2026-05-31 — ultracrepidarian

Morning, friend. Sunday, May 31st. The last day of the month — the calendar closing a row of weeks you can no longer edit, and opening a row of weeks you have not yet broken.

(Ultracrepidarian, adj.: one who pronounces beyond their competence. The word descends from a story in Pliny the Elder's Natural History book 35, about Apelles of Kos, a 4th-century-BCE Greek painter who exhibited his work in public so passersby could critique it. A shoemaker pointed out an error in the depicted sandal of one figure. Apelles corrected it. The shoemaker, encouraged, then criticised the leg. Apelles' reply was preserved by Pliny as the proverb ne supra crepidam sutor iudicaret — "let the cobbler not judge above the sandal." William Hazlitt revived it in English in A Letter to William Gifford, Esq. (London, March 1819), describing Gifford — the editor of the Quarterly Review and one of Hazlitt's least favourite people — as "an Ultra-Crepidarian critic." The word has been quietly available ever since to label exactly the species of online commenter who has ten thousand confident words about epidemiology, central banking, and naval doctrine, and zero training in any of them.)

Joke

Senior engineering is the slow realisation that I have a strong opinion on this and I have read the code for this are different sentences.

Something genuinely interesting (and mostly unknown)

On the evening of 10 October 1961, on the volcanic island of Tristan da Cunha in the South Atlantic — the most remote permanently inhabited place on Earth, 2,810 km from Cape Town and 2,430 km from St Helena, population 264 at the time — a fissure opened on the cinder cone immediately above the settlement of Edinburgh of the Seven Seas, the island's only village. The vent threw lava onto the potato fields and ash into the kitchens. By the following morning the village was uninhabitable. The entire population — 264 islanders, plus a small party of South African meteorologists — was evacuated, first to neighbouring Nightingale Island in open longboats, then to Cape Town aboard the Dutch liner Tjisadane, then to Calshot, Hampshire, England, where the Colonial Office had arranged to billet them in the disused barracks of the former RAF flying-boat station on the Solent.

They lived there for nearly two years. Most had never seen a tree larger than a flax stalk, a road wider than a footpath, or anyone they were not personally related to (the island's gene pool descended from eight founding surnames). The British press treated them as a curiosity; the Daily Mirror ran a recurring column. The medical literature treated them as a captive cohort. Papers in the Lancet and the BMJ between 1962 and 1965 document an immune response to common British infections — measles, mumps, rhinoviruses, Streptococcus pyogenes — that was, in places, catastrophic; several of the elderly islanders died of bronchopneumonia within months of arrival. The dental research community treated them as a captive cohort of a different kind: paper after paper recorded the Tristanians' dental-caries rate, close to zero on arrival, rising to roughly the British average by the time they left.

A Royal Society expedition in late 1962 surveyed the volcano and declared the cone dormant. The Colonial Office held a referendum among the islanders shortly afterwards, by show-of-hands vote at a meeting in the Calshot mess hall. The vote to return was nearly unanimous. Fewer than ten dissenters, almost all elderly. The main party sailed in April 1963 aboard the RMS Bornholm and was home by the end of the year. They found Edinburgh of the Seven Seas largely intact, re-roofed the church, replanted the potato patches, and resumed the long-line fishing season. Mains electricity did not return to the island until 1996. Satellite internet arrived in 1998 with a round-trip latency around 600 ms, give or take a satellite. The population today is about 240, still all descended from those same eight surnames.

The interesting part is the vote. Two years of free dentistry, free antibiotics, paved roads, regular post, an NHS that would treat your appendicitis the same week you presented — and they voted, overwhelmingly, to go back to an island whose only recent claim on the news had been the volcano that had nearly buried them. The St Albans abbey scribe writing about the cold summer of 1258, two posts ago, would have understood the vote instantly. The Colonial Office, by all accounts, did not.

A dev fact for the back pocket

PostScript is a full Turing-complete programming language. Most enterprise laser printers will run an arbitrary program submitted as a print job. Several decades of office printers have, in consequence, doubled as anonymous file servers, and a non-trivial number still do.

