The <unistd.h> header defines miscellaneous symbolic constants and types, and declares miscellaneous functions. The actual values of the constants are unspecified except as shown. The contents of this header are shown below.

> ##### Version Test Macros

> The <unistd.h> header shall define the following symbolic constants. The values shall be suitable for use in #if preprocessing directives.

> _POSIX_VERSION
>   Integer value indicating version of this standard (C-language binding) to which the implementation conforms. For implementations conforming to POSIX.1-2008, the value shall be 200809L.
> _POSIX2_VERSION
>   Integer value indicating version of the Shell and Utilities volume of POSIX.1 to which the implementation conforms. For implementations conforming to POSIX.1-2008, the value shall be 200809L. For profile implementations that define _POSIX_SUBPROFILE (see Subprofiling Considerations) in <unistd.h>, POSIX2_VERSION may be left undefined or be defined with the value -1 to indicate that the Shell and Utilities volume of POSIX.1 is not supported. In this case, a call to sysconf(_SC_2_VERSION) shall return either 200809L or -1 indicating that the Shell and Utilities volume of POSIX.1 is or is not, respectively, supported at runtime.

> The <unistd.h> header shall define the following symbolic constant only if the implementation supports the XSI option; see XSI Conformance. If defined, its value shall be suitable for use in #if preprocessing directives.

> _XOPEN_VERSION
>   [XSI]
>   Integer value indicating version of the X/Open Portability Guide to which the implementation conforms. The value shall be 700.

> ##### Constants for Options and Option Groups

> The following symbolic constants, if defined in <unistd.h>, shall have a value of -1, 0, or greater, unless otherwise specified below. For profile implementations that define _POSIX_SUBPROFILE (see Subprofiling Considerations) in <unistd.h>, constants described below as always having a value greater than zero need not be defined and, if defined, may have a value of -1, 0, or greater. The values shall be suitable for use in #if preprocessing directives.

> If a symbolic constant is not defined or is defined with the value -1, the option is not supported for compilation. If it is defined with a value greater than zero, the option shall always be supported when the application is executed. If it is defined with the value zero, the option shall be supported for compilation and might or might not be supported at runtime. See Options for further information about the conformance requirements of these three categories of support.

