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processctl.html
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<!DOCTYPE HTML>
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<title>进程控制 | 《UNIX环境高级编程》学习笔记</title>
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进程环境
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进程控制
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<h1 id="进程控制">进程控制</h1>
<hr/>
<p>进程控制包括创建新进程，执行进程和终止进程。</p>
<h4 id="进程标识">进程标识</h4>
<p>每个进程都有一个非负数表示的唯一进程ID，因为进程ID具有唯一性，因此常常把它作为其它标识符的一部分，虽然是唯一的，但是进程ID是可复用的，当一个进程结束后，其进程ID就成为复用的候选者，大多数UNIX实现延迟复用算法。这样可以避免把新进程搞成已经被终止掉的进程，系统具有一些专用进程，ID为0的是调度进程，也叫做交换进程，这个进程是内核的一部分，它并不执行任何程序，也叫做系统进程，进程ID为1的是init进程，在自举过程结束的时候由内核调用，这个进程负责在自举内核以后启动一个UNIX系统，init通常读取与系统有关的初始化文件，并将系统引导到一个状态，init进程绝不会终止，它是一个普通的用户进程，但是以超级用户特权来运行，它也是所有孤儿进程的父进程。每个UNIX系统还提供了一套操作系统服务的内核进程，例如在某些UNIX系统的虚拟存储器实现中，进程ID2是页守护进程，此进程负责支持虚拟存储器系统的分页操作。</p>
<h4 id="函数fork">函数fork</h4>
<p>fork创建一个子进程，fork函数调用一次返回两次，子进程的返回值是0，父进程的返回值是子进程的进程ID，注意一个子进程的ID不可能是0，子进程和父进程继续执行fork调用之后的指令，子进程是父进程的副本</p>
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