NAME

unistd.h — standard symbolic constants and types

SYNOPSIS

#include <unistd.h>

DESCRIPTION

The <unistd.h> header defines miscellaneous symbolic constants and types, and declares miscellaneous functions. The actual values of the constants are unspecified except as shown. The contents of this header are shown below.

Version Test Macros

The <unistd.h> header shall define the following symbolic constants. The values shall be suitable for use in #if preprocessing directives.

_POSIX_VERSION

Integer value indicating version of this standard (C-language binding) to which the implementation conforms. For implementations conforming to POSIX.1-2024, the value shall be 202405L.

_POSIX2_VERSION

Integer value indicating version of the Shell and Utilities volume of POSIX.1 to which the implementation conforms. For implementations conforming to POSIX.1-2024, the value shall be 202405L. For profile implementations that define _POSIX_SUBPROFILE (see 2.1.5.1 Subprofiling Considerations) in <unistd.h>, _POSIX2_VERSION may be left undefined or be defined with the value -1 to indicate that the Shell and Utilities volume of POSIX.1 is not supported. In this case, a call to sysconf(_SC_2_VERSION) shall return either 202405L or -1 indicating that the Shell and Utilities volume of POSIX.1 is or is not, respectively, supported at runtime.

The <unistd.h> header shall define the following symbolic constant only if the implementation supports the XSI option; see 2.1.4 XSI Conformance. If defined, its value shall be suitable for use in #if preprocessing directives.

_XOPEN_VERSION

^[XSI]
Integer value indicating version of the X/Open Portability Guide to which the implementation conforms. The value shall be 800.

Constants for Options and Option Groups

The following symbolic constants, if defined in <unistd.h>, shall have a value of -1, 0, or greater, unless otherwise specified below. For profile implementations that define _POSIX_SUBPROFILE (see 2.1.5.1 Subprofiling Considerations) in <unistd.h>, constants described below as always having a value greater than zero need not be defined and, if defined, may have a value of -1, 0, or greater. The values shall be suitable for use in #if preprocessing directives.

If a symbolic constant is not defined or is defined with the value -1, the option is not supported for compilation. If it is defined with a value greater than zero, the option shall always be supported when the application is executed. If it is defined with the value zero, the option shall be supported for compilation and might or might not be supported at runtime. See 2.1.6 Options for further information about the conformance requirements of these three categories of support.

_POSIX_ADVISORY_INFO

^[ADV]
The implementation supports the Advisory Information option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_ASYNCHRONOUS_IO

The implementation supports asynchronous input and output. This symbol shall always be set to the value 202405L.

_POSIX_BARRIERS

The implementation supports barriers. This symbol shall always be set to the value 202405L.

_POSIX_CHOWN_RESTRICTED

The use of chown() and fchown() is restricted to a process with appropriate privileges, and to changing the group ID of a file only to the effective group ID of the process or to one of its supplementary group IDs. This symbol shall be defined with a value other than -1.

_POSIX_CLOCK_SELECTION

The implementation supports clock selection. This symbol shall always be set to the value 202405L.

_POSIX_CPUTIME

^[CPT]
The implementation supports the Process CPU-Time Clocks option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_DEVICE_CONTROL

^[DC]
The implementation supports the device control option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_FSYNC

^[FSC]
The implementation supports the File Synchronization option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_IPV6

^[IP6]
The implementation supports the IPv6 option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_JOB_CONTROL

The implementation supports job control. This symbol shall always be set to a value greater than zero.

_POSIX_MAPPED_FILES

The implementation supports memory mapped Files. This symbol shall always be set to the value 202405L.

_POSIX_MEMLOCK

^[ML]
The implementation supports the Process Memory Locking option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_MEMLOCK_RANGE

^[MLR]
The implementation supports the Range Memory Locking option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_MEMORY_PROTECTION

The implementation supports memory protection. This symbol shall always be set to the value 202405L.

_POSIX_MESSAGE_PASSING

^[MSG]
The implementation supports the Message Passing option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_MONOTONIC_CLOCK

The implementation supports a monotonic clock. This symbol shall always be set to the value 202405L.

_POSIX_NO_TRUNC

Pathname components longer than {NAME_MAX} generate an error. This symbol shall be defined with a value other than -1.

_POSIX_PRIORITIZED_IO

^[PIO]
The implementation supports the Prioritized Input and Output option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_PRIORITY_SCHEDULING

^[PS]
The implementation supports the Process Scheduling option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_RAW_SOCKETS

^[RS]
The implementation supports the Raw Sockets option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_READER_WRITER_LOCKS

The implementation supports read-write locks. This symbol shall always be set to the value 202405L.

