unistd.h(0P)		   POSIX Programmer's Manual		  unistd.h(0P)



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       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
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       not be implemented on Linux.


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 implementa-
	     tions conforming to POSIX.1-2008, the value shall be 200809L.

       _POSIX2_VERSION
	     Integer value indicating version of the Shell and Utilities  vol-
	     ume  of  POSIX.1 to which the implementation conforms. For imple-
	     mentations	 conforming  to	 POSIX.1-2008,	the  value  shall   be
	     200809L.  For  profile implementations that define _POSIX_SUBPRO-
	     FILE  (see	 Section  2.1.5.1,  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 indicat-
	     ing  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 Section 2.1.4, XSI
       Conformance.  If defined, its value shall be suitable for  use  in  #if
       preprocessing directives.

       _XOPEN_VERSION
	     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  Section
       2.1.5.1,	  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 Section 2.1.6, Options for further informa-
       tion about the conformance requirements of these	 three	categories  of
       support.

       _POSIX_ADVISORY_INFO
	     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
	     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
	     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
	     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
	     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
	     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
	     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
	     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
	     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
	     The implementation supports the Raw Sockets option.  If this sym-
	     bol 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
	     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
	     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
	     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
	     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
	     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
	     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
	     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
	     The implementation supports the Non-Robust Mutex Priority Inheri-
	     tance  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
	     The implementation supports the Non-Robust Mutex Priority Protec-
	     tion 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
	     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
	     The  implementation  supports  the Thread Process-Shared Synchro-
	     nization option.  If this symbol is  defined  in  <unistd.h>,  it
	     shall  be defined to be -1, 0, or 200809L. The value of this sym-
	     bol reported by sysconf() shall either be -1 or 200809L.

       _POSIX_THREAD_ROBUST_PRIO_INHERIT
	     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
	     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
	     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
	     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
	     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
	     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
	     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
	     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
	     The implementation provides a C-language compilation  environment
	     with 32-bit int, long, pointer, and off_t types.

       _POSIX_V6_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_V6_LP64_OFF64
	     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
	     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
	     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
	     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
	     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  sym-
	     bol reported by sysconf() shall either be -1 or 200809L.

       _POSIX2_PBS
	     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 sym-
	     bol reported by sysconf() shall either be -1 or 200809L.

       _POSIX2_PBS_ACCOUNTING
	     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
	     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
	     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
	     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
	     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
	     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
	     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
	     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
	     The implementation supports the XSI STREAMS Option Group.

       _XOPEN_UNIX
	     The implementation supports the XSI option.

       _XOPEN_UUCP
	     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 informa-
	     tion (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.

       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>.

       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
       _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 charac-
		     ter  that	shall  disable terminal special character han-
		     dling as described in  Section  11.2.6,  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);
	   char	       *crypt(const char *, const char *);
	   int		dup(int);
	   int		dup2(int, int);
	   void		_exit(int);
	   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);
	   int		fdatasync(int);
	   int		fexecve(int, char *const [], char *const []);
	   pid_t	fork(void);
	   long		fpathconf(int, int);
	   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 []);
	   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);
	   int		lockf(int, int, off_t);
	   off_t	lseek(int, off_t, int);
	   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);
	   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);
	   void		swab(const void *restrict, void *restrict, ssize_t);
	   int		symlink(const char *, const char *);
	   int		symlinkat(const char *, int, const char *);
	   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);

       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 confor-
       mance to it. However, application developers who want to write applica-
       tions 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 standard-
       ized 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	poten-
       tially  problematic. However, they recognized that support for existing
       application binaries is a concern to manufacturers, application	devel-
       opers, 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	imple-
       mentations  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 applica-
       tion.) 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 sup-
       port 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 mecha-
	   nism 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	inter-
	   faces that are provided only as part of the option. The implementa-
	   tion 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  sup-
	   port	 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	imple-
	   mentation  must  provide, at compile time, all data types and func-
	   tion interfaces that are necessary to allow this.  In  this	situa-
	   tion,  there	 must  be  a  mechanism that allows the application to
	   query, at runtime, whether the option is supported. If the applica-
	   tion	 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>

       The System Interfaces volume of POSIX.1-2008, access(), alarm(),
       chown(), close(), confstr(), crypt(), ctermid(), dup(), _Exit(),
       encrypt(), exec, fchdir(), fchown(), fdatasync(), fork(), fpathconf(),
       fsync(), ftruncate(), getcwd(), getegid(), geteuid(), getgid(), get-
       groups(), 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()

COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained	online
       at http://www.unix.org/online.html .

       Any  typographical  or  formatting  errors that appear in this page are
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IEEE/The Open Group		     2013			  unistd.h(0P)