Hey! I'm Julia. Welcome to my blog. Here's every post I've ever written, organized by category. Enjoy! You can subscribe to a weekly digest of these blog posts.
I publish computer zines at Wizard Zines.
Most recent 10 posts
Importing a frontend Javascript library without a build system New microblog with TILs ASCII control characters in my terminal Using less memory to look up IP addresses in Mess With DNS Some notes on upgrading Hugo Terminal colours are tricky Some Go web dev notes Reasons I still love the fish shell Migrating Mess With DNS to use PowerDNS Go structs are copied on assignment (and other things about Go I'd missed)
and all posts by category: (or see popular posts)
Uncategorized
Importing a frontend Javascript library without a build system New microblog with TILs ASCII control characters in my terminal Using less memory to look up IP addresses in Mess With DNS
Cool computer tools / features / ideas
Some Go web dev notes Reasons I still love the fish shell What helps people get comfortable on the command line? Lima: a nice way to run Linux VMs on Mac Writing Javascript without a build system Monitoring tiny web services Notes on running containers with bubblewrap sqlite-utils: a nice way to import data into SQLite for analysis A list of new(ish) command line tools Things that used to be hard and are now easy Hosting my static sites with nginx Some notes on using esbuild Firecracker: start a VM in less than a second Server-sent events: a simple way to stream events from a server Docker Compose: a nice way to set up a dev environment ninja: a simple way to do builds Implementing 'focus and reply' for Fastmail with JMAP scanimage: scan from the command line! entr: rerun your build when files change A little bit of plain Javascript can do a lot PaperWM: tiled window management for GNOME SQLite is really easy to compile Why are monoidal categories interesting? Tailwind: style your site without writing any CSS! An awesome new Python profiler: py-spy! Batch editing files with ed Glitch: write fun small web projects instantly Binder: an awesome tool for hosting Jupyter notebooks Cool vim feature: sessions! Data structure: the treap! a tiny whack-a-mole game Log-structured storage Using the Strict-Transport-Security header The fish shell is awesome homu + highfive: awesome bots that make open source projects easier you can take the derivative of a regular expression?! tcpdump is amazing How to measure your CPU time: clock_gettime! Fast integer sets with Roaring Bitmaps (and, making friends with your modern CPU) Sendfile (a system call for web developers to know about!) PAPERS ARE AMAZING: Profiling threaded programs with Coz LD_PRELOAD is super fun. And easy!
Things I built
Migrating Mess With DNS to use PowerDNS Mounting git commits as folders with NFS Open sourcing the nginx playground New playground: memory spy Introducing "Implement DNS in a Weekend" New playground: integer.exposed A list of programming playgrounds Some tiny personal programs I've written New tool: Mess with DNS! New tool: an nginx playground Notes on building debugging puzzles A tool to spy on your DNS queries: dnspeep A little tool to make DNS queries
Git
Notes on git's error messages Some Git poll results The "current branch" in git How HEAD works in git Popular git config options Dealing with diverged git branches Inside .git Do we think of git commits as diffs, snapshots, and/or histories? git branches: intuition & reality How git cherry-pick and revert use 3-way merge git rebase: what can go wrong? Confusing git terminology Some miscellaneous git facts In a git repository, where do your files live?
Nix
Some notes on NixOS Some notes on nix flakes How do Nix builds work? Some notes on using nix
DNS
Why is DNS still hard to learn? Making a DNS query in Ruby from scratch Why do domain names sometimes end with a dot? The multiple meanings of "nameserver" and "DNS resolver" A toy DNS resolver Some ways DNS can break Why might you run your own DNS server? DNS "propagation" is actually caches expiring What happens when you update your DNS?
Terminals
Terminal colours are tricky Entering text in the terminal is complicated Reasons to use your shell's job control What happens when you press a key in your terminal?
