How to Mock a SIGTERM Handler in Python

Create a graceful shutdown handler for SIGTERM and SIGINT signals, then test it by simulating a signal delivery without terminating the process.

Easy Python 3.9+ Aug 9, 2026 Production deployment patterns 13 views 0 copies

signals graceful-shutdown sigterm threading deployment

Python code

31 lines

Python 3.9+

import signal
import time

class Service:
    def __init__(self):
        self.running = True

    def shutdown(self, signum, frame):
        print(f"Received signal {signum}, shutting down gracefully...")
        self.running = False

    def run(self):
        signal.signal(signal.SIGTERM, self.shutdown)
        signal.signal(signal.SIGINT, self.shutdown)
        print("Service started, press Ctrl+C to stop")
        while self.running:
            time.sleep(0.5)
        print("Service stopped")

    def mock_signal(self, signum):
        # Simulate receiving a signal without killing the process
        self.shutdown(signum, None)

if __name__ == "__main__":
    service = