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‎about/index.html‎

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<p>I love computers and strive to become a hacker and a startupper. Now I&rsquo;m interested in the big data and mobile technologies.</p>
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<p>You can contact me via:<br/>
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Email: <a href="&#109;&#97;&#x69;&#x6c;&#x74;&#x6f;&#58;&#106;&#101;&#114;&#x6f;&#109;&#x65;&#121;&#x6a;&#x6a;&#64;&#x67;&#109;&#x61;&#x69;&#108;&#x2e;&#x63;&#x6f;&#109;">&#106;&#x65;&#x72;&#x6f;&#x6d;&#x65;&#x79;&#106;&#x6a;&#x40;&#x67;&#x6d;&#x61;&#x69;&#x6c;&#46;&#99;&#111;&#x6d;</a></p>
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Email: <a href="&#109;&#x61;&#105;&#x6c;&#x74;&#x6f;&#x3a;&#106;&#101;&#114;&#111;&#109;&#101;&#x79;&#x6a;&#106;&#x40;&#x67;&#109;&#97;&#x69;&#108;&#46;&#99;&#111;&#109;">&#x6a;&#101;&#x72;&#x6f;&#109;&#x65;&#121;&#106;&#x6a;&#64;&#x67;&#109;&#97;&#105;&#x6c;&#46;&#99;&#x6f;&#109;</a></p>
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<p>You can know me better via:<br/>
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This blog<br/>

‎atom.xml‎

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<title><![CDATA[Jiajun Yao]]></title>
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<link href="http://blog.jjyao.me/atom.xml" rel="self"/>
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<link href="http://blog.jjyao.me/"/>
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<updated>2018-11-07T22:39:57-08:00</updated>
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<updated>2018-12-17T22:03:24-08:00</updated>
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<generator uri="http://octopress.org/">Octopress</generator>
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<entry>
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<title type="html"><![CDATA[Linux PID]]></title>
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<link href="http://blog.jjyao.me/blog/2018/12/16/linux-pid/"/>
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<updated>2018-12-16T08:15:30-08:00</updated>
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<id>http://blog.jjyao.me/blog/2018/12/16/linux-pid</id>
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<content type="html"><![CDATA[<p>In the Linux world, pid means two things. It&rsquo;s the id of a process from POSIX&rsquo;s point of view and the id of a task from kernel&rsquo;s point of view.</p>
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<!-- more -->
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<h2>PID</h2>
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<p>In POSIX, process is an instance of a running program and it contains one or more threads. The id of a process is called pid.</p>
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<p>In the Linux kernel, task is the basic execution unit and is thread in the POSIX definition. Task is represented by <code>struct task_struct</code> in the code:</p>
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<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
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</pre></td><td class='code'><pre><code class='c'><span class='line'><span class="k">struct</span> <span class="n">task_struct</span> <span class="p">{</span>
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</span><span class='line'> <span class="p">...</span>
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</span><span class='line'> <span class="kt">pid_t</span> <span class="n">pid</span><span class="p">;</span>
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</span><span class='line'> <span class="kt">pid_t</span> <span class="n">tgid</span><span class="p">;</span>
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</span><span class='line'> <span class="p">...</span>
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</span><span class='line'><span class="p">}</span>
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</span></code></pre></td></tr></table></div></figure>
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<p>Here, pid is the id of a task and tgid is the id of the thread group that contains the task. As we can see, <code>task_struct.pid</code> basically is POSIX thread id and <code>task_struct.tgid</code> is POSIX process id.</p>
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<h2>EXAMPLES</h2>
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<p>Two different meanings of pid can cause lots of confusions and it&rsquo;s important to know whether we are talking about pid in the POSIX context or in the Linux kernel context.</p>
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<h3>getpid</h3>
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<p><code>getpid()</code> is a function defined by the POSIX standard and pid means the id of a process in this context. Linux implements it by returning <code>task_struct.tgid</code>:</p>
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<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
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<span class='line-number'>3</span>
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</pre></td><td class='code'><pre><code class='c'><span class='line'><span class="n">SYSCALL_DEFINE0</span><span class="p">(</span><span class="n">getpid</span><span class="p">)</span> <span class="p">{</span>
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</span><span class='line'> <span class="k">return</span> <span class="n">task_tgid_vnr</span><span class="p">(</span><span class="n">current</span><span class="p">);</span>
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</span><span class='line'><span class="p">}</span>
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</span></code></pre></td></tr></table></div></figure>
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<h3>/proc/[pid]</h3>
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<p>The proc file system is an interface to kernel data structures and pid means the id of a task/thread in this context. For example, <code>/proc/[pid]/status</code> shows status information about the task/thread and the implementation is in <code>fs/proc/array.c</code>.</p>
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<h2>References</h2>
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<p>[1] <a href="https://www.kernel.org/doc/ols/2002/ols2002-pages-330-337.pdf">https://www.kernel.org/doc/ols/2002/ols2002-pages-330-337.pdf</a> <br/>
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[2] <a href="https://stackoverflow.com/questions/9305992/if-threads-share-the-same-pid-how-can-they-be-identified">https://stackoverflow.com/questions/9305992/if-threads-share-the-same-pid-how-can-they-be-identified</a></p>
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]]></content>
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</entry>
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<entry>
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<title type="html"><![CDATA[One-Liners]]></title>
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<link href="http://blog.jjyao.me/blog/2018/11/07/one-liners/"/>

