'\" et
.TH unistd.h "0P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH 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.
.\"
.SH NAME
unistd.h
\(em standard symbolic constants and types
.SH SYNOPSIS
.LP
.nf
#include <unistd.h>
.fi
.SH DESCRIPTION
The
.IR <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.
.SS "Version Test Macros"
.P
The
.IR <unistd.h> 
header shall define the following symbolic constants. The values shall
be suitable for use in
.BR #if
preprocessing directives.
.IP _POSIX_VERSION 6
.br
Integer value indicating version of this standard (C-language
binding) to which the implementation conforms. For implementations
conforming to POSIX.1\(hy2008, the value shall be 200809L.
.IP _POSIX2_VERSION 6
.br
Integer value indicating version of the Shell and Utilities volume of POSIX.1 to which the implementation
conforms. For implementations conforming to POSIX.1\(hy2008, the value shall
be 200809L. For profile implementations that define _POSIX_SUBPROFILE
(see
.IR "Section 2.1.5.1" ", " "Subprofiling Considerations")
in
.IR <unistd.h> ,
_POSIX2_VERSION may be left undefined or be defined with the value \-1
to indicate that the Shell and Utilities volume of POSIX.1 is not supported. In this case, a call to
.IR sysconf(_SC_2_VERSION)
shall return either 200809L or \-1 indicating that the Shell and Utilities volume of POSIX.1 is or is
not, respectively, supported at runtime.
.P
The
.IR <unistd.h> 
header shall define the following symbolic constant only if
the implementation supports the XSI option; see
.IR "Section 2.1.4" ", " "XSI Conformance".
If defined, its value shall be suitable for use in
.BR #if
preprocessing directives.
.IP _XOPEN_VERSION 6
.br
Integer value indicating version of the X/Open Portability Guide
to which the implementation conforms. The value shall be 700.
.SS "Constants for Options and Option Groups"
.P
The following symbolic constants, if defined in
.IR <unistd.h> ,
shall have a value of \-1, 0, or greater, unless otherwise specified
below. For profile implementations that define _POSIX_SUBPROFILE (see
.IR "Section 2.1.5.1" ", " "Subprofiling Considerations")
in
.IR <unistd.h> ,
constants described below as always having a value greater than zero need
not be defined and, if defined, may have a value of \-1, 0, or greater.
The values shall be suitable for use in
.BR #if
preprocessing directives.
.P
If a symbolic constant is not defined or is defined with the value
\-1, the option is not supported for compilation. If it is defined
with a value greater than zero, the option shall always be supported
when the application is executed. If it is defined with the value zero,
the option shall be supported for compilation and might or might not be
supported at runtime. See
.IR "Section 2.1.6" ", " "Options"
for further information about the conformance requirements of these
three categories of support.
.IP _POSIX_ADVISORY_INFO 6
.br
The implementation supports the Advisory Information option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_ASYNCHRONOUS_IO 6
.br
The implementation supports asynchronous input and output.
This symbol shall always be set to the value 200809L.
.IP _POSIX_BARRIERS 6
.br
The implementation supports barriers.
This symbol shall always be set to the value 200809L.
.IP _POSIX_CHOWN_RESTRICTED 6
.br
The use of
\fIchown\fR()
and
\fIfchown\fR()
is restricted to a process with appropriate privileges, and to changing
the group ID of a file only to the effective group ID of the process or
to one of its supplementary group IDs. This symbol shall be defined
with a value other than \-1.
.IP _POSIX_CLOCK_SELECTION 6
.br
The implementation supports clock selection.
This symbol shall always be set to the value 200809L.
.IP _POSIX_CPUTIME 6
.br
The implementation supports the Process CPU-Time Clocks option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_FSYNC 6
.br
The implementation supports the File Synchronization option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_IPV6 6
.br
The implementation supports the IPv6 option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_JOB_CONTROL 6
.br
The implementation supports job control. This symbol shall always be
set to a value greater than zero.
.IP _POSIX_MAPPED_FILES 6
.br
The implementation supports memory mapped Files.
This symbol shall always be set to the value 200809L.
.IP _POSIX_MEMLOCK 6
.br
The implementation supports the Process Memory Locking option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_MEMLOCK_RANGE 6
.br
The implementation supports the Range Memory Locking option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_MEMORY_PROTECTION 6
.br
The implementation supports memory protection.
This symbol shall always be set to the value 200809L.
.IP _POSIX_MESSAGE_PASSING 6
.br
The implementation supports the Message Passing option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_MONOTONIC_CLOCK 6
.br
The implementation supports the Monotonic Clock option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_NO_TRUNC 6
.br
Pathname components longer than
{NAME_MAX}
generate an error. This symbol shall be defined with a value
other than \-1.
.IP _POSIX_PRIORITIZED_IO 6
.br
The implementation supports the Prioritized Input and Output option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_PRIORITY_SCHEDULING 6
.br
The implementation supports the Process Scheduling option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_RAW_SOCKETS 6
.br
The implementation supports the Raw Sockets option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_READER_WRITER_LOCKS 6
.br
The implementation supports read-write locks.
