setitimer(2) get/set value of interval timer

Other Alias



Lb libc


In sys/time.h Fd #define ITIMER_REAL 0 Fd #define ITIMER_VIRTUAL 1 Fd #define ITIMER_PROF 2 Ft int Fn getitimer int which struct itimerval *value Ft int Fn setitimer int which const struct itimerval *value struct itimerval *ovalue


The system provides each process with three interval timers, defined in In sys/time.h . The Fn getitimer system call returns the current value for the timer specified in Fa which in the structure at Fa value . The Fn setitimer system call sets a timer to the specified Fa value (returning the previous value of the timer if Fa ovalue is not a null pointer).

A timer value is defined by the Fa itimerval structure:

struct itimerval {
        struct  timeval it_interval;    /* timer interval */
        struct  timeval it_value;       /* current value */

If Fa it_value is non-zero, it indicates the time to the next timer expiration. If Fa it_interval is non-zero, it specifies a value to be used in reloading Fa it_value when the timer expires. Setting Fa it_value to 0 disables a timer, regardless of the value of Fa it_interval . Setting Fa it_interval to 0 causes a timer to be disabled after its next expiration (assuming Fa 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.

The maximum number of seconds allowed for Fa it_interval and Fa it_value in Fn setitimer is 100000000.


Three macros for manipulating time values are defined in In sys/time.h . The Fn timerclear macro sets a time value to zero, Fn timerisset tests if a time value is non-zero, and Fn timercmp compares two time values.


Rv -std


The Fn getitimer and Fn setitimer system calls will fail if:

The Fa value argument specified a bad address.
The Fa value argument specified a time that was too large to be handled.


The Fn getitimer system call appeared in BSD 4.2