https://blog.mygraphql.com/en/tags/low-tec/ Recent content in Low-Tec on Mark Zhu's Blog Hugo -- gohugo.io en labile.zhu@gmail.com (Mark Zhu) labile.zhu@gmail.com (Mark Zhu) Mark Zhu ©2026, All Rights Reserved Sat, 06 Jul 2024 23:12:15 +0800 https://blog.mygraphql.com/en/notes/low-tec/trace/peekfd/ Sat, 06 Jul 2024 23:12:15 +0800 labile.zhu@gmail.com (Mark Zhu) Sat, 06 Jul 2024 23:12:15 +0800 https://blog.mygraphql.com/en/notes/low-tec/trace/peekfd/ <p><img src="https://blog.mygraphql.com/en/notes/low-tec/trace/peekfd/index.assets/logo.jpeg" alt="img"></p> <h2 id="overview">Overview</h2> <h3 id="introduction">Introduction</h3> <p>Most of the data flows in Linux, including inter-process communication, sockets, etc., are implemented through file descriptors (fd) reading and writing. When troubleshooting, if you can peek at the flow of fd, many problems can be quickly proved/falsified. This article introduces an old tool <code>peekfd</code>, which can complete this task in a certain environment.</p> <h3 id="problems-i-encountered">Problems I encountered</h3> <p>I talked about a scenario in <a href="https://blog.mygraphql.com/zh/notes/low-tec/inter-process/child-process-wait-die-lock/">《I Lost to AI - A Brief Note on a Parent-Child Process Interlocking Trap, I Digged It Myself》</a>. The following is a diagram of the parent-child relationship of the process. I want to use <code>kill -QUIT $</code> (Why not <code>jstack</code>?) to view the jvm stack. Ideally, <code>kill -QUIT $test_case_jvm</code> will make <code>test cases jvm</code> print a stack dump to stdout, and then <code>maven jvm</code> will also copy and print it out. But the reality is that <code>maven jvm</code> eats the stack dump output of <code>test cases jvm</code> and does not spit it out.</p> Mark Zhu inter-process fd trace ptrace low-tec