Name "ia64" consistently.

[thirdparty/man-pages.git] / man7 / posixoptions.7

.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
.\"
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\"
.\" The GNU General Public License's references to "object code"
.\" and "executables" are to be interpreted as the output of any
.\" document formatting or typesetting system, including
.\" intermediate and printed output.
.\"
.\" This manual is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
.\" License along with this manual; if not, write to the Free
.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
.\" USA.
.\"
.TH POSIXOPTIONS 7 2003-08-24 "" "Linux Programmer's Manual"
.SH NAME
posixoptions \- optional parts of the POSIX standard
.SH DESCRIPTION
The POSIX standard (the information below is from POSIX.1-2001)
describes a set of behavior and interfaces for a compliant system.
However, many interfaces are optional and there are feature test macros
to test the availability of interfaces at compile time, and functions
.BR sysconf (3),
.BR fpathconf (3),
.BR pathconf (3),
.BR confstr (3)
to do this at run time.
From shell scripts one can use
.BR getconf (1).
For more detail, see
.BR sysconf (3).
.LP
We give the name of the POSIX abbreviation, the option, the name of the
.BR sysconf ()
parameter used to inquire about the option, and possibly
a very short description.
Much more precise detail can be found in the POSIX standard itself,
versions of which can nowadays be accessed freely on the web.
.SS "ADV - _POSIX_ADVISORY_INFO - _SC_ADVISORY_INFO"
The advisory functions
.br
.nf
.in +4
.IR posix_fadvise (),
.IR posix_fallocate (),
.IR posix_memalign (),
.IR posix_madvise ()
.br
.in -4
.fi
are present.
.SS "AIO - _POSIX_ASYNCHRONOUS_IO - _SC_ASYNCHRONOUS_IO"
The header
.I <aio.h>
is present.
The functions
.br
.nf
.in +4
.IR aio_cancel (),
.IR aio_error (),
.IR aio_fsync (),
.IR aio_read (),
.IR aio_return (),
.IR aio_suspend (),
.IR aio_write (),
.IR lio_listio ()
.br
.in -4
.fi
are present.
.SS "BAR - _POSIX_BARRIERS - _SC_BARRIERS"
This option implies the _POSIX_THREADS and
_POSIX_THREAD_SAFE_FUNCTIONS options.
The functions
.br
.nf
.in +4
.IR pthread_barrier_destroy (),
.IR pthread_barrier_init (),
.IR pthread_barrier_wait (),
.IR pthread_barrierattr_destroy (),
.IR pthread_barrierattr_init ()
.in -4
.br
.fi
are present.
.\" .SS "BE"
.\" Batch environment.
.\" .SS "CD"
.\" C development.
.SS "--- - POSIX_CHOWN_RESTRICTED"
If this option is in effect (as it always is under POSIX.1-2001)
then only root may change the owner of a file, and non-root can only
set the group of a file to one of the groups it belongs to.
This affects the functions
.IR chown (),
.IR fchown ().
.\" What about lchown() ?
.SS "CS - _POSIX_CLOCK_SELECTION - _SC_CLOCK_SELECTION"
This option implies the _POSIX_TIMERS option.
The functions
.br
.nf
.in +4
.IR pthread_condattr_getclock (),
.IR pthread_condattr_setclock (),
.IR clock_nanosleep ()
.in -4
.br
.fi
are present.
If CLOCK_REALTIME is changed by the function
.IR clock_settime (),
then this affects all timers set for an absolute time.
.SS "CPT - _POSIX_CPUTIME - _SC_CPUTIME"
The clockID CLOCK_PROCESS_CPUTIME_ID is supported.
The initial value of this clock is 0 for each process.
This option implies the _POSIX_TIMERS option.
The function
.IR clock_getcpuclockid ()
is present.
.\" .SS "FD"
.\" Fortran development
.\" .SS "FR"
.\" Fortran runtime
.SS "--- - _POSIX_FILE_LOCKING - _SC_FILE_LOCKING"
This option has been deleted.
Not in final XPG6.
.SS "FSC - _POSIX_FSYNC - _SC_FSYNC "
The function
.IR fsync ()
is present.
.SS "IP6 - _POSIX_IPV6 - _SC_IPV6"
Internet Protocol Version 6 is supported.
