PHP set_time_limit() and PHP-FPM request_terminate_timeout: coordination for graceful termination

Answer

The FPM hard timeout (request_terminate_timeout) always takes precedence over PHP’s internal execution limit (set_time_limit() or max_execution_time). When the FPM limit is exceeded, the worker is terminated by SIGTERM then SIGKILL, and PHP gets no chance to run shutdown functions. Only when PHP’s limit is reached first does a fatal error occur, allowing register_shutdown_function(), destructors, or fastcgi_finish_request() to execute.

Confirmed findings

• request_terminate_timeout is a wall‑clock limit enforced by the PHP‑FPM process manager; exceeding it sends SIGTERM then SIGKILL to the worker.
• set_time_limit() only changes PHP’s internal soft limit; it cannot affect or disable the FPM hard limit.
• If the FPM limit fires first, shutdown functions are not executed.
• If PHP’s limit fires first, a fatal error is thrown, shutdown functions run, and the worker remains alive for the next request.
• There is no PHP API to read, change, or disable request_terminate_timeout; it can only be adjusted in the pool configuration (e.g., www.conf) and reloaded via FPM.

Steps for this case

1. Check the current FPM pool setting for request_terminate_timeout (look in /etc/php/*/fpm/pool.d/www.conf or the equivalent).
2. Ensure the value is greater than the maximum execution time you intend to allow via set_time_limit() or max_execution_time. For example, if you need up to 40 seconds of PHP work, set request_terminate_timeout 50.
3. In your script, use set_time_limit() (or rely on max_execution_time) to define the soft limit you want; this will trigger a fatal error and allow cleanup via register_shutdown_function().
4. If you need to change the FPM hard timeout, edit the pool config and reload PHP‑FPM (sudo systemctl reload php8.2-fpm or the appropriate service). No PHP‑only method exists.

Missing diagnostic detail

To confirm whether the FPM limit is the active constraint, please provide the current value of request_terminate_timeout from your pool configuration. If it is lower than the PHP limit you are setting, the FPM timeout will preempt cleanup; otherwise PHP’s limit will govern.