The following symbolic constants shall be defined:

_POSIX_VERSION

Integer value indicating version of IEEE Std 1003.1 (C-language binding) to which the implementation conforms. For implementations conforming to IEEE Std 1003.1-2001, the value shall be 200112L.

_POSIX2_VERSION

Integer value indicating version of the Shell and Utilities volume of IEEE Std 1003.1 to which the implementation conforms. For implementations conforming to IEEE Std 1003.1-2001, the value shall be 200112L.

The following symbolic constant shall be defined only if the implementation supports the XSI option; see XSI Conformance .

_XOPEN_VERSION

Integer value indicating version of the X/Open Portability Guide to which the implementation conforms. The value shall be 600.

The following symbolic constants, if defined in <unistd.h>, shall have a value of -1, 0, or greater, unless otherwise specified below. If these are undefined, the fpathconf(), pathconf(), or sysconf() functions can be used to determine whether the option is provided for a particular invocation of the application.

If a symbolic constant is defined with the value -1, the option is not supported. Headers, data types, and function interfaces required only for the option need not be supplied. An application that attempts to use anything associated only with the option is considered to be requiring an extension.

If a symbolic constant is defined with a value greater than zero, the option shall always be supported when the application is executed. All headers, data types, and functions shall be present and shall operate as specified.

If a symbolic constant is defined with the value zero, all headers, data types, and functions shall be present. The application can check at runtime to see whether the option is supported by calling fpathconf(), pathconf(), or sysconf() with the indicated name parameter.

Unless explicitly specified otherwise, the behavior of functions associated with an unsupported option is unspecified, and an application that uses such functions without first checking fpathconf(), pathconf(), or sysconf() is considered to be requiring an extension.

For conformance requirements, refer to Conformance .

_POSIX_ADVISORY_INFO

The implementation supports the Advisory Information option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_ASYNCHRONOUS_IO

The implementation supports the Asynchronous Input and Output option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_BARRIERS

The implementation supports the Barriers option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_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 always be set to a value other than -1.

_POSIX_CLOCK_SELECTION

The implementation supports the Clock Selection option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_CPUTIME

The implementation supports the Process CPU-Time Clocks option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_FSYNC

The implementation supports the File Synchronization option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_IPV6

The implementation supports the IPv6 option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_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 the Memory Mapped Files option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_MEMLOCK

The implementation supports the Process Memory Locking option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_MEMLOCK_RANGE

The implementation supports the Range Memory Locking option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_MEMORY_PROTECTION

The implementation supports the Memory Protection option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_MESSAGE_PASSING

The implementation supports the Message Passing option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_MONOTONIC_CLOCK

The implementation supports the Monotonic Clock option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_NO_TRUNC

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

_POSIX_PRIORITIZED_IO

The implementation supports the Prioritized Input and Output option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_PRIORITY_SCHEDULING

The implementation supports the Process Scheduling option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_RAW_SOCKETS

The implementation supports the Raw Sockets option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_READER_WRITER_LOCKS

The implementation supports the Read-Write Locks option. This is always set to a value greater than zero if the Threads option is supported. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_REALTIME_SIGNALS

The implementation supports the Realtime Signals Extension option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_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 the Semaphores option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_SHARED_MEMORY_OBJECTS

The implementation supports the Shared Memory Objects option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_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 has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_SPIN_LOCKS

The implementation supports the Spin Locks option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_SPORADIC_SERVER

The implementation supports the Process Sporadic Server option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_SYNCHRONIZED_IO

The implementation supports the Synchronized Input and Output option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_ATTR_STACKADDR

The implementation supports the Thread Stack Address Attribute option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_ATTR_STACKSIZE

The implementation supports the Thread Stack Size Attribute option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_CPUTIME

The implementation supports the Thread CPU-Time Clocks option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_PRIO_INHERIT

The implementation supports the Thread Priority Inheritance option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_PRIO_PROTECT

The implementation supports the Thread Priority Protection option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_PRIORITY_SCHEDULING

The implementation supports the Thread Execution Scheduling option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_PROCESS_SHARED

The implementation supports the Thread Process-Shared Synchronization option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_SAFE_FUNCTIONS

The implementation supports the Thread-Safe Functions option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREAD_SPORADIC_SERVER

The implementation supports the Thread Sporadic Server option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_THREADS

The implementation supports the Threads option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_TIMEOUTS

The implementation supports the Timeouts option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_TIMERS

The implementation supports the Timers option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_TRACE

The implementation supports the Trace option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_TRACE_EVENT_FILTER

The implementation supports the Trace Event Filter option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_TRACE_INHERIT

The implementation supports the Trace Inherit option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_TRACE_LOG

The implementation supports the Trace Log option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_TYPED_MEMORY_OBJECTS

The implementation supports the Typed Memory Objects option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX_VDISABLE

This symbol shall be defined to be the value of a character that shall disable terminal special character handling as described in <termios.h> . This symbol shall always be set to a value other than -1.

