cosmopolitan libc

your build-anywhere run-anywhere c library

Can I Use a System Call?

Cosmopolitan Libc wraps system calls to provide high-level access to binary kernel interfaces. Linux is the gold standard for our suppport. However, if your program works on Linux, then it might not work on other platforms depending on which functions you use. The following table should help illuminate the portability of functions.

Last updated: Thu Apr 3 12:37:24 AM PDT 2025

Function	Linux	FreeBSD	OpenBSD	NetBSD	MacOS	Windows	Metal	Blink
read	best	best	best	best	best	ok	good	best
write	best	best	best	best	best	ok	good	best
pread	best	best	best	best	best	ok	zipos	best
pwrite	best	best	best	best	best	ok	zipos	best
readv	best	best	best	best	best	ok	best	best
writev	best	best	best	best	best	ok	best	best
preadv	2009+	v2.1+	v2.1+	v2.1+	v2.1+	v2.1+	v2.1+	v2.1+
pwritev	2009+	v2.1+	v2.1+	v2.1+	v2.1+	v2.1+	v2.1+	v2.1+
close	best	best	best	best	best	slow	best	best
fstatat	best	best	best	best	best	best	best	best
fstat	best	best	best	best	best	best	best	best
statfs	best	best	best	best	best	best	fault	enosys
fstatfs	best	best	best	best	best	best	fault	enosys
_Exit	best	best	best	best	best	best	reset	best
fork	best	best	slow	best	best	slow	fault	best
vfork	best	best	fork	best	fork	fork	fault	fork
locks	futex	umtx	futex	sem_t	ulock	futex	n/a	futex
tls	%gs/x28	%gs/x28	%fs	%fs/x28	%gs/x28	%gs	%gs	best
pthread_create	best	best	best	best	best	best	fault	best
pthread_kill	good	good	best	good	good	v3.0+	fault	best
pthread_cancel	v2.2	v2.2	v2.2	v2.2	v2.2	v3.0+	fault	best
tmpfd	best	ok	ok	ok	ok	best	todo	best
tmpfile	best	ok	ok	ok	ok	best	todo	best
fopenat O_RDONLY	best	best	best	best	best	best	zipos	best
fopenat O_RDWR	best	best	best	best	best	best	todo	best
/dev/tty	best	best	best	best	best	v3.0+	todo	best
/dev/null	best	best	best	best	best	v3.0+	todo	best
/dev/stdin	best	best	best	best	best	v3.0+	todo	best
/dev/stdout	best	best	best	best	best	v3.0+	todo	best
/dev/stderr	best	best	best	best	best	v3.0+	todo	best
/dev/fd/𝑥	best	best	best	best	best	v3.2.3+	todo	best
/dev/random	best	best	best	best	best	v3.3.4+	todo	best
/dev/urandom	best	best	best	best	best	v3.3.4+	todo	best
mmap MAP_PRIVATE	best	best	best	best	best	no cow	best	best
mmap MAP_SHARED	best	best	yellow	best	best	best	best	wip
mremap	v3.6.0+	enosys	enosys	v3.6.0+	enosys	enosys	enosys	wip
poll	best	best	best	best	best	good	best	good
select	best	best	best	best	best	good	fault	wip
pselect	best	best	best	best	best	good	fault	wip
ppoll	best	best	best	best	non-atomic	good	fault	wip
lseek	best	best	best	best	best	best	best	best
pledge	2.6.23+	ignored	best	ignored	ignored	ignored	fault	ignored
unveil	5.13+	ignored	best	ignored	ignored	ignored	fault	ignored
msync	best	best	best	best	best	partial	todo	ignored
mprotect	best	best	best	best	best	best	todo	best
munmap	best	best	best	best	best	best	best	best
sigaction ucontext_t	best	best	best	best	best	best	enosys	best
sigprocmask	best	best	best	best	best	simulated	no-op	bestp
sigsuspend	best	best	best	best	best	simulated	no-op	best
sigpending	best	best	best	best	best	simulated	no-op	wip
clock_gettime REALTIME	fast	good	good	good	fast	fast	enosys	best
clock_gettime MONOTONIC	fast	good	good	good	rdtsc	fast	enosys	depends
clock_gettime MONOTONIC RAW	fast	good	EINVAL	good	mixed	fast	enosys	depends
clock_gettime BOOTTIME	fast	good	good	good	good	fast	enosys	depends
clock_gettime PROCESS CPUTIME	good	good	good	good	good	good	enosys	good
clock_gettime THREAD CPUTIME	good	good	good	good	good	good	enosys	good
clock_getres	kinda	good	good	ok	faked	faked	enosys	best
ioctl FIONREAD	best	best	best	best	best	best	wip	best
ioctl TIOCGWINSZ	best	best	best	best	best	good	wip	best
ioctl SIOCGIFCONF	best	best	best	best	best	best	fault	ipv4
ioctl SIOCGIFADDR	best	best	best	best	best	best	fault	wip
