NAME

       getitimer, setitimer — get/set value of interval timer

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <sys/time.h>
       #define ITIMER_REAL      0
       #define ITIMER_VIRTUAL   1
       #define ITIMER_PROF      2

       int
       getitimer(int which, struct itimerval *value);

       int
       setitimer(int which, const struct itimerval *value, struct itimerval *ovalue);

DESCRIPTION

       The  system  provides  each process with three interval timers, defined in <sys/time.h>.  The getitimer()
       system call returns the current value for the timer specified in which in the structure  at  value.   The
       setitimer() system call sets a timer to the specified value (returning the previous value of the timer if
       ovalue is not a null pointer).

       A timer value is defined by the itimerval structure:

             struct itimerval {
                     struct  timeval it_interval;    /* timer interval */
                     struct  timeval it_value;       /* current value */
             };

       If it_value is non-zero, it indicates the time to the next timer expiration.  If it_interval is non-zero,
       it  specifies  a  value  to  be used in reloading it_value when the timer expires.  Setting it_value to 0
       disables a timer, regardless of the value of it_interval.  Setting it_interval to 0 causes a timer to  be
       disabled after its next expiration (assuming it_value is non-zero).

       Time  values smaller than the resolution of the system clock are rounded up to this resolution (typically
       10 milliseconds).

       The ITIMER_REAL timer decrements in real time.  A SIGALRM signal is delivered when this timer expires.

       The ITIMER_VIRTUAL timer decrements in process virtual time.  It runs only when the process is executing.
       A SIGVTALRM signal is delivered when it expires.

       The ITIMER_PROF timer decrements both in process virtual time and when the system is running on behalf of
       the process.  It is designed to be used by interpreters  in  statistically  profiling  the  execution  of
       interpreted programs.  Each time the ITIMER_PROF timer expires, the SIGPROF signal is delivered.  Because
       this signal may interrupt in-progress system calls, programs using this timer must be prepared to restart
       interrupted system calls.

       The maximum number of seconds allowed for it_interval and it_value in setitimer() is 100000000.

NOTES

       Three  macros  for  manipulating  time values are defined in <sys/time.h>.  The timerclear() macro sets a
       time value to zero, timerisset() tests if a time value is non-zero,  and  timercmp()  compares  two  time
       values.

RETURN VALUES

       Upon  successful  completion,  the value 0 is returned; otherwise the value -1 is returned and the global
       variable errno is set to indicate the error.

ERRORS

       The getitimer() and setitimer() system calls will fail if:

       [EFAULT]           The value argument specified a bad address.

       [EINVAL]           The value argument specified a time that was too large to be handled.

SEE ALSO

       gettimeofday(2), select(2), sigaction(2), clocks(7)

STANDARDS

       The getitimer() and setitimer() functions conform to IEEE Std 1003.1-2001 (“POSIX.1”).   The  later  IEEE
       Std  1003.1-2008  (“POSIX.1”) revision however marked both functions as obsolescent, recommending the use
       of timer_gettime(2) and timer_settime(2) instead.

HISTORY

       The getitimer() system call appeared in 4.2BSD.

Debian                                             May 1, 2020                                      GETITIMER(2)