_POSIX_REALTIME_SIGNALS

The implementation supports realtime signals. This symbol shall always be set to the value 202405L.

_POSIX_REGEXP

The implementation supports the Regular Expression Handling option. This symbol shall always be set to a value greater than zero.

_POSIX_SAVED_IDS

Each process has a saved set-user-ID and a saved set-group-ID. This symbol shall always be set to a value greater than zero.

_POSIX_SEMAPHORES

The implementation supports semaphores. This symbol shall always be set to the value 202405L.

_POSIX_SHARED_MEMORY_OBJECTS

^[SHM]
The implementation supports the Shared Memory Objects option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_SHELL

The implementation supports the POSIX shell. This symbol shall always be set to a value greater than zero.

_POSIX_SPAWN

^[SPN]
The implementation supports the Spawn option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_SPIN_LOCKS

The implementation supports spin locks. This symbol shall always be set to the value 202405L.

_POSIX_SPORADIC_SERVER

^[SS]
The implementation supports the Process Sporadic Server option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_SYNCHRONIZED_IO

^[SIO]
The implementation supports the Synchronized Input and Output option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_ATTR_STACKADDR

^[TSA]
The implementation supports the Thread Stack Address Attribute option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_ATTR_STACKSIZE

^[TSS]
The implementation supports the Thread Stack Size Attribute option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_CPUTIME

^[TCT]
The implementation supports the Thread CPU-Time Clocks option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_PRIO_INHERIT

^[TPI]
The implementation supports the Non-Robust Mutex Priority Inheritance option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_PRIO_PROTECT

^[TPP]
The implementation supports the Non-Robust Mutex Priority Protection option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_PRIORITY_SCHEDULING

^[TPS]
The implementation supports the Thread Execution Scheduling option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_PROCESS_SHARED

^[TSH]
The implementation supports the Thread Process-Shared Synchronization option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_ROBUST_PRIO_INHERIT

^[RPI]
The implementation supports the Robust Mutex Priority Inheritance option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_ROBUST_PRIO_PROTECT

^[RPP]
The implementation supports the Robust Mutex Priority Protection option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREAD_SAFE_FUNCTIONS

The implementation supports thread-safe functions. This symbol shall always be set to the value 202405L.

_POSIX_THREAD_SPORADIC_SERVER

^[TSP]
The implementation supports the Thread Sporadic Server option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_THREADS

The implementation supports threads. This symbol shall always be set to the value 202405L.

_POSIX_TIMEOUTS

The implementation supports timeouts. This symbol shall always be set to the value 202405L.

_POSIX_TIMERS

The implementation supports timers. This symbol shall always be set to the value 202405L.

_POSIX_TYPED_MEMORY_OBJECTS

^[TYM]
The implementation supports the Typed Memory Objects option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX_V7_ILP32_OFF32

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

_POSIX_V7_ILP32_OFFBIG

^[OB]
The implementation provides a C-language compilation environment with 32-bit int, long, and all pointer types, and an off_t type using at least 64 bits.

_POSIX_V7_LP64_OFF64

^[OB]
The implementation provides a C-language compilation environment with a 32-bit int type and 64-bit long, off_t, and all pointer types.

_POSIX_V7_LPBIG_OFFBIG

^[OB]
The implementation provides a C-language compilation environment with an int type using at least 32 bits and long, off_t, and all pointer types using at least 64 bits.

_POSIX_V8_ILP32_OFF32

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

_POSIX_V8_ILP32_OFFBIG

The implementation provides a C-language compilation environment with 32-bit int, long, and all pointer types, and an off_t type using at least 64 bits.

_POSIX_V8_LP64_OFF64

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

_POSIX_V8_LPBIG_OFFBIG

The implementation provides a C-language compilation environment with an int type using at least 32 bits and long, off_t, and all pointer types using at least 64 bits.

_POSIX2_C_BIND

The implementation supports the C-Language Binding option. This symbol shall always have the value 202405L.

_POSIX2_C_DEV

^[CD]
The implementation supports the C-Language Development Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX2_CHAR_TERM

The implementation supports the Terminal Characteristics option. The value of this symbol reported by sysconf() shall either be -1 or a value greater than zero.

_POSIX2_FORT_RUN

^[FR]
The implementation supports the FORTRAN Runtime Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX2_LOCALEDEF

The implementation supports the creation of locales by the localedef utility. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX2_SW_DEV

^[SD]
The implementation supports the Software Development Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_POSIX2_UPE

^[UP]
The implementation supports the User Portability Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall either be -1 or 202405L.

_XOPEN_CRYPT

^[XSI]
The implementation supports the X/Open Encryption Option Group.