.SS "--- - _POSIX_JOB_CONTROL - _SC_JOB_CONTROL"
If this option is in effect (as it always is under POSIX.1-2001)
then the system implements POSIX-style job control, and the functions
.br
.nf
.in +4
.IR setpgid (),
.IR tcdrain (),
.IR tcflush (),
.IR tcgetpgrp (),
.IR tcsendbreak (),
.IR tcsetattr (),
.IR tcsetpgrp ()
.in -4
are present.
.fi
.SS "MF - _POSIX_MAPPED_FILES - _SC_MAPPED_FILES"
Shared memory is supported.
The include file
.I <sys/mman.h>
is present.
The functions
.IR mmap (),
.IR msync (),
.IR munmap ()
are present.
.SS "ML - _POSIX_MEMLOCK - _SC_MEMLOCK"
Shared memory can be locked into core.
The functions
.IR mlockall (),
.IR munlockall ()
are present.
.SS "MR/MLR - _POSIX_MEMLOCK_RANGE - _SC_MEMLOCK_RANGE"
More precisely, ranges can be locked into core.
The functions
.IR mlock (),
.IR munlock ()
are present.
.SS "MPR - _POSIX_MEMORY_PROTECTION - _SC_MEMORY_PROTECTION"
The function
.IR mprotect ()
is present.
.SS "MSG - _POSIX_MESSAGE_PASSING - _SC_MESSAGE_PASSING"
The include file
.IR <mqueue.h>
is present.
The functions
.br
.nf
.in +4
.IR mq_close (),
.IR mq_getattr (),
.IR mq_notify (),
.IR mq_open (),
.IR mq_receive (),
.IR mq_send (),
.IR mq_setattr (),
.IR mq_unlink ()
.br
.in -4
.fi
are present.
.SS "MON - _POSIX_MONOTONIC_CLOCK - _SC_MONOTONIC_CLOCK"
.nf
CLOCK_MONOTONIC is supported.
This option implies the _POSIX_TIMERS option.
Affected functions are
.in +4
.IR aio_suspend (),
.IR clock_getres (),
.IR clock_gettime (),
.IR clock_settime (),
.IR timer_create ().
.in -4
.fi
.SS "--- - _POSIX_MULTI_PROCESS - _SC_MULTI_PROCESS"
This option has been deleted.
Not in final XPG6.
.\" .SS "MX"
.\" IEC 60559 Floating-Point Option.
.SS "--- - _POSIX_NO_TRUNC"
If this option is in effect (as it always is under POSIX.1-2001)
then pathname components longer than NAME_MAX are not truncated,
but give an error.
This property may be dependent on the path prefix of the component.
.SS "PIO - _POSIX_PRIORITIZED_IO - _SC_PRIORITIZED_IO"
This option says that one can specify priorities for asynchronous I/O.
This affects the functions
.br
.nf
.in +4
.IR aio_read (),
.IR aio_write ().
.in -4
.fi
.SS "PS - _POSIX_PRIORITY_SCHEDULING - _SC_PRIORITY_SCHEDULING"
The include file
.I <sched.h>
is present.
The functions
.br
.nf
.in +4
.IR sched_get_priority_max (),
.IR sched_get_priority_min (),
.IR sched_getparam (),
.IR sched_getscheduler (),
.IR sched_rr_get_interval (),
.IR sched_setparam (),
.IR sched_setscheduler (),
.IR sched_yield ()
.in -4
.br
.fi
are present.
If also _POSIX_SPAWN is in effect, then the functions
.br
.nf
.in +4
.IR posix_spawnattr_getschedparam (),
.IR posix_spawnattr_getschedpolicy (),
.IR posix_spawnattr_setschedparam (),
.IR posix_spawnattr_setschedpolicy ()
.in -4
are present.
.fi
.SS "RS - _POSIX_RAW_SOCKETS"
Raw sockets are supported.
Affected functions are
.IR getsockopt (),
.IR setsockopt ().
.SS "--- - _POSIX_READER_WRITER_LOCKS - _SC_READER_WRITER_LOCKS"
This option implies the _POSIX_THREADS option.
Conversely,
under POSIX.1-2001 the _POSIX_THREADS option implies this option.
