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<unistd.h>(P)			    POSIX Programmer's Manual			    <unistd.h>(P)

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 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.    For     implementations	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 implementation conforms. For implementations  conform-
	      ing 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; see XSI Conformance .

       _XOPEN_VERSION

	      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, unless otherwise specified below. If these  are  undefined,	the  fpathconf(),
       pathconf(), or sysconf() functions can be used 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 interfaces required only for the option need not be supplied. An
       application that attempts to use anything associated only with the option is considered 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 is executed. 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 func-
       tions shall be present. The application can check at runtime to see whether the option  is
       supported by calling fpathconf(), pathconf(), or sysconf() with the indicated name parame-
       ter.

       Unless explicitly specified otherwise, the behavior of functions associated with an unsup-
       ported  option  is  unspecified, and an application that uses such functions without first
       checking fpathconf(), pathconf(), or sysconf() is considered to be requiring an extension.

       For conformance requirements, refer to Conformance .

       _POSIX_ADVISORY_INFO

	      The implementation supports the Advisory Information option. If this symbol  has	a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_ASYNCHRONOUS_IO

	      The implementation supports the Asynchronous Input and Output option.  If this sym-
	      bol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_BARRIERS

	      The implementation supports the Barriers option. If this symbol has a  value  other
	      than -1 or 0, it shall have the value 200112L.

       _POSIX_CHOWN_RESTRICTED
	      The  use of chown() and fchown() is restricted to a process with appropriate privi-
	      leges, 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 always be set
	      to a value other than -1.

       _POSIX_CLOCK_SELECTION

	      The implementation supports the Clock Selection option. If this symbol has a  value
	      other than -1 or 0, it shall have the value 200112L.

       _POSIX_CPUTIME

	      The  implementation supports the Process CPU-Time Clocks option. If this symbol has
	      a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_FSYNC

	      The implementation supports the File Synchronization option. If this symbol  has	a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_IPV6
	      The  implementation supports the IPv6 option. If this symbol has a value other than
	      -1 or 0, it shall have the value 200112L.

       _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  the Memory Mapped Files option. If this symbol has a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_MEMLOCK

	      The implementation supports the Process Memory Locking option. If this symbol has a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_MEMLOCK_RANGE

	      The  implementation  supports the Range Memory Locking option. If this symbol has a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_MEMORY_PROTECTION

	      The implementation supports the Memory Protection option.  If  this  symbol  has	a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_MESSAGE_PASSING

	      The  implementation supports the Message Passing option. If this symbol has a value
	      other than -1 or 0, it shall have the value 200112L.

       _POSIX_MONOTONIC_CLOCK

	      The implementation supports the Monotonic Clock option. If this symbol has a  value
	      other than -1 or 0, it shall have the value 200112L.

       _POSIX_NO_TRUNC
	      Pathname	components  longer  than  {NAME_MAX} generate an error. This symbol shall
	      always be set to a value other than -1.

       _POSIX_PRIORITIZED_IO

	      The implementation supports the Prioritized Input and Output option.  If this  sym-
	      bol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_PRIORITY_SCHEDULING

	      The  implementation  supports  the  Process Scheduling option. If this symbol has a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_RAW_SOCKETS

	      The implementation supports the Raw Sockets option. If  this  symbol  has  a  value
	      other than -1 or 0, it shall have the value 200112L.

       _POSIX_READER_WRITER_LOCKS

	      The  implementation  supports  the Read-Write Locks option. This is always set to a
	      value greater than zero if the Threads option is supported. If this  symbol  has	a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_REALTIME_SIGNALS

	      The  implementation supports the Realtime Signals Extension option.  If this symbol
	      has a value other than -1 or 0, it shall have the value 200112L.

       _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 the Semaphores option. If this symbol has a value other
	      than -1 or 0, it shall have the value 200112L.

       _POSIX_SHARED_MEMORY_OBJECTS

	      The  implementation supports the Shared Memory Objects option. If this symbol has a
	      value other than -1 or 0, it shall have the value 200112L.

       _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 has a value other than
	      -1 or 0, it shall have the value 200112L.

       _POSIX_SPIN_LOCKS

	      The implementation supports the Spin Locks option. If this symbol has a value other
	      than -1 or 0, it shall have the value 200112L.