> _POSIX_ADVISORY_INFO
>   [ADV]
>   The implementation supports the Advisory Information option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_ASYNCHRONOUS_IO
>   The implementation supports asynchronous input and output. This symbol shall always be set to the value 200809L.
> _POSIX_BARRIERS
>   The implementation supports barriers. This symbol shall always be set to the value 200809L.
> _POSIX_CHOWN_RESTRICTED
>   The use of chown() and fchown() is restricted to a process with appropriate privileges, and to changing the group ID of a file only to the effective group ID of the process or to one of its supplementary group IDs. This symbol shall be defined with a value other than -1.
> _POSIX_CLOCK_SELECTION
>   The implementation supports clock selection. This symbol shall always be set to the value 200809L.
> _POSIX_CPUTIME
>   [CPT]
>   The implementation supports the Process CPU-Time Clocks option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_FSYNC
>   [FSC]
>   The implementation supports the File Synchronization option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_IPV6
>   The implementation supports the IPv6 option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_JOB_CONTROL
>   The implementation supports job control. This symbol shall always be set to a value greater than zero.
> _POSIX_MAPPED_FILES
>   The implementation supports memory mapped Files. This symbol shall always be set to the value 200809L.
> _POSIX_MEMLOCK
>   [ML]
>   The implementation supports the Process Memory Locking option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_MEMLOCK_RANGE
>   [MLR]
>   The implementation supports the Range Memory Locking option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_MEMORY_PROTECTION
>   The implementation supports memory protection. This symbol shall always be set to the value 200809L.
> _POSIX_MESSAGE_PASSING
>   [MSG]
>   The implementation supports the Message Passing option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_MONOTONIC_CLOCK
>   [MON]
>   The implementation supports the Monotonic Clock option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_NO_TRUNC
>   Pathname components longer than {NAME_MAX} generate an error. This symbol shall be defined with a value other than -1.
> _POSIX_PRIORITIZED_IO
>   [PIO]
>   The implementation supports the Prioritized Input and Output option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_PRIORITY_SCHEDULING
>   [PS]
>   The implementation supports the Process Scheduling option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_RAW_SOCKETS
>   [RS]
>   The implementation supports the Raw Sockets option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_READER_WRITER_LOCKS
>   The implementation supports read-write locks. This symbol shall always be set to the value 200809L.
> _POSIX_REALTIME_SIGNALS
>   The implementation supports realtime signals. This symbol shall always be set to the value 200809L.
> _POSIX_REGEXP
>   The implementation supports the Regular Expression Handling option. This symbol shall always be set to a value greater than zero.
> _POSIX_SAVED_IDS
>   Each process has a saved set-user-ID and a saved set-group-ID. This symbol shall always be set to a value greater than zero.
> _POSIX_SEMAPHORES
>   The implementation supports semaphores. This symbol shall always be set to the value 200809L.
> _POSIX_SHARED_MEMORY_OBJECTS
>   [SHM]
>   The implementation supports the Shared Memory Objects option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_SHELL
>   The implementation supports the POSIX shell. This symbol shall always be set to a value greater than zero.
> _POSIX_SPAWN
>   [SPN]
>   The implementation supports the Spawn option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_SPIN_LOCKS
>   The implementation supports spin locks. This symbol shall always be set to the value 200809L.
> _POSIX_SPORADIC_SERVER
>   [SS]
>   The implementation supports the Process Sporadic Server option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_SYNCHRONIZED_IO
>   [SIO]
>   The implementation supports the Synchronized Input and Output option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_ATTR_STACKADDR
>   [TSA]
>   The implementation supports the Thread Stack Address Attribute option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_ATTR_STACKSIZE
>   [TSS]
>   The implementation supports the Thread Stack Size Attribute option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_CPUTIME
>   [TCT]
>   The implementation supports the Thread CPU-Time Clocks option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_PRIO_INHERIT
>   [TPI]
>   The implementation supports the Non-Robust Mutex Priority Inheritance option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_PRIO_PROTECT
>   [TPP]
>   The implementation supports the Non-Robust Mutex Priority Protection option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_PRIORITY_SCHEDULING
>   [TPS]
>   The implementation supports the Thread Execution Scheduling option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_PROCESS_SHARED
>   [TSH]
>   The implementation supports the Thread Process-Shared Synchronization option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_ROBUST_PRIO_INHERIT
>   [RPI]
>   The implementation supports the Robust Mutex Priority Inheritance option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_ROBUST_PRIO_PROTECT
>   [RPP]
>   The implementation supports the Robust Mutex Priority Protection option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREAD_SAFE_FUNCTIONS
>   The implementation supports thread-safe functions. This symbol shall always be set to the value 200809L.
> _POSIX_THREAD_SPORADIC_SERVER
>   [TSP]
>   The implementation supports the Thread Sporadic Server option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_THREADS
>   The implementation supports threads. This symbol shall always be set to the value 200809L.
> _POSIX_TIMEOUTS
>   The implementation supports timeouts. This symbol shall always be set to the value 200809L.
> _POSIX_TIMERS
>   The implementation supports timers. This symbol shall always be set to the value 200809L.
> _POSIX_TRACE
>   [OB TRC]
>   The implementation supports the Trace option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_TRACE_EVENT_FILTER
>   [OB TEF]
>   The implementation supports the Trace Event Filter option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_TRACE_INHERIT
>   [OB TRI]
>   The implementation supports the Trace Inherit option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_TRACE_LOG
>   [OB TRL]
>   The implementation supports the Trace Log option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_TYPED_MEMORY_OBJECTS
>   [TYM]
>   The implementation supports the Typed Memory Objects option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX_V6_ILP32_OFF32
>   [OB]
>   The implementation provides a C-language compilation environment with 32-bit int, long, pointer, and off_t types.
> _POSIX_V6_ILP32_OFFBIG
>   [OB]
>   The implementation provides a C-language compilation environment with 32-bit int, long, and pointer types and an off_t type using at least 64 bits.
> _POSIX_V6_LP64_OFF64
>   [OB]
>   The implementation provides a C-language compilation environment with 32-bit int and 64-bit long, pointer, and off_t types.
> _POSIX_V6_LPBIG_OFFBIG
>   [OB]
>   The implementation provides a C-language compilation environment with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
> _POSIX_V7_ILP32_OFF32
>   The implementation provides a C-language compilation environment with 32-bit int, long, pointer, and off_t types.
> _POSIX_V7_ILP32_OFFBIG
>   The implementation provides a C-language compilation environment with 32-bit int, long, and pointer types and an off_t type using at least 64 bits.
> _POSIX_V7_LP64_OFF64
>   The implementation provides a C-language compilation environment with 32-bit int and 64-bit long, pointer, and off_t types.
> _POSIX_V7_LPBIG_OFFBIG
>   The implementation provides a C-language compilation environment with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
> _POSIX2_C_BIND
>   The implementation supports the C-Language Binding option. This symbol shall always have the value 200809L.
> _POSIX2_C_DEV
>   [CD]
>   The implementation supports the C-Language Development Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_CHAR_TERM
>   The implementation supports the Terminal Characteristics option. The value of this symbol reported by sysconf() shall either be -1 or a value greater than zero.
> _POSIX2_FORT_DEV
>   [FD]
>   The implementation supports the FORTRAN Development Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_FORT_RUN
>   [FR]
>   The implementation supports the FORTRAN Runtime Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_LOCALEDEF
>   The implementation supports the creation of locales by the localedef utility. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_PBS
>   [OB BE]
>   The implementation supports the Batch Environment Services and Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_PBS_ACCOUNTING
>   [OB BE]
>   The implementation supports the Batch Accounting option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_PBS_CHECKPOINT
>   [OB BE]
>   The implementation supports the Batch Checkpoint/Restart option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_PBS_LOCATE
>   [OB BE]
>   The implementation supports the Locate Batch Job Request option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_PBS_MESSAGE
>   [OB BE]
>   The implementation supports the Batch Job Message Request option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_PBS_TRACK
>   [OB BE]
>   The implementation supports the Track Batch Job Request option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_SW_DEV
>   [SD]
>   The implementation supports the Software Development Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _POSIX2_UPE
>   [UP]
>   The implementation supports the User Portability Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall either be -1 or 200809L.
> _XOPEN_CRYPT
>   [XSI]
>   The implementation supports the X/Open Encryption Option Group.
> _XOPEN_ENH_I18N
>   The implementation supports the Issue 4, Version 2 Enhanced Internationalization Option Group. This symbol shall always be set to a value other than -1.
> _XOPEN_REALTIME
>   The implementation supports the X/Open Realtime Option Group.
> _XOPEN_REALTIME_THREADS
>   The implementation supports the X/Open Realtime Threads Option Group.
> _XOPEN_SHM
>   The implementation supports the Issue 4, Version 2 Shared Memory Option Group. This symbol shall always be set to a value other than -1.
> _XOPEN_STREAMS
>   [OB XSR]
>   The implementation supports the XSI STREAMS Option Group.
> _XOPEN_UNIX
>   [XSI]
>   The implementation supports the XSI option.
> _XOPEN_UUCP
>   [UU]
>   The implementation supports the UUCP Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by sysconf() shall be either -1 or 200809L.