This symbol shall always be set to the value 200809L.
.IP _POSIX_REALTIME_SIGNALS 6
.br
The implementation supports realtime signals.
This symbol shall always be set to the value 200809L.
.IP _POSIX_REGEXP 6
.br
The implementation supports the Regular Expression Handling option.
This symbol shall always be set to a value greater than zero.
.IP _POSIX_SAVED_IDS 6
.br
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.
.IP _POSIX_SEMAPHORES 6
.br
The implementation supports semaphores.
This symbol shall always be set to the value 200809L.
.IP _POSIX_SHARED_MEMORY_OBJECTS 6
.br
The implementation supports the Shared Memory Objects option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_SHELL 6
.br
The implementation supports the POSIX shell. This symbol shall always
be set to a value greater than zero.
.IP _POSIX_SPAWN 6
.br
The implementation supports the Spawn option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_SPIN_LOCKS 6
.br
The implementation supports spin locks.
This symbol shall always be set to the value 200809L.
.IP _POSIX_SPORADIC_SERVER 6
.br
The implementation supports the Process Sporadic Server option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_SYNCHRONIZED_IO 6
.br
The implementation supports the Synchronized Input and Output option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_ATTR_STACKADDR 6
.br
The implementation supports the Thread Stack Address Attribute option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_ATTR_STACKSIZE 6
.br
The implementation supports the Thread Stack Size Attribute option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_CPUTIME 6
.br
The implementation supports the Thread CPU-Time Clocks option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_PRIO_INHERIT 6
.br
The implementation supports the Non-Robust Mutex Priority
Inheritance option. If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_PRIO_PROTECT 6
.br
The implementation supports the Non-Robust Mutex Priority
Protection option. If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_PRIORITY_SCHEDULING 6
.br
The implementation supports the Thread Execution Scheduling option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_PROCESS_SHARED 6
.br
The implementation supports the Thread Process-Shared Synchronization
option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_ROBUST_PRIO_INHERIT 6
.br
The implementation supports the Robust Mutex Priority Inheritance
option. If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_ROBUST_PRIO_PROTECT 6
.br
The implementation supports the Robust Mutex Priority Protection
option. If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREAD_SAFE_FUNCTIONS 6
.br
The implementation supports thread-safe functions.
This symbol shall always be set to the value 200809L.
.IP _POSIX_THREAD_SPORADIC_SERVER 6
.br
The implementation supports the Thread Sporadic Server option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_THREADS 6
.br
The implementation supports threads.
This symbol shall always be set to the value 200809L.
.IP _POSIX_TIMEOUTS 6
.br
The implementation supports timeouts.
This symbol shall always be set to the value 200809L.
.IP _POSIX_TIMERS 6
.br
The implementation supports timers.
This symbol shall always be set to the value 200809L.
.IP _POSIX_TRACE 6
.br
The implementation supports the Trace option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_TRACE_EVENT_FILTER 6
.br
The implementation supports the Trace Event Filter option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_TRACE_INHERIT 6
.br
The implementation supports the Trace Inherit option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_TRACE_LOG 6
.br
The implementation supports the Trace Log option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_TYPED_MEMORY_OBJECTS 6
.br
The implementation supports the Typed Memory Objects option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX_V6_ILP32_OFF32 6
.br
The implementation provides a C-language compilation environment with
32-bit
.BR int ,
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _POSIX_V6_ILP32_OFFBIG 6
.br
The implementation provides a C-language compilation environment with
32-bit
.BR int ,
.BR long ,
and
.BR pointer
types and an
.BR off_t
type using at least 64 bits.
.IP _POSIX_V6_LP64_OFF64 6
.br
The implementation provides a C-language compilation environment with
32-bit
.BR int
and 64-bit
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _POSIX_V6_LPBIG_OFFBIG 6
.br
The implementation provides a C-language compilation environment with
an
.BR int
type using at least 32 bits and
.BR long ,
.BR pointer ,
and
.BR off_t
types using at least 64 bits.
.IP _POSIX_V7_ILP32_OFF32 6
.br
The implementation provides a C-language compilation environment with
32-bit
.BR int ,
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _POSIX_V7_ILP32_OFFBIG 6
.br
The implementation provides a C-language compilation environment with
32-bit
.BR int ,
.BR long ,
and
.BR pointer
types and an
.BR off_t
type using at least 64 bits.
.IP _POSIX_V7_LP64_OFF64 6
.br
The implementation provides a C-language compilation environment with
32-bit
.BR int
and 64-bit
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _POSIX_V7_LPBIG_OFFBIG 6
.br
The implementation provides a C-language compilation environment with
an
.BR int
type using at least 32 bits and
.BR long ,
.BR pointer ,
and
.BR off_t
types using at least 64 bits.
.IP _POSIX2_C_BIND 6
.br
The implementation supports the C-Language Binding option. This
symbol shall always have the value 200809L.
