Linux on Andrew Quinn's TILs

Save your disk, write files directly into RAM with /dev/shm

Thu, 26 Jun 2025 00:00:00 +0000

Given my interest in extending the life of my SD cards and hard drives as much as possible, I’m surprised I haven’t come across /dev/shm before. In a word it’s a world-accessible RAM scratchpad, which seems baked right into POSIX, so that virtually every ~~Unix~~ EDIT: Linux system already has it mounted as a tmpfs by default:

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❯ mount | grep '/dev/shm'
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,inode64)

Today’s lucky 10,000, indeed. It gets mentioned often in Hacker News comments, but surprisingly I couldn’t find any actual articles talking about it. The existence of /dev/shm is a boon for me mostly because it means I never have to worry about whether /tmp is really RAM-based again.

LLMs make Perl great again

Sat, 24 May 2025 00:00:00 +0000

Perl 5 went through a long nadir of unpopularity due in large part to its deserved “Write Once, Read Never” reputation. So I was surprised to find out not only is it installed by default on Debian, it’s installed nearly everywhere by default. It’s even the non-shell scripting language of choice on OpenBSD!

Perhaps the only thing more impressive than Perl’s utter ubiquity is its longevity. The latest major version of Perl was first released in 1994. It came into existence on this planet less than a year after I did. It’s even arguably more portable than the median shell script - different Unices might use Bash, Zsh, Ksh, or even something newfangled like Fish, but for the most part a Perl 5 program is a Perl 5 program is a Perl 5 program.

Things you should never do: Use Expect to autotype SSH passwords in scripts

Wed, 26 Feb 2025 00:00:00 +0000

Before I moved to Finland, I spent some time in the Hobbesian war of all against all that is Wisconsin¹. Men were men back in that less civilized age, and “cybersecurity” a ninny-word dreamt up by social harmony types who honestly thought they had anything worth stealing in their servers. For those of us doing real work, which I must emphasize you should never do, we had Expect. And to SSH automatically into servers where we didn’t have fancy accoutrements like “keys” or “audit requirements”, we did stuff like

Common-sense security for SSH on a new Debian server

Tue, 24 Sep 2024 00:00:00 +0000

Last night I went to DigitalOcean and spun up a tiny new, $4/month droplet – on my own dime! It sounds crazy, but I’ve never actually wanted to pay for hosting myself before. But I have a fun little web app cooking up, one that might eventually pay that $4/month back with interests, and I decided, why not, it’s time to finally put some of my own skin in the game with this whole sysadmin thing.

Enforce GPL compliance by offering bounties?

Sat, 21 Sep 2024 00:00:00 +0000

Epistemic status: Very unclear, also I Am Not A Lawyer This Is Not Legal Advice Get Off My Lawn

(N.B.: I"m using “GPL” with broad strokes here, to point at “open source licenses it’s straightforward to run afoul of”.)

Policing is always hard in a world of limited resources. Especially when one is targeting sophisticated, well-monied criminal organizations, it can take an awful lot of time and effort merely to credibly reveal that wrongdoing has taken place. Would it surprise you if I said the average criminal software organization is probably, on the margin, more sophisticated than the average criminal organization? If so, you should probably expect that the former’s crimes are brought to life even less often than the latter’s.

What I would recommend to teens in 2024 who want to get into development

Sun, 08 Sep 2024 00:00:00 +0000

tmux is worse is better

Thu, 23 May 2024 00:00:00 +0000

tmux (short for “terminal mux” (short for “multiplexer”)) is i3 for your terminal. Oh, it’s so much more than that, and I recently discovered with some joy that it is installed by default on OpenBSD, but its fundamental value add to any programmer who has to SSH into servers more than once a week is it allows you to split your screen up into multiple independent shells without needing a graphical environment at all. If you want to walk the path of true digital minimalism, vanilla Vim and tmux or its spiritual grandfather screen are all you need.

I'm turning 30 so naturally I'm switching to OpenBSD

Sat, 04 May 2024 00:00:00 +0000

I’m kidding, I’m switching to OpenBSD because I like security or code quality or something.

It’s totally not because the inexorable march of aging is starting to show its effects on my ability to down necessary-evil trivia like me and my friends used to down forties in the Ahhhnald after dark, and so I’d like to settle down with a software ecosystem I can study in real depth once without feeling like 20% of what I absorb in year X will be deprecated by year X+10.

PHP is Web Shell

Mon, 29 Apr 2024 00:00:00 +0000

One of the cooler things about working in a firm founded and run by a lot of dyed-in-the-wool Linux hackers like my current place is that there is a lot of Bash lying around, accumulated over a good 25 years or so. For all their faults, pure shell solutions still set the silver standard for programs which appear almost entirely immune to bit rot.