       _POSIX_SPORADIC_SERVER

	      The  implementation supports the Process Sporadic Server option. If this symbol has
	      a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_SYNCHRONIZED_IO

	      The implementation supports the Synchronized Input and Output option.  If this sym-
	      bol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_ATTR_STACKADDR

	      The  implementation  supports  the  Thread Stack Address Attribute option.  If this
	      symbol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_ATTR_STACKSIZE

	      The implementation supports the Thread Stack Size Attribute option.  If this symbol
	      has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_CPUTIME

	      The implementation supports the Thread CPU-Time Clocks option. If this symbol has a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_PRIO_INHERIT

	      The implementation supports the Thread Priority Inheritance option.  If this symbol
	      has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_PRIO_PROTECT

	      The  implementation supports the Thread Priority Protection option.  If this symbol
	      has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_PRIORITY_SCHEDULING

	      The implementation supports the Thread Execution Scheduling option.  If this symbol
	      has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_PROCESS_SHARED

	      The  implementation  supports  the Thread Process-Shared Synchronization option. If
	      this symbol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_SAFE_FUNCTIONS

	      The implementation supports the Thread-Safe Functions option. If this symbol has	a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREAD_SPORADIC_SERVER

	      The implementation supports the Thread Sporadic Server option. If this symbol has a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_THREADS

	      The implementation supports the Threads option. If this symbol has  a  value  other
	      than -1 or 0, it shall have the value 200112L.

       _POSIX_TIMEOUTS

	      The  implementation  supports the Timeouts option. If this symbol has a value other
	      than -1 or 0, it shall have the value 200112L.

       _POSIX_TIMERS

	      The implementation supports the Timers option. If this symbol  has  a  value  other
	      than -1 or 0, it shall have the value 200112L.

       _POSIX_TRACE

	      The implementation supports the Trace option. If this symbol has a value other than
	      -1 or 0, it shall have the value 200112L.

       _POSIX_TRACE_EVENT_FILTER

	      The implementation supports the Trace Event Filter option. If  this  symbol  has	a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_TRACE_INHERIT

	      The  implementation  supports  the Trace Inherit option. If this symbol has a value
	      other than -1 or 0, it shall have the value 200112L.

       _POSIX_TRACE_LOG

	      The implementation supports the Trace Log option. If this symbol has a value  other
	      than -1 or 0, it shall have the value 200112L.

       _POSIX_TYPED_MEMORY_OBJECTS

	      The  implementation  supports the Typed Memory Objects option. If this symbol has a
	      value other than -1 or 0, it shall have the value 200112L.

       _POSIX_VDISABLE
	      This symbol shall be defined to be the value of a character that shall disable ter-
	      minal  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

	      The  implementation  supports the C-Language Development Utilities option.  If this
	      symbol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_CHAR_TERM
	      The implementation supports at least one terminal type.

       _POSIX2_FORT_DEV

	      The implementation supports the FORTRAN Development Utilities option.  If this sym-
	      bol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_FORT_RUN

	      The  implementation  supports the FORTRAN Runtime Utilities option.  If this symbol
	      has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_LOCALEDEF
	      The implementation supports the creation of locales by the  localedef  utility.  If
	      this symbol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_PBS

	      The implementation supports the Batch Environment Services and Utilities option. If
	      this symbol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_PBS_ACCOUNTING

	      The implementation supports the Batch Accounting option. If this symbol has a value
	      other than -1 or 0, it shall have the value 200112L.

       _POSIX2_PBS_CHECKPOINT

	      The implementation supports the Batch Checkpoint/Restart option. If this symbol has
	      a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_PBS_LOCATE

	      The implementation supports the Locate Batch Job Request option. If this symbol has
	      a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_PBS_MESSAGE

	      The  implementation  supports the Batch Job Message Request option.  If this symbol
	      has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_PBS_TRACK

	      The implementation supports the Track Batch Job Request option. If this symbol  has
	      a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_SW_DEV

	      The  implementation  supports  the  Software Development Utilities option.  If this
	      symbol has a value other than -1 or 0, it shall have the value 200112L.