.IP _POSIX2_C_DEV 6
.br
The implementation supports the C-Language Development Utilities option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_CHAR_TERM 6
.br
The implementation supports the Terminal Characteristics option.
The value of this symbol reported by
\fIsysconf\fR()
shall either be \-1 or a value greater than zero.
.IP _POSIX2_FORT_DEV 6
.br
The implementation supports the FORTRAN Development Utilities option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_FORT_RUN 6
.br
The implementation supports the FORTRAN Runtime Utilities option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_LOCALEDEF 6
.br
The implementation supports the creation of locales by the
.IR localedef
utility.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_PBS 6
.br
The implementation supports the Batch Environment Services and
Utilities option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_PBS_ACCOUNTING 6
.br
The implementation supports the Batch Accounting option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_PBS_CHECKPOINT 6
.br
The implementation supports the Batch Checkpoint/Restart option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_PBS_LOCATE 6
.br
The implementation supports the Locate Batch Job Request option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_PBS_MESSAGE 6
.br
The implementation supports the Batch Job Message Request option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_PBS_TRACK 6
.br
The implementation supports the Track Batch Job Request option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_SW_DEV 6
.br
The implementation supports the Software Development Utilities option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _POSIX2_UPE 6
.br
The implementation supports the User Portability Utilities option.
If this symbol is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this
symbol reported by
\fIsysconf\fR()
shall either be \-1 or 200809L.
.IP _XOPEN_CRYPT 6
.br
The implementation supports the X/Open Encryption Option Group.
.IP _XOPEN_ENH_I18N 6
.br
The implementation supports the Issue 4, Version 2 Enhanced
Internationalization Option Group. This symbol shall always be set
to a value other than \-1.
.IP _XOPEN_REALTIME 6
.br
The implementation supports the X/Open Realtime Option Group.
.IP _XOPEN_REALTIME_THREADS 6
.br
The implementation supports the X/Open Realtime Threads Option Group.
.IP _XOPEN_SHM 6
.br
The implementation supports the Issue 4, Version 2 Shared Memory Option
Group. This symbol shall always be set to a value other than \-1.
.IP _XOPEN_STREAMS 6
.br
The implementation supports the XSI STREAMS Option Group.
.IP _XOPEN_UNIX 6
.br
The implementation supports the XSI option.
.IP _XOPEN_UUCP 6
.br
The implementation supports the UUCP Utilities option. If this symbol
is defined in
.IR <unistd.h> ,
it shall be defined to be \-1, 0, or 200809L. The value of this symbol
reported by
\fIsysconf\fR()
shall be either \-1 or 200809L.
.SS "Execution-Time Symbolic Constants"
.P
If any of the following symbolic constants are not defined in the
.IR <unistd.h> 
header, the value shall vary depending on the file to which it
is applied. If defined, they shall have values suitable for use in
.BR #if
preprocessing directives.
.P
If any of the following symbolic constants are defined to have value
\-1 in the
.IR <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
.IR <unistd.h> 
header, the implementation shall provide the option on all applicable
files.
.P
All of the following values, whether defined as symbolic constants in
.IR <unistd.h> 
or not, may be queried with respect to a specific file using the
\fIpathconf\fR()
or
\fIfpathconf\fR()
functions:
.IP _POSIX_ASYNC_IO 6
.br
Asynchronous input or output operations may be performed for the
associated file.
.IP _POSIX_PRIO_IO 6
.br
Prioritized input or output operations may be performed for the
associated file.
.IP _POSIX_SYNC_IO 6
.br
Synchronized input or output operations may be performed for the
associated file.
.P
If the following symbolic constants are defined in the
.IR <unistd.h> 
header, they apply to files and all paths in all file systems on
the implementation:
.IP _POSIX_TIMESTAMP_RESOLUTION 6
.br
The resolution in nanoseconds for all file timestamps.
.IP _POSIX2_SYMLINKS 6
.br
Symbolic links can be created.
.SS "Constants for Functions"
.P
The
.IR <unistd.h> 
header shall define NULL as described in
.IR <stddef.h> .
.P
The
.IR <unistd.h> 
header shall define the following symbolic constants for use with the
\fIaccess\fR()
function. The values shall be suitable for use in
.BR #if
preprocessing directives.
.IP F_OK 12
Test for existence of file.
.IP R_OK 12
Test for read permission.
.IP W_OK 12
Test for write permission.
.IP X_OK 12
Test for execute (search) permission.
.P
The constants F_OK, R_OK, W_OK, and X_OK and the expressions
\fIR_OK\fP|\fIW_OK\fP, \fIR_OK\fP|\fIX_OK\fP, and
\fIR_OK\fP|\fIW_OK\fP|\fIX_OK\fP shall all have distinct values.
.P
The
.IR <unistd.h> 
header shall define the following symbolic constants for the
\fIconfstr\fR()
function:
.IP _CS_PATH 6
.br
This is the value for the
.IR PATH
environment variable that finds all of the standard utilities that are
provided in a manner accessible via the
.IR exec
family of functions.
