This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
The nanosleep() function shall cause the current thread to be
suspended from execution until either the time interval specified by
the rqtp argument has elapsed or a signal is delivered to the calling
thread, and its action is to invoke a signal-catching function or to
terminate the process. The suspension time may be longer than
requested because the argument value is rounded up to an integer
multiple of the sleep resolution or because of the scheduling of
other activity by the system. But, except for the case of being
interrupted by a signal, the suspension time shall not be less than
the time specified by rqtp, as measured by the system clock
The use of the nanosleep() function has no effect on the action or
blockage of any signal.
If the nanosleep() function returns because the requested time has
elapsed, its return value shall be zero.
If the nanosleep() function returns because it has been interrupted
by a signal, it shall return a value of −1 and set errno to indicate
the interruption. If the rmtp argument is non-NULL, the timespec
structure referenced by it is updated to contain the amount of time
remaining in the interval (the requested time minus the time actually
slept). The rqtp and rmtp arguments may point to the same object. If
the rmtp argument is NULL, the remaining time is not returned.
If nanosleep() fails, it shall return a value of −1 and set errno to
indicate the error.
The nanosleep() function shall fail if:
EINTR The nanosleep() function was interrupted by a signal.
EINVAL The rqtp argument specified a nanosecond value less than zero
or greater than or equal to 1000 million.
The following sections are informative.
It is common to suspend execution of a thread for an interval in
order to poll the status of a non-interrupting function. A large
number of actual needs can be met with a simple extension to sleep()
that provides finer resolution.
In the POSIX.1‐1990 standard and SVR4, it is possible to implement
such a routine, but the frequency of wakeup is limited by the
resolution of the alarm() and sleep() functions. In 4.3 BSD, it is
possible to write such a routine using no static storage and
reserving no system facilities. Although it is possible to write a
function with similar functionality to sleep() using the remainder of
the timer_*() functions, such a function requires the use of signals
and the reservation of some signal number. This volume of
POSIX.1‐2008 requires that nanosleep() be non-intrusive of the
The nanosleep() function shall return a value of 0 on success and −1
on failure or if interrupted. This latter case is different from
sleep(). This was done because the remaining time is returned via an
argument structure pointer, rmtp, instead of as the return value.
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 NANOSLEEP(3P)