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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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GETITIMER(3P) POSIX Programmer's Manual GETITIMER(3P)
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.
getitimer, setitimer — get and set value of interval timer
#include <sys/time.h>
int getitimer(int which, struct itimerval *value);
int setitimer(int which, const struct itimerval *restrict value,
struct itimerval *restrict ovalue);
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.
Upon successful completion, getitimer() or setitimer() shall
return 0; otherwise, -1 shall be returned and errno set to
indicate the error.
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.
None.
Applications should use the timer_gettime() and timer_settime()
functions instead of the obsolescent getitimer() and setitimer()
functions, respectively.
None.
The getitimer() and setitimer() functions may be removed in a
future version.
alarm(3p), exec(1p), sleep(3p), timer_getoverrun(3p)
The Base Definitions volume of POSIX.1‐2017, signal.h(0p),
sys_time.h(0p)
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 .
IEEE/The Open Group 2017 GETITIMER(3P)
Pages that refer to this page: sys_time.h(0p), alarm(3p), exec(3p), pselect(3p), setitimer(3p), sleep(3p)
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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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