.IP _CS_POSIX_V7_ILP32_OFF32_CFLAGS 6
.br
If \fIsysconf\fP(_SC_V7_ILP32_OFF32) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of initial
options to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int ,
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _CS_POSIX_V7_ILP32_OFF32_LDFLAGS 6
.br
If \fIsysconf\fP(_SC_V7_ILP32_OFF32) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of final
options to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int ,
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _CS_POSIX_V7_ILP32_OFF32_LIBS 6
.br
If \fIsysconf\fP(_SC_V7_ILP32_OFF32) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of
libraries to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int ,
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _CS_POSIX_V7_ILP32_OFFBIG_CFLAGS 6
.br
If \fIsysconf\fP(_SC_V7_ILP32_OFFBIG) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of initial
options to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int ,
.BR long ,
and
.BR pointer
types, and an
.BR off_t
type using at least 64 bits.
.IP _CS_POSIX_V7_ILP32_OFFBIG_LDFLAGS 6
.br
If \fIsysconf\fP(_SC_V7_ILP32_OFFBIG) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of final
options to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int ,
.BR long ,
and
.BR pointer
types, and an
.BR off_t
type using at least 64 bits.
.IP _CS_POSIX_V7_ILP32_OFFBIG_LIBS 6
.br
If \fIsysconf\fP(_SC_V7_ILP32_OFFBIG) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of
libraries to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int ,
.BR long ,
and
.BR pointer
types, and an
.BR off_t
type using at least 64 bits.
.IP _CS_POSIX_V7_LP64_OFF64_CFLAGS 6
.br
If \fIsysconf\fP(_SC_V7_LP64_OFF64) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of initial
options to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int
and 64-bit
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _CS_POSIX_V7_LP64_OFF64_LDFLAGS 6
.br
If \fIsysconf\fP(_SC_V7_LP64_OFF64) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of final
options to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int
and 64-bit
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _CS_POSIX_V7_LP64_OFF64_LIBS 6
.br
If \fIsysconf\fP(_SC_V7_LP64_OFF64) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of
libraries to be given to the
.IR c99
utility to build an application using a programming model with 32-bit
.BR int
and 64-bit
.BR long ,
.BR pointer ,
and
.BR off_t
types.
.IP _CS_POSIX_V7_LPBIG_OFFBIG_CFLAGS 6
.br
If \fIsysconf\fP(_SC_V7_LPBIG_OFFBIG) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of initial
options to be given to the
.IR c99
utility to build an application using a programming model with an
.BR int
type using at least 32 bits and
.BR long ,
.BR pointer ,
and
.BR off_t
types using at least 64 bits.
.IP _CS_POSIX_V7_LPBIG_OFFBIG_LDFLAGS 6
.br
If \fIsysconf\fP(_SC_V7_LPBIG_OFFBIG) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of final
options to be given to the
.IR c99
utility to build an application using a programming model with an
.BR int
type using at least 32 bits and
.BR long ,
.BR pointer ,
and
.BR off_t
types using at least 64 bits.
.IP _CS_POSIX_V7_LPBIG_OFFBIG_LIBS 6
.br
If \fIsysconf\fP(_SC_V7_LPBIG_OFFBIG) returns \-1, the meaning of
this value is unspecified. Otherwise, this value is the set of
libraries to be given to the
.IR c99
utility to build an application using a programming model with an
.BR int
type using at least 32 bits and
.BR long ,
.BR pointer ,
and
.BR off_t
types using at least 64 bits.
.IP _CS_POSIX_V7_THREADS_CFLAGS 6
.br
If
.IR sysconf (_SC_POSIX_THREADS)
returns \-1, the meaning of this value is unspecified. Otherwise,
this value is the set of initial options to be given to the
.IR c99
utility to build a multi-threaded application. These flags are in addition
to those associated with any of the other _CS_POSIX_V7_*_CFLAGS values
used to specify particular type size programing environments.
.IP _CS_POSIX_V7_THREADS_LDFLAGS 6
.br
If
.IR sysconf (_SC_POSIX_THREADS)
returns \-1, the meaning of this value is unspecified. Otherwise,
this value is the set of final options to be given to the
.IR c99
utility to build a multi-threaded application. These flags are in addition
to those associated with any of the other _CS_POSIX_V7_*_LDFLAGS values
used to specify particular type size programing environments.
.IP _CS_POSIX_V7_WIDTH_RESTRICTED_ENVS 6
.br
This value is a
<newline>-separated
list of names of programming environments supported by the
implementation in which the widths of the
.BR blksize_t ,
.BR cc_t ,
.BR mode_t ,
.BR nfds_t ,
.BR pid_t ,
.BR ptrdiff_t ,
.BR size_t ,
.BR speed_t ,
.BR ssize_t ,
.BR suseconds_t ,
.BR tcflag_t ,
.BR wchar_t ,
and
.BR wint_t
types are no greater than the width of type
.BR long .