> ##### Execution-Time Symbolic Constants

> If any of the following symbolic constants are not defined in the <unistd.h> header, the value shall vary depending on the file to which it is applied. If defined, they shall have values suitable for use in #if preprocessing directives.

> If any of the following symbolic constants are defined to have value -1 in the <unistd.h> header, the implementation shall not provide the option on any file; if any are defined to have a value other than -1 in the <unistd.h> header, the implementation shall provide the option on all applicable files.

> All of the following values, whether defined as symbolic constants in <unistd.h> or not, may be queried with respect to a specific file using the pathconf() or fpathconf() functions:

> _POSIX_ASYNC_IO
>   Asynchronous input or output operations may be performed for the associated file.
> _POSIX_PRIO_IO
>   Prioritized input or output operations may be performed for the associated file.
> _POSIX_SYNC_IO
>   Synchronized input or output operations may be performed for the associated file.

> If the following symbolic constants are defined in the <unistd.h> header, they apply to files and all paths in all file systems on the implementation:

> _POSIX_TIMESTAMP_RESOLUTION
>   The resolution in nanoseconds for all file timestamps.
> _POSIX2_SYMLINKS
>   Symbolic links can be created.

> ##### Constants for Functions

> The <unistd.h> header shall define NULL as described in <stddef.h>.

> The <unistd.h> header shall define the following symbolic constants for use with the access() function. The values shall be suitable for use in #if preprocessing directives.

> F_OK
>   Test for existence of file.
> R_OK
>   Test for read permission.
> W_OK
>   Test for write permission.
> X_OK
>   Test for execute (search) permission.

> The constants F_OK, R_OK, W_OK, and X_OK and the expressions R_OK|W_OK, R_OK|X_OK, and R_OK|W_OK|X_OK shall all have distinct values.

> The <unistd.h> header shall define the following symbolic constants for the confstr() function:

> _CS_PATH
>   This is the value for the PATH environment variable that finds all standard utilities.
> _CS_POSIX_V7_ILP32_OFF32_CFLAGS
>   If sysconf(_SC_V7_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the c99 utility to build an application using a programming model with 32-bit int, long, pointer, and off_t types.
> _CS_POSIX_V7_ILP32_OFF32_LDFLAGS
>   If sysconf(_SC_V7_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the c99 utility to build an application using a programming model with 32-bit int, long, pointer, and off_t types.
> _CS_POSIX_V7_ILP32_OFF32_LIBS
>   If sysconf(_SC_V7_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the c99 utility to build an application using a programming model with 32-bit int, long, pointer, and off_t types.
> _CS_POSIX_V7_ILP32_OFFBIG_CFLAGS
>   If sysconf(_SC_V7_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the c99 utility to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.
> _CS_POSIX_V7_ILP32_OFFBIG_LDFLAGS
>   If sysconf(_SC_V7_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the c99 utility to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.
> _CS_POSIX_V7_ILP32_OFFBIG_LIBS
>   If sysconf(_SC_V7_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the c99 utility to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.
> _CS_POSIX_V7_LP64_OFF64_CFLAGS
>   If sysconf(_SC_V7_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the c99 utility to build an application using a programming model with 32-bit int and 64-bit long, pointer, and off_t types.
> _CS_POSIX_V7_LP64_OFF64_LDFLAGS
>   If sysconf(_SC_V7_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the c99 utility to build an application using a programming model with 32-bit int and 64-bit long, pointer, and off_t types.
> _CS_POSIX_V7_LP64_OFF64_LIBS
>   If sysconf(_SC_V7_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the c99 utility to build an application using a programming model with 32-bit int and 64-bit long, pointer, and off_t types.
> _CS_POSIX_V7_LPBIG_OFFBIG_CFLAGS
>   If sysconf(_SC_V7_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the c99 utility to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
> _CS_POSIX_V7_LPBIG_OFFBIG_LDFLAGS
>   If sysconf(_SC_V7_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the c99 utility to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
> _CS_POSIX_V7_LPBIG_OFFBIG_LIBS
>   If sysconf(_SC_V7_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the c99 utility to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
> _CS_POSIX_V7_THREADS_CFLAGS
>   If sysconf(_SC_POSIX_THREADS) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the c99 utility to build a multi-threaded application. These flags are in addition to those associated with any of the other _CS_POSIX_V7_*_CFLAGS values used to specify particular type size programing environments.
> _CS_POSIX_V7_THREADS_LDFLAGS
>   If sysconf(_SC_POSIX_THREADS) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the c99 utility to build a multi-threaded application. These flags are in addition to those associated with any of the other _CS_POSIX_V7_*_LDFLAGS values used to specify particular type size programing environments.
> _CS_POSIX_V7_WIDTH_RESTRICTED_ENVS
>   This value is a <newline>-separated list of names of programming environments supported by the implementation in which the widths of the blksize_t, cc_t, mode_t, nfds_t, pid_t, ptrdiff_t, size_t, speed_t, ssize_t, suseconds_t, tcflag_t, wchar_t, and wint_t types are no greater than the width of type long. The format of each name shall be suitable for use with the getconf -v option.
> _CS_V7_ENV
>   This is the value that provides the environment variable information (other than that provided by _CS_PATH) that is required by the implementation to create a conforming environment, as described in the implementation's conformance documentation.

