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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. Theactual values of the constants are unspecified except as shown. The contents of this header are shown below.

Version Test Macros

The following symbolic constants shall be defined:

_POSIX_VERSION

Integer value indicating version of IEEE Std 1003.1 (C-language binding) to which the implementation conforms. Forimplementations conforming to IEEE Std 1003.1-2001, the value shall be 200112L.

_POSIX2_VERSION

Integer value indicating version of the Shell and Utilities volume of IEEE Std 1003.1 to which the implementationconforms. For implementations conforming to IEEE Std 1003.1-2001, the value shall be 200112L.

The following symbolic constant shall be defined only if the implementation supports the XSI option; seeXSI Conformance.

_XOPEN_VERSION

^[XSI]
Integer value indicating version of the X/Open Portability Guide to which the implementation conforms. The value shall be 600.

Constants for Options and Option Groups

The following symbolic constants, if defined in<unistd.h>, shall have a value of -1, 0, or greater, unlessotherwise specified below. If these are undefined, thefpathconf(),pathconf(), orsysconf() functions can beused to determine whether the option is provided for a particular invocation of the application.

If a symbolic constant is defined with the value -1, the option is not supported. Headers, data types, and function interfacesrequired only for the option need not be supplied. An application that attempts to use anything associated only with the option isconsidered to be requiring an extension.

If a symbolic constant is defined with a value greater than zero, the option shall always be supported when the application isexecuted. All headers, data types, and functions shall be present and shall operate as specified.

If a symbolic constant is defined with the value zero, all headers, data types, and functions shall be present. The applicationcan check at runtime to see whether the option is supported by callingfpathconf(),pathconf(), orsysconf() with the indicatedname parameter.

Unless explicitly specified otherwise, the behavior of functions associated with an unsupported option is unspecified, and anapplication that uses such functions without first checkingfpathconf(),pathconf(), orsysconf() is considered to berequiring an extension.

For conformance requirements, refer toConformance.

_POSIX_ADVISORY_INFO

^[ADV]
The implementation supports the Advisory Information option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_ASYNCHRONOUS_IO

^[AIO]
The implementation supports the Asynchronous Input and Output option. If this symbol is defined in<unistd.h>, itshall be defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or 200112L.

_POSIX_BARRIERS

^[BAR]
The implementation supports the Barriers option. If this symbol is defined in<unistd.h>, it shall be defined to be-1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1or 200112L.

_POSIX_CHOWN_RESTRICTED

The use ofchown() andfchown() isrestricted to a process with appropriate privileges, and to changing the group ID of a file only to the effective group ID of theprocess or to one of its supplementary group IDs. This symbol shall either be undefined or defined with a value other than -1.

_POSIX_CLOCK_SELECTION

^[CS]
The implementation supports the Clock Selection option. If this symbol is defined in<unistd.h>, it shall be definedto be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall eitherbe -1 or 200112L.

_POSIX_CPUTIME

^[CPT]
The implementation supports the Process CPU-Time Clocks option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_FSYNC

^[FSC]
The implementation supports the File Synchronization option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_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 200112L. The value of this symbol reported bysysconf() shall either be -1 or200112L.

_POSIX_JOB_CONTROL

The implementation supports job control. This symbol shall always be set to a value greater than zero.

_POSIX_MAPPED_FILES

^[MF]
The implementation supports the Memory Mapped Files option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_MEMLOCK

^[ML]
The implementation supports the Process Memory Locking option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_MEMLOCK_RANGE

^[MR]
The implementation supports the Range Memory Locking option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_MEMORY_PROTECTION

^[MPR]
The implementation supports the Memory Protection option. If this symbol is defined in<unistd.h>, it shall be definedto be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall eitherbe -1 or 200112L.

_POSIX_MESSAGE_PASSING

^[MSG]
The implementation supports the Message Passing option. If this symbol is defined in<unistd.h>, it shall be definedto be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall eitherbe -1 or 200112L.

