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A signal reports the occurrence of an exceptional event. These are some
of the events that can cause (or generate, or raise) a
signal:
-
A program error such as dividing by zero or issuing an address outside
the valid range.
-
A user request to interrupt or terminate the program. Most environments
are set up to let a user suspend the program by typing C-z, or
terminate it with C-c. Whatever key sequence is used, the
operating system sends the proper signal to interrupt the process.
-
The termination of a child process.
-
Expiration of a timer or alarm.
-
A call to
kill
or raise
by the same process.
-
A call to
kill
from another process. Signals are a limited but
useful form of interprocess communication.
-
An attempt to perform an I/O operation that cannot be done. Examples
are reading from a pipe that has no writer (see section Pipes and FIFOs),
and reading or writing to a terminal in certain situations (see section Job Control).
Each of these kinds of events (excepting explicit calls to kill
and raise
) generates its own particular kind of signal. The
various kinds of signals are listed and described in detail in
section Standard Signals.
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