.nf
The functions
.in +4
.IR pthread_rwlock_destroy (),
.IR pthread_rwlock_init (),
.IR pthread_rwlock_rdlock (),
.IR pthread_rwlock_tryrdlock (),
.IR pthread_rwlock_trywrlock (),
.IR pthread_rwlock_unlock (),
.IR pthread_rwlock_wrlock (),
.IR pthread_rwlockattr_destroy (),
.IR pthread_rwlockattr_init ()
.in -4
are present.
.fi
.SS "RTS - _POSIX_REALTIME_SIGNALS - _SC_REALTIME_SIGNALS"
Realtime signals are supported.
The functions
.br
.nf
.in +4
.IR sigqueue (),
.IR sigtimedwait (),
.IR sigwaitinfo ()
.br
.in -4
.fi
are present.
.SS "--- - _POSIX_REGEXP - _SC_REGEXP"
If this option is in effect (as it always is under POSIX.1-2001)
then POSIX regular expressions are supported and the functions
.br
.nf
.in +4
.IR regcomp (),
.IR regerror (),
.IR regexec (),
.IR regfree ()
.br
.in -4
.fi
are present.
.SS "--- - _POSIX_SAVED_IDS - _SC_SAVED_IDS"
If this option is in effect (as it always is under POSIX.1-2001)
then a process has a saved set-user-ID and a saved set-group-ID.
Affected functions are
.br
.nf
.in +4
.IR exec (),
.IR kill (),
.IR seteuid (),
.IR setegid (),
.IR setgid (),
.IR setuid ().
.br
.in -4
.fi
.\" .SS "SD"
.\" Software development
.SS "SEM - _POSIX_SEMAPHORES - _SC_SEMAPHORES"
The include file
.I <semaphore.h>
is present.
The functions
.br
.nf
.in +4
.IR sem_close (),
.IR sem_destroy (),
.IR sem_getvalue (),
.IR sem_init (),
.IR sem_open (),
.IR sem_post (),
.IR sem_trywait (),
.IR sem_unlink (),
.IR sem_wait ()
.br
.in -4
.fi
are present.
.SS "SHM - _POSIX_SHARED_MEMORY_OBJECTS - _SC_SHARED_MEMORY_OBJECTS"
The functions
.br
.nf
.in +4
.IR mmap (),
.IR munmap (),
.IR shm_open (),
.IR shm_unlink ()
.br
.in -4
.fi
are present.
.SS "--- - _POSIX_SHELL - _SC_SHELL"
If this option is in effect (as it always is under POSIX.1-2001),
the function
.IR system ()
is present.
.SS "SPN - _POSIX_SPAWN - _SC_SPAWN"
This option describes support for process creation in a context where
it is difficult or impossible to use
.IR fork (),
for example, because no MMU is present.
If _POSIX_SPAWN is in effect, then the include file
.I <spawn.h>
and the functions
.br
.nf
.in +4
.IR posix_spawn (),
.IR posix_spawn_file_actions_addclose (),
.IR posix_spawn_file_actions_adddup2 (),
.IR posix_spawn_file_actions_addopen (),
.IR posix_spawn_file_actions_destroy (),
.IR posix_spawn_file_actions_init (),
.IR posix_spawnattr_destroy (),
.IR posix_spawnattr_getsigdefault (),
.IR posix_spawnattr_getflags (),
.IR posix_spawnattr_getpgroup (),
.IR posix_spawnattr_getsigmask (),
.IR posix_spawnattr_init (),
.IR posix_spawnattr_setsigdefault (),
.IR posix_spawnattr_setflags (),
.IR posix_spawnattr_setpgroup (),
.IR posix_spawnattr_setsigmask (),
.IR posix_spawnp ()
.in -4
.br
.fi
are present.
If also _POSIX_PRIORITY_SCHEDULING is in effect, then
the functions
.br
.nf
.in +4
.IR posix_spawnattr_getschedparam (),
.IR posix_spawnattr_getschedpolicy (),
.IR posix_spawnattr_setschedparam (),
.IR posix_spawnattr_setschedpolicy ()
.in -4
are present.
.fi
.SS "SPI - _POSIX_SPIN_LOCKS - _SC_SPIN_LOCKS"
This option implies the _POSIX_THREADS and
_POSIX_THREAD_SAFE_FUNCTIONS options.
The functions
.br
.nf
.in +4
.IR pthread_spin_destroy (),
.IR pthread_spin_init (),
.IR pthread_spin_lock (),
.IR pthread_spin_trylock (),
.IR pthread_spin_unlock ()
.in -4
.br
.fi
are present.
.SS "SS - _POSIX_SPORADIC_SERVER - _SC_SPORADIC_SERVER"
The scheduling policy SCHED_SPORADIC is supported.
This option implies the _POSIX_PRIORITY_SCHEDULING option.
Affected functions are
.br
.nf
.in +4
.IR sched_setparam (),
.IR sched_setscheduler ().
.in -4
.br
.fi
.SS "SIO - _POSIX_SYNCHRONIZED_IO - _SC_SYNCHRONIZED_IO"
Affected functions are
.IR open (),
.IR msync (),
.IR fsync (),
.IR fdatasync ().
.SS "TSA - _POSIX_THREAD_ATTR_STACKADDR - _SC_THREAD_ATTR_STACKADDR"
Affected functions are
.br
.nf
.in +4
.IR pthread_attr_getstack (),
.IR pthread_attr_getstackaddr (),
.IR pthread_attr_setstack (),
.IR pthread_attr_setstackaddr ().
.in -4
.br
.fi
.SS "TSS - _POSIX_THREAD_ATTR_STACKSIZE - _SC_THREAD_ATTR_STACKSIZE"
Affected functions are
.br
.nf
.in +4
.IR pthread_attr_getstack (),
.IR pthread_attr_getstacksize (),
.IR pthread_attr_setstack (),
.IR pthread_attr_setstacksize ().
.in -4
.br
.fi
.SS "TCT - _POSIX_THREAD_CPUTIME - _SC_THREAD_CPUTIME"
The clockID CLOCK_THREAD_CPUTIME_ID is supported.
This option implies the _POSIX_TIMERS option.
Affected functions are
.br
.nf
.in +4
.IR pthread_getcpuclockid (),
.IR clock_getres (),
.IR clock_gettime (),
.IR clock_settime (),
.IR timer_create ().
.in -4
.br
.fi
.SS "TPI - _POSIX_THREAD_PRIO_INHERIT - _SC_THREAD_PRIO_INHERIT"
Affected functions are
.br
.nf
.in +4
.IR pthread_mutexattr_getprotocol (),
.IR pthread_mutexattr_setprotocol ().
.in -4
.br
.fi
.SS "TPP - _POSIX_THREAD_PRIO_PROTECT - _SC_THREAD_PRIO_PROTECT"
Affected functions are
.br
.nf
.in +4
.IR pthread_mutex_getprioceiling (),
.IR pthread_mutex_setprioceiling (),
.IR pthread_mutexattr_getprioceiling (),
.IR pthread_mutexattr_getprotocol (),
.IR pthread_mutexattr_setprioceiling (),
.IR pthread_mutexattr_setprotocol ().
.in -4
.br
.fi
.SS "TPS - _POSIX_THREAD_PRIORITY_SCHEDULING - _SC_THREAD_PRIORITY_SCHEDULING"
If this option is in effect, the different threads inside a process
can run with different priorities and/or different schedulers.
Affected functions are
.br
.nf
.in +4
.IR pthread_attr_getinheritsched (),
.IR pthread_attr_getschedpolicy (),
.IR pthread_attr_getscope (),
.IR pthread_attr_setinheritsched (),
.IR pthread_attr_setschedpolicy (),
.IR pthread_attr_setscope (),
.IR pthread_getschedparam (),
.IR pthread_setschedparam (),
.IR pthread_setschedprio ().
.in -4
.br
.fi
.SS "TSH - _POSIX_THREAD_PROCESS_SHARED - _SC_THREAD_PROCESS_SHARED"
Affected functions are
.br
.nf
.in +4
.IR pthread_barrierattr_getpshared (),
.IR pthread_barrierattr_setpshared (),
.IR pthread_condattr_getpshared (),
.IR pthread_condattr_setpshared (),
.IR pthread_mutexattr_getpshared (),
.IR pthread_mutexattr_setpshared (),
.IR pthread_rwlockattr_getpshared (),
.IR pthread_rwlockattr_setpshared ().
