linux下如何创建守护进程的步骤

用心打字 發表於 2023-9-9 00:00:00

<p>
这两天学习了linux 守护进程这个地方知识点挺多的，而且很重要，所以，今天添加一点小笔记。</p>
<p>
<strong>1，进程的概念：程序的一次动态执行过程。 </strong></p>
<p>
进程存在于内存当中，存在着创建，调度，执行和消亡，进程号是进程的唯一标志，每一个进程都有自己独立的内存空间，在32位操作系统中，进程拥有0-4G的内存空间，其中0-3G属于用户，3G-4G属于内核，所以就出现了进程的执行模式：用户模式和内核模式。 </p>
<p>
<strong>2，进程的类型：</strong>交互进程，批处理进程，守护进程 </p>
<p>
<strong>3，守护进程：</strong>Linux中的后台服务进程，daemon进程 </p>
<p>
<strong>4，守护进程的创建步骤： </strong></p>
<p>
（1）创建子进程，父进程退出。 </p>
<p>
经过这步以后，子进程就会成为孤儿进程（父进程先于子进程退出，此时的子进程，成为孤儿进程，会被init进程收养）。使用fork（）函数，如果返回值大于0，表示为父进程，exit（0），父进程退出，子进程继续。 </p>
<p>
（2）在子进程中创建新会话，使当前进程成为新会话组的组长。 </p>
<p>
使用setsid()函数，如果当前进程不是进程组的组长，则为当前进程创建一个新的会话期，使当前进程成为这个会话组的首进程，成为这个进程组的组长。 </p>
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（3）改变当前目录为根目录。 </p>
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由于守护进程在后台运行，开始于系统开启，终止于系统关闭，所以要将其目录改为系统的根目录下。进程在执行时，其文件系统不能被卸下。 </p>
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（4）重新设置文件权限掩码。 </p>
<p>
进程从父进程那里继承了文件创建掩码，所以可能会修改守护进程存取权限位，所以要将文件创建掩码清除，umask（0）； </p>
<p>
（5）关闭文件描述符。 </p>
<p>
子进程从父进程那里继承了打开文件描述符。所以使用close即可关闭。 </p>
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在这里要用到getdtablesize()函数得到这个进程打开文件的数目。 </p>
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按照上面的步骤即可完成守护进程的创建。 </p>
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具体的代码如下，守护进程的功能写的较为简单，往文件里写东西： </p>
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<code class="cpp preprocessor">#include <stdio.h></code>
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<code class="cpp preprocessor">#include <sys/types.h></code>
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<code class="cpp preprocessor">#include <unistd.h></code>
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<code class="cpp preprocessor">#include <fcntl.h></code>
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<code class="cpp preprocessor">#include <sys/stat.h></code>
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<code class="cpp preprocessor">#include <stdlib.h></code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">main()</code>
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<code class="cpp plain">{   </code><code class="cpp comments">// 1创建子进程，父进程退出</code>
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<code class="cpp spaces">  </code><code class="cpp plain">pid_t pid = fork();</code>
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<code class="cpp spaces">  </code><code class="cpp keyword bold">if</code><code class="cpp plain">(pid<0)</code>
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<code class="cpp spaces">  </code><code class="cpp plain">{</code>
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<code class="cpp spaces">   </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"fork error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces">   </code><code class="cpp keyword bold">return</code> <code class="cpp plain">-1;</code>
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<code class="cpp spaces">  </code><code class="cpp plain">}</code>
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<code class="cpp spaces">  </code><code class="cpp keyword bold">else</code> <code class="cpp keyword bold">if</code><code class="cpp plain">(pid>0)</code>
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<code class="cpp spaces">  </code><code class="cpp plain">{</code>
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<code class="cpp spaces">   </code><code class="cpp functions bold">exit</code><code class="cpp plain">(0);</code>
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<code class="cpp spaces">  </code><code class="cpp plain">}</code>
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<code class="cpp spaces">  </code><code class="cpp keyword bold">else</code>
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<code class="cpp spaces">  </code><code class="cpp plain">{</code>
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<code class="cpp spaces">    </code><code class="cpp keyword bold">while</code><code class="cpp plain">(1)</code>
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<code class="cpp spaces">    </code><code class="cpp plain">{</code>
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<code class="cpp spaces">      </code><code class="cpp comments">//2 组长</code>
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<code class="cpp spaces">      </code><code class="cpp plain">setsid();</code>
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<code class="cpp spaces">      </code><code class="cpp comments">// 改变路径至根目录</code>
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<code class="cpp spaces">      </code><code class="cpp plain">chdir(</code><code class="cpp string">"/tmp"</code><code class="cpp plain">); </code>
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<code class="cpp spaces">      </code><code class="cpp comments">//重设文件掩码</code>
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<code class="cpp spaces">      </code><code class="cpp plain">umask(0);</code>
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<code class="cpp spaces">      </code><code class="cpp comments">//关闭文件描述符</code>
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<code class="cpp spaces">      </code><code class="cpp color1 bold">int</code> <code class="cpp plain">des=getdtablesize();</code>
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<code class="cpp spaces">      </code><code class="cpp color1 bold">int</code> <code class="cpp plain">i=0;</code>
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<code class="cpp spaces">      </code><code class="cpp keyword bold">for</code><code class="cpp plain">(i=0;i<des;i++)</code>
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<code class="cpp spaces">      </code><code class="cpp plain">{</code>
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<code class="cpp spaces">        </code><code class="cpp plain">close(i);</code>
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<code class="cpp spaces">      </code><code class="cpp plain">}</code>
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<code class="cpp spaces">    </code><code class="cpp plain">} </code>
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<code class="cpp spaces">    </code><code class="cpp color1 bold">char</code> <code class="cpp plain">buf[]=</code><code class="cpp string">"bat xld come!\n"</code><code class="cpp plain">;</code>
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<code class="cpp spaces">    </code><code class="cpp color1 bold">int</code> <code class="cpp plain">fd=open(</code><code class="cpp string">"xld.txt"</code><code class="cpp plain">,O_WRONLY|O_CREAT |O_APPEND,0666);</code>
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<code class="cpp spaces">     </code><code class="cpp plain">write(fd,buf,</code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(buf));</code>
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<code class="cpp spaces">     </code><code class="cpp plain">sleep(2);</code>
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<code class="cpp spaces">    </code><code class="cpp plain">}</code>
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<code class="cpp spaces">  </code><code class="cpp keyword bold">return</code> <code class="cpp plain">0;</code>
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<code class="cpp plain">}</code>
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以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。</p>
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原文链接：http://blog.csdn.net/xld_hung/article/details/75208190</p>

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linux下如何创建守护进程的步骤