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<header>
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<h1 class="entry-title">A debugging manifesto</h1>
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<time class="date" datetime="2022-12-08T12:21:01" pubdate data-updated="true">
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December 8, 2022
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</p>
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</header>
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<main>
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<p>Hello! I’ve been working on a zine about debugging for the last 6 months with
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my friend <a href="https://marieflanagan.com/">Marie</a>, and one of the problems we ran
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into was figuring out how to explain the right <em>attitude</em> to take when debugging.</p>
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<p>We ended up writing a short debugging manifesto to start the zine with, and I’m
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pretty happy with how it came out. Here it is as an image, and as text (with
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some extra explanations)</p>
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<img src="https://jvns.ca/images/manifesto.png">
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<h3 id="1-inspect-don-t-squash" class="post-heading">
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<a href="#1-inspect-don-t-squash">
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1. Inspect, don’t squash
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</a>
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</h3>
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<p>When you run into a bug, the natural instinct is to try to <em>fix it</em> as fast as
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possible. And of course, sometimes that’s what you have to do – if the bug is
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causing a huge production incident, you have to mitigate it quickly before
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diving into figuring out the root cause.</p>
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<p>But in my day to day debugging, I find that it’s generally more effective (and
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faster!) to <strong>leave the bug in place</strong>, figure out exactly what’s gone wrong,
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and then fix it after I’ve understood what happened.</p>
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<p>Trying to fix it or add workarounds without fully understanding what happened
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usually ends up just leaving me <em>more</em> confused.</p>
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<h3 id="2-being-stuck-is-temporary" class="post-heading">
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<a href="#2-being-stuck-is-temporary">
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2. Being stuck is temporary
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</a>
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</h3>
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<p>Sometimes I get really demoralized when debugging and it feels like I’ll NEVER
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make progress.</p>
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<p>I have to remind myself that I’ve fixed a lot of bugs before, and I’ll probably
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fix this one too :)</p>
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<h3 id="3-trust-nobody-and-nothing" class="post-heading">
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<a href="#3-trust-nobody-and-nothing">
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3. Trust nobody and nothing
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</a>
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</h3>
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<p>Sometimes bugs come from surprising sources! For example, in <a href="https://jvns.ca/blog/2018/01/28/mac-freeze/">I think I found a Mac kernel bug?</a> I describe how,
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the first time I tried to write a program for Mac OS, I had a bug in my program
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that was caused by a Mac OS kernel bug.</p>
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<p>This was really surprising (usually the operating system is not at fault!!),
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but sometimes even normally-trustworthy sources are wrong. Even it’s a popular
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library, your operating system, the official documentation, or an extremely
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smart and competent coworker!</p>
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<h3 id="4-it-s-probably-your-code" class="post-heading">
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<a href="#4-it-s-probably-your-code">
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4. It’s probably your code
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</a>
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</h3>
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<p>That said, <strong>almost all of the time</strong> the problem is not “there’s a bug in Mac
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OS”. I can only speak for myself, but 95% of the time something is going wrong
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with my program, it’s because I did something silly.</p>
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<p>So it’s important to look for the problem in your own code first before trying
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to blame some external source.</p>
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<h3 id="5-don-t-go-it-alone" class="post-heading">
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<a href="#5-don-t-go-it-alone">
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5. Don’t go it alone
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</a>
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</h3>
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<p>I’ve learned SO much by asking coworkers or friends for help with debugging. I
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think it’s one of the most fun ways to collaborate because you have a specific
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goal, and there are tons of opportunities to share information like:</p>
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<ul>
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<li>how to use a specific debugging tool (“here’s how to use GDB to inspect the memory here….”)</li>
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<li>how a computer thing works (“hey, can you explain CORS?”)</li>
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<li>similar past bugs (“I’ve seen this break in X way in the past, maybe it’s that?”)</li>
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</ul>
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<h3 id="6-there-s-always-a-reason" class="post-heading">
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<a href="#6-there-s-always-a-reason">
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6. There’s always a reason
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</a>
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</h3>
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<p>This one kind of speaks for itself: sometimes it <em>feels</em> like things are just
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randomly breaking for no reason, but that’s never true.</p>
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<p>Even if something truly weird is happening (like a hardware problem), that’s
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still a reason.</p>
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<h3 id="7-build-your-toolkit" class="post-heading">
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<a href="#7-build-your-toolkit">
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7. Build your toolkit
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</a>
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</h3>
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<p>I’ve written a LOT about my love for debugging tools like tcpdump, strace, and
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more on this blog.</p>
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<p>To fix bugs you need information about what your program is doing, and to get
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that information sometimes you need to learn a new tool.</p>
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<p>Also, sometimes you need to build your own better tools, like by improving your
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test suite, pretty printing, etc.</p>
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<h3 id="8-it-can-be-an-adventure" class="post-heading">
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<a href="#8-it-can-be-an-adventure">
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8. It can be an adventure
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</a>
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</h3>
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<p>As you probably know if you’re a regular reader of this blog, I love debugging
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and I’ve learned a lot from doing it. You get to learn something new! Sometimes
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you get a great war story to tell! What could be more fun?</p>
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<p>I really think of debugging as an investment in my future knowledge – if
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something is breaking, it’s often because there’s something wrong in my mental
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model, and that’s an opportunity to learn and make sure that I know it for next
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time.</p>
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<p>Of course, not <em>all</em> bugs are adventures (that off-by-one error I was debugging
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today certainly did not feel like a fun adventure). But I think it’s important
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to (as much as you can) reflect on your bugs and see what you can learn from
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<a class="basic-alignment left" href="https://jvns.ca/blog/2022/12/07/tips-for-analyzing-logs/" title="Previous Post: Tips for analyzing logs">Tips for analyzing logs</a>
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<a class="basic-alignment right" href="https://jvns.ca/blog/2022/12/21/new-zine--the-pocket-guide-to-debugging/" title="Next Post: New zine: The Pocket Guide to Debugging">New zine: The Pocket Guide to Debugging</a>
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<span>If you like this, you may like <a href="https://web.archive.org/web/20181228051203/http://www.uliaea.ca/">Ulia Ea</a> or, more seriously, this list of <a href="https://jvns.ca/blogroll">blogs I love</a> or some <a href="https://jvns.ca/bookshelf">books I've read</a>. <br>
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You might also like the <a class="rc-scout__link" href="https://www.recurse.com/scout/click?t=546ea46360584b522270b8c3e5d830f8">Recurse Center</a>, my very favorite programming community <a href="/categories/hackerschool/">(my posts about it)</a></p>
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