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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |STANDARDS |HISTORY |NOTES |SEE ALSO |COLOPHON | |
clock_nanosleep(2) System Calls Manualclock_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_tclockid, intflags,const struct timespec *t,struct timespec *_Nullableremain); Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):clock_nanosleep(): _POSIX_C_SOURCE >= 200112L
Likenanosleep(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 usingtimespec(3) structures. Theclockid 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 toCLOCK_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. Seeclock_getres(2) for further details on these clocks. In addition, the CPU clock IDs returned byclock_getcpuclockid(3) andpthread_getcpuclockid(3) can also be passed inclockid. Ifflags is 0, then the value specified int is interpreted as an interval relative to the current value of the clock specified byclockid. Ifflags isTIMER_ABSTIME, thent is interpreted as an absolute time as measured by the clock,clockid. Ift is less than or equal to the current value of the clock, thenclock_nanosleep() returns immediately without suspending the calling thread.clock_nanosleep() suspends the execution of the calling thread until either at least the time specified byt 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 errorEINTR. In addition, ifremain is not NULL, andflags was notTIMER_ABSTIME, it returns the remaining unslept time inremain. This value can then be used to callclock_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.
EFAULTt orremain specified an invalid address.EINTRThe sleep was interrupted by a signal handler; seesignal(7).EINVALThe value in thetv_nsec field was not in the range [0, 999999999] ortv_sec was negative.EINVALclockid was invalid. (CLOCK_THREAD_CPUTIME_IDis not a permitted value forclockid.)ENOTSUP The kernel does not support sleeping against thisclockid.
POSIX.1-2008.
POSIX.1-2001. Linux 2.6, glibc 2.1.
If the interval specified int is not an exact multiple of the granularity underlying clock (seetime(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 innanosleep(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, callclock_gettime(2) for the desired clock, add the desired interval to the returned time value, and then callclock_nanosleep() with theTIMER_ABSTIME flag.clock_nanosleep() is never restarted after being interrupted by a signal handler, regardless of the use of thesigaction(2)SA_RESTARTflag. Theremain argument is unused, and unnecessary, whenflags isTIMER_ABSTIME. (An absolute sleep can be restarted using the samet argument.) POSIX.1 specifies thatclock_nanosleep() has no effect on signals dispositions or the signal mask. POSIX.1 specifies that after changing the value of theCLOCK_REALTIMEclock viaclock_settime(2), the new clock value shall be used to determine the time at which a thread blocked on an absoluteclock_nanosleep() will wake up; if the new clock value falls past the end of the sleep interval, then theclock_nanosleep() call will return immediately. POSIX.1 specifies that changing the value of theCLOCK_REALTIME clock viaclock_settime(2) shall have no effect on a thread that is blocked on a relativeclock_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 theman-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 isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17clock_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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