These signals are used to indicate the expiration of timers. See Setting an Alarm, for information about functions that cause these signals to be sent.
The default behavior for these signals is to cause program termination. This default is rarely useful, but no other default would be useful; most of the ways of using these signals would require handler functions in any case.
This signal typically indicates expiration of a timer that measures real or clock time. It is used by the
alarmfunction, for example.