_XOPEN_ENH_I18N

The implementation supports the Issue 4, Version 2 Enhanced Internationalization Option Group. This symbol shall always be set to a value other than -1.

_XOPEN_REALTIME

The implementation supports the X/Open Realtime Option Group.

_XOPEN_REALTIME_THREADS

The implementation supports the X/Open Realtime Threads Option Group.

_XOPEN_SHM

The implementation supports the Issue 4, Version 2 Shared Memory Option Group. This symbol shall always be set to a value other than -1.

_XOPEN_UNIX

The implementation supports the XSI option.

_XOPEN_UUCP

^[UU]
The implementation supports the UUCP Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 202405L. The value of this symbol reported by sysconf() shall be either -1 or 202405L.

Execution-Time Symbolic Constants

If any of the following symbolic constants are not defined in the <unistd.h> header, the value shall vary depending on the file to which it is applied. If defined, they shall have values suitable for use in #if preprocessing directives.

If any of the following symbolic constants are defined to have value -1 in the <unistd.h> header, the implementation shall not provide the option on any file; if any are defined to have a value other than -1 in the <unistd.h> header, the implementation shall provide the option on all applicable files.

All of the following values, whether defined as symbolic constants in <unistd.h> or not, may be queried with respect to a specific file using the pathconf() or fpathconf() functions:

_POSIX_ASYNC_IO

Asynchronous input or output operations may be performed for the associated file.

_POSIX_FALLOC

The posix_fallocate() function is supported by the associated file.

_POSIX_PRIO_IO

Prioritized input or output operations may be performed for the associated file.

_POSIX_SYNC_IO

Synchronized input or output operations may be performed for the associated file.

If the following symbolic constants are defined in the <unistd.h> header, they apply to files and all paths in all file systems on the implementation:

_POSIX_TIMESTAMP_RESOLUTION

The resolution in nanoseconds for all file timestamps.

_POSIX2_SYMLINKS

Symbolic links can be created.

Constants for Functions

The <unistd.h> header shall define NULL as described in <stddef.h>.

The <unistd.h> header shall define the symbolic constants O_CLOEXEC and O_CLOFORK as described in <fcntl.h>.

The <unistd.h> header shall define the following symbolic constants for use with the access() function. The values shall be suitable for use in #if preprocessing directives.

F_OK

Test for existence of file.

R_OK

Test for read permission.

W_OK

Test for write permission.

X_OK

Test for execute (search) permission.

The constants F_OK, R_OK, W_OK, and X_OK and the expressions R_OK|W_OK, R_OK|X_OK, and R_OK|W_OK|X_OK shall all have distinct values.

The <unistd.h> header shall define the following symbolic constants for the confstr() function:

_CS_PATH

This is the value for the PATH environment variable that finds all of the standard utilities that are provided in a manner accessible via the exec family of functions.

_CS_POSIX_V8_ILP32_OFF32_CFLAGS

If sysconf(_SC_V8_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 c17 utility to build an application using a programming model with 32-bit int, long, off_t, and all pointer types.

_CS_POSIX_V8_ILP32_OFF32_LDFLAGS

If sysconf(_SC_V8_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 c17 utility to build an application using a programming model with 32-bit int, long, off_t, and all pointer types.

_CS_POSIX_V8_ILP32_OFF32_LIBS

If sysconf(_SC_V8_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the c17 utility to build an application using a programming model with 32-bit int, long, off_t, and all pointer types.

_CS_POSIX_V8_ILP32_OFFBIG_CFLAGS

If sysconf(_SC_V8_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 c17 utility to build an application using a programming model with 32-bit int, long, and all pointer types, and an off_t type using at least 64 bits.

_CS_POSIX_V8_ILP32_OFFBIG_LDFLAGS

If sysconf(_SC_V8_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 c17 utility to build an application using a programming model with 32-bit int, long, and all pointer types, and an off_t type using at least 64 bits.

_CS_POSIX_V8_ILP32_OFFBIG_LIBS

If sysconf(_SC_V8_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the c17 utility to build an application using a programming model with 32-bit int, long, and all pointer types, and an off_t type using at least 64 bits.

_CS_POSIX_V8_LP64_OFF64_CFLAGS

If sysconf(_SC_V8_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 c17 utility to build an application using a programming model with a 32-bit int type and 64-bit long, off_t, and all pointer types.

_CS_POSIX_V8_LP64_OFF64_LDFLAGS

If sysconf(_SC_V8_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 c17 utility to build an application using a programming model with a 32-bit int type and 64-bit long, off_t, and all pointer types.