‎blog/2018/11/07/one-liners/index.html‎

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<a class="basic-alignment left" href="/blog/2017/11/27/hugetlbfs-read-bug/" title="Previous Post: HugeTLBFS Read Bug">&laquo; HugeTLBFS Read Bug</a>
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<a class="basic-alignment right" href="/blog/2018/12/16/linux-pid/" title="Next Post: Linux PID">Linux PID &raquo;</a>
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‎blog/2018/12/16/linux-pid/index.html‎

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<meta name="description" content="In the Linux world, pid means two things. It&rsquo;s the id of a process from POSIX&rsquo;s point of view and the id of a task from kernel&rsquo;s &hellip;">
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<h1 class="entry-title">Linux PID</h1>
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<p class="meta">
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<time class='entry-date' datetime='2018-12-16T08:15:30-08:00'><span class='date'><span class='date-month'>Dec</span> <span class='date-day'>16</span><span class='date-suffix'>th</span>, <span class='date-year'>2018</span></span> <span class='time'>8:15 am</span></time>
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</p>
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</header>
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<div class="entry-content"><p>In the Linux world, pid means two things. It&rsquo;s the id of a process from POSIX&rsquo;s point of view and the id of a task from kernel&rsquo;s point of view.</p>
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<!-- more -->
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<h2>PID</h2>
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<p>In POSIX, process is an instance of a running program and it contains one or more threads. The id of a process is called pid.</p>
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<p>In the Linux kernel, task is the basic execution unit and is thread in the POSIX definition. Task is represented by <code>struct task_struct</code> in the code:</p>
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<div class='bogus-wrapper'><notextile><figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
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<span class='line-number'>2</span>
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<span class='line-number'>3</span>
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<span class='line-number'>4</span>
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<span class='line-number'>5</span>
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<span class='line-number'>6</span>
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</pre></td><td class='code'><pre><code class='c'><span class='line'><span class="k">struct</span> <span class="n">task_struct</span> <span class="p">{</span>
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</span><span class='line'> <span class="p">...</span>
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</span><span class='line'> <span class="kt">pid_t</span> <span class="n">pid</span><span class="p">;</span>
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</span><span class='line'> <span class="kt">pid_t</span> <span class="n">tgid</span><span class="p">;</span>
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</span><span class='line'> <span class="p">...</span>
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</span><span class='line'><span class="p">}</span>
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</span></code></pre></td></tr></table></div></figure></notextile></div>
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<p>Here, pid is the id of a task and tgid is the id of the thread group that contains the task. As we can see, <code>task_struct.pid</code> basically is POSIX thread id and <code>task_struct.tgid</code> is POSIX process id.</p>
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<h2>EXAMPLES</h2>
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<p>Two different meanings of pid can cause lots of confusions and it&rsquo;s important to know whether we are talking about pid in the POSIX context or in the Linux kernel context.</p>
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<h3>getpid</h3>
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<p><code>getpid()</code> is a function defined by the POSIX standard and pid means the id of a process in this context. Linux implements it by returning <code>task_struct.tgid</code>:</p>
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<div class='bogus-wrapper'><notextile><figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
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<span class='line-number'>2</span>
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</pre></td><td class='code'><pre><code class='c'><span class='line'><span class="n">SYSCALL_DEFINE0</span><span class="p">(</span><span class="n">getpid</span><span class="p">)</span> <span class="p">{</span>
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</span><span class='line'> <span class="k">return</span> <span class="n">task_tgid_vnr</span><span class="p">(</span><span class="n">current</span><span class="p">);</span>
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</span><span class='line'><span class="p">}</span>
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</span></code></pre></td></tr></table></div></figure></notextile></div>
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<h3>/proc/[pid]</h3>
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<p>The proc file system is an interface to kernel data structures and pid means the id of a task/thread in this context. For example, <code>/proc/[pid]/status</code> shows status information about the task/thread and the implementation is in <code>fs/proc/array.c</code>.</p>
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<h2>References</h2>
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<p>[1] <a href="https://www.kernel.org/doc/ols/2002/ols2002-pages-330-337.pdf">https://www.kernel.org/doc/ols/2002/ols2002-pages-330-337.pdf</a> <br/>
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[2] <a href="https://stackoverflow.com/questions/9305992/if-threads-share-the-same-pid-how-can-they-be-identified">https://stackoverflow.com/questions/9305992/if-threads-share-the-same-pid-how-can-they-be-identified</a></p>
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<span class="byline author vcard">Posted by <span class="fn">jjyao</span></span>
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<time class='entry-date' datetime='2018-12-16T08:15:30-08:00'><span class='date'><span class='date-month'>Dec</span> <span class='date-day'>16</span><span class='date-suffix'>th</span>, <span class='date-year'>2018</span></span> <span class='time'>8:15 am</span></time>
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<p style="margin-bottom:3px">Welcome to here! I'm jjyao and am working on the distributed graph database team at LinkedIn. My current interests are database systems and distributed systems.</p>
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‎blog/archives/index.html‎

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Dec 16 2018 One-Liners
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Nov 07 2018 2017 HugeTLBFS Read Bug
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Nov 27 2017 Jonathan Lee
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Sep 10 2017 You Don't Exist, Go Away!
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Aug 30 2017 posted &hellip;">
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Sep 10 2017 You Don't Exist, Go Away &hellip;">
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<h1><a href="/blog/2018/12/16/linux-pid/">Linux PID</a></h1>
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<time datetime="2018-12-16T08:15:30-08:00" pubdate><span class='month'>Dec</span> <span class='day'>16</span> <span class='year'>2018</span></time>
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<h1><a href="/blog/2018/11/07/one-liners/">One-Liners</a></h1>

‎blog/categories/coding/atom.xml‎

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<title><![CDATA[Category: coding | Jiajun Yao]]></title>
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