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



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       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 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  implementa-
	      tions  conforming	 to  IEEE Std 1003.1-2001,  the value shall be
	      200112L.

       _POSIX2_VERSION
	      Integer value indicating version of the Shell and Utilities vol-
	      ume 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 implemen-
       tation 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() func-
       tions 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	fpath-
       conf(), pathconf(), or sysconf() with the indicated name parameter.

       Unless  explicitly specified otherwise, the behavior of functions asso-
       ciated with an unsupported option is unspecified,  and  an  application
       that  uses  such	 functions  without  first checking fpathconf(), path-
       conf(), 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 sym-
	      bol 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 sym-
	      bol 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 sym-
	      bol 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 Synchro-
	      nization 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  ini-
	      tial options to be given to the c99 utility to build an applica-
	      tion 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  ini-
	      tial options to be given to the c99 utility to build an applica-
	      tion 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  ini-
	      tial options to be given to the c99 utility to build an applica-
	      tion 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 Specifica-
       tion 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  run-
       time  via  sysconf()  to	 determine  whether the current version of the
       operating system supports the necessary functionality as in the follow-
       ing 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  val-
       ues) 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
       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 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
       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  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. 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 par-
       ticular, it cannot require that a function associated  with  an	unsup-
       ported  option  will fail if it does not perform as specified. However,
       this policy does not prevent a standard from  requiring	certain	 func-
       tions  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 implemen-
       tation  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	inter-
       faces 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 neces-
       sary  to	 allow this. In this situation, there must be a mechanism that
       allows the application to query, at runtime, whether the option is sup-
       ported.	 If  the application attempts to use the option when it is not
       supported, the result is unspecified unless explicitly specified other-
       wise 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(),  gethost-
       name(),	getlogin(),  getpgid(),	 getpgrp(),  getpid(), getppid(), get-
       sid(), 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(), tcsetp-
       grp(), 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 .



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