unistd(4)

unistd -- header file for symbolic constants

Synopsis

   #include <unistd.h>

Description

The unistd.h header file defines the symbolic constants and structures not already defined or declared in some other header file. The contents of this file are shown below.

The following symbolic constants are defined for the access function (see access(2)):

R_OK: Test for read permission.
W_OK: Test for write permission.
X_OK: Test for execute (search) permission.
F_OK: Test for existence of file.
EFF_ONLY_OK: Use effective ids instead of real ids.

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 all have distinct values. EFF_ONLY_OK can be ORed with any of these.

unistd declares the constant

NULL: null pointer

The following symbolic constants are defined for the lockf(3C) function:

F_ULOCK: Unlock a previously locked region.
F_LOCK: Lock a region for exclusive use.
F_TLOCK: Test and lock a region for exclusive use.
F_TEST: Test a region for other processes locks.

The following symbolic constants are defined for the lseek(2) and fcntl(2) functions (they have distinct values):

SEEK_SET: Set file offset to offset.
SEEK_CUR: Set file offset to current plus offset.
SEEK_END: Set file offset to EOF plus offset.

The following symbolic constants are defined (with fixed values):

_POSIX_VERSION: Integer value indicating version of the POSIX standard.
_XOPEN_VERSION: Integer value indicating version of the XPG to which system is compliant.

The following symbolic constant is defined for the confstr function:

_CS_PATH: Indicates whether to use the default PATH environment variable that finds all the standard utilities.

The following symbolic constants are defined to indicate that the option is present:

_POSIX_JOB_CONTROL: Implementation supports job control.
_POSIX_SAVED_IDS: The exec(2) functions save the effective user and group.
_POSIX_VDISABLE: Terminal special characters defined in termios.h (see termio(7)) can be disabled using this character.

The following symbolic constants are defined for version test macros:

_LFS_LARGEFILE: Defined to be ``1'' if the implementation supports the fseeko(3S) and ftello(3S) functions.
_LFS_ASYNCHRONOUS_IO: Defined to be ``1'' if the implementation supports the aio_read(3aio), aio_write(3aio), and lio_listio(3S) functions.
_LFS64_LARGEFILE: Defined to be ``1'' if the implementation supports the transitional functions creat64(2), fstat64(2), fstatvfs64(2), ftruncate64(3C), ftw64(3C), getrlimit64(2), lockf64(3C), lseek64(2), lstat64(2), mmap64(2), nftw64(3C), open64(2), readdir64(3C), stat64(2), setrlimit64(2), statvfs64(2), truncate64(3C),
_LFS64_ASYNCHRONOUS_IO: Defined to be ``1'' if the implementation supports the transitional functions aio_cancel64(3aio), aio_error64(3aio), aio_fsync64(3aio), aio_read64(3aio), aio_return64(3aio), aio_suspend64(3aio), aio_write64(3aio), and lio_listio64(3S).
_LFS64_STDIO: Defined to be ``1'' if the implementation supports the transitional functions fgetpos64(3C), freopen64(3S), fsetpos64(3C), tmpfile64(3S), fopen64(3S), fseeko64(3S), and ftello64(3S),

The following symbolic constants are defined for sysconf(3C):

   _SC_ARG_MAX 
   _SC_CHILD_MAX 
   _SC_CLK_TCK 
   _SC_JOB_CONTROL 
   _SC_LOGNAME_MAX 
   _SC_NGROUPS_MAX 
   _SC_OPEN_MAX 
   _SC_PAGESIZE 
   _SC_PASS_MAX 
   _SC_SAVED_IDS 
   _SC_VERSION 
   _SC_XOPEN_VERSION 
   _SC_TZNAME_MAX 
   _SC_STREAM_MAX 
   _SC_XOPEN_SHM 
   _SC_XOPEN_CRYPT 
   _SC_XOPEN_ENH_I18N 
   _SC_2_LOCALDEF 
   _SC_BC_BASE_MAX 
   _SC_BC_DIM_MAX 
   _SC_BC_SCALE_MAX 
   _SC_BC_STRING_MAX 
   _SC_COLL_WEIGHTS_MAX 
   _SC_EXPR_NEST_MAX 
   _SC_LINE_MAX 
   _SC_RE_DUP_MAX 
   _SC_XOPEN_UNIX 
   _SC_2_VERSION 
   _SC_2_C_DEV 
   _SC_2_C_BIND 
   _SC_2_C_VERSION 
   _SC_2_CHAR_TERM 
   _SC_2_FORT_DEV 
   _SC_2_SW_DEV 
   _SC_2_UPE

The following symbolic constants are defined for fpathconf(2):

   _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_VDISABLE

The following symbolic constants are defined for file streams:

STDIN_FILENO: File number of stdin. It is 0.
STDOUT_FILENO: File number of stout. It is 1.
STDERR_FILENO: File number of stderr. It is 2.

The following pathnames are defined:

GF_PATH: Pathname of the group file.
PF_PATH: Pathname of the passwd file.

References

access(2), exec(2), fcntl(2), fork(2), fpathconf(2), group(4), lseek(2), passwd(4), pread(2), pwrite(2), sysconf(3C), termio(7), termios(3C)

Notices

The following values for constants are defined for UnixWare:

_POSIX_VERSION: 199009L
_XOPEN_VERSION: 4
_XOPEN_ENH_I18N: (-1L)
_XOPEN_XPG4: 1
_POSIX2_C_VERSION: (-1L)
_XOPEN_XCU_VERSION: 3