--- name: "posixoptions" section: "7" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/posixoptions" --- # posixoptions(7) optional parts of the POSIX standard ## NAME posixoptions - optional parts of the POSIX standard ## DESCRIPTION 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)](/sysconf/3.md), [**fpathconf**(3)](/fpathconf/3.md), [**pathconf**(3)](/pathconf/3.md), [**confstr**(3)](/confstr/3.md) to do this at run time. From shell scripts one can use [**getconf**(1)](/getconf/1.md). For more detail, see [**sysconf**(3)](/sysconf/3.md). We give the name of the POSIX abbreviation, the option, the name of the [**sysconf**(3)](/sysconf/3.md) 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. ### ADV - \_POSIX\_ADVISORY\_INFO - \_SC\_ADVISORY\_INFO The following advisory functions are present: ``` posix_fadvise() posix_fallocate() posix_memalign() posix_madvise() ``` ### AIO - \_POSIX\_ASYNCHRONOUS\_IO - \_SC\_ASYNCHRONOUS\_IO The header *\* is present. The following functions are present: ``` aio_cancel() aio_error() aio_fsync() aio_read() aio_return() aio_suspend() aio_write() lio_listio() ``` ### BAR - \_POSIX\_BARRIERS - \_SC\_BARRIERS 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() ``` ### --- - 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 nonroot can set the group of a file only to one of the groups it belongs to. This affects the following functions: ``` chown() fchown() ``` ### CS - \_POSIX\_CLOCK\_SELECTION - \_SC\_CLOCK\_SELECTION 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. ### CPT - \_POSIX\_CPUTIME - \_SC\_CPUTIME 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. ### --- - \_POSIX\_FILE\_LOCKING - \_SC\_FILE\_LOCKING This option has been deleted. Not in final XPG6. ### FSC - \_POSIX\_FSYNC - \_SC\_FSYNC The function *fsync*() is present. ### IP6 - \_POSIX\_IPV6 - \_SC\_IPV6 Internet Protocol Version 6 is supported. ### --- - \_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 following functions are present: ``` setpgid() tcdrain() tcflush() tcgetpgrp() tcsendbreak() tcsetattr() tcsetpgrp() ``` ### MF - \_POSIX\_MAPPED\_FILES - \_SC\_MAPPED\_FILES Shared memory is supported. The include file *\* is present. The following functions are present: ``` mmap() msync() munmap() ``` ### ML - \_POSIX\_MEMLOCK - \_SC\_MEMLOCK Shared memory can be locked into core. The following functions are present: ``` mlockall() munlockall() ``` ### MR/MLR - \_POSIX\_MEMLOCK\_RANGE - \_SC\_MEMLOCK\_RANGE More precisely, ranges can be locked into core. The following functions are present: ``` mlock() munlock() ``` ### MPR - \_POSIX\_MEMORY\_PROTECTION - \_SC\_MEMORY\_PROTECTION The function *mprotect*() is present. ### MSG - \_POSIX\_MESSAGE\_PASSING - \_SC\_MESSAGE\_PASSING The include file *\* is present. The following functions are present: ``` mq_close() mq_getattr() mq_notify() mq_open() mq_receive() mq_send() mq_setattr() mq_unlink() ``` ### MON - \_POSIX\_MONOTONIC\_CLOCK - \_SC\_MONOTONIC\_CLOCK **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() ``` ### --- - \_POSIX\_MULTI\_PROCESS - \_SC\_MULTI\_PROCESS This option has been deleted. Not in final XPG6. ### --- - \_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. ### PIO - \_POSIX\_PRIORITIZED\_IO - \_SC\_PRIORITIZED\_IO This option says that one can specify priorities for asynchronous I/O. This affects the functions ``` aio_read() aio_write() ``` ### PS - \_POSIX\_PRIORITY\_SCHEDULING - \_SC\_PRIORITY\_SCHEDULING The include file *\* 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() ``` ### RS - \_POSIX\_RAW\_SOCKETS Raw sockets are supported. The following functions are affected: ``` getsockopt() setsockopt() ``` ### --- - \_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. 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() ``` ### RTS - \_POSIX\_REALTIME\_SIGNALS - \_SC\_REALTIME\_SIGNALS Realtime signals are supported. The following functions are present: ``` sigqueue() sigtimedwait() sigwaitinfo() ``` ### --- - \_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 following functions are present: ``` regcomp() regerror() regexec() regfree() ``` ### --- - \_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. The following functions are affected: ``` exec() kill() seteuid() setegid() setgid() setuid() ``` ### SEM - \_POSIX\_SEMAPHORES - \_SC\_SEMAPHORES The include file *\* 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() ``` ### SHM - \_POSIX\_SHARED\_MEMORY\_OBJECTS - \_SC\_SHARED\_MEMORY\_OBJECTS The following functions are present: ``` mmap() munmap() shm_open() shm_unlink() ``` ### --- - \_POSIX\_SHELL - \_SC\_SHELL If this option is in effect (as it always is under POSIX.1-2001), the function *system*() is present. ### SPN - \_POSIX\_SPAWN - \_SC\_SPAWN 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 *\* 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() ``` ### SPI - \_POSIX\_SPIN\_LOCKS - \_SC\_SPIN\_LOCKS 