Files Reference

unistd.h File

Purpose

Defines implementation characteristics identified by POSIX standard.

Description

The /usr/include/unistd.h file includes files that contain definitions that are required for compatibility with the POSIX standard:

access.h

Defines symbolic constants for the access subroutine.

The unistd.h file also defines symbolic constants for the pathconf, fpathconf, and sysconf subroutines. The unistd.h file also defines the following symbols, which are used by POSIX applications to determine implementation characteristics:

_POSIX_JOB_CONTROL	POSIX-compatible job control is supported.
_POSIX_SAVED_IDS	An exec subroutine saves the effective user and group IDs.
_POSIX_VERSION	The version of the POSIX standard with which this version of the operating system complies. The value of this symbol is 198808L.
_POSIX_CHOWN_RESTRICTED	The use of the chown function is restricted to a process with the appropriate privileges. The group ID of a file can be changed only to the effective group ID or a supplementary group ID of the process. The value of this symbol is -1.
_POSIX_VDISABLE	The terminal special characters, which are defined in the termios.h file, can be disabled if this character value is defined by the tcsetattr subroutine. The value of this symbol is -1.
_POSIX_NO_TRUNC	Path name components that are longer than NAME_MAX will generate an error.

The unistd.h file also defines the following symbol, which is used by X/OPEN applications:

_XOPEN_VERSION

The version of the X/OPEN standard with which this version of the operating system complies.

Implementation Specifics

This file is provided for POSIX compatibility.

This file is part of Base Operating System (BOS) Runtime.

Related Information

The limits.h file, sys/types.h file, termios.h file, values.h file.

The access subroutine, exec subroutine.

Header Files Overview.