alarm, ualarm - Sets or changes the timeout of interval timers.
unsigned int alarm(
unsigned int seconds ); useconds_t ualarm(
unseconds_t interval );
Standard C Library (libc)
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
alarm(), ualarm(): XSH5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
Specifies a number of real-time seconds. Specifies a number of real-
time microseconds. Specifies the interval for repeating the timer.
The alarm() function is used to obtain notification of a timeout after
the number of real-time seconds specified by the seconds parameter has
elapsed. At some time after seconds seconds have elapsed, a signal is
delivered to the process. Each call resets the timer to the new value.
A value of 0 (zero) disables the timer. When the notification signal is
caught or ignored, no action takes place; otherwise the calling process
is terminated. The alarm() function uses the ITIMER_REAL interval
The ualarm() function is used to obtain notification of a timeout after
the number of real-time microseconds specified by the useconds parame‐
ter has elapsed. When the interval parameter is nonzero, timeout noti‐
fication occurs after the number of microseconds specified by the
interval parameter has been added to the useconds parameter. When the
notification signal is caught or ignored, no action takes place; other‐
wise the calling process is terminated. The ualarm() function is the
simplified interface to the setitimer() function, and uses the
ITIMER_REAL interval timer.
The alarm() and ualarm() functions are supported for multithreaded
Although the alarm() and ualarm() functions are reentrant, it should be
noted that just as the second of two calls from a single thread to
alarm() resets the timer, this is also true if two calls are made from
If there is a previous alarm() request with time remaining, the alarm()
function returns a non-zero value that is the number of seconds until
the previous request would have generated a SIGALRM signal. Otherwise,
alarm() returns 0 (zero).
The ualarm() function returns the number of microseconds remaining from
the previous ualarm() call. If no timeouts are pending or if ualarm()
has not previously been called, ualarm() returns 0 (zero).
The alarm() function sets errno to the specified values for the follow‐
[Tru64 UNIX] The seconds parameter specifies a value greater than