The format of each name shall be suitable for use with the
.IR getconf
.BR \-v
option.
.IP _CS_V7_ENV 6
.br
This is the value that provides the environment variable information
(other than that provided by _CS_PATH) that is required by the
implementation to create a conforming environment, as described in the
implementation's conformance documentation.
.br
.P
The following symbolic constants are reserved for compatibility
with Issue 6:
.P
.nf
_CS_POSIX_V6_ILP32_OFF32_CFLAGS
_CS_POSIX_V6_ILP32_OFF32_LDFLAGS
_CS_POSIX_V6_ILP32_OFF32_LIBS
_CS_POSIX_V6_ILP32_OFFBIG_CFLAGS
_CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS
_CS_POSIX_V6_ILP32_OFFBIG_LIBS
_CS_POSIX_V6_LP64_OFF64_CFLAGS
_CS_POSIX_V6_LP64_OFF64_LDFLAGS
_CS_POSIX_V6_LP64_OFF64_LIBS
_CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS
_CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS
_CS_POSIX_V6_LPBIG_OFFBIG_LIBS
_CS_POSIX_V6_WIDTH_RESTRICTED_ENVS
_CS_V6_ENV
.fi
.P
The
.IR <unistd.h> 
header shall define SEEK_CUR, SEEK_END, and SEEK_SET as described in
.IR <stdio.h> .
.P
The
.IR <unistd.h> 
header shall define the following symbolic constants as possible
values for the
.IR function
argument to the
\fIlockf\fR()
function:
.IP F_LOCK 12
Lock a section for exclusive use.
.IP F_TEST 12
Test section for locks by other processes.
.IP F_TLOCK 12
Test and lock a section for exclusive use.
.IP F_ULOCK 12
Unlock locked sections.
.P
The
.IR <unistd.h> 
header shall define the following symbolic constants for
\fIpathconf\fR():
.P
.nf
_PC_2_SYMLINKS
_PC_ALLOC_SIZE_MIN
_PC_ASYNC_IO
_PC_CHOWN_RESTRICTED
_PC_FILESIZEBITS
_PC_LINK_MAX
_PC_MAX_CANON
_PC_MAX_INPUT
_PC_NAME_MAX
_PC_NO_TRUNC
_PC_PATH_MAX
_PC_PIPE_BUF
_PC_PRIO_IO
_PC_REC_INCR_XFER_SIZE
_PC_REC_MAX_XFER_SIZE
_PC_REC_MIN_XFER_SIZE
_PC_REC_XFER_ALIGN
_PC_SYMLINK_MAX
_PC_SYNC_IO
_PC_TIMESTAMP_RESOLUTION
_PC_VDISABLE
.fi
.P
The
.IR <unistd.h> 
header shall define the following symbolic constants for
\fIsysconf\fR():
.P
.nf
_SC_2_C_BIND
_SC_2_C_DEV
_SC_2_CHAR_TERM
_SC_2_FORT_DEV
_SC_2_FORT_RUN
_SC_2_LOCALEDEF
_SC_2_PBS
_SC_2_PBS_ACCOUNTING
_SC_2_PBS_CHECKPOINT
_SC_2_PBS_LOCATE
_SC_2_PBS_MESSAGE
_SC_2_PBS_TRACK
_SC_2_SW_DEV
_SC_2_UPE
_SC_2_VERSION
_SC_ADVISORY_INFO
_SC_AIO_LISTIO_MAX
_SC_AIO_MAX
_SC_AIO_PRIO_DELTA_MAX
_SC_ARG_MAX
_SC_ASYNCHRONOUS_IO
_SC_ATEXIT_MAX
_SC_BARRIERS
_SC_BC_BASE_MAX
_SC_BC_DIM_MAX
_SC_BC_SCALE_MAX
_SC_BC_STRING_MAX
_SC_CHILD_MAX
_SC_CLK_TCK
_SC_CLOCK_SELECTION
_SC_COLL_WEIGHTS_MAX
_SC_CPUTIME
_SC_DELAYTIMER_MAX
_SC_EXPR_NEST_MAX
_SC_FSYNC
_SC_GETGR_R_SIZE_MAX
_SC_GETPW_R_SIZE_MAX
_SC_HOST_NAME_MAX
_SC_IOV_MAX
_SC_IPV6
_SC_JOB_CONTROL
_SC_LINE_MAX
_SC_LOGIN_NAME_MAX
_SC_MAPPED_FILES
_SC_MEMLOCK