> [OB] The following symbolic constants are reserved for compatibility with Issue 6:

> _CS_POSIX_V6_ILP32_OFF32_CFLAGS
> _CS_POSIX_V6_ILP32_OFF32_LDFLAGS
> _CS_POSIX_V6_ILP32_OFF32_LIBS
> _CS_POSIX_V6_ILP32_OFFBIG_CFLAGS
> _CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS
> _CS_POSIX_V6_ILP32_OFFBIG_LIBS
> _CS_POSIX_V6_LP64_OFF64_CFLAGS
> _CS_POSIX_V6_LP64_OFF64_LDFLAGS
> _CS_POSIX_V6_LP64_OFF64_LIBS
> _CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS
> _CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS
> _CS_POSIX_V6_LPBIG_OFFBIG_LIBS
> _CS_POSIX_V6_WIDTH_RESTRICTED_ENVS
> _CS_V6_ENV

> The <unistd.h> header shall define SEEK_CUR, SEEK_END, and SEEK_SET as described in <stdio.h>.

> [XSI] The <unistd.h> header shall define the following symbolic constants as possible values for the function argument to the lockf() function:

> F_LOCK
>   Lock a section for exclusive use.
> F_TEST
>   Test section for locks by other processes.
> F_TLOCK
>   Test and lock a section for exclusive use.
> F_ULOCK
>   Unlock locked sections.

> The <unistd.h> header shall define the following symbolic constants for pathconf():

> _PC_2_SYMLINKS
> _PC_ALLOC_SIZE_MIN
> _PC_ASYNC_IO
> _PC_CHOWN_RESTRICTED
> _PC_FILESIZEBITS
> _PC_LINK_MAX
> _PC_MAX_CANON
> _PC_MAX_INPUT
> _PC_NAME_MAX
> _PC_NO_TRUNC
> _PC_PATH_MAX
> _PC_PIPE_BUF
> _PC_PRIO_IO
> _PC_REC_INCR_XFER_SIZE
> _PC_REC_MAX_XFER_SIZE
> _PC_REC_MIN_XFER_SIZE
> _PC_REC_XFER_ALIGN
> _PC_SYMLINK_MAX
> _PC_SYNC_IO
> _PC_TIMESTAMP_RESOLUTION
> _PC_VDISABLE

> The <unistd.h> header shall define the following symbolic constants for sysconf():

> _SC_2_C_BIND
> _SC_2_C_DEV
> _SC_2_CHAR_TERM
> _SC_2_FORT_DEV
> _SC_2_FORT_RUN
> _SC_2_LOCALEDEF
> _SC_2_PBS
> _SC_2_PBS_ACCOUNTING
> _SC_2_PBS_CHECKPOINT
> _SC_2_PBS_LOCATE
> _SC_2_PBS_MESSAGE
> _SC_2_PBS_TRACK
> _SC_2_SW_DEV
> _SC_2_UPE
> _SC_2_VERSION
> _SC_ADVISORY_INFO
> _SC_AIO_LISTIO_MAX
> _SC_AIO_MAX
> _SC_AIO_PRIO_DELTA_MAX
> _SC_ARG_MAX
> _SC_ASYNCHRONOUS_IO
> _SC_ATEXIT_MAX
> _SC_BARRIERS
> _SC_BC_BASE_MAX
> _SC_BC_DIM_MAX
> _SC_BC_SCALE_MAX
> _SC_BC_STRING_MAX
> _SC_CHILD_MAX
> _SC_CLK_TCK
> _SC_CLOCK_SELECTION
> _SC_COLL_WEIGHTS_MAX
> _SC_CPUTIME
> _SC_DELAYTIMER_MAX
> _SC_EXPR_NEST_MAX
> _SC_FSYNC
> _SC_GETGR_R_SIZE_MAX
> _SC_GETPW_R_SIZE_MAX
> _SC_HOST_NAME_MAX
> _SC_IOV_MAX
> _SC_IPV6
> _SC_JOB_CONTROL
> _SC_LINE_MAX
> _SC_LOGIN_NAME_MAX
> _SC_MAPPED_FILES
> _SC_MEMLOCK
> _SC_MEMLOCK_RANGE
> _SC_MEMORY_PROTECTION
> _SC_MESSAGE_PASSING
> _SC_MONOTONIC_CLOCK
> _SC_MQ_OPEN_MAX
> _SC_MQ_PRIO_MAX
> _SC_NGROUPS_MAX
> _SC_OPEN_MAX
> _SC_PAGE_SIZE
> _SC_PAGESIZE
> _SC_PRIORITIZED_IO
> _SC_PRIORITY_SCHEDULING
> _SC_RAW_SOCKETS
> _SC_RE_DUP_MAX
> _SC_READER_WRITER_LOCKS
> _SC_REALTIME_SIGNALS
> _SC_REGEXP
> _SC_RTSIG_MAX
> _SC_SAVED_IDS
> _SC_SEM_NSEMS_MAX
> _SC_SEM_VALUE_MAX
> _SC_SEMAPHORES
> _SC_SHARED_MEMORY_OBJECTS
> _SC_SHELL
> _SC_SIGQUEUE_MAX
> _SC_SPAWN
> _SC_SPIN_LOCKS
> _SC_SPORADIC_SERVER
> _SC_SS_REPL_MAX
> _SC_STREAM_MAX
> _SC_SYMLOOP_MAX
> _SC_SYNCHRONIZED_IO
> _SC_THREAD_ATTR_STACKADDR
> _SC_THREAD_ATTR_STACKSIZE
> _SC_THREAD_CPUTIME
> _SC_THREAD_DESTRUCTOR_ITERATIONS
> _SC_THREAD_KEYS_MAX
> _SC_THREAD_PRIO_INHERIT
> _SC_THREAD_PRIO_PROTECT
> _SC_THREAD_PRIORITY_SCHEDULING
> _SC_THREAD_PROCESS_SHARED
> _SC_THREAD_ROBUST_PRIO_INHERIT
> _SC_THREAD_ROBUST_PRIO_PROTECT
> _SC_THREAD_SAFE_FUNCTIONS
> _SC_THREAD_SPORADIC_SERVER
> _SC_THREAD_STACK_MIN
> _SC_THREAD_THREADS_MAX
> _SC_THREADS
> _SC_TIMEOUTS
> _SC_TIMER_MAX
> _SC_TIMERS
> _SC_TRACE
> _SC_TRACE_EVENT_FILTER
> _SC_TRACE_EVENT_NAME_MAX
> _SC_TRACE_INHERIT
> _SC_TRACE_LOG
> _SC_TRACE_NAME_MAX
> _SC_TRACE_SYS_MAX
> _SC_TRACE_USER_EVENT_MAX
> _SC_TTY_NAME_MAX
> _SC_TYPED_MEMORY_OBJECTS
> _SC_TZNAME_MAX
> _SC_V7_ILP32_OFF32
> _SC_V7_ILP32_OFFBIG
> _SC_V7_LP64_OFF64
> _SC_V7_LPBIG_OFFBIG
> [OB]
> _SC_V6_ILP32_OFF32
> _SC_V6_ILP32_OFFBIG
> _SC_V6_LP64_OFF64
> _SC_V6_LPBIG_OFFBIG
> _SC_VERSION
> _SC_XOPEN_CRYPT
> _SC_XOPEN_ENH_I18N
> _SC_XOPEN_REALTIME
> _SC_XOPEN_REALTIME_THREADS
> _SC_XOPEN_SHM
> _SC_XOPEN_STREAMS
> _SC_XOPEN_UNIX
> _SC_XOPEN_UUCP
> _SC_XOPEN_VERSION

