Manpages - unistd.h.0p

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.1‐2008, the value shall be 200809L.

_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.1‐2008, the value shall be 200809L. For profile implementations that define _POSIX_SUBPROFILE (see Section 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 200809L 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 Section 2.1.4, XSI Conformance. If defined, its value shall be suitable for use in #if preprocessing directives.

_XOPEN_VERSION

Integer value indicating version of the X/Open Portability Guide to which the implementation conforms. The value shall be 700.

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 Section 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 Section 2.1.6, Options for further information about the conformance requirements of these three categories of support.

_POSIX_ADVISORY_INFO

The implementation supports the Advisory Information option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_ASYNCHRONOUS_IO

The implementation supports asynchronous input and output. This symbol shall always be set to the value 200809L.

_POSIX_BARRIERS

The implementation supports barriers. This symbol shall always be set to the value 200809L.

_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 200809L.

_POSIX_CPUTIME

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_FSYNC

The implementation supports the File Synchronization option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_IPV6

The implementation supports the IPv6 option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_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 200809L.

_POSIX_MEMLOCK

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_MEMLOCK_RANGE

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_MEMORY_PROTECTION

The implementation supports memory protection. This symbol shall always be set to the value 200809L.

_POSIX_MESSAGE_PASSING

The implementation supports the Message Passing option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_MONOTONIC_CLOCK

The implementation supports the Monotonic Clock option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_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

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_PRIORITY_SCHEDULING

The implementation supports the Process Scheduling option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_RAW_SOCKETS

The implementation supports the Raw Sockets option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_READER_WRITER_LOCKS

The implementation supports read-write locks. This symbol shall always be set to the value 200809L.

_POSIX_REALTIME_SIGNALS

The implementation supports realtime signals. This symbol shall always be set to the value 200809L.

_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 200809L.

_POSIX_SHARED_MEMORY_OBJECTS

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_SHELL

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

_POSIX_SPAWN

The implementation supports the Spawn option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_SPIN_LOCKS

The implementation supports spin locks. This symbol shall always be set to the value 200809L.

_POSIX_SPORADIC_SERVER

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_SYNCHRONIZED_IO

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_ATTR_STACKADDR

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_ATTR_STACKSIZE

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_CPUTIME

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_PRIO_INHERIT

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_PRIO_PROTECT

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_PRIORITY_SCHEDULING

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_PROCESS_SHARED

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_ROBUST_PRIO_INHERIT

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_ROBUST_PRIO_PROTECT

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREAD_SAFE_FUNCTIONS

The implementation supports thread-safe functions. This symbol shall always be set to the value 200809L.

_POSIX_THREAD_SPORADIC_SERVER

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_THREADS

The implementation supports threads. This symbol shall always be set to the value 200809L.

_POSIX_TIMEOUTS

The implementation supports timeouts. This symbol shall always be set to the value 200809L.

_POSIX_TIMERS

The implementation supports timers. This symbol shall always be set to the value 200809L.

_POSIX_TRACE

The implementation supports the Trace option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_TRACE_EVENT_FILTER

The implementation supports the Trace Event Filter option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_TRACE_INHERIT

The implementation supports the Trace Inherit option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_TRACE_LOG

The implementation supports the Trace Log option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_TYPED_MEMORY_OBJECTS

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX_V6_ILP32_OFF32

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

_POSIX_V6_ILP32_OFFBIG

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

_POSIX_V6_LP64_OFF64

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

_POSIX_V6_LPBIG_OFFBIG

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

_POSIX_V7_ILP32_OFF32

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

_POSIX_V7_ILP32_OFFBIG

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

_POSIX_V7_LP64_OFF64

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

_POSIX_V7_LPBIG_OFFBIG

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

_POSIX2_C_BIND

The implementation supports the C-Language Binding option. This symbol shall always have the value 200809L.

_POSIX2_C_DEV

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_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_DEV

The implementation supports the FORTRAN Development Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_FORT_RUN

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_PBS

The implementation supports the Batch Environment Services and Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_PBS_ACCOUNTING

The implementation supports the Batch Accounting option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_PBS_CHECKPOINT

The implementation supports the Batch Checkpoint/Restart option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_PBS_LOCATE

The implementation supports the Locate Batch Job Request option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_PBS_MESSAGE

The implementation supports the Batch Job Message Request option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_PBS_TRACK

The implementation supports the Track Batch Job Request option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_SW_DEV

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_POSIX2_UPE

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 200809L. The value of this symbol reported by /sysconf/() shall either be -1 or 200809L.

_XOPEN_CRYPT

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_STREAMS

The implementation supports the XSI STREAMS Option Group.

_XOPEN_UNIX

The implementation supports the XSI option.

_XOPEN_UUCP

The implementation supports the UUCP Utilities option. If this symbol is defined in <unistd.h>, it shall be defined to be -1, 0, or 200809L. The value of this symbol reported by /sysconf/() shall be either -1 or 200809L.

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_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.

The <unistd.h> header shall define NULL as described in <stddef.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_V7_ILP32_OFF32_CFLAGS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int, long, pointer, and off_t types.

_CS_POSIX_V7_ILP32_OFF32_LDFLAGS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int, long, pointer, and off_t types.

_CS_POSIX_V7_ILP32_OFF32_LIBS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int, long, pointer, and off_t types.

_CS_POSIX_V7_ILP32_OFFBIG_CFLAGS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.

_CS_POSIX_V7_ILP32_OFFBIG_LDFLAGS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.

_CS_POSIX_V7_ILP32_OFFBIG_LIBS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.

_CS_POSIX_V7_LP64_OFF64_CFLAGS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int and 64-bit long, pointer, and off_t types.

_CS_POSIX_V7_LP64_OFF64_LDFLAGS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int and 64-bit long, pointer, and off_t types.

_CS_POSIX_V7_LP64_OFF64_LIBS

If /sysconf/(_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 c99 utility to build an application using a programming model with 32-bit int and 64-bit long, pointer, and off_t types.

_CS_POSIX_V7_LPBIG_OFFBIG_CFLAGS

If /sysconf/(_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 c99 utility to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.

_CS_POSIX_V7_LPBIG_OFFBIG_LDFLAGS

If /sysconf/(_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 c99 utility to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.

_CS_POSIX_V7_LPBIG_OFFBIG_LIBS

If /sysconf/(_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 c99 utility to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.

_CS_POSIX_V7_THREADS_CFLAGS

If /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 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.

_CS_POSIX_V7_THREADS_LDFLAGS

If /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 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.

_CS_POSIX_V7_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_V7_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.

The following symbolic constants are reserved for compatibility with Issue 6:

  _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

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

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_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

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_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

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

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 Section 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 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>.

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);
    char        *crypt(const char *, const char *);
    int          dup(int);


    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);


    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);

Implementations may also include the pthread_atfork/() prototype as defined in /<pthread.h>. Implementations may also include the ctermid/() prototype as defined in /<stdio.h>.

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 <stddef.h>, <stdint.h>, and <stdio.h>.

The following sections are informative.

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.1‐2008.

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 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.

POSIX.1‐2008 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.1‐2008 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.1‐2008, 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.1‐2008.