关于linux下core dump【总结】
<p><span><strong>1、前言 </strong></span></p>
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一直在从事linux下后台开发，经常与core文件打交道。还记得刚开始从事linux下开发时，程序突然崩溃了，也没有任何日志。我不知所措，同事叫我看看core，我却问什么是core，怎么看。同事鄙视的眼神，我依然在目。后来学会了从core文件中分析原因，通过gdb看出程序挂再哪里，分析前后的变量，找出问题的原因。当时就觉得很神奇，core文件是怎么产生的呢？难道系统会自动产生，可是我在自己的linux系统上面写个非法程序测试，并没有产生core问题？这又是怎么回事呢？今天在ngnix的源码时候，发现可以在程序中设置core dump，又是怎么回事呢？在公司发现生成的core文件都带有进程名称、进程id、和时间，这又是怎么做到的呢？今天带着这些疑问来说说core文件是如何生成，如何配置。</p>
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<span><strong>2、基本概念</strong></span></p>
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当程序运行的过程中异常终止或崩溃，操作系统会将程序当时的内存状态记录下来，保存在一个文件中，这种行为就叫做core dump（中文有的翻译成“核心转储”)。我们可以认为 core dump 是“内存快照”，但实际上，除了内存信息之外，还有些关键的程序运行状态也会同时 dump 下来，例如寄存器信息（包括程序指针、栈指针等）、内存管理信息、其他处理器和操作系统状态和信息。core dump 对于编程人员诊断和调试程序是非常有帮助的，因为对于有些程序错误是很难重现的，例如指针异常，而 core dump 文件可以再现程序出错时的情景。</p>
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<span><strong>3、开启core dump</strong></span></p>
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可以使用命令ulimit开启，也可以在程序中通过setrlimit系统调用开启。</p>
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<img title="关于linux下core dump【总结】" alt="关于linux下core dump【总结】" src="https://zhuji.jb51.net/uploads/img/202305/85112eb602c215d868b545c5e170dca4.jpg"></p>
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程序中开启core dump，通过如下api可以查看和设置rlimit_core</p>
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<code class="xhtml plain">#include <</code><code class="xhtml keyword">sys</code><code class="xhtml plain">/resource.h></code>
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<code class="xhtml plain">int getrlimit(int resource, struct rlimit *rlim);</code>
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<code class="xhtml plain">int setrlimit(int resource, const struct rlimit *rlim);</code>
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<strong>参考程序如下所示：</strong></p>
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<code class="xhtml plain">#include <</code><code class="xhtml keyword">unistd.h</code><code class="xhtml plain">></code>
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<code class="xhtml plain">#include <</code><code class="xhtml keyword">sys</code><code class="xhtml plain">/time.h></code>
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<code class="xhtml plain">#include <</code><code class="xhtml keyword">sys</code><code class="xhtml plain">/resource.h></code>
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<code class="xhtml plain">#include <</code><code class="xhtml keyword">stdio.h</code><code class="xhtml plain">></code>
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<code class="xhtml plain">#define core_size 1024 * 1024 * 500</code>
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<code class="xhtml plain">int main()</code>
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<code class="xhtml plain">{</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">struct rlimit rlmt;</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">if (getrlimit(rlimit_core, &rlmt) == -1) {</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">return -1; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">} </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">printf("before set rlimit core dump current is:%d, max is:%d\n", (int)rlmt.rlim_cur, (int)rlmt.rlim_max);</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">rlmt.rlim_cur = (rlim_t)core_size;</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">rlmt.rlim_max = (rlim_t)core_size;</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">if (setrlimit(rlimit_core, &rlmt) == -1) {</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">return -1; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">} </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">if (getrlimit(rlimit_core, &rlmt) == -1) {</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">return -1; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">} </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">printf("after set rlimit core dump current is:%d, max is:%d\n", (int)rlmt.rlim_cur, (int)rlmt.rlim_max);</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">/*测试非法内存，产生core文件*/</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int *ptr = null;</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">*ptr = 10; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">return 0;</code>
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<code class="xhtml plain">}</code>
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执行./main, 生成的core文件如下所示</p>
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<img title="关于linux下core dump【总结】" alt="关于linux下core dump【总结】" src="https://zhuji.jb51.net/uploads/img/202305/65cc1d7c6436ba103d204d8e3ede76ab.jpg"></p>
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gdb调试core文件，查看程序挂在位置。当core dump 之后，使用命令<span> <strong><font color="#000000" face="nsimsun">gdb program core</font></strong></span> 来查看 core 文件，其中 program 为可执行程序名，core 为生成的 core 文件名。</p>
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<img title="关于linux下core dump【总结】" alt="关于linux下core dump【总结】" src="https://zhuji.jb51.net/uploads/img/202305/9c468264c4733483869693724aabda7c.jpg"></p>
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以上这篇关于linux下core dump【总结】就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持。</p>
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