       _POSIX2_UPE

	      The implementation supports the User Portability Utilities option.  If this  symbol
	      has a value other than -1 or 0, it shall have the value 200112L.

       _V6_ILP32_OFF32
	      The  implementation  provides a C-language compilation environment with 32-bit int,
	      long, pointer, and off_t types.

       _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.

       _V6_LP64_OFF64
	      The  implementation  provides  a C-language compilation environment with 32-bit int
	      and 64-bit long, pointer, and off_t types.

       _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.

       _XBS5_ILP32_OFF32 (LEGACY)

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

       _XBS5_ILP32_OFFBIG (LEGACY)

	      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.

       _XBS5_LP64_OFF64 (LEGACY)

	      The  implementation  provides  a C-language compilation environment with 32-bit int
	      and 64-bit long, pointer, and off_t types.

       _XBS5_LPBIG_OFFBIG (LEGACY)

	      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.

       _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_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 other than -1.

       _XOPEN_STREAMS
	      The implementation supports the XSI STREAMS Option Group.

       _XOPEN_UNIX

	      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 the file to which it is applied.

       If any of the following 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 constants, whether defined 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.

   Constants for Functions
       The following symbolic constant shall be defined:

       NULL   Null pointer

       The following symbolic constants shall be defined for the access() 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  expressions  R_OK|W_OK,  R_OK|X_OK,  and
       R_OK|W_OK|X_OK shall all have distinct values.

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

       _CS_PATH
	      This  is the value for the PATH environment variable that finds all standard utili-
	      ties.

       _CS_POSIX_V6_ILP32_OFF32_CFLAGS
	      If sysconf(_SC_V6_ILP32_OFF32) returns -1, the meaning of this  value  is  unspeci-
	      fied.  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_V6_ILP32_OFF32_LDFLAGS
	      If  sysconf(_SC_V6_ILP32_OFF32)  returns	-1, the meaning of this value is unspeci-
	      fied. 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_V6_ILP32_OFF32_LIBS
	      If sysconf(_SC_V6_ILP32_OFF32) returns -1, the meaning of this  value  is  unspeci-
	      fied.  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_V6_ILP32_OFFBIG_CFLAGS
	      If  sysconf(_SC_V6_ILP32_OFFBIG)	returns -1, the meaning of this value is unspeci-
	      fied. 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_V6_ILP32_OFFBIG_LDFLAGS
	      If sysconf(_SC_V6_ILP32_OFFBIG) returns -1, the meaning of this value  is  unspeci-
	      fied.  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_V6_ILP32_OFFBIG_LIBS
	      If  sysconf(_SC_V6_ILP32_OFFBIG)	returns -1, the meaning of this value is unspeci-
	      fied. 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_V6_LP64_OFF64_CFLAGS
	      If sysconf(_SC_V6_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_V6_LP64_OFF64_LDFLAGS
	      If sysconf(_SC_V6_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_V6_LP64_OFF64_LIBS
	      If sysconf(_SC_V6_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_V6_LPBIG_OFFBIG_CFLAGS
	      If  sysconf(_SC_V6_LPBIG_OFFBIG)	returns -1, the meaning of this value is unspeci-
	      fied. 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_V6_LPBIG_OFFBIG_LDFLAGS
	      If sysconf(_SC_V6_LPBIG_OFFBIG) returns -1, the meaning of this value  is  unspeci-
	      fied.  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_V6_LPBIG_OFFBIG_LIBS
	      If  sysconf(_SC_V6_LPBIG_OFFBIG)	returns -1, the meaning of this value is unspeci-
	      fied. 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_V6_WIDTH_RESTRICTED_ENVS
	      This value is a <newline>-separated list of names of programming environments  sup-
	      ported  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,  usec-
	      onds_t, wchar_t, and wint_t types are no greater than the width of type long.

       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 the lseek() and fcntl() functions
       and shall have distinct values:

       SEEK_CUR
	      Set file offset to current plus offset.

       SEEK_END
	      Set file offset to EOF plus offset.

       SEEK_SET
	      Set file offset to offset.