_CS_POSIX_V8_LP64_OFF64_LIBS

If sysconf(_SC_V8_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the c17 utility to build an application using a programming model with a 32-bit int type and 64-bit long, off_t, and all pointer types.

_CS_POSIX_V8_LPBIG_OFFBIG_CFLAGS

If sysconf(_SC_V8_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 c17 utility to build an application using a programming model with an int type using at least 32 bits and long, off_t, and all pointer types using at least 64 bits.

_CS_POSIX_V8_LPBIG_OFFBIG_LDFLAGS

If sysconf(_SC_V8_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 c17 utility to build an application using a programming model with an int type using at least 32 bits and long, off_t, and all pointer types using at least 64 bits.

_CS_POSIX_V8_LPBIG_OFFBIG_LIBS

If sysconf(_SC_V8_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the c17 utility to build an application using a programming model with an int type using at least 32 bits and long, off_t, and all pointer types using at least 64 bits.

_CS_POSIX_V8_THREADS_CFLAGS

This value is the set of initial options to be given to the c17 utility to build a multi-threaded application. These flags are in addition to those associated with any of the other _CS_POSIX_V8_*_CFLAGS values used to specify particular type size programming environments.

_CS_POSIX_V8_THREADS_LDFLAGS

This value is the set of final options to be given to the c17 utility to build a multi-threaded application. These flags are in addition to those associated with any of the other _CS_POSIX_V8_*_LDFLAGS values used to specify particular type size programming environments.

_CS_POSIX_V8_WIDTH_RESTRICTED_ENVS

This value is a <newline>-separated list of names of programming environments supported by the implementation in which the widths of the blksize_t, cc_t, mode_t, nfds_t, pid_t, ptrdiff_t, size_t, speed_t, ssize_t, suseconds_t, tcflag_t, wchar_t, and wint_t types are no greater than the width of type long. The format of each name shall be suitable for use with the getconf -v option.

_CS_V8_ENV

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.

^[OB] The following symbolic constants are reserved for compatibility with Issue 7:

_CS_POSIX_V7_ILP32_OFF32_CFLAGS
_CS_POSIX_V7_ILP32_OFF32_LDFLAGS
_CS_POSIX_V7_ILP32_OFF32_LIBS
_CS_POSIX_V7_ILP32_OFFBIG_CFLAGS
_CS_POSIX_V7_ILP32_OFFBIG_LDFLAGS
_CS_POSIX_V7_ILP32_OFFBIG_LIBS
_CS_POSIX_V7_LP64_OFF64_CFLAGS
_CS_POSIX_V7_LP64_OFF64_LDFLAGS
_CS_POSIX_V7_LP64_OFF64_LIBS
_CS_POSIX_V7_LPBIG_OFFBIG_CFLAGS
_CS_POSIX_V7_LPBIG_OFFBIG_LDFLAGS
_CS_POSIX_V7_LPBIG_OFFBIG_LIBS
_CS_POSIX_V7_THREADS_CFLAGS
_CS_POSIX_V7_THREADS_LDFLAGS
_CS_POSIX_V7_WIDTH_RESTRICTED_ENVS
_CS_V7_ENV

The implementation may define additional symbolic constants beginning with _CS_ for use by confstr().

The <unistd.h> header shall define SEEK_CUR, SEEK_END, and SEEK_SET as described in <stdio.h>.

Additionally, it shall define the following macros which shall expand to integer constant expressions with values that are distinct from each other and from SEEK_CUR, SEEK_END, and SEEK_SET:

SEEK_HOLE

Seek forwards from offset relative to start-of-file for a position within a hole.

SEEK_DATA

Seek forwards from offset relative to start-of-file for a position not within a hole

^[XSI] The <unistd.h> header shall define the following symbolic constants as possible values for the function argument to the lockf() function:

F_LOCK

Lock a section for exclusive use.

F_TEST

Test section for locks by other processes.

F_TLOCK

Test and lock a section for exclusive use.

F_ULOCK

Unlock locked sections.

The <unistd.h> header shall define the following symbolic constants for pathconf():

_PC_2_SYMLINKS
_PC_ALLOC_SIZE_MIN
_PC_ASYNC_IO
_PC_CHOWN_RESTRICTED
_PC_FALLOC
_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_TEXTDOMAIN_MAX
_PC_TIMESTAMP_RESOLUTION
_PC_VDISABLE

The implementation may define additional symbolic constants beginning with _PC_ for use by pathconf().