> The two constants _SC_PAGESIZE and _SC_PAGE_SIZE may be defined to have the same value.

> The <unistd.h> header shall define the following symbolic constants for file streams:

> STDERR_FILENO
>   File number of stderr; 2.
> STDIN_FILENO
>   File number of stdin; 0.
> STDOUT_FILENO
>   File number of stdout; 1.

> The <unistd.h> header shall define the following symbolic constant for terminal special character handling:

> _POSIX_VDISABLE
>   This symbol shall be defined to be the value of a character that shall disable terminal special character handling as described in Special Control Characters. This symbol shall always be set to a value other than -1.

> ##### Type Definitions

> The <unistd.h> header shall define the size_t, ssize_t, uid_t, gid_t, off_t, and pid_t types as described in <sys/types.h>.

> The <unistd.h> header shall define the intptr_t type as described in <inttypes.h>.

> ##### Declarations

> The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

>     int          access(const char *, int);
>     unsigned     alarm(unsigned);
>     int          chdir(const char *);
>     int          chown(const char *, uid_t, gid_t);
>     int          close(int);
>     size_t       confstr(int, char *, size_t);
>     [XSI]
>     char        *crypt(const char *, const char *);

>     int          dup(int);

>     int          dup2(int, int);
>     void         _exit(int);
>     [XSI]
>     void         encrypt(char [64], int);

>     int          execl(const char *, const char *, ...);
>     int          execle(const char *, const char *, ...);
>     int          execlp(const char *, const char *, ...);
>     int          execv(const char *, char *const []);
>     int          execve(const char *, char *const [], char *const []);
>     int          execvp(const char *, char *const []);
>     int          faccessat(int, const char *, int, int);
>     int          fchdir(int);
>     int          fchown(int, uid_t, gid_t);
>     int          fchownat(int, const char *, uid_t, gid_t, int);
>     [SIO]
>     int          fdatasync(int);

>     int          fexecve(int, char *const [], char *const []);
>     pid_t        fork(void);
>     long         fpathconf(int, int);
>     [FSC]
>     int          fsync(int);

>     int          ftruncate(int, off_t);
>     char        *getcwd(char *, size_t);
>     gid_t        getegid(void);
>     uid_t        geteuid(void);
>     gid_t        getgid(void);
>     int          getgroups(int, gid_t []);
>     [XSI]
>     long         gethostid(void);

>     int          gethostname(char *, size_t);
>     char        *getlogin(void);
>     int          getlogin_r(char *, size_t);
>     int          getopt(int, char * const [], const char *);
>     pid_t        getpgid(pid_t);
>     pid_t        getpgrp(void);
>     pid_t        getpid(void);
>     pid_t        getppid(void);
>     pid_t        getsid(pid_t);
>     uid_t        getuid(void);
>     int          isatty(int);
>     int          lchown(const char *, uid_t, gid_t);
>     int          link(const char *, const char *);
>     int          linkat(int, const char *, int, const char *, int);
>     [XSI]
>     int          lockf(int, int, off_t);

>     off_t        lseek(int, off_t, int);
>     [XSI]
>     int          nice(int);

