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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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timer_settime(2) System Calls Manual timer_settime(2)
timer_settime, timer_gettime - arm/disarm and fetch state of POSIX
per-process timer
Real-time library (librt, -lrt)
#include <time.h>
int timer_gettime(timer_t timerid, struct itimerspec *curr_value);
int timer_settime(timer_t timerid, int flags,
const struct itimerspec *restrict new_value,
struct itimerspec *_Nullable restrict old_value);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
timer_settime(), timer_gettime():
_POSIX_C_SOURCE >= 199309L
timer_settime() arms or disarms the timer identified by timerid.
The new_value argument is pointer to an itimerspec structure that
specifies the new initial value and the new interval for the
timer. The itimerspec structure is described in
itimerspec(3type).
Each of the substructures of the itimerspec structure is a
timespec(3) structure that allows a time value to be specified in
seconds and nanoseconds. These time values are measured according
to the clock that was specified when the timer was created by
timer_create(2).
If new_value->it_value specifies a nonzero value (i.e., either
subfield is nonzero), then timer_settime() arms (starts) the
timer, setting it to initially expire at the given time. (If the
timer was already armed, then the previous settings are
overwritten.) If new_value->it_value specifies a zero value
(i.e., both subfields are zero), then the timer is disarmed.
The new_value->it_interval field specifies the period of the
timer, in seconds and nanoseconds. If this field is nonzero, then
each time that an armed timer expires, the timer is reloaded from
the value specified in new_value->it_interval. If
new_value->it_interval specifies a zero value, then the timer
expires just once, at the time specified by it_value.
By default, the initial expiration time specified in
new_value->it_value is interpreted relative to the current time on
the timer's clock at the time of the call. This can be modified
by specifying TIMER_ABSTIME in flags, in which case
new_value->it_value is interpreted as an absolute value as
measured on the timer's clock; that is, the timer will expire when
the clock value reaches the value specified by
new_value->it_value. If the specified absolute time has already
passed, then the timer expires immediately, and the overrun count
(see timer_getoverrun(2)) will be set correctly.
If the value of the CLOCK_REALTIME clock is adjusted while an
absolute timer based on that clock is armed, then the expiration
of the timer will be appropriately adjusted. Adjustments to the
CLOCK_REALTIME clock have no effect on relative timers based on
that clock.
If old_value is not NULL, then it points to a buffer that is used
to return the previous interval of the timer (in
old_value->it_interval) and the amount of time until the timer
would previously have next expired (in old_value->it_value).
timer_gettime() returns the time until next expiration, and the
interval, for the timer specified by timerid, in the buffer
pointed to by curr_value. The time remaining until the next timer
expiration is returned in curr_value->it_value; this is always a
relative value, regardless of whether the TIMER_ABSTIME flag was
used when arming the timer. If the value returned in
curr_value->it_value is zero, then the timer is currently
disarmed. The timer interval is returned in
curr_value->it_interval. If the value returned in
curr_value->it_interval is zero, then this is a "one-shot" timer.
On success, timer_settime() and timer_gettime() return 0. On
error, -1 is returned, and errno is set to indicate the error.
These functions may fail with the following errors:
EFAULT new_value, old_value, or curr_value is not a valid pointer.
EINVAL timerid is invalid.
timer_settime() may fail with the following errors:
EINVAL new_value.it_value is negative; or
new_value.it_value.tv_nsec is negative or greater than
999,999,999.
POSIX.1-2008.
Linux 2.6. POSIX.1-2001.
See timer_create(2).
timer_create(2), timer_getoverrun(2), timespec(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
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 timer_settime(2)
Pages that refer to this page: getitimer(2), syscalls(2), timer_create(2), timer_delete(2), timerfd_create(2), timer_getoverrun(2), itimerspec(3type), timer_t(3type), timespec(3type), ualarm(3), usleep(3), signal-safety(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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