_POSIX_MONOTONIC_CLOCK

^[MON]
The implementation supports the Monotonic Clock option. If this symbol is defined in<unistd.h>, it shall be definedto be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall eitherbe -1 or 200112L.

_POSIX_NO_TRUNC

Pathname components longer than {NAME_MAX} generate an error. This symbol shall either be undefined or defined with a value otherthan -1.

_POSIX_PRIORITIZED_IO

^[PIO]
The implementation supports the Prioritized Input and Output option. If this symbol is defined in<unistd.h>, it shallbe defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_PRIORITY_SCHEDULING

^[PS]
The implementation supports the Process Scheduling option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_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 200112L. The value of this symbol reported bysysconf() shall either be -1or 200112L.

_POSIX_READER_WRITER_LOCKS

^[THR]
The implementation supports the Read-Write Locks option. This is always set to a value greater than zero if the Threads option issupported. If this symbol is defined in<unistd.h>, it shall be defined to be -1, 0, or 200112L. The value of thissymbol reported bysysconf() shall either be -1 or 200112L.

_POSIX_REALTIME_SIGNALS

^[RTS]
The implementation supports the Realtime Signals Extension option. If this symbol is defined in<unistd.h>, it shallbe defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_REGEXP

The implementation supports the Regular Expression Handling option. This symbol shall always be set to a value greater thanzero.

_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

^[SEM]
The implementation supports the Semaphores option. If this symbol is defined in<unistd.h>, it shall be defined to be-1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1or 200112L.

_POSIX_SHARED_MEMORY_OBJECTS

^[SHM]
The implementation supports the Shared Memory Objects option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_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 200112L. The value of this symbol reported bysysconf() shall either be -1 or200112L.

_POSIX_SPIN_LOCKS

^[SPI]
The implementation supports the Spin Locks option. If this symbol is defined in<unistd.h>, it shall be defined to be-1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1or 200112L.

_POSIX_SPORADIC_SERVER

^[SS]
The implementation supports the Process Sporadic Server option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_SYNCHRONIZED_IO

^[SIO]
The implementation supports the Synchronized Input and Output option. If this symbol is defined in<unistd.h>, itshall be defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or 200112L.

_POSIX_THREAD_ATTR_STACKADDR

^[TSA]
The implementation supports the Thread Stack Address Attribute option. If this symbol is defined in<unistd.h>, itshall be defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or 200112L.

_POSIX_THREAD_ATTR_STACKSIZE

^[TSS]
The implementation supports the Thread Stack Size Attribute option. If this symbol is defined in<unistd.h>, it shallbe defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_THREAD_CPUTIME

^[TCT]
The implementation supports the Thread CPU-Time Clocks option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_THREAD_PRIO_INHERIT

^[TPI]
The implementation supports the Thread Priority Inheritance option. If this symbol is defined in<unistd.h>, it shallbe defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_THREAD_PRIO_PROTECT

^[TPP]
The implementation supports the Thread Priority Protection option. If this symbol is defined in<unistd.h>, it shallbe defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_THREAD_PRIORITY_SCHEDULING

^[TPS]
The implementation supports the Thread Execution Scheduling option. If this symbol is defined in<unistd.h>, it shallbe defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_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 200112L. The value of this symbol reported bysysconf() shall either be -1 or 200112L.

_POSIX_THREAD_SAFE_FUNCTIONS

^[TSF]
The implementation supports the Thread-Safe Functions option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_THREAD_SPORADIC_SERVER

^[TSP]
The implementation supports the Thread Sporadic Server option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_THREADS

^[THR]
The implementation supports the Threads option. If this symbol is defined in<unistd.h>, it shall be defined to be -1,0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or200112L.

_POSIX_TIMEOUTS

^[TMO]
The implementation supports the Timeouts option. If this symbol is defined in<unistd.h>, it shall be defined to be-1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1or 200112L.