Computer networking
How to send raw network packets in Python with tun/tap A toy remote login server Reasons for servers to support IPv6 How to put an HTML page on the internet Networking tool comics! An example of how C++ destructors are useful in Envoy Some Envoy basics Editing my blog's HTTP headers with Cloudflare workers IP addresses & routing netdev day 2: moving away from "as fast as possible" in networking code netdev day 1: IPsec! How I use Wireshark A few things I've learned about computer networking Finding out if/why a server is dropping packets What's a network interface? Iptables basics netdev conference, day 3 netdev conference, day 2 How to filter packets super fast: XDP & eBPF! netdev conference, day 1 Slow down your internet with tc How big can a packet get? Dissecting an SSL certificate What's interesting about UDP? Why do UDP packets get dropped? How do HTTP requests get sent to the right place? ★ Why do we use the Linux kernel's TCP stack? What are SSL ciphers & session keys? CDNs aren't just for caching
How a computer thing works
Go structs are copied on assignment (and other things about Go I'd missed) Notes on using a single-person Mastodon server Behind "Hello World" on Linux Implementing a toy version of TLS 1.3 How to use undocumented web APIs Some things about getaddrinfo that surprised me How to find a domain's authoritative nameservers How to use dig How do you tell if a problem is caused by DNS? Tools to explore BGP Quadratic algorithms are slow (and hashmaps are fast) How to look at the stack with gdb The OSI model doesn't map well to TCP/IP Why strace doesn't work in Docker Getting started with shaders: signed distance functions! "server" is hard to define How tracking pixels work How containers work: overlayfs SQL queries don't start with SELECT How does gdb call functions? How do groups work on Linux? Async IO on Linux: select, poll, and epoll Weird unix thing: 'cd //' ★ What happens when you start a process on Linux? How does gdb work? Should you be scared of Unix signals? I conquered thread pools! For today, at least. Thread pools! How do I use them? What is "the stack"? Why Ruby’s Timeout is dangerous (and Thread.raise is terrifying) ★ Why you should understand (a little) about TCP How the locate command works (and let's write a faster version in one minute!) ★ How gzip uses Huffman coding ★ Diving into concurrency: trying out mutexes and atomics How does SQLite work? Part 2: btrees! (or: disk seeks are slow don't do them!) ★ How does SQLite work? Part 1: pages! How is a binary executable organized? Let's explore it! ★ What happens if you write a TCP stack in Python? Diving into HDFS Three steps to learning GDB
binary representations of things
Some possible reasons for 8-bit bytes Why does 0.1 + 0.2 = 0.30000000000000004? Examples of problems with integers Examples of floating point problems
Kubernetes / containers
Operating a Kubernetes network Reasons Kubernetes is cool How Kubernetes certificate authorities work Cherry picking commits & shell scripting in golang How does the Kubernetes scheduler work? A few things I've learned about Kubernetes Swapping, memory limits, and cgroups A container networking overview What happens when you run a rkt container? Running containers without Docker What even is a container: namespaces and cgroups A list of Linux container software "I just want to run a container!" Some questions about Docker and rkt Docker is amazing
Zines / comics
New zine: How Git Works! New zine: How Integers and Floats Work Print copies of The Pocket Guide to Debugging have arrived New zine: The Pocket Guide to Debugging Pages that didn't make it into "How DNS Works" New zine: How DNS Works! All my zines are now available in print! You can now buy print version of my zines! I put all of my comics online! New zine: Hell Yes! CSS! Wizard Zines' first print run: Help! I have a Manager! Some more CSS comics Some CSS comics New zine: How Containers Work! New zine: Become a SELECT Star! Your Linux Toolbox: a box set of my free zines New zine: HTTP: Learn your browser's language! New zine: Bite Size Networking! New zine: Oh shit, git! New zine: Help! I have a manager! New zine: Bite Size Command Line! New zine: Profiling & tracing with perf!! New zine: So you want to be a wizard Linux comics: a small zine Linux tracing zine "Let's learn tcpdump" zine: now available for everyone New zine: let's learn tcpdump! New zine: "Networking! ACK!" A tiny zine about machine learning More drawings about computers A few drawings about Linux New zine: Linux debugging tools you'll love A few sketches A zine about strace
Exercises
Questions to help people decide what to learn Challenge: find Twitter memes with suffix arrays Solutions to the tiny window manager challenge Challenge: Write a bouncy window manager What makes a programming exercise good? Notes on building SQL exercises git exercises: navigate a repository curl exercises
On writing words
Some tactics for writing in public Some blogging myths Teaching by filling in knowledge gaps Patterns in confusing explanations Write good examples by starting with real code
On writing comics / zines
Building a custom site for zine feedback How I write useful programming comics A new way I'm getting feedback on my zines: beta readers! Some possible future zines An attempt to make a font look more handwritten Some notes on vector drawing apps Some research on shipping print zines Zine revenue for 2019 Taking a year to explain computer things How to write zines with simple tools How do you document a tech project with comics? When does teaching with comics work well? Why sell zines? How to teach technical concepts with cartoons Handwritten books An idea for a programming book Why cute drawings? How (and why) I made a zine
Conferences
!!Con 2019: submit a talk! Systems We Love 2016 PolyConf 2016 Women in Machine Learning 2015 (fun!!!) AdaCamp Montreal 2015 Data Day Texas 2015 PyData NYC (I gave a machine learning talk! yay!) Strange Loop 2014 !!Con talks are up ♥ PyCon CUSEC = fun PyData Boston 2013 Open Data Exchange 2013 Montreal All-Girl Hack Night #2: now with cookies Montreal All-Girl Hack Night #1: AMAZING
Organizing conferences
Ideas for making better conference talks & conferences You can choose who submits talks to your conference Should my conference do anonymous review? Anonymous talk review is amazing.
