The Most Arrogant Document in Computer History: Unix V3 init’s ‘BUGS none possible’ Claim

At the end of the Unix V3 (February 1973) init(VII) manual page, a remarkably confident statement appears: BUGS none possible – absolutely no bugs . This is the only known Unix manual that openly claims zero bugs.

The manual is unsigned, but the author of init was likely Ken Thompson, who also designed the surrounding process‑startup mechanism (fork, getty, etc.) largely on his own.

On the PDP‑11, the entire init program consisted of only a few hundred lines of assembly. Thompson apparently reasoned that such a short program could not contain bugs.

By Unix V4, the confidence disappeared; the DIAGNOSTICS and BUGS sections were removed entirely from the manual.

Four special preconditions made the “no bugs” claim plausible:

Minimal code size : the program could fit entirely in one person’s mind.

Fixed hardware environment : only a few PDP‑11 machines and terminals were used.

Very few users : just a small group of researchers at Bell Labs.

Author as maintainer : the same person who wrote the code was the only one fixing bugs.

In such a constrained setting, saying “there will never be a bug” may not have been hyperbole.

After Unix V4, these conditions eroded. The user base grew, hardware platforms diversified, and init began to rely on external scripts, making the system too complex for a single person to fully control.

The transition from the Unix V3 init claim to today’s systemd (millions of lines of code with a comprehensive bug‑tracking system) mirrors the broader shift of software engineering from a handcrafted workshop to an industrialized process.