_POSIX_TIMERS

^[TMR]
The implementation supports the Timers option. If this symbol is defined in<unistd.h>, it shall be defined to be -1,0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or200112L.

_POSIX_TRACE

^[TRC]
The implementation supports the Trace option. If this symbol is defined in<unistd.h>, it shall be defined to be -1,0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or200112L.

_POSIX_TRACE_EVENT_FILTER

^[TEF]
The implementation supports the Trace Event Filter option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_TRACE_INHERIT

^[TRI]
The implementation supports the Trace Inherit option. If this symbol is defined in<unistd.h>, it shall be defined tobe -1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be-1 or 200112L.

_POSIX_TRACE_LOG

^[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 200112L. The value of this symbol reported bysysconf() shall either be -1or 200112L.

_POSIX_TYPED_MEMORY_OBJECTS

^[TYM]
The implementation supports the Typed Memory Objects option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_VDISABLE

This symbol shall be defined to be the value of a character that shall disable terminal special character handling as described in<termios.h>. This symbol shall always be set to a value other than -1.

_POSIX2_C_BIND

The implementation supports the C-Language Binding option. This symbol shall always have the value 200112L.

_POSIX2_C_DEV

^[CD]
The implementation supports the C-Language Development Utilities option. If this symbol is defined in<unistd.h>, itshall be defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or 200112L.

_POSIX2_CHAR_TERM

The implementation supports at least one terminal type.

_POSIX2_FORT_DEV

^[FD]
The implementation supports the FORTRAN Development Utilities option. If this symbol is defined in<unistd.h>, itshall be defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or 200112L.

_POSIX2_FORT_RUN

^[FR]
The implementation supports the FORTRAN Runtime Utilities option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX2_LOCALEDEF

The implementation supports the creation of locales by thelocaledef utility. Ifthis symbol is defined in<unistd.h>, it shall be defined to be -1, 0, or 200112L. The value of this symbol reportedbysysconf() shall either be -1 or 200112L.

_POSIX2_PBS

^[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 200112L. The value of this symbol reported bysysconf() shall either be -1 or 200112L.

_POSIX2_PBS_ACCOUNTING

^[BE]
The implementation supports the Batch Accounting option. If this symbol is defined in<unistd.h>, it shall be definedto be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall eitherbe -1 or 200112L.

_POSIX2_PBS_CHECKPOINT

^[BE]
The implementation supports the Batch Checkpoint/Restart option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX2_PBS_LOCATE

^[BE]
The implementation supports the Locate Batch Job Request option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX2_PBS_MESSAGE

^[BE]
The implementation supports the Batch Job Message Request option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX2_PBS_TRACK

^[BE]
The implementation supports the Track Batch Job Request option. If this symbol is defined in<unistd.h>, it shall bedefined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX2_SW_DEV

^[SD]
The implementation supports the Software Development Utilities option. If this symbol is defined in<unistd.h>, itshall be defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf() shall either be -1 or 200112L.

_POSIX2_UPE

^[UP]
The implementation supports the User Portability Utilities option. If this symbol is defined in<unistd.h>, it shallbe defined to be -1, 0, or 200112L. The value of this symbol reported bysysconf()shall either be -1 or 200112L.

_POSIX_V6_ILP32_OFF32

The implementation provides a C-language compilation environment with 32-bitint,long,pointer, andoff_t types.

_POSIX_V6_ILP32_OFFBIG

The implementation provides a C-language compilation environment with 32-bitint,long, andpointer types andanoff_t type using at least 64 bits.

_POSIX_V6_LP64_OFF64

The implementation provides a C-language compilation environment with 32-bitint and 64-bitlong,pointer, andoff_t types.

_POSIX_V6_LPBIG_OFFBIG

The implementation provides a C-language compilation environment with anint type using at least 32 bits andlong,pointer, andoff_t types using at least 64 bits.

_XBS5_ILP32_OFF32 (LEGACY)

^[XSI]
The implementation provides a C-language compilation environment with 32-bitint,long,pointer, andoff_t types.

_XBS5_ILP32_OFFBIG (LEGACY)

^[XSI]
The implementation provides a C-language compilation environment with 32-bitint,long, andpointer types andanoff_t type using at least 64 bits.

_XBS5_LP64_OFF64 (LEGACY)

^[XSI]
The implementation provides a C-language compilation environment with 32-bitint and 64-bitlong,pointer, andoff_t types.

_XBS5_LPBIG_OFFBIG (LEGACY)

^[XSI]
The implementation provides a C-language compilation environment with anint type using at least 32 bits andlong,pointer, andoff_t types using at least 64 bits.

_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 avalue other than -1.

_XOPEN_LEGACY

The implementation supports the Legacy Option Group.

_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 otherthan -1.

_XOPEN_STREAMS

The implementation supports the XSI STREAMS Option Group.

_XOPEN_UNIX

^[XSI]
The implementation supports the XSI extension.

Execution-Time Symbolic Constants

If any of the following constants are not defined in the<unistd.h> header, the value shall vary depending on thefile to which it is applied.

If any of the following constants are defined to have value -1 in the<unistd.h> header, the implementation shallnot provide the option on any file; if any are defined to have a value other than -1 in the<unistd.h> header, theimplementation shall provide the option on all applicable files.

All of the following constants, whether defined in<unistd.h> or not, may be queried with respect to a specificfile using thepathconf() orfpathconf() 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.

Constants for Functions

The following symbolic constant shall be defined:

NULL

Null pointer

The following symbolic constants shall be defined for theaccess() function:

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 expressionsR_OK|W_OK,R_OK|X_OK, andR_OK|W_OK|X_OK shall all have distinct values.

The following symbolic constants shall be defined for theconfstr() function:

_CS_PATH

This is the value for thePATH environment variable that finds all standard utilities.

_CS_POSIX_V6_ILP32_OFF32_CFLAGS

Ifsysconf(_SC_V6_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set ofinitial options to be given to thec99 utility to build an application using aprogramming model with 32-bitint,long,pointer, andoff_t types.

_CS_POSIX_V6_ILP32_OFF32_LDFLAGS

Ifsysconf(_SC_V6_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set offinal options to be given to thec99 utility to build an application using a programmingmodel with 32-bitint,long,pointer, andoff_t types.

_CS_POSIX_V6_ILP32_OFF32_LIBS

Ifsysconf(_SC_V6_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set oflibraries to be given to thec99 utility to build an application using a programmingmodel with 32-bitint,long,pointer, andoff_t types.

_CS_POSIX_V6_ILP32_OFFBIG_CFLAGS

Ifsysconf(_SC_V6_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set ofinitial options to be given to thec99 utility to build an application using aprogramming model with 32-bitint,long, andpointer types, and anoff_t type using at least 64bits.

_CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS

Ifsysconf(_SC_V6_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set offinal options to be given to thec99 utility to build an application using a programmingmodel with 32-bitint,long, andpointer types, and anoff_t type using at least 64 bits.

_CS_POSIX_V6_ILP32_OFFBIG_LIBS

Ifsysconf(_SC_V6_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set oflibraries to be given to thec99 utility to build an application using a programmingmodel with 32-bitint,long, andpointer types, and anoff_t type using at least 64 bits.

_CS_POSIX_V6_LP64_OFF64_CFLAGS

Ifsysconf(_SC_V6_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set ofinitial options to be given to thec99 utility to build an application using aprogramming model with 32-bitint and 64-bitlong,pointer, andoff_t types.

_CS_POSIX_V6_LP64_OFF64_LDFLAGS

Ifsysconf(_SC_V6_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set offinal options to be given to thec99 utility to build an application using a programmingmodel with 32-bitint and 64-bitlong,pointer, andoff_t types.