Businesses / marketing
A few things I've learned about email marketing saturday comics: a weekly mailing list of programming comics A few early marketing thoughts Who pays to educate developers? I started a corporation!
Statistics / machine learning / data analysis
An attempt at implementing char-rnn with PyTorch Some nonparametric statistics math Some good "Statistics for programmers" resources How do these "neural network style transfer" tools work? A few reasons to be skeptical of machine learning Looking inside machine learning black boxes Winning the bias-variance tradeoff ★ How to trick a neural network into thinking a panda is a vulture Is machine learning safe to use? Some easy statistics: Bootstrap confidence intervals A/A testing Fun with machine learning: logistic regression! Fun with machine learning: does your model actually work? Fun with stats: How big of a sample size do I need? Machine learning isn't Kaggle competitions ★ A pandas cookbook Graphing bike path data with IPython Notebook and pandas
Year in review
2023: Year in review Some business graphs for 2022 2021: Year in review 2020: Year in review 2019: Year in review 2018: Year in review 2017: Year in review 2016: Year in review 2015: Year in review
Talks
New talk: Making Hard Things Easy New talk: Learning DNS in 10 years New talk: High Reliability Infrastructure Migrations Build impossible programs So you want to be a wizard
Infrastructure / operations engineering
Some notes on running new software in production What can developers learn from being on call? Bash scripting quirks & safety tips Ideas about how to use AWS Service discovery at Stripe Consistency vs availability (wat?) What's devops? Operations for software developers for beginners How do you do capacity planning? Why I love log files ★ TIL: clock skew exists Fear makes you a worse programmer
Career / work
Get better at programming by learning how things work Things your manager might not know When your coworker does great work, tell their manager Tell candidates what to expect from your job interviews Questions you can ask about compensation Get your work recognized: write a brag document What's a senior engineer's job? Some possible career goals Open source sabbatical = awesome Writing performance reviews with positive constructive feedback Taking a sabbatical to work on Ruby profiling tools Telling people what you're working on Writing down my career Hiring & opportunity Choosing the "best software" ★ Getting things done How I got a CS degree without learning what a system call is Release it, then build it ★ How do you decide what to work on? Three ways to solve hard programming problems Talking about stock options = awesome ★ Things you should know about stock options before negotiating an offer 1:1 topic ideas ★ How I learned to program in 10 years Stopping to think Becoming a better developer (it's not just writing more programs) Sounding confident in interviews What my technical interviews have looked like ★ Questions I'm asking in interviews
Working with others / communication
Making small culture changes How do you make an awesome team? Learning to like design documents Senior engineering & fantasy heroes On reading the source code, not the docs Pair programming is amazing! Except... when it's not. Pair programming
Remote work
Working remotely, 4 years in Surviving meetings while remote Working remote, 8 months in (seeing humans is important!) Working remote, 3 months in Reports from remote-land: remote pairing works great!
Talks transcripts / podcasts
A few recent podcasts Talk: Building a Ruby profiler How does the internet work? podcast A swiss army knife of debugging tools: talk & transcript Notes from my PyData Berlin keynote A few notes on my CUSEC talk Ruby Rogues podcast: systems programming tricks!
