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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. 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  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; 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 functions 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
       parameter.

       Unless  explicitly  specified  otherwise,  the  behavior  of  functions
       associated  with  an  unsupported  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 symbol 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 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 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 symbol 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 symbol 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 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

              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 symbol 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 utilities.

       _CS_POSIX_V6_ILP32_OFF32_CFLAGS
              If sysconf(_SC_V6_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_V6_ILP32_OFF32_LDFLAGS
              If sysconf(_SC_V6_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_V6_ILP32_OFF32_LIBS
              If sysconf(_SC_V6_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_V6_ILP32_OFFBIG_CFLAGS
              If sysconf(_SC_V6_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_V6_ILP32_OFFBIG_LDFLAGS
              If sysconf(_SC_V6_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_V6_ILP32_OFFBIG_LIBS
              If sysconf(_SC_V6_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_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  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_V6_LPBIG_OFFBIG_LDFLAGS
              If  sysconf(_SC_V6_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_V6_LPBIG_OFFBIG_LIBS
              If sysconf(_SC_V6_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_V6_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,  useconds_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 versions 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
       potentially problematic.  However, they  recognized  that  support  for
       existing   application   binaries   is   a  concern  to  manufacturers,
       application developers, and the users of implementations conforming  to
       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  conform  to  the  expectations  of  the
       application.) For the reasons outlined in the preceding paragraphs  and
       in  the  APPLICATION  USAGE section, the standard developers elected to
       retain the _POSIX_VERSION and _SC_VERSION functionality.

   Compile-Time Symbolic Constants for System-Wide Options
       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  provide  anything  associated with that option
           beyond the announcement that it does not support it.

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

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

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

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 original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .