当满足一定的条件是，怎样使一个进程挂起和继续运行？？？
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信号通知,sleep挂起
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The pause() function forces a process to pause until a signal is received from either the kill(2) function or an interval timer (see setitimer(2)).
Upon termination of a signal handler started during a pause(), the pause() call will return.
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在《unix高级环境编程？的书里关于信号的章节有非常不错的解释