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POSIXOPTIONS(7) Linux Programmer's Manual POSIXOPTIONS(7)

posixoptions - optional parts of the POSIX standard

The POSIX standard (the information below is from POSIX.1-2001) describes a set of behaviors 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 sysconf(3), fpathconf(3), pathconf(3), confstr(3) to do this at run time. From shell scripts one can use getconf(1). For more detail, see sysconf(3).

We give the name of the POSIX abbreviation, the option, the name of the sysconf(3) 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.

The following advisory functions are present:


posix_fadvise() posix_fallocate() posix_memalign() posix_madvise()

The header <aio.h> is present. The following functions are present:


aio_cancel() aio_error() aio_fsync() aio_read() aio_return() aio_suspend() aio_write() lio_listio()

This option implies the _POSIX_THREADS and _POSIX_THREAD_SAFE_FUNCTIONS options. The following functions are present:


pthread_barrier_destroy() pthread_barrier_init() pthread_barrier_wait() pthread_barrierattr_destroy() pthread_barrierattr_init()

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 nonroot can set the group of a file only to one of the groups it belongs to. This affects the following functions


chown() fchown()

This option implies the _POSIX_TIMERS option. The following functions are present:


pthread_condattr_getclock() pthread_condattr_setclock() clock_nanosleep()

If CLOCK_REALTIME is changed by the function clock_settime(), then this affects all timers set for an absolute time.

The CLOCK_PROCESS_CPUTIME_ID clock ID is supported. The initial value of this clock is 0 for each process. This option implies the _POSIX_TIMERS option. The function clock_getcpuclockid() is present.

This option has been deleted. Not in final XPG6.

The function fsync() is present.

Internet Protocol Version 6 is supported.

If this option is in effect (as it always is under POSIX.1-2001), then the system implements POSIX-style job control, and the following functions are present:


setpgid() tcdrain() tcflush() tcgetpgrp() tcsendbreak() tcsetattr() tcsetpgrp()

Shared memory is supported. The include file <sys/mman.h> is present. The following functions are present:


mmap() msync() munmap()

Shared memory can be locked into core. The following functions are present:


mlockall() munlockall()

More precisely, ranges can be locked into core. The following functions are present:


mlock() munlock()

The function mprotect() is present.

The include file <mqueue.h> is present. The following functions are present:


mq_close() mq_getattr() mq_notify() mq_open() mq_receive() mq_send() mq_setattr() mq_unlink()

CLOCK_MONOTONIC is supported. This option implies the _POSIX_TIMERS option. The following functions are affected:


aio_suspend() clock_getres() clock_gettime() clock_settime() timer_create()

This option has been deleted. Not in final XPG6.

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.

This option says that one can specify priorities for asynchronous I/O. This affects the functions


aio_read() aio_write()

The include file <sched.h> is present. The following functions are present:


sched_get_priority_max() sched_get_priority_min() sched_getparam() sched_getscheduler() sched_rr_get_interval() sched_setparam() sched_setscheduler() sched_yield()

If also _POSIX_SPAWN is in effect, then the following functions are present:


posix_spawnattr_getschedparam() posix_spawnattr_getschedpolicy() posix_spawnattr_setschedparam() posix_spawnattr_setschedpolicy()

Raw sockets are supported. The following functions are affected:


getsockopt() setsockopt()

This option implies the _POSIX_THREADS option. Conversely, under POSIX.1-2001 the _POSIX_THREADS option implies this option.