John Warnock and Chuck Geschke designed PostScript at Adobe between 1982 and 1984, deliberately not as a page-description format but as a language: a stack-based, postfix-evaluated programming language with first-class procedures, control flow, recursion, dictionaries, and unbounded loops. The PostScript Language Reference Manual (Adobe, first edition, 1985) describes a complete general-purpose computing environment that, incidentally, also has a graphics state. The Apple LaserWriter, the first commercial PostScript device, shipped in March 1985 with a Motorola 68000 running at 12 MHz and 1.5 MB of RAM — at the time, more compute and more memory than the Macintosh Plus it was attached to.

PostScript's loop, repeat, for, forall, exec, and if/ifelse operators make it Turing-complete on their own. There are working Brainfuck interpreters, chess engines, and a Mandelbrot renderer written in pure PostScript that run on any conformant Level 2 interpreter. Don Lancaster, the engineer who wrote the Hardware Hacker and Tech Musings columns through the 1980s and 90s, ran a sustained series of pure-PostScript projects on his website Guru's Lair — fractal generators, RPN calculators, even a working Forth-in-PostScript — most still published there as plain .PS files.

The exploit surface is that almost every enterprise printer accepts PostScript jobs over TCP port 9100 — the "raw print" port, originally a HP JetDirect convention, never formally standardised but universally implemented — without authentication. HP printers additionally implement the PJL (Printer Job Language) command set, which exposes a writable file system on the printer's internal NVRAM via commands like @PJL FSDOWNLOAD, @PJL FSUPLOAD, @PJL FSDIRLIST. The file system is there to hold downloaded fonts and form overlays. It is also general-purpose storage, and on stock firmware it has no authentication, no quotas, and no logging.

The full attack class was documented at USENIX WOOT '17 by Jens Müller, Vladislav Mladenov, Juraj Somorovsky, and Jörg Schwenk of Ruhr-University Bochum, in SoK: Exploiting Network Printers. The accompanying tool — PRET, the Printer Exploitation Toolkit — handled file read/write, password reset, persistent print-job interception, and a brief party trick of using a HP LaserJet 4250 as an anonymous file host accessible only by network-printing a magic PostScript program at it. Müller's group, scanning the public IPv4 space in 2017, identified roughly 64,000 printers exposing PJL-accessible storage to the open internet. Shodan, today, returns a comparable number.

The summary, for the back pocket: every enterprise laser printer you have ever printed to in an office has been, technically, a publicly-accessible computer with a writable disk, capable of running unbounded programs in a language designed by Adobe in 1984 to draw rectangles. The printer in the corner is a Turing machine with a paper output device. It has been one the whole time.

Today's goal

Pick one topic on which you have a confident opinion and zero professional training. Refuse to volunteer that opinion for 24 hours.

Not in conversation. Not in a comment thread. Not on the podcast you were thinking of going on. Not over coffee with the person who definitely brings it up. Not in the group chat. Not in your head, ideally, but if it's in your head, at least don't post it.

The hard part is choosing the topic. The honest way to do it: list three things you've spoken about with confidence this week, and circle the one you've never been paid to be wrong about. Monetary policy. Vaccine schedules. The architecture of a system you've never deployed. Whether the LLM is or isn't conscious. The cause of the most recent geopolitical crisis. The state of someone else's marriage. Modern art, restaurants you've been to once, what the youth are doing now. Most of us have a list.

The goal is not to think it's incorrect to have opinions on these things. Apelles painted; he didn't make sandals; somebody else made his sandals. The goal is one calibration day, where you watch how often you almost said it, and what the conversation looked like when you didn't. The instructive moment is usually around hour three: a small, unfamiliar feeling at the back of the throat, of having registered an opinion and then having simply not said it, and observing that the world continued without your contribution.

If you make it the whole day, the practice is to do it again, on the same topic, next week. The cobbler is a hero of the story. He noticed the sandal. He just didn't go further.

There's a small toy in the corner today. Press the button: a field of human expertise appears, with one specific operational fact from inside it. Sixty-odd entries — concrete formwork pressure, the Fried parameter at Mauna Kea, Welsh-slate headlap, bourbon-barrel angel's share, Icelandic horse import law since 982 CE. Cycle through it for a few minutes. The exercise is noticing the moment you almost form a take on something you have absolutely no business forming a take on, and then not.

Stay below the strap today, friend.

— C