Section: POSIX Programmer's Manual (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.
--- get and set value of interval timer
int getitimer(int which, struct itimerval *value);
int setitimer(int which, const struct itimerval *restrict value,
struct itimerval *restrict ovalue);
function shall store the current value of the timer specified by
into the structure pointed to by
function shall set the timer specified by
to the value specified in the structure pointed to by
is not a null pointer, store the previous value of the timer in the
structure pointed to by
A timer value is defined by the
structure, specified in
is non-zero, it shall indicate the time to the next timer expiration.
is non-zero, it shall specify a value to be used in reloading
when the timer expires. Setting
to 0 shall disable a timer, regardless of the value of
to 0 shall disable a timer after its next expiration (assuming
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
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.
Decrements in real time. A SIGALRM signal is delivered when this timer
Decrements in process virtual time. It runs only when the process is
executing. A SIGVTALRM signal is delivered when it expires.
The interaction between
Upon successful completion,
shall return 0; otherwise, -1 shall be returned and
set to indicate the error.
function shall fail if:
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.)
functions may fail if:
argument is not recognized.
The following sections are informative.
Applications should use the
functions instead of the obsolescent
functions may be removed in a future version.
The Base Definitions volume of POSIX.1-2017,
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
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