_SC_MEMLOCK_RANGE
_SC_MEMORY_PROTECTION
_SC_MESSAGE_PASSING
_SC_MONOTONIC_CLOCK
_SC_MQ_OPEN_MAX
_SC_MQ_PRIO_MAX
_SC_NGROUPS_MAX
_SC_OPEN_MAX
_SC_PAGE_SIZE
_SC_PAGESIZE
_SC_PRIORITIZED_IO
_SC_PRIORITY_SCHEDULING
_SC_RAW_SOCKETS
_SC_RE_DUP_MAX
_SC_READER_WRITER_LOCKS
_SC_REALTIME_SIGNALS
_SC_REGEXP
_SC_RTSIG_MAX
_SC_SAVED_IDS
_SC_SEM_NSEMS_MAX
_SC_SEM_VALUE_MAX
_SC_SEMAPHORES
_SC_SHARED_MEMORY_OBJECTS
_SC_SHELL
_SC_SIGQUEUE_MAX
_SC_SPAWN
_SC_SPIN_LOCKS
_SC_SPORADIC_SERVER
_SC_SS_REPL_MAX
_SC_STREAM_MAX
_SC_SYMLOOP_MAX
_SC_SYNCHRONIZED_IO
_SC_THREAD_ATTR_STACKADDR
_SC_THREAD_ATTR_STACKSIZE
_SC_THREAD_CPUTIME
_SC_THREAD_DESTRUCTOR_ITERATIONS
_SC_THREAD_KEYS_MAX
_SC_THREAD_PRIO_INHERIT
_SC_THREAD_PRIO_PROTECT
_SC_THREAD_PRIORITY_SCHEDULING
_SC_THREAD_PROCESS_SHARED
_SC_THREAD_ROBUST_PRIO_INHERIT
_SC_THREAD_ROBUST_PRIO_PROTECT
_SC_THREAD_SAFE_FUNCTIONS
_SC_THREAD_SPORADIC_SERVER
_SC_THREAD_STACK_MIN
_SC_THREAD_THREADS_MAX
_SC_THREADS
_SC_TIMEOUTS
_SC_TIMER_MAX
_SC_TIMERS
_SC_TRACE
_SC_TRACE_EVENT_FILTER
_SC_TRACE_EVENT_NAME_MAX
_SC_TRACE_INHERIT
_SC_TRACE_LOG
_SC_TRACE_NAME_MAX
_SC_TRACE_SYS_MAX
_SC_TRACE_USER_EVENT_MAX
_SC_TTY_NAME_MAX
_SC_TYPED_MEMORY_OBJECTS
_SC_TZNAME_MAX
_SC_V7_ILP32_OFF32
_SC_V7_ILP32_OFFBIG
_SC_V7_LP64_OFF64
_SC_V7_LPBIG_OFFBIG
_SC_V6_ILP32_OFF32
_SC_V6_ILP32_OFFBIG
_SC_V6_LP64_OFF64
_SC_V6_LPBIG_OFFBIG
_SC_VERSION
_SC_XOPEN_CRYPT
_SC_XOPEN_ENH_I18N
_SC_XOPEN_REALTIME
_SC_XOPEN_REALTIME_THREADS
_SC_XOPEN_SHM
_SC_XOPEN_STREAMS
_SC_XOPEN_UNIX
_SC_XOPEN_UUCP
_SC_XOPEN_VERSION
.fi
.P
The two constants _SC_PAGESIZE and _SC_PAGE_SIZE may be defined to
have the same value.
.P
The
.IR <unistd.h> 
header shall define the following symbolic constants for file streams:
.IP STDERR_FILENO 14
File number of
.IR stderr ;
2.
.IP STDIN_FILENO 14
File number of
.IR stdin ;
0.
.IP STDOUT_FILENO 14
File number of
.IR stdout ;
1.
.P
The
.IR <unistd.h> 
header shall define the following symbolic constant for terminal
special character handling:
.IP _POSIX_VDISABLE 14
This symbol shall be defined to be the value of a character that shall
disable terminal special character handling as described in
.IR "Section 11.2.6" ", " "Special Control Characters".
This symbol shall always be set to a value other than \-1.
.SS "Type Definitions"
.P
The
.IR <unistd.h> 
header shall define the
.BR size_t ,
.BR ssize_t ,
.BR uid_t ,
.BR gid_t ,
.BR off_t ,
and
.BR pid_t
types as described in
.IR <sys/types.h> .
.P
The
.IR <unistd.h> 
header shall define the
.BR intptr_t
type as described in
.IR <stdint.h> .
.SS "Declarations"
.P
The following shall be declared as functions and may also be defined
as macros. Function prototypes shall be provided.