.in -4
.br
.fi
.SS "TSF - _POSIX_THREAD_SAFE_FUNCTIONS - _SC_THREAD_SAFE_FUNCTIONS"
Affected functions are
.br
.nf
.in +4
.IR readdir_r (),
.IR getgrgid_r (),
.IR getgrnam_r (),
.IR getpwnam_r (),
.IR getpwuid_r (),
.IR flockfile (),
.IR ftrylockfile (),
.IR funlockfile (),
.IR getc_unlocked (),
.IR getchar_unlocked (),
.IR putc_unlocked (),
.IR putchar_unlocked (),
.IR rand_r (),
.IR strerror_r (),
.IR strtok_r (),
.IR asctime_r (),
.IR ctime_r (),
.IR gmtime_r (),
.IR localtime_r ().
.in -4
.br
.fi
.SS "TSP - _POSIX_THREAD_SPORADIC_SERVER - _SC_THREAD_SPORADIC_SERVER"
This option implies the _POSIX_THREAD_PRIORITY_SCHEDULING option.
Affected functions are
.br
.nf
.in +4
.IR sched_getparam (),
.IR sched_setparam (),
.IR sched_setscheduler ().
.in -4
.br
.fi
.SS "THR - _POSIX_THREADS - _SC_THREADS"
Basic support for POSIX threads is available.
The functions
.br
.nf
.in +4
.IR pthread_atfork (),
.IR pthread_attr_destroy (),
.IR pthread_attr_getdetachstate (),
.IR pthread_attr_getschedparam (),
.IR pthread_attr_init (),
.IR pthread_attr_setdetachstate (),
.IR pthread_attr_setschedparam (),
.IR pthread_cancel (),
.IR pthread_cleanup_push (),
.IR pthread_cleanup_pop (),
.IR pthread_cond_broadcast (),
.IR pthread_cond_destroy (),
.IR pthread_cond_init (),
.IR pthread_cond_signal (),
.IR pthread_cond_timedwait (),
.IR pthread_cond_wait (),
.IR pthread_condattr_destroy (),
.IR pthread_condattr_init (),
.IR pthread_create (),
.IR pthread_detach (),
.IR pthread_equal (),
.IR pthread_exit (),
.IR pthread_getspecific (),
.IR pthread_join (),
.IR pthread_key_create (),
.IR pthread_key_delete (),
.IR pthread_mutex_destroy (),
.IR pthread_mutex_init (),
.IR pthread_mutex_lock (),
.IR pthread_mutex_trylock (),
.IR pthread_mutex_unlock (),
.IR pthread_mutexattr_destroy (),
.IR pthread_mutexattr_init (),
.IR pthread_once (),
.IR pthread_rwlock_destroy (),
.IR pthread_rwlock_init (),
.IR pthread_rwlock_rdlock (),
.IR pthread_rwlock_tryrdlock (),
.IR pthread_rwlock_trywrlock (),
.IR pthread_rwlock_unlock (),
.IR pthread_rwlock_wrlock (),
.IR pthread_rwlockattr_destroy (),
.IR pthread_rwlockattr_init (),
.IR pthread_self (),
.IR pthread_setcancelstate (),
.IR pthread_setcanceltype (),
.IR pthread_setspecific (),
.IR pthread_testcancel ()
.in -4
.br
.fi
are present.
.SS "TMO - _POSIX_TIMEOUTS - _SC_TIMEOUTS"
The functions
.br
.nf
.in +4
.IR mq_timedreceive (),
.IR mq_timedsend (),
.IR pthread_mutex_timedlock (),
.IR pthread_rwlock_timedrdlock (),
.IR pthread_rwlock_timedwrlock (),
.IR sem_timedwait (),
.IR posix_trace_timedgetnext_event ()
.in -4
.br
.fi
are present.
.SS "TMR - _POSIX_TIMERS - _SC_TIMERS"
The functions
.br
.nf
.in +4
.IR clock_getres (),
.IR clock_gettime (),
.IR clock_settime (),
.IR nanosleep (),
.IR timer_create (),
.IR timer_delete (),
.IR timer_gettime (),
.IR timer_getoverrun (),
.IR timer_settime ()
.in -4
.br
.fi
are present.