On blogging / speaking
Some notes on upgrading Hugo Blog about what you've struggled with Metaphors in man pages Organizing this blog into categories Talks I'd love to see at RustConf Measuring a blog's success: focus on conversations, not page views How I set up an automatic weekly blog digest Blogging principles I use Switching to Hugo "advice" for aspiring tech bloggers Reproducing awesomeness How to set up a blog in 5 minutes Open sourced talks! You should give talks. They will be awesome. Here's why! Trying out Octopress
On learning
Celebrate tiny learning milestones How to get useful answers to your questions How to teach yourself hard things How to answer questions in a helpful way Learning at work Rules of programming experiments How to ask good questions Asking good questions is hard (but worth it) How does knowledge get locked up in people's heads? Asking questions is a superpower "Ask if you have questions" isn't enough
Rust
A couple of Rust error messages Rust in 2018: it's way easier to use! My first Rust macro Debugging a segfault in my Rust program Bindgen: awesome Rust tool for generating C bindings What's a reference in Rust? ★ Learning systems programming with Rust A second try at using Rust Calling C from Rust ★ Why I ❤ Rust My Rust OS will never be finished (and it's a success!) ★ Writing an OS in Rust in tiny steps (Steps 1-5) Some things my kernel can't do
Linux debugging / tracing tools
What problems do people solve with strace? A perf cheat sheet Linux tracing systems & how they fit together Notes on BPF & eBPF 3 short screencasts (/proc, tcpdump, strace) ftrace: trace your kernel functions! ★ Linux debugging tools I love Using ltrace to debug a memory leak A useful new strace feature A workshop on strace & tcpdump How does perf work? (in which we read the Linux kernel source) perf top: an awesome way to spy on CPU usage A few spy tools for your operating system (other than strace!) Seeing system calls with perf instead of strace Spying on Hadoop with strace I can spy on my CPU cycles with perf! ★ Debug your programs like they're closed source! Debugging shared library problems with strace More practical uses for strace! Using strace to avoid reading Ruby code Spying on ssh with strace Understanding how killall works using strace
Debugging
A debugging manifesto Tips for analyzing logs Some ways to get better at debugging Debugging by starting a REPL at a breakpoint is fun Reasons why bugs might feel "impossible" When debugging, your attitude matters What does debugging a program look like? ★ How I got better at debugging Coding strategies
Debugging stories
Debugging a weird 'file not found' error Reverse engineering the Notability file format Debugging netlink requests A small website mystery Investigating Erlang by reading its system calls Surprises in Ruby HTTP libraries Nancy Drew and the Case of the Slow Program
Fan posts about awesome work by other people
Awesome NLP tutorials by Allison Parrish Like zines about computers? You might love Bubblesort Zines A magical machine learning art tool "A Critique of the CAP Theorem" Some of my favorite blogs A few blogs I really like Julia Serano's 'Excluded' Transit maps: 1941 vs 2011
Inclusion
No feigning surprise A litmus test for job descriptions Women-only spaces are a hack An argument for hiring junior developers Programming doesn't belong to men (it belongs to me) What women in technology really think (150 of them, at least) ★ When is "guys" gender neutral? I did a survey!
not about computers
rbspy
Documentation site for rbspy! Prototyping an ltrace clone using eBPF Profiler week 6/7: more experiments, and a `report` subcommand! Profiler week 5: Mac support, experiments profiling memory allocations Writing eBPF tracing tools in Rust Spying on a Ruby process's memory allocations with eBPF Profiler week 4: callgrind support, containers, Mac progress! I think I found a Mac kernel bug? How do you spy on a program running in a container? How do you read the memory maps of a Mac process? Profiler week 3: refactoring, better testing, and an alpha release! Profiler week 2: support for 1.9.3 -> 2.5.0, and line numbers! Should I pause a Ruby process to collect its stack? Profiler adventures: resolving symbol addresses is hard! Profiler week 1: testing & profiling stripped binaries How are Ruby's headers different from Python's headers? How often do Ruby's stack struct definitions change? How do Ruby & Python profilers work? ★ How to spy on a Ruby program
Performance
Profiling Go programs with pprof How much memory is my process using? Benchmarking correctly is hard (and techniques for doing it better) The Etsy site performance report is amazing Some links on Java garbage collection Java garbage collection can be really slow I/O matters. Have high expectations for your computers How CPU load averages work (and using them to triage webserver performance!) Java isn't slow ★ A millisecond isn't fast (and how we made it 100x faster) ★ Computers are *fast*!