.sp
.RS 4
.nf

int          access(const char *, int);
unsigned     alarm(unsigned);
int          chdir(const char *);
int          chown(const char *, uid_t, gid_t);
int          close(int);
size_t       confstr(int, char *, size_t);
char        *crypt(const char *, const char *);
int          dup(int);
.br
int          dup2(int, int);
void         _exit(int);
void         encrypt(char [64], int);
int          execl(const char *, const char *, ...);
int          execle(const char *, const char *, ...);
int          execlp(const char *, const char *, ...);
int          execv(const char *, char *const []);
int          execve(const char *, char *const [], char *const []);
int          execvp(const char *, char *const []);
int          faccessat(int, const char *, int, int);
int          fchdir(int);
int          fchown(int, uid_t, gid_t);
int          fchownat(int, const char *, uid_t, gid_t, int);
int          fdatasync(int);
int          fexecve(int, char *const [], char *const []);
pid_t        fork(void);
long         fpathconf(int, int);
int          fsync(int);
int          ftruncate(int, off_t);
char        *getcwd(char *, size_t);
gid_t        getegid(void);
uid_t        geteuid(void);
gid_t        getgid(void);
int          getgroups(int, gid_t []);
long         gethostid(void);
int          gethostname(char *, size_t);
char        *getlogin(void);
int          getlogin_r(char *, size_t);
int          getopt(int, char * const [], const char *);
pid_t        getpgid(pid_t);
pid_t        getpgrp(void);
pid_t        getpid(void);
pid_t        getppid(void);
pid_t        getsid(pid_t);
uid_t        getuid(void);
int          isatty(int);
int          lchown(const char *, uid_t, gid_t);
int          link(const char *, const char *);
int          linkat(int, const char *, int, const char *, int);
int          lockf(int, int, off_t);
off_t        lseek(int, off_t, int);
int          nice(int);
long         pathconf(const char *, int);
int          pause(void);
int          pipe(int [2]);
ssize_t      pread(int, void *, size_t, off_t);
ssize_t      pwrite(int, const void *, size_t, off_t);
ssize_t      read(int, void *, size_t);
ssize_t      readlink(const char *restrict, char *restrict, size_t);
ssize_t      readlinkat(int, const char *restrict, char *restrict, size_t);
int          rmdir(const char *);
int          setegid(gid_t);
int          seteuid(uid_t);
int          setgid(gid_t);
.br
int          setpgid(pid_t, pid_t);
pid_t        setpgrp(void);
int          setregid(gid_t, gid_t);
int          setreuid(uid_t, uid_t);
pid_t        setsid(void);
int          setuid(uid_t);
unsigned     sleep(unsigned);
void         swab(const void *restrict, void *restrict, ssize_t);
int          symlink(const char *, const char *);
int          symlinkat(const char *, int, const char *);
void         sync(void);
long         sysconf(int);
pid_t        tcgetpgrp(int);
int          tcsetpgrp(int, pid_t);
int          truncate(const char *, off_t);
char        *ttyname(int);
int          ttyname_r(int, char *, size_t);
int          unlink(const char *);
int          unlinkat(int, const char *, int);
ssize_t      write(int, const void *, size_t);
.fi
.P
.RE
.P
Implementations may also include the
\fIpthread_atfork\fR()
prototype as defined in
.IR <pthread.h> .
Implementations may also include the
\fIctermid\fR()
prototype as defined in
.IR <stdio.h> .
.P
The
.IR <unistd.h> 
header shall declare the following external variables:
.sp
.RS 4
.nf

extern char  *optarg;
extern int    opterr, optind, optopt;
.fi
.P
.RE
.P
Inclusion of the
.IR <unistd.h> 
header may make visible all symbols from the headers
.IR <stddef.h> ,
.IR <stdint.h> ,
and
.IR <stdio.h> .
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
POSIX.1\(hy2008 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 this standard (or to systems that do not
conform to any POSIX standard) may find it useful to code them so as to
conditionally compile different code depending on the value of
_POSIX_VERSION, for example:
.sp
.RS 4
.nf

#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
.fi
.P
.RE
.P
Earlier versions of POSIX.1\(hy2008 and of the Single UNIX Specification
can be identified by the following macros:
.IP "POSIX.1\(hy1988 standard" 6
.br
_POSIX_VERSION\|=\^=\|198808L
.IP "POSIX.1\(hy1990 standard" 6
.br
_POSIX_VERSION\|=\^=\|199009L
.IP "ISO\ POSIX\(hy1:\|1996 standard" 6
.br
_POSIX_VERSION\|=\^=\|199506L
.IP "Single UNIX Specification, Version 1" 6
.br
_XOPEN_UNIX and _XOPEN_VERSION\|=\^=\|4
.IP "Single UNIX Specification, Version 2" 6
.br
_XOPEN_UNIX and _XOPEN_VERSION\|=\^=\|500
.IP "ISO POSIX\(hy1:\|2001 and Single UNIX Specification, Version 3" 6
.br
_POSIX_VERSION\|=\^=\|200112L, plus (if the XSI option is supported)
_XOPEN_UNIX and _XOPEN_VERSION\|=\^=\|600
.P
POSIX.1\(hy2008 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
\fIsysconf\fR()
to determine whether the current version of the operating system
supports the necessary functionality as in the following program
fragment:
.sp
.RS 4
.nf

if (sysconf(_SC_VERSION) < 200809L) {
    fprintf(stderr, "POSIX.1-2008 system required, terminating \en");
    exit(1);
}
.fi
.P
.RE
.P
New applications should not use _XOPEN_SHM or _XOPEN_ENH_I18N.
.SH RATIONALE
As POSIX.1\(hy2008 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.