ioctl SIOCGIFNETMASK	best	best	best	best	best	best	fault	wip
ioctl SIOCGIFBRDADDR	best	best	best	best	best	best	fault	wip
ioctl SIOCGIFDSTADDR	best	best	best	best	best	best	fault	wip
ioctl SIOCGIFFLAGS	best	best	best	best	best	best	fault	wip
openpty	v2.0+	v2.1+	v2.1+	v2.1+	v2.1+	enosys	enosys	wip
ptsname	v2.0+	v2.1+	hairy	v2.1+	v2.1+	enosys	enosys	wip
flock	good	good	good	good	good	good	fault	wip
sync	notest	notest	notest	notest	notest	flush	fault	wip
fsync	notest	notest	notest	notest	hairy	flush	fault	best
fdatasync	notest	notest	notest	notest	notest	flush	fault	best
copy_file_range	5.9+	13+	enosys	enosys	enosys	enosys	fault	wip
sendfile	best	best	enosys	enosys	best	best	enosys	wip
splice	5.9+	enosys	enosys	enosys	enosys	enosys	fault	wip
closefrom	5.9+	best	best	v2.2	enosys	enosys	enosys	best
close_range	5.9+	13+	enosys	enosys	enosys	enosys	enosys	best
fadvise	best	best	enosys	best	enosys	most	enosys	wip
posix_fadvise	best	best	enosys	best	enosys	most	enosys	wip
truncate	best	best	best	best	best	best	fault	best
ftruncate	best	best	best	best	best	best	enosys	best
faccessat	good	best	best	best	best	best	zipos	best
pipe	best	best	best	best	best	best	fault	best
pipe2	2008+	best	best	best	non-atomic	best	fault	best
socketpair	best	best	best	best	best	best	fault	wip
getcwd	best	best	best	best	best	best	fault	best
chdir	best	best	best	best	best	hairy	fault	best
fchdir	best	best	best	best	best	hairy	fault	best
renameat	best	best	best	best	best	best	fault	best
mkdirat	best	best	best	best	best	best	fault	best
linkat	best	best	best	best	best	admin-only	fault	best
unlinkat	best	best	best	best	best	hairy	fault	best
readlinkat	best	best	best	best	best	best	fault	best
sched_yield	best	best	best	best	select	best	no-op	best
memfd_create	best	enosys	enosys	enosys	enosys	enosys	fault	wip
mincore	best	best	enosys	best	best	enosys	fault	wip
madvise	best	best	best	best	best	some	fault	ignored
dup	best	best	best	best	best	best	fault	best
dup2	best	best	best	best	best	best	fault	best
dup3	2008+	non-atomic	best	best	non-atomic	best	fault	best
fcntl F_DUPFD	best	best	best	best	best	best	fault	best
fcntl F_DUPFD_CLOEXEC	2008+	best	best	best	best	best	fault	best
fcntl POSIX Locks	good	good	good	good	good	ok	fault	wip
fcntl OFD Locks	best	none	none	none	none	none	fault	wip
fcntl F_GETFL	best	best	best	best	best	best	fault	best
fcntl F_SETFL	best	best	best	best	best	v3.0+	fault	best
fcntl F_GETFD	best	best	best	best	best	best	fault	best
fcntl F_SETFD	best	best	best	best	best	best	fault	best
fcntl F_NOTIFY	best	einval	einval	einval	einval	einval	fault	wip
fcntl F_FULLFSYNC	einval	einval	einval	einval	best	einval	fault	einval
fcntl F_GETPATH	einval	einval	einval	best	best	einval	fault	einval
nanosleep	best	best	best	best	micros	micros	enosys	best
setitimer	best	best	best	best	best	thread	fault	best
gettid	best	good	good	good	good	good	fault	best
getpid	best	best	best	best	best	best	best	best
getppid	best	best	best	best	best	slow	best	best
getuid	best	best	best	best	best	faked	best	best
getgid	best	best	best	best	best	faked	best	best
getrandom	2014+	sysctl	getentropy	sysctl	getentropy	ProcessPrng	rdrand	best
getentropy	v2.2	v2.2	v2.2	v2.2	v2.2	v2.2	v2.2	best
umask	best	best	best	best	best	no-op	fault	best
issetugid	best	best	best	best	best	best	zero	wip
setuid	best	best	best	best	best	no-op	fault	best
setgid	best	best	best	best	best	no-op	fault	best
setreuid	best	best	best	best	best	enosys	fault	wip
setregid	best	best	best	best	best	enosys	fault	wip
setresuid	best	best	best	faked	faked	enosys	fault	wip
setresgid	best	best	best	faked	faked	enosys	fault	wip
socket	best	best	best	best	best	best	fault	ipv4
bind	best	best	best	best	best	good	fault	best
connect	best	best	best	best	best	good	fault	best
accept	best	best	best	best	best	good	fault	best
accept4	2009+	best	best	best	non-atomic	good	fault	best
