first unblocks the
signal, and then raises that signal for the calling process.
This results in the abnormal termination of the process unless the
signal is caught and the signal handler does not return
function causes process termination,
all open streams are closed and flushed.
signal is ignored, or caught by a handler that returns, the
function will still terminate the process.
It does this by restoring the default disposition for
and then raising the signal for a second time.