1. 信号产生：a signal is generated for a process (or sent to a process) when the event that causes the signal occurs. The event could be a hardware exception (e.g., divide by 0), a software condition (e.g., an alarm timer expiring), a terminal-generated signal, or a call to the kill function. When the signal is generated, the kernel usually sets a flag of some form in the process table.

2. 信号传递：a signal is delivered to a process when the action for a signal is taken.

3. pending: During the time between the generation of a signal and its delivery, the signal is said to be pending.

4. A process has the option of blocking the delivery of a signal. If a signal that is blocked is generated for a process, and if the action for that signal is either the default action or to catch the signal, then the signal remains pending for the process until the process either (a) unblocks the signal or (b) changes the action to ignore the signal.