sendto	best	best	best	best	best	good	fault	wip
recvfrom	best	best	best	best	best	good	fault	wip
sendmsg	good	ok	ok	ok	ok	ok	fault	wip
recvmsg	good	ok	ok	ok	ok	ok	fault	wip
shutdown	best	best	best	best	good	best	fault	best
getsockname	best	best	best	best	best	best	fault	best
getpeername	best	best	best	best	best	best	fault	best
getsockopt	best	narrow	narrow	narrow	narrow	narrow	fault	some
setsockopt SO_TYPE	best	best	best	best	best	best	fault	tbd
setsockopt SO_DEBUG	best	best	best	best	best	best	fault	tbd
setsockopt SO_ERROR	best	best	best	best	best	best	fault	tbd
setsockopt SO_BROADCAST	best	best	best	best	best	best	fault	tbd
setsockopt SO_REUSEADDR	best	best	best	best	best	n/a	fault	tbd
setsockopt SO_REUSEPORT	best	unsure	best	best	best	best	fault	tbd
setsockopt SO_KEEPALIVE	best	best	best	best	best	best	fault	tbd
setsockopt SO_ACCEPTCONN	best	best	best	best	best	best	fault	tbd
setsockopt SO_DONTROUTE	best	best	best	best	best	best	fault	tbd
setsockopt SO_SNDBUF	best	best	best	best	best	best	fault	tbd
setsockopt SO_RCVBUF	best	best	best	best	best	best	fault	tbd
setsockopt SO_SNDLOWAT	best	best	best	best	best	best	fault	tbd
setsockopt SO_RCVLOWAT	best	best	best	best	best	best	fault	tbd
setsockopt TCP_NODELAY	best	best	best	best	best	best	fault	tbd
setsockopt TCP_CORK	best	best	best	best	best	best	fault	tbd
setsockopt TCP_FASTOPEN	best	best	enopro	enopro	enopro	best	enosys	tbd
setsockopt TCP_QUICKACK	best	enopro	enopro	enopro	enopro	enopro	fault	tbd
execve	best	best	best	best	best	kludge	fault	tbd
fexecve	best	best	enosys	enosys	enosys	enosys	enosys	tbd
execve #!	best	best	best	best	best	v3.3.7+	fault	tbd
wait4	best	best	best	best	best	v4.0.0	fault	best
kill	best	best	best	best	best	v4.0.0	fault	best
sysinfo	best	partial	partial	partial	partial	partial	enosys	faked
uname	best	best	best	best	best	weird	enosys	tbd
gethostname	best	best	best	best	best	best	fault	tbd
getdomainname	best	best	best	best	best	best	fault	tbd
fchmodat	best	best	best	best	best	limited	fault	tbd
fchownat	best	best	best	best	best	enosys	fault	tbd
chroot	works	works	works	works	works	enosys	fault	tbd
mount	notest	notest	notest	notest	notest	enosys	fault	tbd
reboot	notest	notest	notest	notest	notest	notest	fault	tbd
utimes	1e-6	1e-6	1e-6	1e-6	1e-6	1e-6	enosys	tbd
futimes	2008+	1e-6	1e-6	1e-6	1e-6	1e-6	enosys	tbd
utimensat	2008+	1e-9	1e-9	1e-9	1e-6	1e-7	enosys	tbd
futimens	2008+	1e-9	1e-9	1e-9	1e-6	1e-7	fault	tbd
setpriority	v2.2	v2.2	v2.2	v2.2	v2.2	quantized	fault	tbd
getpriority	v2.2	v2.2	v2.2	v2.2	v2.2	quantized	fault	tbd
sem_init	best	best	best	best	best	best	fault	tbd
sem_wait	best	best	best	ok	good	best	fault	tbd
sem_open	best	best	best	best	best	best	fault	tbd
pthread_setname_np	best	best	enosys	best	enosys	enosys	fault	tbd
pthread_getname_np	best	best	enosys	best	enosys	enosys	fault	tbd
pthread_setaffinity_np	best	best	none	broken	none	best	fault	tbd
pthread_getaffinity_np	best	best	none	broken	none	none	fault	tbd
sched_setaffinity	best	best	none	broken	none	best	fault	tbd
sched_getaffinity	best	best	none	broken	none	best	fault	tbd
sched_setscheduler	best	good	none	good	none	none	fault	no-op
sched_getscheduler	best	good	none	good	none	none	fault	no-op
sched_setparam	best	good	none	good	none	none	fault	no-op
sched_getparam	best	good	none	good	none	none	fault	no-op
sched_get_priority_max	best	best	none	best	none	none	fault	no-op
sched_get_priority_min	best	best	none	best	none	none	fault	no-op
sched_rr_get_interval	best	best	none	none	none	none	fault	enosys
epoll	best	enosys	enosys	enosys	enosys	wepoll	fault	enosys
clock	cgt	cgt	cgt	cgt	getrusage	gpt	fault	cgt
getrusage	some	best	best	best	best	some	fault	best
setrlimit	best	ok	ok	ok	ok	RLIMIT_AS	fault	best
opendir	best	best	best	best	best	best	fault	good
getlogin_r	getenv	sys	sys	sys	sys	sys	enoent	tbd
login_tty	best	best	best	best	best	enosys	enosys	tbd