But you know what? So does vanilla PHP. That pink stuff that was made from the ground up to get you from zero to working dynamic web page as fast as possible.

Vagrant lets you wrap VDI images

Tue, 05 Dec 2023 00:00:00 +0000

At work I’m currently experimenting with using Vagrant to automate getting an entire local network of our tiny embedded Linux systems running all on my local box.

Alas! One of our devices uses a custom Yocto distribution! But wait, we have scripts to run these as VDI images, and apparently that’s enough for Vagrant to get to work!

`1`	`vagrant package --base my-virtual-machine`

Further reading materials for future me: Creating a Base Box, and the Box File Format.

traceroute uses UDP by default, not ICMP

Wed, 29 Nov 2023 00:00:00 +0000

At least on Linux.

Don’t believe me? Run tcpdump -nn -i <interface> 'host example.com' in one shell and traceroute example.com in another. tcpdump will pick up all 3 of {ICMP, UDP, TCP}, and on my machine the pattern is clear:

20:58:47.187086 IP 1.2.3.4.41369 > 93.184.216.34.33434: UDP, length 32
20:58:47.187160 IP 1.2.3.4.39830 > 93.184.216.34.33435: UDP, length 32
20:58:47.187190 IP 1.2.3.4.43467 > 93.184.216.34.33436: UDP, length 32
20:58:47.187221 IP 1.2.3.4.50462 > 93.184.216.34.33437: UDP, length 32
20:58:47.187254 IP 1.2.3.4.35842 > 93.184.216.34.33438: UDP, length 32
20:58:47.187285 IP 1.2.3.4.44146 > 93.184.216.34.33439: UDP, length 32
20:58:47.187318 IP 1.2.3.4.50311 > 93.184.216.34.33440: UDP, length 32
20:58:47.187346 IP 1.2.3.4.34388 > 93.184.216.34.33441: UDP, length 32
20:58:47.187375 IP 1.2.3.4.43703 > 93.184.216.34.33442: UDP, length 32
20:58:47.187405 IP 1.2.3.4.35304 > 93.184.216.34.33443: UDP, length 32
20:58:47.187448 IP 1.2.3.4.50157 > 93.184.216.34.33444: UDP, length 32
20:58:47.187474 IP 1.2.3.4.58392 > 93.184.216.34.33445: UDP, length 32
20:58:47.187503 IP 1.2.3.4.45918 > 93.184.216.34.33446: UDP, length 32
20:58:47.187530 IP 1.2.3.4.38313 > 93.184.216.34.33447: UDP, length 32
20:58:47.187556 IP 1.2.3.4.41520 > 93.184.216.34.33448: UDP, length 32
20:58:47.187582 IP 1.2.3.4.55240 > 93.184.216.34.33449: UDP, length 32
20:58:47.225929 IP 1.2.3.4.60724 > 93.184.216.34.33450: UDP, length 32
20:58:47.225970 IP 1.2.3.4.43648 > 93.184.216.34.33451: UDP, length 32
20:58:47.226016 IP 1.2.3.4.52561 > 93.184.216.34.33452: UDP, length 32

I have no idea why. Performance? Getting around sysadmins who unwitting block all ICMP packets? It surprised me, at least.

One problem with user-scoped `systemd` timers

Sun, 26 Nov 2023 00:00:00 +0000

I’ve discovered one big downside of [putting systemd times into ~/.config/systemd/user/][1]: They stop running when you log out.

Two ways around this problem:

Bite the bullet, and install the timers into /etc/systemd/. This means giving up chezmoi version control, making the overall system more snowflake-y. I’m not crazy about it.
Remote in with tmux, instead of ever logging out, just use C-b d to detach from the session.

I’m going with #2. The lead developer of ktty is known not to like tmux, so there’s probably a way to detach long-running SSH sections inside of kitty itself – but I haven’t found it yet. Have you?

A good place to symlink local builds

Sat, 18 Nov 2023 00:00:00 +0000

I’ve been a big fan of both spaced repetition in general and the Anki spaced repetition system in particular for a long time now. So today, after a fresh new install and blinging out of Ubuntu 23.10, I decided to take the next step, as I often do with programs I use a lot, and try to build and compile it myself.

This turned out to be pretty easy! The docs warn that ./run is slower than the non-optimized build, but I don’t notice much of a difference on my machine. It did however leave me with the question: Where should I put the anki symlink to ./run?