The <unistd.h> header shall define the following symbolic constants for sysconf():

_SC_2_C_BIND
_SC_2_C_DEV
_SC_2_CHAR_TERM
_SC_2_FORT_RUN
_SC_2_LOCALEDEF
_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_DEVICE_CONTROL
_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_NPROCESSORS_CONF
_SC_NPROCESSORS_ONLN
_SC_NSIG
_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_TTY_NAME_MAX
_SC_TYPED_MEMORY_OBJECTS
_SC_TZNAME_MAX
_SC_V8_ILP32_OFF32
_SC_V8_ILP32_OFFBIG
_SC_V8_LP64_OFF64
_SC_V8_LPBIG_OFFBIG
^[OB]
_SC_V7_ILP32_OFF32
_SC_V7_ILP32_OFFBIG
_SC_V7_LP64_OFF64
_SC_V7_LPBIG_OFFBIG

_SC_VERSION
_SC_XOPEN_CRYPT
_SC_XOPEN_ENH_I18N
_SC_XOPEN_REALTIME
_SC_XOPEN_REALTIME_THREADS
_SC_XOPEN_SHM
_SC_XOPEN_UNIX
_SC_XOPEN_UUCP
_SC_XOPEN_VERSION

The two constants _SC_PAGESIZE and _SC_PAGE_SIZE may be defined to have the same value.

The implementation may define additional symbolic constants beginning with _SC_ for use by sysconf().

The <unistd.h> header shall define the following symbolic constants for file streams:

STDERR_FILENO

File number of stderr; 2.

STDIN_FILENO

File number of stdin; 0.

STDOUT_FILENO

File number of stdout; 1.

The <unistd.h> header shall define the following symbolic constant for terminal special character handling:

_POSIX_VDISABLE

This symbol shall be defined to be the value of a character that shall disable terminal special character handling as described in 11.2.6 Special Control Characters. This symbol shall always be set to a value other than -1.

The <unistd.h> header shall define the following symbolic constant as a value for the flag used by posix_close():

POSIX_CLOSE_RESTART

Allows restarts if a signal interrupts a close operation. This constant shall not be 0 unless posix_close() never returns -1 with errno set to [EINTR].

Type Definitions

The <unistd.h> header shall define the size_t, ssize_t, uid_t, gid_t, off_t, and pid_t types as described in <sys/types.h>.

The <unistd.h> header shall define the intptr_t type as described in <stdint.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);
[XSI]
char        *crypt(const char *, const char *);

int          dup(int);


int          dup2(int, int);
int          dup3(int, int, int);
_Noreturn void
             _exit(int);
[OB XSI]
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);
[SIO]
int          fdatasync(int);

int          fexecve(int, char *const [], char *const []);
pid_t        _Fork(void);
pid_t        fork(void);
long         fpathconf(int, int);
[FSC]
int          fsync(int);

int          ftruncate(int, off_t);
char        *getcwd(char *, size_t);
gid_t        getegid(void);
int          getentropy(void *, size_t);
uid_t        geteuid(void);
gid_t        getgid(void);
int          getgroups(int, gid_t []);
[XSI]
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);
[XSI]
int          getresgid(gid_t *restrict, gid_t *restrict,
                 gid_t *restrict);
int          getresuid(uid_t *restrict, uid_t *restrict,
                 uid_t *restrict);

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);
[XSI]
int          lockf(int, int, off_t);

off_t        lseek(int, off_t, int);
[XSI]
int          nice(int);

long         pathconf(const char *, int);
int          pause(void);
int          pipe(int [2]);
int          pipe2(int [2], int);
int          posix_close(int, int);
ssize_t      pread(int, void *, size_t, off_t);
ssize_t      pwrite(int, const void *, size_t, off_t);
ssize_t      read(int, void *, size_t);
ssize_t      readlink(const char *restrict, char *restrict, size_t);
ssize_t      readlinkat(int, const char *restrict, char *restrict,
                 size_t);
int          rmdir(const char *);
int          setegid(gid_t);
int          seteuid(uid_t);
int          setgid(gid_t);


int          setpgid(pid_t, pid_t);
[XSI]
int          setregid(gid_t, gid_t);
int          setresgid(gid_t, gid_t, gid_t);
int          setresuid(uid_t, uid_t, uid_t);
int          setreuid(uid_t, uid_t);

pid_t        setsid(void);
int          setuid(uid_t);
unsigned     sleep(unsigned);
[XSI]
void         swab(const void *restrict, void *restrict, ssize_t);

int          symlink(const char *, const char *);
int          symlinkat(const char *, int, const char *);
[XSI]
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);

The <unistd.h> header shall declare the following external variables:

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

Inclusion of the <unistd.h> header may make visible all symbols from the headers <fcntl.h>, <stddef.h>, <stdint.h>, and <stdio.h>.

