nanosleep - pause execution for a specified time
int nanosleep(const struct timespec *req, struct timespec
nanosleep delays the execution of the program for at least
the time specified in *req. The function can return earlier
if a signal has been delivered to the process. In this case,
it returns -1, sets errno to EINTR, and writes the remaining
time into the structure pointed to by rem unless rem is
NULL. The value of *rem can then be used to call nanosleep
again and complete the specified pause.
The structure timespec is used to specify intervals of time
with nanosecond precision. It is specified in <time.h> and
has the form
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
The value of the nanoseconds field must be in the range 0 to
999 999 999.
Compared to sleep(3) and usleep(3), nanosleep has the advan-
tage of not affecting any signals, it is standardized by
POSIX, it provides higher timing resolution, and it allows
to continue a sleep that has been interrupted by a signal
In case of an error or exception, the nanosleep system call
returns -1 instead of 0 and sets errno to one of the follow-
EINTR The pause has been interrupted by a non-blocked sig-
nal that was delivered to the process. The remaining
sleep time has been written into *rem so that the
process can easily call nanosleep again and continue
with the pause.
EINVAL The value in the tv_nsec field was not in the range
0 to 999 999 999 or tv_sec was negative.
The current implementation of nanosleep is based on the nor-
mal kernel timer mechanism, which has a resolution of 1/HZ s
(i.e, 10 ms on Linux/i386 and 1 ms on Linux/Alpha). There-
fore, nanosleep pauses always for at least the specified
time, however it can take up to 10 ms longer than specified
until the process becomes runnable again. For the same rea-
son, the value returned in case of a delivered signal in
*rem is usually rounded to the next larger multiple of
As some applications require much more precise pauses (e.g.,
in order to control some time-critical hardware), nanosleep
is also capable of short high-precision pauses. If the pro-
cess is scheduled under a real-time policy like SCHED_FIFO
or SCHED_RR, then pauses of up to 2 ms will be performed as
busy waits with microsecond precision.
POSIX.1b (formerly POSIX.4).
sleep(3), usleep(3), sched_setscheduler(2), and