_POSIX2_C_BIND

The implementation supports the C-Language Binding option. This symbol shall always have the value 200112L.

_POSIX2_C_DEV

The implementation supports the C-Language Development Utilities option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_CHAR_TERM

The implementation supports at least one terminal type.

_POSIX2_FORT_DEV

The implementation supports the FORTRAN Development Utilities option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_FORT_RUN

The implementation supports the FORTRAN Runtime Utilities option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_LOCALEDEF

The implementation supports the creation of locales by the localedef utility. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_PBS

The implementation supports the Batch Environment Services and Utilities option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_PBS_ACCOUNTING

The implementation supports the Batch Accounting option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_PBS_CHECKPOINT

The implementation supports the Batch Checkpoint/Restart option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_PBS_LOCATE

The implementation supports the Locate Batch Job Request option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_PBS_MESSAGE

The implementation supports the Batch Job Message Request option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_PBS_TRACK

The implementation supports the Track Batch Job Request option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_SW_DEV

The implementation supports the Software Development Utilities option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_POSIX2_UPE

The implementation supports the User Portability Utilities option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.

_V6_ILP32_OFF32

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

_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.

_V6_LP64_OFF64

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

_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.

_XBS5_ILP32_OFF32 (LEGACY)

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

_XBS5_ILP32_OFFBIG (LEGACY)

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.

_XBS5_LP64_OFF64 (LEGACY)

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

_XBS5_LPBIG_OFFBIG (LEGACY)

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.

_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_LEGACY

The implementation supports the Legacy Option Group.

_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 extension.

If any of the following constants are not defined in the <unistd.h> header, the value shall vary depending on the file to which it is applied.

If any of the following 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 constants, whether defined 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.

The following symbolic constant shall be defined:

NULL

Null pointer

The following symbolic constants shall be defined for the access() function:

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 following symbolic constants shall be defined for the confstr() function:

_CS_PATH

This is the value for the PATH environment variable that finds all standard utilities.

_CS_POSIX_V6_ILP32_OFF32_CFLAGS

If sysconf(_SC_V6_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_V6_ILP32_OFF32_LDFLAGS

If sysconf(_SC_V6_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_V6_ILP32_OFF32_LIBS

If sysconf(_SC_V6_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_V6_ILP32_OFFBIG_CFLAGS

If sysconf(_SC_V6_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_V6_ILP32_OFFBIG_LDFLAGS

If sysconf(_SC_V6_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_V6_ILP32_OFFBIG_LIBS

If sysconf(_SC_V6_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_V6_LP64_OFF64_CFLAGS

If sysconf(_SC_V6_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_V6_LP64_OFF64_LDFLAGS

If sysconf(_SC_V6_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_V6_LP64_OFF64_LIBS

If sysconf(_SC_V6_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_V6_LPBIG_OFFBIG_CFLAGS

If sysconf(_SC_V6_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_V6_LPBIG_OFFBIG_LDFLAGS

If sysconf(_SC_V6_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_V6_LPBIG_OFFBIG_LIBS

If sysconf(_SC_V6_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_V6_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, useconds_t, wchar_t, and wint_t types are no greater than the width of type long.

The following symbolic constants are reserved for compatibility with Issue 5:

_CS_XBS5_ILP32_OFF32_CFLAGS (LEGACY)

_CS_XBS5_ILP32_OFF32_LDFLAGS (LEGACY)

_CS_XBS5_ILP32_OFF32_LIBS (LEGACY)

_CS_XBS5_ILP32_OFF32_LINTFLAGS (LEGACY)

_CS_XBS5_ILP32_OFFBIG_CFLAGS (LEGACY)

_CS_XBS5_ILP32_OFFBIG_LDFLAGS (LEGACY)

_CS_XBS5_ILP32_OFFBIG_LIBS (LEGACY)

