TIMER_SETTIME(2)            Linux Programmer's Manual           TIMER_SETTIME(2)

       timer_settime, timer_gettime - arm/disarm and fetch state of POSIX per-
       process timer

       #include <time.h>

       int timer_settime(timer_t timerid, int flags,
                         const struct itimerspec *new_value,
                         struct itimerspec *old_value);
       int timer_gettime(timer_t timerid, struct itimerspec *curr_value);

       Link with -lrt.

   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 defined as follows:

           struct timespec {
               time_t tv_sec;                /* Seconds */
               long   tv_nsec;               /* Nanoseconds */

           struct itimerspec {
               struct timespec it_interval;  /* Timer interval */
               struct timespec it_value;     /* Initial expiration */

       Each of the substructures of the itimerspec structure is a timespec
       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

       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

       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

       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

       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.

       These system calls are available since Linux 2.6.

       POSIX.1-2001, POSIX.1-2008.

       See timer_create(2).

       timer_create(2), timer_getoverrun(2), time(7)

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       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                              2020-06-09                   TIMER_SETTIME(2)