>     long         pathconf(const char *, int);
>     int          pause(void);
>     int          pipe(int [2]);
>     ssize_t      pread(int, void *, size_t, off_t);
>     ssize_t      pwrite(int, const void *, size_t, off_t);
>     ssize_t      read(int, void *, size_t);
>     ssize_t      readlink(const char *restrict, char *restrict, size_t);
>     ssize_t      readlinkat(int, const char *restrict, char *restrict, size_t);
>     int          rmdir(const char *);
>     int          setegid(gid_t);
>     int          seteuid(uid_t);
>     int          setgid(gid_t);

>     int          setpgid(pid_t, pid_t);
>     [OB XSI]
>     pid_t        setpgrp(void);

>     [XSI]
>     int          setregid(gid_t, gid_t);
>     int          setreuid(uid_t, uid_t);

>     pid_t        setsid(void);
>     int          setuid(uid_t);
>     unsigned     sleep(unsigned);
>     [XSI]
>     void         swab(const void *restrict, void *restrict, ssize_t);

>     int          symlink(const char *, const char *);
>     int          symlinkat(const char *, int, const char *);
>     [XSI]
>     void         sync(void);

>     long         sysconf(int);
>     pid_t        tcgetpgrp(int);
>     int          tcsetpgrp(int, pid_t);
>     int          truncate(const char *, off_t);
>     char        *ttyname(int);
>     int          ttyname_r(int, char *, size_t);
>     int          unlink(const char *);
>     int          unlinkat(int, const char *, int);
>     ssize_t      write(int, const void *, size_t);

> [OB] Implementations may also include the pthread_atfork() prototype as defined in <pthread.h>. Implementations may also include the ctermid() prototype as defined in <stdio.h>.

> The <unistd.h> header shall declare the following external variables:

>     extern char  *optarg;
>     extern int    opterr, optind, optopt;

The following sections are informative.

#### APPLICATION USAGE

> POSIX.1-2008 only describes the behavior of systems that claim conformance to it. However, application developers who want to write applications that adapt to other versions of this standard (or to systems that do not conform to any POSIX standard) may find it useful to code them so as to conditionally compile different code depending on the value of _POSIX_VERSION, for example:

>     #if _POSIX_VERSION >= 200112L
>     /* Use the newer function that copes with large files. */
>     off_t pos=ftello(fp);
>     #else
>     /* Either this is an old version of POSIX, or _POSIX_VERSION is
>        not even defined, so use the traditional function. */
>     long pos=ftell(fp);
>     #endif

> Earlier versions of POSIX.1-2008 and of the Single UNIX Specification can be identified by the following macros:

> POSIX.1-1988 standard
>   _POSIX_VERSION==198808L
> POSIX.1-1990 standard
>   _POSIX_VERSION==199009L
> ISO POSIX-1:1996 standard
>   _POSIX_VERSION==199506L
> Single UNIX Specification, Version 1
>   _XOPEN_UNIX and _XOPEN_VERSION==4
> Single UNIX Specification, Version 2
>   _XOPEN_UNIX and _XOPEN_VERSION==500
> ISO POSIX-1:2001 and Single UNIX Specification, Version 3
>   _POSIX_VERSION==200112L, plus (if the XSI option is supported) _XOPEN_UNIX and _XOPEN_VERSION==600

> POSIX.1-2008 does not make any attempt to define application binary interaction with the underlying operating system. However, application developers may find it useful to query _SC_VERSION at runtime via sysconf() to determine whether the current version of the operating system supports the necessary functionality as in the following program fragment:

>     if (sysconf(_SC_VERSION) < 200809L) {
>         fprintf(stderr, "POSIX.1-2008 system required, terminating \n");
>         exit(1);
>     }

> New applications should not use _XOPEN_SHM or _XOPEN_ENH_I18N.

#### RATIONALE

> As POSIX.1-2008 evolved, certain options became sufficiently standardized that it was concluded that simply requiring one of the option choices was simpler than retaining the option. However, for backwards-compatibility, the option flags (with required constant values) are retained.

> ##### Version Test Macros

> The standard developers considered altering the definition of _POSIX_VERSION and removing _SC_VERSION from the specification of sysconf() since the utility to an application was deemed by some to be minimal, and since the implementation of the functionality is potentially problematic. However, they recognized that support for existing application binaries is a concern to manufacturers, application developers, and the users of implementations conforming to POSIX.1-2008.

> While the example using _SC_VERSION in the APPLICATION USAGE section does not provide the greatest degree of imaginable utility to the application developer or user, it is arguably better than a core file or some other equally obscure result. (It is also possible for implementations to encode and recognize application binaries compiled in various POSIX.1-conforming environments, and modify the semantics of the underlying system to conform to the expectations of the application.) For the reasons outlined in the preceding paragraphs and in the APPLICATION USAGE section, the standard developers elected to retain the _POSIX_VERSION and _SC_VERSION functionality.

> ##### Compile-Time Symbolic Constants for System-Wide Options

> POSIX.1-2008 includes support in certain areas for the newly adopted policy governing options and stubs.

> This policy provides flexibility for implementations in how they support options. It also specifies how conforming applications can adapt to different implementations that support different sets of options. It allows the following:

> 1. If an implementation has no interest in supporting an option, it does not have to provide anything associated with that option beyond the announcement that it does not support it.

> 2. An implementation can support a partial or incompatible version of an option (as a non-standard extension) as long as it does not claim to support the option.

> 3. An application can determine whether the option is supported. A strictly conforming application must check this announcement mechanism before first using anything associated with the option.

> There is an important implication of this policy. POSIX.1-2008 cannot dictate the behavior of interfaces associated with an option when the implementation does not claim to support the option. In particular, it cannot require that a function associated with an unsupported option will fail if it does not perform as specified. However, this policy does not prevent a standard from requiring certain functions to always be present, but that they shall always fail on some implementations. The setpgid() function in the POSIX.1-1990 standard, for example, is considered appropriate.