.SS "Version Test Macros"
.P
The standard developers considered altering the definition of
_POSIX_VERSION and removing _SC_VERSION from the specification of
\fIsysconf\fR()
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 POSIX.1\(hy2008.
.P
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
.BR 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.
.SS "Compile-Time Symbolic Constants for System-Wide Options"
.P
POSIX.1\(hy2008 includes support in certain areas for the newly adopted
policy governing options and stubs.
.P
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:
.IP " 1." 4
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.
.IP " 2." 4
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.
.IP " 3." 4
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.
.P
There is an important implication of this policy. POSIX.1\(hy2008 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
\fIsetpgid\fR()
function in the POSIX.1\(hy1990 standard, for example, is considered appropriate.
.P
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.
.P
Any application must consider the following three cases for each
option:
.IP " 1." 4
Option never supported.
.RS 4 
.P
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
POSIX.1\(hy2008, but there is no guarantee for any particular behavior.
.RE
.IP " 2." 4
Option always supported.
.RS 4 
.P
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.
.RE
.IP " 3." 4
Option might or might not be supported.
.RS 4 
.P
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 POSIX.1\(hy2008.
.RE
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fB<limits.h>\fP",
.IR "\fB<stddef.h>\fP",
.IR "\fB<stdint.h>\fP",
.IR "\fB<stdio.h>\fP",
.IR "\fB<sys_socket.h>\fP",
.IR "\fB<sys_types.h>\fP",
.IR "\fB<termios.h>\fP",
.IR "\fB<wctype.h>\fP"
.P
.ad l
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fIaccess\fR\^(\|)",
.IR "\fIalarm\fR\^(\|)",
.IR "\fIchown\fR\^(\|)",
.IR "\fIclose\fR\^(\|)",
.IR "\fIconfstr\fR\^(\|)",
.IR "\fIcrypt\fR\^(\|)",
.IR "\fIctermid\fR\^(\|)",
.IR "\fIdup\fR\^(\|)",
.IR "\fI_Exit\fR\^(\|)",
.IR "\fIencrypt\fR\^(\|)",
.IR "\fIexec\fR\^",
.IR "\fIfchdir\fR\^(\|)",
.IR "\fIfchown\fR\^(\|)",
.IR "\fIfdatasync\fR\^(\|)",
.IR "\fIfork\fR\^(\|)",
.IR "\fIfpathconf\fR\^(\|)",
.IR "\fIfsync\fR\^(\|)",
.IR "\fIftruncate\fR\^(\|)",
.IR "\fIgetcwd\fR\^(\|)",
.IR "\fIgetegid\fR\^(\|)",
.IR "\fIgeteuid\fR\^(\|)",
.IR "\fIgetgid\fR\^(\|)",
.IR "\fIgetgroups\fR\^(\|)",
.IR "\fIgethostid\fR\^(\|)",
.IR "\fIgethostname\fR\^(\|)",
.IR "\fIgetlogin\fR\^(\|)",
.IR "\fIgetopt\fR\^(\|)",
.IR "\fIgetpgid\fR\^(\|)",
.IR "\fIgetpgrp\fR\^(\|)",
.IR "\fIgetpid\fR\^(\|)",
.IR "\fIgetppid\fR\^(\|)",
.IR "\fIgetsid\fR\^(\|)",
.IR "\fIgetuid\fR\^(\|)",
.IR "\fIisatty\fR\^(\|)",
.IR "\fIlchown\fR\^(\|)",
.IR "\fIlink\fR\^(\|)",
.IR "\fIlockf\fR\^(\|)",
.IR "\fIlseek\fR\^(\|)",
.IR "\fInice\fR\^(\|)",
.IR "\fIpause\fR\^(\|)",
.IR "\fIpipe\fR\^(\|)",
.IR "\fIread\fR\^(\|)",
.IR "\fIreadlink\fR\^(\|)",
.IR "\fIrmdir\fR\^(\|)",
.IR "\fIsetegid\fR\^(\|)",
.IR "\fIseteuid\fR\^(\|)",
.IR "\fIsetgid\fR\^(\|)",
.IR "\fIsetpgid\fR\^(\|)",
.IR "\fIsetpgrp\fR\^(\|)",
.IR "\fIsetregid\fR\^(\|)",
.IR "\fIsetreuid\fR\^(\|)",
.IR "\fIsetsid\fR\^(\|)",
.IR "\fIsetuid\fR\^(\|)",
.IR "\fIsleep\fR\^(\|)",
.IR "\fIswab\fR\^(\|)",
.IR "\fIsymlink\fR\^(\|)",
.IR "\fIsync\fR\^(\|)",
.IR "\fIsysconf\fR\^(\|)",
.IR "\fItcgetpgrp\fR\^(\|)",
.IR "\fItcsetpgrp\fR\^(\|)",
.IR "\fItruncate\fR\^(\|)",
.IR "\fIttyname\fR\^(\|)",
.IR "\fIunlink\fR\^(\|)",
.IR "\fIwrite\fR\^(\|)"
.ad b
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .