We Disabled PHP's Stack Guard Ourselves: Containing Segfaults in a Single-Process PHP Server

Sun, 06 Sep 2026 15:05:00 -0700

php-fpm has a property nobody thinks about until they leave it. When a worker segfaults, you lose one request. The master forks a new child and life goes on. ePHPm runs every tenant’s PHP as threads inside one process. That’s where the memory and latency wins come from. It also means one tenant’s segfault takes down every other tenant on the box.

This is the story of closing that gap in four steps over about two weeks. The last step turned out to be a bug we’d put there ourselves. It’s also the payoff for the thread pool work in the previous post. Everything below that actually shipped depends on ePHPm owning its own PHP threads.

Segfault on Luther Monson

We Disabled PHP's Stack Guard Ourselves: Containing Segfaults in a Single-Process PHP Server