APPLICATION USAGE

POSIX.1-2024 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:

#if _POSIX_VERSION >= 200112L
/* Use the newer function that copes with large files. */
off_t pos=ftello(fp);
#else
/* Either this is an old version of POSIX, or _POSIX_VERSION is
   not even defined, so use the traditional function. */
long pos=ftell(fp);
#endif

Earlier versions of POSIX.1-2024 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

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

POSIX.1-2001 and Single UNIX Specification, Version 3

_POSIX_VERSION==200112L, plus (if the XSI option is supported) _XOPEN_UNIX and _XOPEN_VERSION==600

POSIX.1-2008, POSIX.1-2017, and Single UNIX Specification, Version 4

_POSIX_VERSION==200809L, plus (if the XSI option is supported) _XOPEN_UNIX and _XOPEN_VERSION==700

Note that _POSIX_VERSION did not change in POSIX.1-2017 as it was technically identical to POSIX.1-2008 with its two technical corrigenda applied.

POSIX.1-2024 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) < 202405L) {
    fprintf(stderr, "POSIX.1-2024 system required, terminating \n");
    exit(1);
}

Implementations may support multiple programming environments with some of them conforming to this standard and some not conforming. The _POSIX_Vn_ILP* and _POSIX_Vn_LP* constants, and corresponding sysconf() and getconf calls, only indicate whether each programming environment is supported; they do not indicate anything about conformance of the environments that are supported. For example, an implementation may support the ILP32_OFF32 environment for legacy reasons with a 32-bit time_t, whereas in a conforming environment time_t is required to have a width of at least 64 bits. Application writers should consult an implementation's POSIX Conformance Document for information about the conformance of each supported programming environment.

New applications should not use _XOPEN_SHM or _XOPEN_ENH_I18N.

RATIONALE

As POSIX.1-2024 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 POSIX.1-2024.

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 the production of a core image 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

POSIX.1-2024 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. POSIX.1-2024 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 POSIX.1-2024, 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 POSIX.1-2024.

FUTURE DIRECTIONS

None.

SEE ALSO

<limits.h>, <stddef.h>, <stdint.h>, <stdio.h>, <sys/socket.h>, <sys/types.h>, <termios.h>, <wctype.h>

XSH access, alarm, chown, close, confstr, crypt, ctermid, dup, _Exit, encrypt, exec, fchdir, fchown, fdatasync, fork, fpathconf, fsync, ftruncate, getcwd, getentropy, getegid, geteuid, getgid, getgroups, gethostid, gethostname, getlogin, getopt, getpgid, getpgrp, getpid, getppid, getresgid, getresuid, getsid, getuid, isatty, lchown, link, lockf, lseek, nice, pause, pipe, read, readlink, rmdir, setegid, seteuid, setgid, setpgid, setregid, setresgid, setresuid, setreuid, setsid, setuid, sleep, swab, symlink, sync, sysconf, tcgetpgrp, tcsetpgrp, truncate, ttyname, unlink, write

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

The DESCRIPTION is updated for alignment with the POSIX Realtime Extension and the POSIX Threads Extension.

The symbolic constants _XOPEN_REALTIME and _XOPEN_REALTIME_THREADS are added. _POSIX2_C_BIND, _XOPEN_ENH_I18N, and _XOPEN_SHM must now be set to a value other than -1 by a conforming implementation.

Large File System extensions are added.

The type of the argument to sbrk() is changed from int to intptr_t.

_XBS_ constants are added to the list of constants for Options and Option Groups, to the list of constants for the confstr() function, and to the list of constants to the sysconf() function. These are all marked EX.

Issue 6

_POSIX2_C_VERSION is removed.

The Open Group Corrigendum U026/4 is applied, adding the prototype for fdatasync().

The Open Group Corrigendum U026/1 is applied, adding the symbols _SC_XOPEN_LEGACY, _SC_XOPEN_REALTIME, and _SC_XOPEN_REALTIME_THREADS.

The symbols _XOPEN_STREAMS and _SC_XOPEN_STREAMS are added to support the XSI STREAMS Option Group.

Text in the DESCRIPTION relating to conformance requirements is moved elsewhere in IEEE Std 1003.1-2001.

The LEGACY symbol _SC_PASS_MAX is removed.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

• The _CS_POSIX_* and _CS_XBS5_* constants are added for the confstr() function.

• The _SC_XBS5_* constants are added for the sysconf() function.

• The symbolic constants F_ULOCK, F_LOCK, F_TLOCK, and F_TEST are added.

• The uid_t, gid_t, off_t, pid_t, and useconds_t types are mandated.

The gethostname() prototype is added for sockets.

A new section is added for System-Wide Options.

Function prototypes for setegid() and seteuid() are added.

