# systemd ptyfwd.c — Resize Forwarding Implementation

## Metadata

| Field | Value |
|---|---|
| Institute | Molodetz Institute — Research & Retrieval Division |
| Subject | shell-multiplexer-auto-attach |
| Document type | Source Dossier |
| Tier | 1 |
| Source title | ptyfwd: optionally override terminal width/height (commit) |
| Source URL | https://git.alternativebit.fr/picnoir/Systemd/commit/d435a18244ff52132d873859126e7a3ece66a9ba |
| Source publisher / author | systemd project (mirrored) |
| Source type | repository |
| Source date (published) | Unknown — not stated |
| Date researched | 2026-10-09 |
| Researched by | tai (agent), model: Claude Sonnet 5, on behalf of retoor |
| Research method | web search synthesis |
| Confidence | High |
| Status | Active |

## Summary

A real commit in systemd's `ptyfwd.c` implementing the mirror-image of the StalkR dossier's design: reading the size from the local stdout and applying it to a pty master via `TIOCSWINSZ`, i.e. the production-grade version of the same resize-forwarding pattern in a widely-deployed init system's own pty-forwarding code.

## Key findings

- Confirms the `TIOCGWINSZ`/`TIOCSWINSZ` pattern is not just a hobby-project technique — it's how one of the most widely deployed pieces of Linux infrastructure (systemd) forwards terminal size across a pty boundary.

## Pros / strengths

- Production code in a security- and correctness-sensitive project (systemd); a strong confidence signal for the pattern's correctness and necessity.

## Cons / limitations / caveats

- A single commit diff; doesn't show the full surrounding event-loop integration (how/when the resize check gets triggered) in this excerpt.

## Relevance to tai

Second independent confirmation (alongside StalkR) of the exact resize-forwarding mechanism — further strengthens the case that this is solved, known, and would be pure reinvention-cost if a from-scratch multiplexer were built instead of wrapping tmux (which already implements this internally and transparently).

## Changelog

| Date | Change |
|---|---|
| 2026-10-09 | Initial dossier created. |