---
name: "getitimer"
section: "2"
platform: "macos"
package: "xnu"
version: "12377.121.6"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/getitimer"
---

# getitimer(2)

get/set value of interval timer

## NAME

**getitimer**, **setitimer** – get/set value of interval timer

## 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 \*restrict value*, *struct itimerval \*restrict ovalue*);

## DESCRIPTION

The system provides each process with three interval timers, defined in ⟨*sys/time.h*⟩. The **getitimer**() call returns the current value for the timer specified in *which* in the structure at *value*. The **setitimer**() call sets a timer to the specified *value* (returning the previous value of the timer if *ovalue* is non-nil).

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.  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.

## NOTES

Three macros for manipulating time values are defined in ⟨*sys/time.h*⟩. *Timerclear* sets a time value to zero, *timerisset* tests if a time value is non-zero, and *timercmp* compares two time values (beware that \>= and \<= do not work with this macro).

## RETURN VALUES

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the global integer variable *errno* is set to indicate the error.

## ERRORS

**getitimer**() and **setitimer**() will fail if:

- \[EFAULT\]

  The *value* parameter specified a bad address.

- \[EINVAL\]

  The *value* parameter specified a time that was too large to be handled or not in the canonical form.

- \[EINVAL\]

  The *which* parameter was invalid.

## SEE ALSO

[gettimeofday(2)](/gettimeofday/2.md), [select(2)](/select/2.md), [sigaction(2)](/sigaction/2.md)

## HISTORY

The **getitimer**() function call appeared in 4.2BSD.