.SS "TRC - _POSIX_TRACE - _SC_TRACE"
POSIX tracing is available.
The functions
.br
.nf
.in +4
.IR posix_trace_attr_destroy (),
.IR posix_trace_attr_getclockres (),
.IR posix_trace_attr_getcreatetime (),
.IR posix_trace_attr_getgenversion (),
.IR posix_trace_attr_getmaxdatasize (),
.IR posix_trace_attr_getmaxsystemeventsize (),
.IR posix_trace_attr_getmaxusereventsize (),
.IR posix_trace_attr_getname (),
.IR posix_trace_attr_getstreamfullpolicy (),
.IR posix_trace_attr_getstreamsize (),
.IR posix_trace_attr_init (),
.IR posix_trace_attr_setmaxdatasize (),
.IR posix_trace_attr_setname (),
.IR posix_trace_attr_setstreamsize (),
.IR posix_trace_attr_setstreamfullpolicy (),
.IR posix_trace_clear (),
.IR posix_trace_create (),
.IR posix_trace_event (),
.IR posix_trace_eventid_equal (),
.IR posix_trace_eventid_get_name (),
.IR posix_trace_eventid_open (),
.IR posix_trace_eventtypelist_getnext_id (),
.IR posix_trace_eventtypelist_rewind (),
.IR posix_trace_flush (),
.IR posix_trace_get_attr (),
.IR posix_trace_get_status (),
.IR posix_trace_getnext_event (),
.IR posix_trace_shutdown (),
.IR posix_trace_start (),
.IR posix_trace_stop (),
.IR posix_trace_trygetnext_event ()
.in -4
.br
.fi
are present.
.SS "TEF - _POSIX_TRACE_EVENT_FILTER - _SC_TRACE_EVENT_FILTER"
This option implies the _POSIX_TRACE option.
The functions
.br
.nf
.in +4
.IR posix_trace_eventset_add (),
.IR posix_trace_eventset_del (),
.IR posix_trace_eventset_empty (),
.IR posix_trace_eventset_fill (),
.IR posix_trace_eventset_ismember (),
.IR posix_trace_get_filter (),
.IR posix_trace_set_filter (),
.IR posix_trace_trid_eventid_open ()
.in -4
.br
.fi
are present.
.SS "TRI - _POSIX_TRACE_INHERIT - _SC_TRACE_INHERIT"
Tracing children of the traced process is supported.
This option implies the _POSIX_TRACE option.
The functions
.br
.nf
.in +4
.IR posix_trace_attr_getinherited (),
.IR posix_trace_attr_setinherited ()
.in -4
.br
.fi
are present.
.SS "TRL - _POSIX_TRACE_LOG - _SC_TRACE_LOG"
This option implies the _POSIX_TRACE option.
The functions
.br
.nf
.in +4
.IR posix_trace_attr_getlogfullpolicy (),
.IR posix_trace_attr_getlogsize (),
.IR posix_trace_attr_setlogfullpolicy (),
.IR posix_trace_attr_setlogsize (),
.IR posix_trace_close (),
.IR posix_trace_create_withlog (),
.IR posix_trace_open (),
.IR posix_trace_rewind ()
.in -4
.br
.fi
are present.
.SS "TYM - _POSIX_TYPED_MEMORY_OBJECTS - _SC_TYPED_MEMORY_OBJECT"
The functions
.br
.nf
.in +4
.IR posix_mem_offset (),
.IR posix_typed_mem_get_info (),
.IR posix_typed_mem_open ()
.in -4
.br
.fi
are present.
.SS "--- - _POSIX_VDISABLE"
Always present (probably 0).
Value to set a changeable special control
character to indicate that it is disabled.
.SH "XOPEN EXTENSIONS"
.BR _XOPEN_CRYPT ,
.BR _XOPEN_LEGACY ,
.BR _XOPEN_REALTIME ,
.BR _XOPEN_REALTIME_THREADS ,
.BR _XOPEN_UNIX .
.\" To be described.
.SH "SEE ALSO"
.BR sysconf (3)