> The POSIX standards include various options, and the C-language binding support for an option implies that the implementation must supply data types and function interfaces. An application must be able to discover whether the implementation supports each option.

> Any application must consider the following three cases for each option:

> 1. Option never supported.

>    The implementation advertises at compile time that the option will never be supported. In this case, it is not necessary for the implementation to supply any of the data types or function interfaces that are provided only as part of the option. The implementation might provide data types and functions that are similar to those defined by POSIX.1-2008, but there is no guarantee for any particular behavior.

> 2. Option always supported.

>    The implementation advertises at compile time that the option will always be supported. In this case, all data types and function interfaces shall be available and shall operate as specified.

> 3. Option might or might not be supported.

>    Some implementations might not provide a mechanism to specify support of options at compile time. In addition, the implementation might be unable or unwilling to specify support or non-support at compile time. In either case, any application that might use the option at runtime must be able to compile and execute. The implementation must provide, at compile time, all data types and function interfaces that are necessary to allow this. In this situation, there must be a mechanism that allows the application to query, at runtime, whether the option is supported. If the application attempts to use the option when it is not supported, the result is unspecified unless explicitly specified otherwise in POSIX.1-2008.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> <inttypes.h>, <limits.h>, <stddef.h>, <stdio.h>, <sys/socket.h>, <sys/types.h>, <termios.h>, <wctype.h>

> XSH access, alarm, chown, close, confstr, crypt, ctermid, dup, _Exit, encrypt, exec, fchdir, fchown, fdatasync, fork, fpathconf, fsync, ftruncate, getcwd, getegid, geteuid, getgid, getgroups, gethostid, gethostname, getlogin, getopt, getpgid, getpgrp, getpid, getppid, getsid, getuid, isatty, lchown, link, lockf, lseek, nice, pause, pipe, read, readlink, rmdir, setegid, seteuid, setgid, setpgid, setpgrp, setregid, setreuid, setsid, setuid, sleep, swab, symlink, sync, sysconf, tcgetpgrp, tcsetpgrp, truncate, ttyname, unlink, write

#### CHANGE HISTORY

> First released in Issue 1. Derived from Issue 1 of the SVID.

#### Issue 5

> The DESCRIPTION is updated for alignment with the POSIX Realtime Extension and the POSIX Threads Extension.

> The symbolic constants _XOPEN_REALTIME and _XOPEN_REALTIME_THREADS are added. _POSIX2_C_BIND, _XOPEN_ENH_I18N, and _XOPEN_SHM must now be set to a value other than -1 by a conforming implementation.

> Large File System extensions are added.

> The type of the argument to sbrk() is changed from int to intptr_t.

> _XBS_ constants are added to the list of constants for Options and Option Groups, to the list of constants for the confstr() function, and to the list of constants to the sysconf() function. These are all marked EX.

#### Issue 6

> _POSIX2_C_VERSION is removed.

> The Open Group Corrigendum U026/4 is applied, adding the prototype for fdatasync().

> The Open Group Corrigendum U026/1 is applied, adding the symbols _SC_XOPEN_LEGACY, _SC_XOPEN_REALTIME, and _SC_XOPEN_REALTIME_THREADS.

> The symbols _XOPEN_STREAMS and _SC_XOPEN_STREAMS are added to support the XSI STREAMS Option Group.

> Text in the DESCRIPTION relating to conformance requirements is moved elsewhere in IEEE Std 1003.1-2001.

> The LEGACY symbol _SC_PASS_MAX is removed.

> The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

> - The _CS_POSIX_* and _CS_XBS5_* constants are added for the confstr() function.

> - The _SC_XBS5_* constants are added for the sysconf() function.

> - The symbolic constants F_ULOCK, F_LOCK, F_TLOCK, and F_TEST are added.

> - The uid_t, gid_t, off_t, pid_t, and useconds_t types are mandated.

> The gethostname() prototype is added for sockets.

> A new section is added for System-Wide Options.

> Function prototypes for setegid() and seteuid() are added.

> Option symbolic constants are added for _POSIX_ADVISORY_INFO, _POSIX_CPUTIME, _POSIX_SPAWN, _POSIX_SPORADIC_SERVER, _POSIX_THREAD_CPUTIME, _POSIX_THREAD_SPORADIC_SERVER, and _POSIX_TIMEOUTS, and pathconf() variables are added for _PC_ALLOC_SIZE_MIN, _PC_REC_INCR_XFER_SIZE, _PC_REC_MAX_XFER_SIZE, _PC_REC_MIN_XFER_SIZE, and _PC_REC_XFER_ALIGN for alignment with IEEE Std 1003.1d-1999.

> The following are added for alignment with IEEE Std 1003.1j-2000:

> - Option symbolic constants _POSIX_BARRIERS, _POSIX_CLOCK_SELECTION, _POSIX_MONOTONIC_CLOCK, _POSIX_READER_WRITER_LOCKS, _POSIX_SPIN_LOCKS, and _POSIX_TYPED_MEMORY_OBJECTS

> - sysconf() variables _SC_BARRIERS, _SC_CLOCK_SELECTION, _SC_MONOTONIC_CLOCK, _SC_READER_WRITER_LOCKS, _SC_SPIN_LOCKS, and _SC_TYPED_MEMORY_OBJECTS

> The _SC_XBS5 macros associated with the ISO/IEC 9899:1990 standard are marked LEGACY, and new equivalent _SC_V6 macros associated with the ISO/IEC 9899:1999 standard are introduced.