_CS_POSIX_V6_LP64_OFF64_LIBS

Ifsysconf(_SC_V6_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set oflibraries to be given to thec99 utility to build an application using a programmingmodel with 32-bitint and 64-bitlong,pointer, andoff_t types.

_CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS

Ifsysconf(_SC_V6_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set ofinitial options to be given to thec99 utility to build an application using aprogramming model with anint type using at least 32 bits andlong,pointer, andoff_t types using atleast 64 bits.

_CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS

Ifsysconf(_SC_V6_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set offinal options to be given to thec99 utility to build an application using a programmingmodel with anint type using at least 32 bits andlong,pointer, andoff_t types using at least 64bits.

_CS_POSIX_V6_LPBIG_OFFBIG_LIBS

Ifsysconf(_SC_V6_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set oflibraries to be given to thec99 utility to build an application using a programmingmodel with anint type using at least 32 bits andlong,pointer, andoff_t types using at least 64bits.

_CS_POSIX_V6_WIDTH_RESTRICTED_ENVS

This value is a <newline>-separated list of names of programming environments supported by the implementation in which thewidths of theblksize_t,cc_t,mode_t,nfds_t,pid_t,ptrdiff_t,size_t,speed_t,ssize_t,suseconds_t,tcflag_t,useconds_t,wchar_t, andwint_t types areno greater than the width of typelong. The format of each name shall be suitable for use with thegetconf-v option.

^[XSI]The following symbolic constants are reserved for compatibility with Issue 5:

_CS_XBS5_ILP32_OFF32_CFLAGS (LEGACY)
_CS_XBS5_ILP32_OFF32_LDFLAGS (LEGACY)
_CS_XBS5_ILP32_OFF32_LIBS (LEGACY)
_CS_XBS5_ILP32_OFF32_LINTFLAGS (LEGACY)
_CS_XBS5_ILP32_OFFBIG_CFLAGS (LEGACY)
_CS_XBS5_ILP32_OFFBIG_LDFLAGS (LEGACY)
_CS_XBS5_ILP32_OFFBIG_LIBS (LEGACY)
_CS_XBS5_ILP32_OFFBIG_LINTFLAGS (LEGACY)
_CS_XBS5_LP64_OFF64_CFLAGS (LEGACY)
_CS_XBS5_LP64_OFF64_LDFLAGS (LEGACY)
_CS_XBS5_LP64_OFF64_LIBS (LEGACY)
_CS_XBS5_LP64_OFF64_LINTFLAGS (LEGACY)
_CS_XBS5_LPBIG_OFFBIG_CFLAGS (LEGACY)
_CS_XBS5_LPBIG_OFFBIG_LDFLAGS (LEGACY)
_CS_XBS5_LPBIG_OFFBIG_LIBS (LEGACY)
_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS (LEGACY)

The following symbolic constants shall be defined for thelseek() andfcntl() functions and shall have distinct values:

SEEK_CUR

Set file offset to current plusoffset.

SEEK_END

Set file offset to EOF plusoffset.

SEEK_SET

Set file offset tooffset.

The following symbolic constants shall be defined as possible values for thefunction argument to thelockf() 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 following symbolic constants shall be defined forpathconf():

_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_MIN_XFER_SIZE
_PC_REC_XFER_ALIGN
_PC_SYMLINK_MAX
_PC_SYNC_IO
_PC_VDISABLE

The following symbolic constants shall be defined forsysconf():

_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_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_V6_ILP32_OFF32
_SC_V6_ILP32_OFFBIG
_SC_V6_LP64_OFF64
_SC_V6_LPBIG_OFFBIG
_SC_VERSION
_SC_XBS5_ILP32_OFF32 (LEGACY)
_SC_XBS5_ILP32_OFFBIG (LEGACY)
_SC_XBS5_LP64_OFF64 (LEGACY)
_SC_XBS5_LPBIG_OFFBIG (LEGACY)
_SC_XOPEN_CRYPT
_SC_XOPEN_ENH_I18N
_SC_XOPEN_LEGACY
_SC_XOPEN_REALTIME
_SC_XOPEN_REALTIME_THREADS
_SC_XOPEN_SHM
_SC_XOPEN_STREAMS
_SC_XOPEN_UNIX
_SC_XOPEN_VERSION

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

The following symbolic constants shall be defined for file streams:

STDERR_FILENO

File number ofstderr; 2.

