FILE DESCRIPTORS

Three levels between a number and a file: what two numbers of one description share, what two descriptions do not — and where the offset lives

Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.

Three sizes in one archive — from a sheet on the fridge to a poster on the wall.

Formats: A4 · A3 · A2
What you get: Print-ready PDFs, one per size, with every letterform converted to outlines — nothing to install, nothing to shift.
Subject: code · everyone · memo · study

Read from top to bottom: the number belongs to the process, the description to one opening, the content to the file. The two schemes differ only in the middle row.

A LOCK IS DROPPED BY SOMEBODY ELSE’S CLOSE()

A lock taken through fcntl F_SETLK belongs neither to the description nor to the descriptor, but to the pair “process and file”. The standard requires every such lock to be released as soon as the process closes any descriptor of that file — “even if via a different open file description”. Open the file a second time, read a line, close it, and the lock is gone.

That is why Base Specifications Issue 8 added a second kind of lock — one owned by the description, which holds for as long as the description itself.

On the sheet

Read from top to bottom: the number belongs to the process, the description to one opening, the content to the file. The two schemes differ only in the middle row.
Colour carries meaning, but meaning never rests on colour alone — the sheet reads in black and white.
Nothing about how it was made: the sheet carries only what the reader needs.

Printing

Three sizes in the archive: A4 — 210×297 mm, A3 — 297×420 mm, A2 — 420×594 mm.
All text is converted to outlines. No fonts to install, and nothing shifts on another machine.
White background and sparing fills — it prints on a home printer without draining the cartridge.
Margins of at least 10 mm: a home printer cannot print to the edge.
No stroke thinner than 0.3 mm, so nothing disappears in print.

Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 11 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.

FILE DESCRIPTORS

A LOCK IS DROPPED BY SOMEBODY ELSE’S CLOSE()

On the sheet

Printing

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