When a signal is generated, it becomes pending. Normally it
remains pending for just a short period of time and then is
delivered to the process that was signaled. However, if that
kind of signal is currently blocked, it may remain pending
indefinitely—until signals of that kind are unblocked. Once
unblocked, it will be delivered immediately. See Blocking
Signals. When the signal is delivered, whether right away or
after a long delay, the specified action for that signal is
taken. For certain signals, such as SIGSTOP, the action is
fixed, but for most signals, the program has a choice: ignore
the signal, specify a handler function, or accept the default
action for that kind of signal. The program specifies its choice
using functions sigaction (see Signal Actions). We sometimes say
that a handler catches the signal. While the handler is running,
that particular signal is normally blocked. If the specified
action for a kind of signal is to ignore it, then any such
signal which is generated is discarded immediat