timer_settime(2) — Linux manual page


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

NAME         top

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

SYNOPSIS         top

       #include <time.h>

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

       Link with -lrt.

   Feature Test Macro Requirements for glibc (see

       timer_settime(), timer_gettime():
           _POSIX_C_SOURCE >= 199309L

DESCRIPTION         top

       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 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.

RETURN VALUE         top

       On success, timer_settime() and timer_gettime() return 0.  On
       error, -1 is returned, and errno is set to indicate the error.

ERRORS         top

       These functions may fail with the following errors:

       EFAULT new_value, old_value, or curr_value is not a valid

       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

VERSIONS         top

       These system calls are available since Linux 2.6.

CONFORMING TO         top

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

EXAMPLES         top

       See timer_create(2).

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

Linux                          2021-03-22               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)ualarm(3)usleep(3)signal-safety(7)system_data_types(7)time_namespaces(7)