> The getwd() function is marked LEGACY.

> The restrict keyword is added to the prototypes for readlink() and swab().

> Constants for options are now harmonized, so when supported they take the year of approval of IEEE Std 1003.1-2001 as the value.

> The following are added for alignment with IEEE Std 1003.1q-2000:

> - Optional symbolic constants _POSIX_TRACE, _POSIX_TRACE_EVENT_FILTER, _POSIX_TRACE_LOG, and _POSIX_TRACE_INHERIT

> - The sysconf() symbolic constants _SC_TRACE, _SC_TRACE_EVENT_FILTER, _SC_TRACE_LOG, and _SC_TRACE_INHERIT

> The brk() and sbrk() LEGACY functions are removed.

> The Open Group Base Resolution bwg2001-006 is applied, which reworks the XSI versioning information.

> The Open Group Base Resolution bwg2001-008 is applied, changing the namelen parameter for gethostname() from socklen_t to size_t.

> IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/2 is applied, changing ``Thread Stack Address Size'' to ``Thread Stack Size Attribute''.

> IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/20 is applied, adding the _POSIX_IPV6, _SC_V6, and _SC_RAW_SOCKETS symbols.

> IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/21 is applied, correcting the description in ``Constants for Functions'' for the _CS_POSIX_V6_LP64_OFF64_CFLAGS, _CS_POSIX_V6_LP64_OFF64_LDFLAGS, and _CS_POSIX_V6_LP64_OFF64_LIBS symbols.

> IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/22 is applied, removing the shading for the _PC* and _SC* constants, since these are mandatory on all implementations.

> IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/23 is applied, adding the _PC_SYMLINK_MAX and _SC_SYMLOOP_MAX constants.

> IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/24 is applied, correcting the shading and margin code for the fsync() function.

> IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/25 is applied, adding the following text to the APPLICATION USAGE section: ``New applications should not use _XOPEN_SHM or _XOPEN_ENH_I18N.''.

> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/29 is applied, clarifying the requirements for when constants for Options and Option Groups can be defined or undefined.

> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/30 is applied, changing the _V6_ILP32_OFF32, _V6_ILP32_OFFBIG, _V6_LP64_OFF64, and _V6_LPBIG_OFFBIG symbols to _POSIX_V6_ILP32_OFF32, _POSIX_V6_ILP32_OFFBIG, _POSIX_V6_LP64_OFF64, and _POSIX_V6_LPBIG_OFFBIG, respectively. This is for consistency with the sysconf() and c99 reference pages.

> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/31 is applied, adding that the format of names of programming environments can be obtained using the getconf -v option.

> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/32 is applied, deleting the _SC_FILE_LOCKING, _SC_2_C_VERSION, and _SC_XOPEN_XCU_VERSION constants.

> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/33 is applied, adding _SC_SS_REPL_MAX, _SC_TRACE_EVENT_NAME_MAX, _SC_TRACE_NAME_MAX, _SC_TRACE_SYS_MAX, and _SC_TRACE_USER_EVENT_MAX to the list of symbolic constants for sysconf().

> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/34 is applied, updating the prototype for the symlink() function to match that in the System Interfaces volume of IEEE Std 1003.1-2001.

> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/35 is applied, adding _PC_2_SYMLINKS to the symbolic constants list for pathconf(). This corresponds to the definition of POSIX2_SYMLINKS in the Shell and Utilities volume of IEEE Std 1003.1-2001.

#### Issue 7

> Austin Group Interpretations 1003.1-2001 #026 and #047 are applied.

> Austin Group Interpretation 1003.1-2001 #166 is applied to permit an additional compiler flag to enable threads.

> Austin Group Interpretation 1003.1-2001 #178 is applied, clarifying the values allowed for _POSIX2_CHAR_TERM.

> SD5-XBD-ERN-41 is applied, adding the _POSIX2_SYMLINKS constant.

> SD5-XBD-ERN-76 and SD5-XBD-ERN-77 are applied.

> Symbols to support the UUCP Utilities option are added.

> The variables for the supported programming environments are updated to be V7.

> The LEGACY and obsolescent symbols are removed.

> The faccessat(), fchownat(), fexecve(), linkat(), readlinkat(), symlinkat(), and unlinkat() functions are added from The Open Group Technical Standard, 2006, Extended API Set Part 2.

> The _POSIX_TRACE* constants from the Trace option are marked obsolescent.

> The _POSIX2_PBS* constants from the Batch Environment Services and Utilities option are marked obsolescent.

> Functionality relating to the Asynchronous Input and Output, Barriers, Clock Selection, Memory Mapped Files, Memory Protection, Realtime Signals Extension, Semaphores, Spin Locks, Threads, Timeouts, and Timers options is moved to the Base.

> Functionality relating to the Thread Priority Protection and Thread Priority Inheritance options is changed to be Non-Robust Mutex or Robust Mutex Priority Protection and Non-Robust Mutex or Robust Mutex Priority Inheritance, respectively.

> This reference page is clarified with respect to macros and symbolic constants.

> Changes are made related to support for finegrained timestamps and the _POSIX_TIMESTAMP_RESOLUTION constant is added.

> The _SC_THREAD_ROBUST_PRIO_INHERIT and _SC_THREAD_ROBUST_PRIO_PROTECT symbolic constants are added.

> POSIX.1-2008, Technical Corrigendum 1, XBD/TC1-2008/0078 [311], XBD/TC1-2008/0079 [209], and XBD/TC1-2008/0080 [360] are applied.

End of informative text.

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