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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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clock_nanosleep(2) System Calls Manual clock_nanosleep(2)
clock_nanosleep - high-resolution sleep with specifiable clock
Standard C library (libc, -lc), since glibc 2.17
Before glibc 2.17, Real-time library (librt, -lrt)
#include <time.h>
int clock_nanosleep(clockid_t clockid, int flags,
const struct timespec *t,
struct timespec *_Nullable remain);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
clock_nanosleep():
_POSIX_C_SOURCE >= 200112L
Like nanosleep(2), clock_nanosleep() allows the calling thread to
sleep for an interval specified with nanosecond precision. It
differs in allowing the caller to select the clock against which
the sleep interval is to be measured, and in allowing the sleep
interval to be specified as either an absolute or a relative
value.
The time values passed to and returned by this call are specified
using timespec(3) structures.
The clockid argument specifies the clock against which the sleep
interval is to be measured. This argument can have one of the
following values:
CLOCK_REALTIME
A settable system-wide real-time clock.
CLOCK_TAI (since Linux 3.10)
A system-wide clock derived from wall-clock time but
counting leap seconds.
CLOCK_MONOTONIC
A nonsettable, monotonically increasing clock that measures
time since some unspecified point in the past that does not
change after system startup.
CLOCK_BOOTTIME (since Linux 2.6.39)
Identical to CLOCK_MONOTONIC, except that it also includes
any time that the system is suspended.
CLOCK_PROCESS_CPUTIME_ID
A settable per-process clock that measures CPU time
consumed by all threads in the process.
See clock_getres(2) for further details on these clocks. In
addition, the CPU clock IDs returned by clock_getcpuclockid(3) and
pthread_getcpuclockid(3) can also be passed in clockid.
If flags is 0, then the value specified in t is interpreted as an
interval relative to the current value of the clock specified by
clockid.
If flags is TIMER_ABSTIME, then t is interpreted as an absolute
time as measured by the clock, clockid. If t is less than or
equal to the current value of the clock, then clock_nanosleep()
returns immediately without suspending the calling thread.
clock_nanosleep() suspends the execution of the calling thread
until either at least the time specified by t has elapsed, or a
signal is delivered that causes a signal handler to be called or
that terminates the process.
If the call is interrupted by a signal handler, clock_nanosleep()
fails with the error EINTR. In addition, if remain is not NULL,
and flags was not TIMER_ABSTIME, it returns the remaining unslept
time in remain. This value can then be used to call
clock_nanosleep() again and complete a (relative) sleep.
On successfully sleeping for the requested interval,
clock_nanosleep() returns 0. If the call is interrupted by a
signal handler or encounters an error, then it returns one of the
positive error number listed in ERRORS.
EFAULT t or remain specified an invalid address.
EINTR The sleep was interrupted by a signal handler; see
signal(7).
EINVAL The value in the tv_nsec field was not in the range [0,
999999999] or tv_sec was negative.
EINVAL clockid was invalid. (CLOCK_THREAD_CPUTIME_ID is not a
permitted value for clockid.)
ENOTSUP
The kernel does not support sleeping against this clockid.
POSIX.1-2008.
POSIX.1-2001. Linux 2.6, glibc 2.1.
If the interval specified in t is not an exact multiple of the
granularity underlying clock (see time(7)), then the interval will
be rounded up to the next multiple. Furthermore, after the sleep
completes, there may still be a delay before the CPU becomes free
to once again execute the calling thread.
Using an absolute timer is useful for preventing timer drift
problems of the type described in nanosleep(2). (Such problems
are exacerbated in programs that try to restart a relative sleep
that is repeatedly interrupted by signals.) To perform a relative
sleep that avoids these problems, call clock_gettime(2) for the
desired clock, add the desired interval to the returned time
value, and then call clock_nanosleep() with the TIMER_ABSTIME
flag.
clock_nanosleep() is never restarted after being interrupted by a
signal handler, regardless of the use of the sigaction(2)
SA_RESTART flag.
The remain argument is unused, and unnecessary, when flags is
TIMER_ABSTIME. (An absolute sleep can be restarted using the same
t argument.)
POSIX.1 specifies that clock_nanosleep() has no effect on signals
dispositions or the signal mask.
POSIX.1 specifies that after changing the value of the
CLOCK_REALTIME clock via clock_settime(2), the new clock value
shall be used to determine the time at which a thread blocked on
an absolute clock_nanosleep() will wake up; if the new clock value
falls past the end of the sleep interval, then the
clock_nanosleep() call will return immediately.
POSIX.1 specifies that changing the value of the CLOCK_REALTIME
clock via clock_settime(2) shall have no effect on a thread that
is blocked on a relative clock_nanosleep().
clock_getres(2), nanosleep(2), restart_syscall(2),
timer_create(2), sleep(3), timespec(3), usleep(3), time(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 clock_nanosleep(2)
Pages that refer to this page: nanosleep(2), PR_SET_TIMERSLACK(2const), restart_syscall(2), syscalls(2), clockid_t(3type), timespec(3type), signal(7), time(7), time_namespaces(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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