STDIN_FILENO

File number ofstdin; 0.

STDOUT_FILENO

File number ofstdout; 1.

Type Definitions

Thesize_t,ssize_t,uid_t,gid_t,off_t,pid_t, anduseconds_t types shall bedefined as described in<sys/types.h>.

Theintptr_t type shall be defined 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 *);char        *ctermid(char *);int          dup(int);
int          dup2(int, 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 []);void        _exit(int);int          fchown(int, uid_t, gid_t);[XSI]int          fchdir(int);[SIO]int          fdatasync(int);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 *);[XSI]pid_t        getpgid(pid_t);pid_t        getpgrp(void);pid_t        getpid(void);pid_t        getppid(void);[XSI]pid_t        getsid(pid_t);uid_t        getuid(void);[XSI]char        *getwd(char *); (LEGACY)int          isatty(int);[XSI]int          lchown(const char *, uid_t, gid_t);int          link(const char *, const char *);[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]);[XSI]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);int          rmdir(const char *);int          setegid(gid_t);int          seteuid(uid_t);int          setgid(gid_t);
int          setpgid(pid_t, pid_t);[XSI]pid_t        setpgrp(void);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 *);[XSI]void         sync(void);long         sysconf(int);pid_t        tcgetpgrp(int);int          tcsetpgrp(int, pid_t);[XSI]int          truncate(const char *, off_t);char        *ttyname(int);int          ttyname_r(int, char *, size_t);[XSI]useconds_t   ualarm(useconds_t, useconds_t);int          unlink(const char *);[XSI]int          usleep(useconds_t);pid_t        vfork(void);ssize_t      write(int, const void *, size_t);

Implementations may also include thepthread_atfork() prototype as definedin<pthread.h>.

The following external variables shall be declared:

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

APPLICATION USAGE

IEEE Std 1003.1-2001 only describes the behavior of systems that claim conformance to it. However, applicationdevelopers who want to write applications that adapt to other versions of IEEE Std 1003.1 (or to systems that do notconform to any POSIX standard) may find it useful to code them so as to conditionally compile different code depending on the valueof _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 IEEE Std 1003.1 and of the Single UNIX Specification can be identified by the followingmacros:

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

IEEE Std 1003.1-2001 does not make any attempt to define application binary interaction with the underlying operatingsystem. However, application developers may find it useful to query _SC_VERSION at runtime viasysconf() to determine whether the current version of the operating system supports thenecessary functionality as in the following program fragment:

if (sysconf(_SC_VERSION) < 200112L) {    fprintf(stderr, "POSIX.1-2001 system required, terminating \n");    exit(1);}

New applications should not use _XOPEN_SHM or _XOPEN_ENH_I18N.

RATIONALE

As IEEE Std 1003.1-2001 evolved, certain options became sufficiently standardized that it was concluded that simplyrequiring 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 ofsysconf() since the utility to an application was deemed by some to be minimal, andsince the implementation of the functionality is potentially problematic. However, they recognized that support for existingapplication binaries is a concern to manufacturers, application developers, and the users of implementations conforming toIEEE Std 1003.1-2001.

While the example using _SC_VERSION in the APPLICATION USAGE section does not provide the greatest degree of imaginable utilityto the application developer or user, it is arguably better than acore file or some other equally obscure result. (It isalso 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 inthe 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

IEEE Std 1003.1-2001 now includes support in certain areas for the newly adopted policy governing options andstubs.

This policy provides flexibility for implementations in how they support options. It also specifies how conforming applicationscan 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 optionbeyond 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 doesnot claim to support the option.