The following functions are present:


pthread_rwlock_destroy()
pthread_rwlock_init()
pthread_rwlock_rdlock()
pthread_rwlock_tryrdlock()
pthread_rwlock_trywrlock()
pthread_rwlock_unlock()
pthread_rwlock_wrlock()
pthread_rwlockattr_destroy()
pthread_rwlockattr_init()

Realtime signals are supported. The following functions are present:


sigqueue() sigtimedwait() sigwaitinfo()

If this option is in effect (as it always is under POSIX.1-2001), then POSIX regular expressions are supported and the following functions are present:


regcomp() regerror() regexec() regfree()

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. The following functions are affected:


exec() kill() seteuid() setegid() setgid() setuid()

The include file <semaphore.h> is present. The following functions are present:


sem_close() sem_destroy() sem_getvalue() sem_init() sem_open() sem_post() sem_trywait() sem_unlink() sem_wait()

The following functions are present:


mmap() munmap() shm_open() shm_unlink()

If this option is in effect (as it always is under POSIX.1-2001), the function system() is present.

This option describes support for process creation in a context where it is difficult or impossible to use fork(), for example, because no MMU is present.

If _POSIX_SPAWN is in effect, then the include file <spawn.h> and the following functions are present:


posix_spawn() posix_spawn_file_actions_addclose() posix_spawn_file_actions_adddup2() posix_spawn_file_actions_addopen() posix_spawn_file_actions_destroy() posix_spawn_file_actions_init() posix_spawnattr_destroy() posix_spawnattr_getsigdefault() posix_spawnattr_getflags() posix_spawnattr_getpgroup() posix_spawnattr_getsigmask() posix_spawnattr_init() posix_spawnattr_setsigdefault() posix_spawnattr_setflags() posix_spawnattr_setpgroup() posix_spawnattr_setsigmask() posix_spawnp()

If also _POSIX_PRIORITY_SCHEDULING is in effect, then the following functions are present:


posix_spawnattr_getschedparam() posix_spawnattr_getschedpolicy() posix_spawnattr_setschedparam() posix_spawnattr_setschedpolicy()

This option implies the _POSIX_THREADS and _POSIX_THREAD_SAFE_FUNCTIONS options. The following functions are present:


pthread_spin_destroy() pthread_spin_init() pthread_spin_lock() pthread_spin_trylock() pthread_spin_unlock()

The scheduling policy SCHED_SPORADIC is supported. This option implies the _POSIX_PRIORITY_SCHEDULING option. The following functions are affected:


sched_setparam() sched_setscheduler()

The following functions are affected:


open() msync() fsync() fdatasync()

The following functions are affected:


pthread_attr_getstack() pthread_attr_getstackaddr() pthread_attr_setstack() pthread_attr_setstackaddr()

The following functions are affected:


pthread_attr_getstack() pthread_attr_getstacksize() pthread_attr_setstack() pthread_attr_setstacksize()

The clockID CLOCK_THREAD_CPUTIME_ID is supported. This option implies the _POSIX_TIMERS option. The following functions are affected:


pthread_getcpuclockid() clock_getres() clock_gettime() clock_settime() timer_create()

The following functions are affected:


pthread_mutexattr_getprotocol() pthread_mutexattr_setprotocol()

The following functions are affected:


pthread_mutex_getprioceiling() pthread_mutex_setprioceiling() pthread_mutexattr_getprioceiling() pthread_mutexattr_getprotocol() pthread_mutexattr_setprioceiling() pthread_mutexattr_setprotocol()

If this option is in effect, the different threads inside a process can run with different priorities and/or different schedulers. The following functions are affected:


pthread_attr_getinheritsched() pthread_attr_getschedpolicy() pthread_attr_getscope() pthread_attr_setinheritsched() pthread_attr_setschedpolicy() pthread_attr_setscope() pthread_getschedparam() pthread_setschedparam() pthread_setschedprio()

The following functions are affected:


pthread_barrierattr_getpshared() pthread_barrierattr_setpshared() pthread_condattr_getpshared() pthread_condattr_setpshared() pthread_mutexattr_getpshared() pthread_mutexattr_setpshared() pthread_rwlockattr_getpshared() pthread_rwlockattr_setpshared()

The following functions are affected:


readdir_r() getgrgid_r() getgrnam_r() getpwnam_r() getpwuid_r() flockfile() ftrylockfile() funlockfile() getc_unlocked() getchar_unlocked() putc_unlocked() putchar_unlocked() rand_r() strerror_r() strtok_r() asctime_r() ctime_r() gmtime_r() localtime_r()

