posixoptions(7)

📦

version 6.20 · 13 versions

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6.13 · opensuse-leap 16.0
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6.19 · arch rolling, ubuntu stonking
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💖 NAME 💖

posixoptions — the optional lil extras of the POSIX standard ✨ no cap, this is your cheat sheet bestie 🫶

✨ DESCRIPTION ✨

okay so 🌸 the POSIX standard (and fr, everything below is straight from POSIX.1-2001) describes a whole set of behaviours and interfaces for a system that's tryna be compliant 💅

but here's the tea: lots of those interfaces are optional 😭 and there's a whole toolkit for checking what's actually there:

feature test macros — to test availability of interfaces at compile time 👑
sysconf(3), fpathconf(3), pathconf(3), confstr(3) — to do that same check at run time 🌸
from shell scripts you've got getconf(1) 🦋
for way more detail, slide into sysconf(3) 💜

so how do you read the rest of this page? every entry hands you:

the POSIX abbreviation 👑
the option
the sysconf(3) parameter you use to ask about it 🎀
and possibly a very short description ✨

real talk though — much more precise detail lives in the POSIX standard itself, and versions of that can nowadays be accessed freely on the web 🌈

💅 ADV — `_POSIX_ADVISORY_INFO` — `_SC_ADVISORY_INFO` 💅

the following advisory functions are present, bestie:

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

🦋 AIO — `_POSIX_ASYNCHRONOUS_IO` — `_SC_ASYNCHRONOUS_IO` 🦋

the header <aio.h> is present 📋 and these functions are too:

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 💜 and 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 (and it always is under POSIX.1-2001, periodt), 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 🕐 and the following functions are present:

pthread_condattr_getclock()
pthread_condattr_setclock()
clock_nanosleep()

also: 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, and the function clock_getcpuclockid() is present 🎀

💀 --- — `_POSIX_FILE_LOCKING` — `_SC_FILE_LOCKING` 💀

this option has been deleted 😭 not in final XPG6. rip, moving on.

🍓 FSC — `_POSIX_FSYNC` — `_SC_FSYNC` 🍓

the function fsync() is present 💾 that's it, that's the whole vibe.

🌈 IP6 — `_POSIX_IPV6` — `_SC_IPV6` 🌈

Internet Protocol Version 6 is supported 🛰️✨

💜 --- — `_POSIX_JOB_CONTROL` — `_SC_JOB_CONTROL` 💜

if this option is in effect (and yes, 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 <sys/mman.h> is present, and so are these:

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 (iykyk): 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 🛡️ so iconic.

🦋 MSG — `_POSIX_MESSAGE_PASSING` — `_SC_MESSAGE_PASSING` 🦋

the include file <mqueue.h> is present 📬 and these functions are too:

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 💜 and 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. gone girl fr.

🧚 --- — `_POSIX_NO_TRUNC` 🧚

if this option is in effect (and it always is under POSIX.1-2001), then pathname components longer than NAME_MAX are not truncated ✂️ — nope, they give an error 🚨

heads up though: this property may be dependent on the path prefix of the component 🌀

⭐ PIO — `_POSIX_PRIORITIZED_IO` — `_SC_PRIORITIZED_IO` ⭐

this option says you can specify priorities for asynchronous I/O 🏆 it affects the functions:

aio_read()
aio_write()

👑 PS — `_POSIX_PRIORITY_SCHEDULING` — `_SC_PRIORITY_SCHEDULING` 👑

the include file <sched.h> is present 📋 and these functions are too:

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

and if _POSIX_SPAWN is also in effect, then you also get:

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

🌈 RS — `_POSIX_RAW_SOCKETS` 🌈

raw sockets are supported 🕳️🔌 and the following functions are affected:

getsockopt()
setsockopt()

💅 --- — `_POSIX_READER_WRITER_LOCKS` — `_SC_READER_WRITER_LOCKS` 💅

this option implies the _POSIX_THREADS option 🔒 and conversely, under POSIX.1-2001, the _POSIX_THREADS option implies this option 🔁 mutual besties fr fr

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 (and 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 (and yep, 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 <semaphore.h> is present 🚦 and the following functions are too:

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 (and it always is under POSIX.1-2001), the function system() is present 🐚 periodt.

🦋 SPN — `_POSIX_SPAWN` — `_SC_SPAWN` 🦋

this option describes support for process creation in a context where it's 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()

and if _POSIX_PRIORITY_SCHEDULING is also in effect, then you also get:

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()