PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       getitimer, setitimer — get and set value of interval timer

SYNOPSIS

       #include <sys/time.h>

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

DESCRIPTION

       The getitimer() function shall store the current value of the timer specified by which into the structure
       pointed to by value.  The setitimer() function shall set the  timer  specified  by  which  to  the  value
       specified  in  the structure pointed to by value, and if ovalue is not a null pointer, store the previous
       value of the timer in the structure pointed to by ovalue.

       A timer value is defined by the itimerval structure, specified in <sys/time.h>.  If it_value is non-zero,
       it  shall indicate the time to the next timer expiration.  If it_interval is non-zero, it shall specify a
       value to be used in reloading it_value when the timer expires. Setting it_value  to  0  shall  disable  a
       timer,  regardless of the value of it_interval.  Setting it_interval to 0 shall disable a timer after its
       next expiration (assuming it_value is non-zero).

       Implementations may place limitations on the granularity of timer values. For each interval timer, if the
       requested  timer  value  requires  a finer granularity than the implementation supports, the actual timer
       value shall be rounded up to the next supported value.

       An XSI-conforming implementation provides each process with at least three  interval  timers,  which  are
       indicated by the which argument:

       ITIMER_PROF   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.

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

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

       The interaction between setitimer() and alarm() or sleep() is unspecified.

RETURN VALUE

       Upon  successful  completion,  getitimer() or setitimer() shall return 0; otherwise, -1 shall be returned
       and errno set to indicate the error.

ERRORS

       The setitimer() function shall fail if:

       EINVAL The value argument is not in canonical form. (In canonical form, the number of microseconds  is  a
              non-negative integer less than 1000000 and the number of seconds is a non-negative integer.)

       The getitimer() and setitimer() functions may fail if:

       EINVAL The which argument is not recognized.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Applications  should  use  the  timer_gettime()  and timer_settime() functions instead of the obsolescent
       getitimer() and setitimer() functions, respectively.

RATIONALE

       None.

FUTURE DIRECTIONS

       The getitimer() and setitimer() functions may be removed in a future version.

SEE ALSO

       alarm(), exec, sleep(), timer_getoverrun()

       The Base Definitions volume of POSIX.1‐2017, <signal.h>, <sys_time.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical  and  Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .