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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 alarm function, for example.
This signal typically indicates expiration of a timer that measures CPU time used by the current process. The name is an abbreviation for “virtual time alarm”.
This signal typically indicates expiration of a timer that measures both CPU time used by the current process, and CPU time expended on behalf of the process by the system. Such a timer is used to implement code profiling facilities, hence the name of this signal.