This option implies the _POSIX_THREAD_PRIORITY_SCHEDULING option. The following functions are affected:


sched_getparam() sched_setparam() sched_setscheduler()

Basic support for POSIX threads is available. The following functions are present:


pthread_atfork() pthread_attr_destroy() pthread_attr_getdetachstate() pthread_attr_getschedparam() pthread_attr_init() pthread_attr_setdetachstate() pthread_attr_setschedparam() pthread_cancel() pthread_cleanup_push() pthread_cleanup_pop() pthread_cond_broadcast() pthread_cond_destroy() pthread_cond_init() pthread_cond_signal() pthread_cond_timedwait() pthread_cond_wait() pthread_condattr_destroy() pthread_condattr_init() pthread_create() pthread_detach() pthread_equal() pthread_exit() pthread_getspecific() pthread_join() pthread_key_create() pthread_key_delete() pthread_mutex_destroy() pthread_mutex_init() pthread_mutex_lock() pthread_mutex_trylock() pthread_mutex_unlock() pthread_mutexattr_destroy() pthread_mutexattr_init() pthread_once() pthread_rwlock_destroy() pthread_rwlock_init() pthread_rwlock_rdlock() pthread_rwlock_tryrdlock() pthread_rwlock_trywrlock() pthread_rwlock_unlock() pthread_rwlock_wrlock() pthread_rwlockattr_destroy() pthread_rwlockattr_init() pthread_self() pthread_setcancelstate() pthread_setcanceltype() pthread_setspecific() pthread_testcancel()

The following functions are present:


mq_timedreceive() mq_timedsend() pthread_mutex_timedlock() pthread_rwlock_timedrdlock() pthread_rwlock_timedwrlock() sem_timedwait() posix_trace_timedgetnext_event()

The following functions are present:


clock_getres() clock_gettime() clock_settime() nanosleep() timer_create() timer_delete() timer_gettime() timer_getoverrun() timer_settime()

POSIX tracing is available. The following functions are present:


posix_trace_attr_destroy() posix_trace_attr_getclockres() posix_trace_attr_getcreatetime() posix_trace_attr_getgenversion() posix_trace_attr_getmaxdatasize() posix_trace_attr_getmaxsystemeventsize() posix_trace_attr_getmaxusereventsize() posix_trace_attr_getname() posix_trace_attr_getstreamfullpolicy() posix_trace_attr_getstreamsize() posix_trace_attr_init() posix_trace_attr_setmaxdatasize() posix_trace_attr_setname() posix_trace_attr_setstreamsize() posix_trace_attr_setstreamfullpolicy() posix_trace_clear() posix_trace_create() posix_trace_event() posix_trace_eventid_equal() posix_trace_eventid_get_name() posix_trace_eventid_open() posix_trace_eventtypelist_getnext_id() posix_trace_eventtypelist_rewind() posix_trace_flush() posix_trace_get_attr() posix_trace_get_status() posix_trace_getnext_event() posix_trace_shutdown() posix_trace_start() posix_trace_stop() posix_trace_trygetnext_event()

This option implies the _POSIX_TRACE option. The following functions are present:


posix_trace_eventset_add() posix_trace_eventset_del() posix_trace_eventset_empty() posix_trace_eventset_fill() posix_trace_eventset_ismember() posix_trace_get_filter() posix_trace_set_filter() posix_trace_trid_eventid_open()

Tracing children of the traced process is supported. This option implies the _POSIX_TRACE option. The following functions are present:


posix_trace_attr_getinherited() posix_trace_attr_setinherited()

This option implies the _POSIX_TRACE option. The following functions are present:


posix_trace_attr_getlogfullpolicy() posix_trace_attr_getlogsize() posix_trace_attr_setlogfullpolicy() posix_trace_attr_setlogsize() posix_trace_close() posix_trace_create_withlog() posix_trace_open() posix_trace_rewind()

The following functions are present:


posix_mem_offset() posix_typed_mem_get_info() posix_typed_mem_open()

Always present (probably 0). Value to set a changeable special control character to indicate that it is disabled.