       The following symbolic constants shall be defined 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 following symbolic constants shall be defined for pathconf():

       _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 for sysconf():

       _SC_2_C_BIND
       _SC_2_C_DEV
       _SC_2_C_VERSION
       _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_ARG_MAX
       _SC_AIO_LISTIO_MAX
       _SC_AIO_MAX
       _SC_AIO_PRIO_DELTA_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_FILE_LOCKING
       _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_SEMAPHORES
       _SC_SEM_NSEMS_MAX
       _SC_SEM_VALUE_MAX
       _SC_SHARED_MEMORY_OBJECTS
       _SC_SHELL
       _SC_SIGQUEUE_MAX
       _SC_SPAWN
       _SC_SPIN_LOCKS
       _SC_SPORADIC_SERVER
       _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_TIMEOUTS
       _SC_THREADS
       _SC_TIMER_MAX
       _SC_TIMERS
       _SC_TRACE
       _SC_TRACE_EVENT_FILTER
       _SC_TRACE_INHERIT
       _SC_TRACE_LOG
       _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
       _SC_XOPEN_XCU_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 of stderr; 2.

       STDIN_FILENO
	      File number of stdin; 0.

       STDOUT_FILENO
	      File number of stdout; 1.

   Type Definitions
       The  size_t, ssize_t, uid_t, gid_t, off_t, pid_t, and useconds_t types shall be defined as
       described in <sys/types.h>.

       The intptr_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);

	      char	  *crypt(const char *, const char *);
	      char	  *ctermid(char *);

	      int	   dup(int);

	      int	   dup2(int, 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 []);
	      void	  _exit(int);
	      int	   fchown(int, uid_t, gid_t);

	      int	   fchdir(int);

	      int	   fdatasync(int);

	      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);

	      char	  *getwd(char *); (LEGACY )

	      int	   isatty(int);

	      int	   lchown(const char *, uid_t, gid_t);

	      int	   link(const char *, const char *);

	      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);
	      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 *);
	      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);

	      useconds_t   ualarm(useconds_t, useconds_t);

	      int	   unlink(const char *);

	      int	   usleep(useconds_t);
	      pid_t	   vfork(void);

	      ssize_t	   write(int, const void *, size_t);

       Implementations	may also include the pthread_atfork() prototype as defined in <pthread.h>
       .

       The following external variables shall be declared:

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

       The following sections are informative.

APPLICATION USAGE
       IEEE Std 1003.1-2001 only describes the behavior of systems that claim conformance to  it.
       However,  application  developers  who want to write applications that adapt to other ver-
       sions of IEEE Std 1003.1 (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 IEEE Std 1003.1 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

       IEEE Std 1003.1-2001  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) < 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 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 bina-
       ries is a concern to manufacturers, application developers, and the users  of  implementa-
       tions conforming to IEEE Std 1003.1-2001.

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

   Compile-Time Symbolic Constants for System-Wide Options
       IEEE Std 1003.1-2001 now includes support in certain areas for the  newly  adopted  policy
       governing options and stubs.

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

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

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

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

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

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

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

	1. Option never supported.

       The implementation advertises at compile time that the option will never be supported.  In
       this  case,  it is not necessary for the implementation to supply any of the data types or
       function interfaces that are provided only as part of the option. The implementation might
       provide	 data	types	and   functions   that	 are   similar	 to   those   defined  by
       IEEE Std 1003.1-2001, but there is no guarantee for any particular behavior.

	2. Option always supported.

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

	3. Option might or might not be supported.

       Some implementations might not provide a mechanism to specify support of options  at  com-
       pile time. In addition, the implementation might be unable or unwilling to specify support
       or non-support at compile time. In either case, any application that might use the  option
       at  runtime must be able to compile and execute.  The implementation must provide, at com-
       pile time, all data types and function interfaces that are necessary  to  allow	this.  In
       this  situation,  there	must be a mechanism that allows the application to query, at run-
       time, whether the option is supported.  If the application attempts to use the option when
       it  is  not  supported, the result is unspecified unless explicitly specified otherwise in
       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 volume of 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(), get-
       gid(), getgroups(), gethostid(), gethostname(),	getlogin(),  getpgid(),  getpgrp(),  get-
       pid(),  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()

COPYRIGHT
       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable	Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				    <unistd.h>(P)
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