This section lists the names for various standard kinds of signals and describes what kind of event they mean. Each signal name is a macro which stands for a positive integer—the signal number for that kind of signal. Your programs should never make assumptions about the numeric code for a particular kind of signal, but rather refer to them always by the names defined here. This is because the number for a given kind of signal can vary from system to system, but the meanings of the names are standardized and fairly uniform.
The signal names are defined in the header file signal.h.
The value of this symbolic constant is the total number of signals
defined. Since the signal numbers are allocated consecutively,
NSIG is also one greater than the largest defined signal number.