Option symbolic constants are added for _POSIX_ADVISORY_INFO, _POSIX_CPUTIME, _POSIX_SPAWN, _POSIX_SPORADIC_SERVER, _POSIX_THREAD_CPUTIME, _POSIX_THREAD_SPORADIC_SERVER, and _POSIX_TIMEOUTS, and pathconf() variables are added for _PC_ALLOC_SIZE_MIN, _PC_REC_INCR_XFER_SIZE, _PC_REC_MAX_XFER_SIZE, _PC_REC_MIN_XFER_SIZE, and _PC_REC_XFER_ALIGN for alignment with IEEE Std 1003.1d-1999.

The following are added for alignment with IEEE Std 1003.1j-2000:

• Option symbolic constants _POSIX_BARRIERS, _POSIX_CLOCK_SELECTION, _POSIX_MONOTONIC_CLOCK, _POSIX_READER_WRITER_LOCKS, _POSIX_SPIN_LOCKS, and _POSIX_TYPED_MEMORY_OBJECTS

• sysconf() variables _SC_BARRIERS, _SC_CLOCK_SELECTION, _SC_MONOTONIC_CLOCK, _SC_READER_WRITER_LOCKS, _SC_SPIN_LOCKS, and _SC_TYPED_MEMORY_OBJECTS

The _SC_XBS5 macros associated with the ISO/IEC 9899:1990 standard are marked LEGACY, and new equivalent _SC_V6 macros associated with the ISO/IEC 9899:1999 standard are introduced.

The getwd() function is marked LEGACY.

The restrict keyword is added to the prototypes for readlink() and swab().

Constants for options are now harmonized, so when supported they take the year of approval of IEEE Std 1003.1-2001 as the value.

The following are added for alignment with IEEE Std 1003.1q-2000:

• Optional symbolic constants _POSIX_TRACE, _POSIX_TRACE_EVENT_FILTER, _POSIX_TRACE_LOG, and _POSIX_TRACE_INHERIT

• The sysconf() symbolic constants _SC_TRACE, _SC_TRACE_EVENT_FILTER, _SC_TRACE_LOG, and _SC_TRACE_INHERIT

The brk() and sbrk() LEGACY functions are removed.

The Open Group Base Resolution bwg2001-006 is applied, which reworks the XSI versioning information.

The Open Group Base Resolution bwg2001-008 is applied, changing the namelen parameter for gethostname() from socklen_t to size_t.

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/2 is applied, changing "Thread Stack Address Size" to "Thread Stack Size Attribute".

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/20 is applied, adding the _POSIX_IPV6, _SC_V6, and _SC_RAW_SOCKETS symbols.

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/21 is applied, correcting the description in "Constants for Functions" for the _CS_POSIX_V6_LP64_OFF64_CFLAGS, _CS_POSIX_V6_LP64_OFF64_LDFLAGS, and _CS_POSIX_V6_LP64_OFF64_LIBS symbols.

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/22 is applied, removing the shading for the _PC* and _SC* constants, since these are mandatory on all implementations.

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/23 is applied, adding the _PC_SYMLINK_MAX and _SC_SYMLOOP_MAX constants.

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/24 is applied, correcting the shading and margin code for the fsync() function.

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/25 is applied, adding the following text to the APPLICATION USAGE section: "New applications should not use _XOPEN_SHM or _XOPEN_ENH_I18N.".

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/29 is applied, clarifying the requirements for when constants for Options and Option Groups can be defined or undefined.

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/30 is applied, changing the _V6_ILP32_OFF32, _V6_ILP32_OFFBIG, _V6_LP64_OFF64, and _V6_LPBIG_OFFBIG symbols to _POSIX_V6_ILP32_OFF32, _POSIX_V6_ILP32_OFFBIG, _POSIX_V6_LP64_OFF64, and _POSIX_V6_LPBIG_OFFBIG, respectively. This is for consistency with the sysconf() and c99 reference pages.

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/31 is applied, adding that the format of names of programming environments can be obtained using the getconf -v option.

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/32 is applied, deleting the _SC_FILE_LOCKING, _SC_2_C_VERSION, and _SC_XOPEN_XCU_VERSION constants.

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/33 is applied, adding _SC_SS_REPL_MAX, _SC_TRACE_EVENT_NAME_MAX, _SC_TRACE_NAME_MAX, _SC_TRACE_SYS_MAX, and _SC_TRACE_USER_EVENT_MAX to the list of symbolic constants for sysconf().

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/34 is applied, updating the prototype for the symlink() function to match that in the System Interfaces volume of IEEE Std 1003.1-2001.

IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/35 is applied, adding _PC_2_SYMLINKS to the symbolic constants list for pathconf(). This corresponds to the definition of POSIX2_SYMLINKS in the Shell and Utilities volume of IEEE Std 1003.1-2001.

Issue 7

Austin Group Interpretations 1003.1-2001 #026 and #047 are applied.

Austin Group Interpretation 1003.1-2001 #166 is applied to permit an additional compiler flag to enable threads.

Austin Group Interpretation 1003.1-2001 #178 is applied, clarifying the values allowed for _POSIX2_CHAR_TERM.

SD5-XBD-ERN-41 is applied, adding the _POSIX2_SYMLINKS constant.

SD5-XBD-ERN-76 and SD5-XBD-ERN-77 are applied.

Symbols to support the UUCP Utilities option are added.

The variables for the supported programming environments are updated to be V7.

The LEGACY and obsolescent symbols are removed.

The faccessat(), fchownat(), fexecve(), linkat(), readlinkat(), symlinkat(), and unlinkat() functions are added from The Open Group Technical Standard, 2006, Extended API Set Part 2.

The _POSIX_TRACE* constants from the Trace option are marked obsolescent.

The _POSIX2_PBS* constants from the Batch Environment Services and Utilities option are marked obsolescent.

Functionality relating to the Asynchronous Input and Output, Barriers, Clock Selection, Memory Mapped Files, Memory Protection, Realtime Signals Extension, Semaphores, Spin Locks, Threads, Timeouts, and Timers options is moved to the Base.

Functionality relating to the Thread Priority Protection and Thread Priority Inheritance options is changed to be Non-Robust Mutex or Robust Mutex Priority Protection and Non-Robust Mutex or Robust Mutex Priority Inheritance, respectively.

This reference page is clarified with respect to macros and symbolic constants.

Changes are made related to support for finegrained timestamps and the _POSIX_TIMESTAMP_RESOLUTION constant is added.

The _SC_THREAD_ROBUST_PRIO_INHERIT and _SC_THREAD_ROBUST_PRIO_PROTECT symbolic constants are added.

POSIX.1-2008, Technical Corrigendum 1, XBD/TC1-2008/0078 [311], XBD/TC1-2008/0079 [209], and XBD/TC1-2008/0080 [360] are applied.

POSIX.1-2008, Technical Corrigendum 2, XBD/TC2-2008/0085 [783], XBD/TC2-2008/0086 [911], and XBD/TC2-2008/0087 [566] are applied.

Issue 8

Austin Group Defect 62 is applied, adding the _Fork() function.

Austin Group Defect 339 is applied, adding _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN.

Austin Group Defects 411 and 598 are applied, adding dup3() and pipe2().

Austin Group Defects 415 and 1357 are applied, adding SEEK_HOLE and SEEK_DATA.

Austin Group Defect 529 is applied, adding the POSIX_CLOSE_RESTART symbolic constant and the posix_close() function.

Austin Group Defect 687 is applied, adding _POSIX_FALLOC and _PC_FALLOC.

Austin Group Defect 729 is applied, adding _POSIX_DEVICE_CONTROL and _SC_DEVICE_CONTROL.

Austin Group Defect 741 is applied, adding _SC_NSIG.

Austin Group Defects 1074 and 1116 are applied, changing the descriptions of _CS_POSIX_V8_THREADS_CFLAGS and _CS_POSIX_V8_THREADS_LDFLAGS.

Austin Group Defect 1122 is applied, adding _PC_TEXTDOMAIN_MAX.

Austin Group Defect 1134 is applied, adding getentropy().

Austin Group Defect 1141 is applied, changing the RATIONALE section.

Austin Group Defect 1192 is applied, marking the encrypt() function as obsolescent.

Austin Group Defect 1302 is applied, adding _Noreturn to _exit().

Austin Group Defects 1330 and 1595 are applied, removing obsolescent interfaces and changing "_V7_" to "_V8_" and "_V6_" to "_V7_".

Austin Group Defects 1344 and 1666 are applied, adding getresgid(), getresuid(), setresgid(), and setresuid().

Austin Group Defect 1346 is applied, requiring support for Monotonic Clock.

Austin Group Defect 1456 is applied, clarifying the reservation of symbolic constants with the prefix _CS_, _PC_, and _SC_.

Austin Group Defect 1462 is applied, adding a paragraph to APPLICATION USAGE about conformance of supported programming environments.

Austin Group Defect 1473 is applied, updating the list of earlier versions of this standard in the APPLICATION USAGE section.

Austin Group Defect 1518 is applied, correcting the spelling of "programming".

Austin Group Defect 1569 is applied, changing references to a pointer type to "all pointer types".