The following functions are present:


crypt() encrypt() setkey()

This option implies the following options:

_POSIX_ASYNCHRONOUS_IO==200112L
_POSIX_FSYNC
_POSIX_MAPPED_FILES
_POSIX_MEMLOCK==200112L
_POSIX_MEMLOCK_RANGE==200112L
_POSIX_MEMORY_PROTECTION
_POSIX_MESSAGE_PASSING==200112L
_POSIX_PRIORITIZED_IO
_POSIX_PRIORITY_SCHEDULING==200112L
_POSIX_REALTIME_SIGNALS==200112L
_POSIX_SEMAPHORES==200112L
_POSIX_SHARED_MEMORY_OBJECTS==200112L
_POSIX_SYNCHRONIZED_IO==200112L
_POSIX_TIMERS==200112L

The Advanced Realtime option group implies that the following options are all defined to 200112L:

_POSIX_ADVISORY_INFO
_POSIX_CLOCK_SELECTION
(implies _POSIX_TIMERS)
_POSIX_CPUTIME
(implies _POSIX_TIMERS)
_POSIX_MONOTONIC_CLOCK
(implies _POSIX_TIMERS)
_POSIX_SPAWN
_POSIX_SPORADIC_SERVER
(implies _POSIX_PRIORITY_SCHEDULING)
_POSIX_TIMEOUTS
_POSIX_TYPED_MEMORY_OBJECTS

This option implies that the following options are all defined to 200112L:

_POSIX_THREAD_PRIO_INHERIT
_POSIX_THREAD_PRIO_PROTECT
_POSIX_THREAD_PRIORITY_SCHEDULING

This option implies that the following options are all defined to 200112L:

_POSIX_BARRIERS
(implies _POSIX_THREADS, _POSIX_THREAD_SAFE_FUNCTIONS)
_POSIX_SPIN_LOCKS
(implies _POSIX_THREADS, _POSIX_THREAD_SAFE_FUNCTIONS)
_POSIX_THREAD_CPUTIME
(implies _POSIX_TIMERS)
_POSIX_THREAD_SPORADIC_SERVER
(implies _POSIX_THREAD_PRIORITY_SCHEDULING)

This option implies that the following options are all defined to 200112L:

_POSIX_TRACE
_POSIX_TRACE_EVENT_FILTER
_POSIX_TRACE_LOG
_POSIX_TRACE_INHERIT

The following functions are present:


fattach() fdetach() getmsg() getpmsg() ioctl() isastream() putmsg() putpmsg()

Functions included in the legacy option group were previously mandatory, but are now optional in this version. The following functions are present:


bcmp() bcopy() bzero() ecvt() fcvt() ftime() gcvt() getcwd() index() mktemp() rindex() utimes() wcswcs()

The following functions are present:


mmap() munmap() msync()

This option implies the following options:

_POSIX_FSYNC
_POSIX_MAPPED_FILES
_POSIX_MEMORY_PROTECTION
_POSIX_THREAD_ATTR_STACKADDR
_POSIX_THREAD_ATTR_STACKSIZE
_POSIX_THREAD_PROCESS_SHARED
_POSIX_THREAD_SAFE_FUNCTIONS
_POSIX_THREADS

This option may imply the following options from the XSI option groups:

Encryption (_XOPEN_CRYPT)
Realtime (_XOPEN_REALTIME)
Advanced Realtime (ADB)
Realtime Threads (_XOPEN_REALTIME_THREADS)
Advanced Realtime Threads (ADVANCED REALTIME THREADS)
Tracing (TRACING)
XSI Streams (STREAMS)
Legacy (_XOPEN_LEGACY)

sysconf(3), standards(7)

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2018-04-30