_CS_XBS5_ILP32_OFFBIG_LINTFLAGS (LEGACY)

_CS_XBS5_LP64_OFF64_CFLAGS (LEGACY)

_CS_XBS5_LP64_OFF64_LDFLAGS (LEGACY)

_CS_XBS5_LP64_OFF64_LIBS (LEGACY)

_CS_XBS5_LP64_OFF64_LINTFLAGS (LEGACY)

_CS_XBS5_LPBIG_OFFBIG_CFLAGS (LEGACY)

_CS_XBS5_LPBIG_OFFBIG_LDFLAGS (LEGACY)

_CS_XBS5_LPBIG_OFFBIG_LIBS (LEGACY)

_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS (LEGACY)

The following symbolic constants shall be defined for the lseek() and fcntl() functions and shall have distinct values:

SEEK_CUR

Set file offset to current plus offset.

SEEK_END

Set file offset to EOF plus offset.

SEEK_SET

Set file offset to offset.

The following symbolic constants shall be defined 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 following symbolic constants shall be defined for pathconf():

_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_MIN_XFER_SIZE

_PC_REC_XFER_ALIGN

_PC_SYMLINK_MAX

_PC_SYNC_IO

_PC_VDISABLE

The following symbolic constants shall be defined for sysconf():

_SC_2_C_BIND

_SC_2_C_DEV

_SC_2_C_VERSION

_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_ARG_MAX

_SC_AIO_LISTIO_MAX

_SC_AIO_MAX

_SC_AIO_PRIO_DELTA_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_FILE_LOCKING

_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_SEMAPHORES

_SC_SEM_NSEMS_MAX

_SC_SEM_VALUE_MAX

_SC_SHARED_MEMORY_OBJECTS

_SC_SHELL

_SC_SIGQUEUE_MAX

_SC_SPAWN

_SC_SPIN_LOCKS

_SC_SPORADIC_SERVER

_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_SAFE_FUNCTIONS

_SC_THREAD_SPORADIC_SERVER

_SC_THREAD_STACK_MIN

_SC_THREAD_THREADS_MAX

_SC_TIMEOUTS

_SC_THREADS

_SC_TIMER_MAX

_SC_TIMERS

_SC_TRACE

_SC_TRACE_EVENT_FILTER

_SC_TRACE_INHERIT

_SC_TRACE_LOG

_SC_TTY_NAME_MAX

_SC_TYPED_MEMORY_OBJECTS

_SC_TZNAME_MAX

_SC_V6_ILP32_OFF32

_SC_V6_ILP32_OFFBIG

_SC_V6_LP64_OFF64

_SC_V6_LPBIG_OFFBIG

_SC_VERSION

_SC_XBS5_ILP32_OFF32 (LEGACY)

_SC_XBS5_ILP32_OFFBIG (LEGACY)

_SC_XBS5_LP64_OFF64 (LEGACY)

_SC_XBS5_LPBIG_OFFBIG (LEGACY)

_SC_XOPEN_CRYPT

_SC_XOPEN_ENH_I18N

_SC_XOPEN_LEGACY

_SC_XOPEN_REALTIME

_SC_XOPEN_REALTIME_THREADS

_SC_XOPEN_SHM

_SC_XOPEN_STREAMS

_SC_XOPEN_UNIX

_SC_XOPEN_VERSION

_SC_XOPEN_XCU_VERSION

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

The following symbolic constants shall be defined 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 size_t, ssize_t, uid_t, gid_t, off_t, pid_t, and useconds_t types shall be defined as described in <sys/types.h>.

The intptr_t type shall be defined as described in <inttypes.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 *); char *ctermid(char *);

int dup(int);

int dup2(int, 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 []); void _exit(int); int fchown(int, uid_t, gid_t);

int fchdir(int);

int fdatasync(int);

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);

char *getwd(char *); (LEGACY )

int isatty(int);

int lchown(const char *, uid_t, gid_t);

int link(const char *, const char *);

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); 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 *); 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);

useconds_t ualarm(useconds_t, useconds_t);

int unlink(const char *);

int usleep(useconds_t); pid_t vfork(void);

ssize_t write(int, const void *, size_t);

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

The following external variables shall be declared:

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

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 IEEE Std 1003.1-2001.

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.

IEEE Std 1003.1-2001 now 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. IEEE Std 1003.1-2001 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 IEEE Std 1003.1-2001, 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 IEEE Std 1003.1-2001.