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

There is an important implication of this policy. IEEE Std 1003.1-2001 cannot dictate the behavior of interfacesassociated with an option when the implementation does not claim to support the option. In particular, it cannot require that afunction associated with an unsupported option will fail if it does not perform as specified. However, this policy does not preventa standard from requiring certain functions to always be present, but that they shall always fail on some implementations. Thesetpgid() function in the POSIX.1-1990 standard, for example, is consideredappropriate.

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

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 theimplementation to supply any of the data types or function interfaces that are provided only as part of the option. Theimplementation might provide data types and functions that are similar to those defined by IEEE Std 1003.1-2001, butthere 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 andfunction 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, theimplementation might be unable or unwilling to specify support or non-support at compile time. In either case, any application thatmight use the option at runtime must be able to compile and execute. The implementation must provide, at compile time, all datatypes and function interfaces that are necessary to allow this. In this situation, there must be a mechanism that allows theapplication to query, at runtime, whether the option is supported. If the application attempts to use the option when it is notsupported, the result is unspecified unless explicitly specified otherwise in IEEE Std 1003.1-2001.

FUTURE DIRECTIONS

None.

SEE ALSO

<inttypes.h>,<limits.h>,<sys/socket.h>,<sys/types.h>,<termios.h>,<wctype.h>, the System Interfaces volumeof IEEE Std 1003.1-2001,access(),alarm(),chdir(),chown(),close(),crypt(),ctermid(),dup(),encrypt(),environ,exec,exit(),fchdir(),fchown(),fcntl(),fork(),fpathconf(),fsync(),ftruncate(),getcwd(),getegid(),geteuid(),getgid(),getgroups(),gethostid(),gethostname(),getlogin(),getpgid(),getpgrp(),getpid(),getppid(),getsid(),getuid(),isatty(),lchown(),link(),lockf(),lseek(),nice(),pathconf(),pause(),pipe(),read(),readlink(),rmdir(),setgid(),setpgid(),setpgrp(),setregid(),setreuid(),setsid(),setuid(),sleep(),swab(),symlink(),sync(),sysconf(),tcgetpgrp(),tcsetpgrp(),truncate(),ttyname(),ualarm(),unlink(),usleep(),vfork(),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_SHMmust now be set to a value other than -1 by a conforming implementation.

Large File System extensions are added.

The type of the argument tosbrk() is changed fromint tointptr_t.

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

Issue 6

_POSIX2_C_VERSION is removed.

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

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 theconfstr()function.

• The _SC_XBS5_* constants are added for thesysconf() function.

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

• Theuid_t,gid_t,off_t,pid_t, anduseconds_t types are mandated.

Thegethostname() prototype is added for sockets.

A new section is added for System-Wide Options.

Function prototypes forsetegid() andseteuid() 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, andpathconf() 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 macrosassociated with the ISO/IEC 9899:1999 standard are introduced.

Thegetwd() function is marked LEGACY.

Therestrict keyword is added to the prototypes forreadlink() andswab().

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

• Thesysconf() symbolic constants _SC_TRACE, _SC_TRACE_EVENT_FILTER,_SC_TRACE_LOG, and _SC_TRACE_INHERIT

Thebrk() andsbrk() 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 thenamelen parameter forgethostname() fromsocklen_t tosize_t.

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

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/21 is applied, correcting the description in ``Constants forFunctions'' 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_MAXconstants.

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

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/25 is applied, adding the following text to the APPLICATION USAGEsection: ``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 constantsfor 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 thesysconf() andc99 reference pages.

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/31 is applied, adding that the format of names of programmingenvironments can be obtained using thegetconf-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 forsysconf().

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/34 is applied, updating the prototype for thesymlink() function to match that in the System Interfaces volume ofIEEE 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 constantslist forpathconf(). This corresponds to the definition of POSIX2_SYMLINKS in theShell and Utilities volume of IEEE Std 1003.1-2001.