Open source
Figuring out how to contribute to open source A few questions about open source Learning at open source sprints (no preparation required) ★ Don't feel guilty about not contributing to open source
Linux systems stuff
How to get a core dump for a segfault on Linux Things to learn about Linux Guessing Linux kernel registers You can be a kernel hacker! Recovering files using /proc (and spying, too!) ★ 4 paths to being a kernel hacker
Recurse Center 2020
Day 57: Trying to set up GitHub Actions Day 56: A little WebAssembly Day 53: a little nginx, IPv6, and wireguard Day 52: testing how many Firecracker VMs I can run Day 51: Fixed my logging and made a couple of puzzles Day 50: Building some tarballs for puzzles, and trying to make a kernel boot faster Day 49: making the VMs boot faster Day 48: Another Go program, and a little vim configuration Day 47: Using device mapper to manage Firecracker images Day 46: debugging an iptables problem Day 44: Building my VMs with Docker Day 43: Building VM images Day 42: Writing a Go program to manage Firecracker VMs Day 41: Trying to understand what a bridge is Day 40: screen flickering & a talk about containers Day 39: Customizing gotty's terminal Day 38: Modifying gotty to serve many different terminal applications at once Day 37: A new laptop and a little Vue Day 35: Launching my VMs more reliably Daily blog posts about my time at RC Day 34: Learning about qemu Day 33: pairing is magic and beautiful git diffs Day 32: A Rails model that doesn't use the database with ActiveHash Day 24: a short talk about blogging myths, and a debugging tip Day 23: a little Rails testing Day 22: getting OAuth to work in Rails Day 21: wrangling systemd & setting up git deploys to a VM Day 19: Clustering faces (poorly) using an autoencoder Day 20: trying to figure out how Google Cloud IAM works Day 18: an answer to an autoencoder question Day 17: trying to wrap my head around autoencoders Day 13: BPTT, and debugging why a model isn't training is hard Day 11: learning about learning rates Day 10: Training an RNN to count to three Day 9: Generating a lot of nonsense with an RNN Day 8: Start with something that works Day 5: drawing lots of faces with sketch-rnn How do you write simple explanations without sounding condescending? Day 3: an infinitely tall fridge Day 2: Rails associations & dragging divs around Day 1: a confusing Rails error message I'm doing another Recurse Center batch!
Recurse Center 2013
How I spent my time at the Recurse Center How I did Hacker School: ignoring things I understand and doing the impossible Hacker School's Secret Strategy for Being Super Productive (or: Help.) "How was Hacker School?" Day 46: Never Graduate Day 45: I now have Rust code for executing executables! Day 44: qemu + gdb = so great ★ Day 43: SOMETHING IS ERASING MY PROGRAM WHILE IT’S RUNNING (oh wait oops) Day 42: How to run a simple ELF executable, from scratch (I don't know) Day 41: Linkers are upsetting Day 39: Writing malloc wrong, for fun Day 40: 12 things I learned today about linkers. Day 40: Linkers are amazing. Day 38: After 6 days, I have problems that I can't understand at all ★ Day 37: After 5 days, my OS doesn't crash when I press a key ★ Day 36: On programming without malloc Day 35: Types in Rust, for beginners How to call Rust from assembly, and vice versa Videos from PyData NYC are up! ★ What happens when you run 'Hello, world' Writing a kernel using rustboot & rust-core Day 34b: Writing curl using my TCP stack Day 34: The tiniest operating system Day 33: How to make music with ClojureScript Day 32: Magical Orchestra!!! Day 31: Binary trees with core.logic! Day 30: Making music in Clojure with Overtone. Clojure bugs with laziness! Fun! Day 29: Trying out Emacs! Day 28: Made a git workflow visualization webapp! Day 27: Automatically testing changes in state! Visualizing my Git workflow! Floats! Day 25: ACK all the things Day 26: Trying to describe the TCP state machine in a readable way. Failing. Women in Technology workshop at PyData NYC Day 24: Unit testing this TCP library Day 22: Got some TCP packets back! Day 23: Started writing a TCP stack in Python NYC Python talk Day 21: Trying to TCP Day 19: A few reasons why networking is hard ★ Day 20: Traceroute in 15 lines of code using Scapy Day 18: ARP cache poisoning (or: In ur connection, sniffing ur packets) Day 17: How to write a buffer overflow exploit ★ Day 16: gzip + poetry = awesome Do Rails programmers use node.js? Visualizing correlations in command usage Day 15: How a .gz file is structured, redux Day 14: When it's hard to write tests, that's when I should be testing Day 13: Off by one errors Day 12: Why Julia likes Julia Day 10: Goals. Goals? Maybe I need to be *reading* more code? Day 11: How does gzip work? Day 9: Bytecode is made of bytes! CPython isn't scary! Day 8: Julia writes Julia! And remembers that open source is hard. Day 7: An echo server in Clojure Day 6: I wrote a rootkit! Day 5: I wrote a kernel module!!! Where to find bike sharing systems' data feeds Day 4: Processes vs threads, and kernel modules! Day 3: What does the Linux kernel even do? Day 2: netcat fun! Day 1: What does a shell even do? Hacker School Day 1: Messing around with the stack in C Hacker School Day -4: unit testing in C. checkmk!