Defines implementation characteristics identified by POSIX standard.
The /usr/include/unistd.h file includes files that contain definitions that are required for compatibility with the POSIX standard:
| Item | Description |
|---|---|
| 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:
| Item | Description |
|---|---|
| _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:
| Item | Description |
|---|---|
| _XOPEN_VERSION | The version of the X/OPEN standard with which this version of the operating system complies. |