GETITIMER(2) | System Calls Manual | GETITIMER(2)

# 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 *value, struct itimerval *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-null).

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.

# 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

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

[`EFAULT`]
  The value parameter specified a bad address.
[`EINVAL`]
  An unrecognized value for which was specified.

In addition, `setitimer`() may return the following error:

[`EINVAL`]
  value or ovalue specified a time that was too large to be handled.

# SEE ALSO

clock_gettime(2), gettimeofday(2), poll(2), select(2), sigaction(2)

# STANDARDS

The `getitimer`() and `setitimer`() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

# HISTORY

The `getitimer`() and `setitimer`() system calls first appeared in 4.1cBSD.

June 24, 2019 | Debian