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() ``` ### SS - \_POSIX\_SPORADIC\_SERVER - \_SC\_SPORADIC\_SERVER The scheduling policy **SCHED\_SPORADIC** is supported. This option implies the **\_POSIX\_PRIORITY\_SCHEDULING** option. The following functions are affected: ``` sched_setparam() sched_setscheduler() ``` ### SIO - \_POSIX\_SYNCHRONIZED\_IO - \_SC\_SYNCHRONIZED\_IO The following functions are affected: ``` open() msync() fsync() fdatasync() ``` ### TSA - \_POSIX\_THREAD\_ATTR\_STACKADDR - \_SC\_THREAD\_ATTR\_STACKADDR The following functions are affected: ``` pthread_attr_getstack() pthread_attr_getstackaddr() pthread_attr_setstack() pthread_attr_setstackaddr() ``` ### TSS - \_POSIX\_THREAD\_ATTR\_STACKSIZE - \_SC\_THREAD\_ATTR\_STACKSIZE The following functions are affected: ``` pthread_attr_getstack() pthread_attr_getstacksize() pthread_attr_setstack() pthread_attr_setstacksize() ``` ### TCT - \_POSIX\_THREAD\_CPUTIME - \_SC\_THREAD\_CPUTIME 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() ``` ### TPI - \_POSIX\_THREAD\_PRIO\_INHERIT - \_SC\_THREAD\_PRIO\_INHERIT The following functions are affected: ``` pthread_mutexattr_getprotocol() pthread_mutexattr_setprotocol() ``` ### TPP - \_POSIX\_THREAD\_PRIO\_PROTECT - \_SC\_THREAD\_PRIO\_PROTECT The following functions are affected: ``` pthread_mutex_getprioceiling() pthread_mutex_setprioceiling() pthread_mutexattr_getprioceiling() pthread_mutexattr_getprotocol() pthread_mutexattr_setprioceiling() pthread_mutexattr_setprotocol() ``` ### 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. 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() ``` ### TSH - \_POSIX\_THREAD\_PROCESS\_SHARED - \_SC\_THREAD\_PROCESS\_SHARED 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() ``` ### TSF - \_POSIX\_THREAD\_SAFE\_FUNCTIONS - \_SC\_THREAD\_SAFE\_FUNCTIONS 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() ``` ### TSP - \_POSIX\_THREAD\_SPORADIC\_SERVER - \_SC\_THREAD\_SPORADIC\_SERVER This option implies the **\_POSIX\_THREAD\_PRIORITY\_SCHEDULING** option. The following functions are affected: ``` sched_getparam() sched_setparam() sched_setscheduler() ``` ### THR - \_POSIX\_THREADS - \_SC\_THREADS 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() ``` ### TMO - \_POSIX\_TIMEOUTS - \_SC\_TIMEOUTS The following functions are present: ``` mq_timedreceive() mq_timedsend() pthread_mutex_timedlock() pthread_rwlock_timedrdlock() pthread_rwlock_timedwrlock() sem_timedwait() posix_trace_timedgetnext_event() ``` ### TMR - \_POSIX\_TIMERS - \_SC\_TIMERS The following functions are present: ``` clock_getres() clock_gettime() clock_settime() nanosleep() timer_create() timer_delete() timer_gettime() timer_getoverrun() timer_settime() ``` ### TRC - \_POSIX\_TRACE - \_SC\_TRACE 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() ``` ### TEF - \_POSIX\_TRACE\_EVENT\_FILTER - \_SC\_TRACE\_EVENT\_FILTER 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() ``` ### TRI - \_POSIX\_TRACE\_INHERIT - \_SC\_TRACE\_INHERIT 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() ``` ### TRL - \_POSIX\_TRACE\_LOG - \_SC\_TRACE\_LOG 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() ``` ### TYM - \_POSIX\_TYPED\_MEMORY\_OBJECTS - \_SC\_TYPED\_MEMORY\_OBJECT The following functions are present: ``` posix_mem_offset() posix_typed_mem_get_info() posix_typed_mem_open() ``` ### --- - \_POSIX\_VDISABLE Always present (probably 0). Value to set a changeable special control character to indicate that it is disabled. ## X/OPEN SYSTEM INTERFACE EXTENSIONS ### XSI - \_XOPEN\_CRYPT - \_SC\_XOPEN\_CRYPT The following functions are present: ``` crypt() encrypt() setkey() ``` ### XSI - \_XOPEN\_REALTIME - \_SC\_XOPEN\_REALTIME 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** ### ADV - --- - --- 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** ### XSI - \_XOPEN\_REALTIME\_THREADS - \_SC\_XOPEN\_REALTIME\_THREADS This option implies that the following options are all defined to 200112L: - **\_POSIX\_THREAD\_PRIO\_INHERIT** - **\_POSIX\_THREAD\_PRIO\_PROTECT** - **\_POSIX\_THREAD\_PRIORITY\_SCHEDULING** ### ADVANCED REALTIME THREADS - --- - --- 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**) ### TRACING - --- - --- This option implies that the following options are all defined to 200112L: - **\_POSIX\_TRACE** - **\_POSIX\_TRACE\_EVENT\_FILTER** - **\_POSIX\_TRACE\_LOG** - **\_POSIX\_TRACE\_INHERIT** ### STREAMS - \_XOPEN\_STREAMS - \_SC\_XOPEN\_STREAMS The following functions are present: ``` fattach() fdetach() getmsg() getpmsg() ioctl() isastream() putmsg() putpmsg() ``` ### XSI - \_XOPEN\_LEGACY - \_SC\_XOPEN\_LEGACY 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() getwd() index() mktemp() rindex() utimes() wcswcs() ``` ### XSI - \_XOPEN\_UNIX - \_SC\_XOPEN\_UNIX 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**) ## SEE ALSO [**sysconf**(3)](/sysconf/3.md), [**standards**(7)](/standards/7.md)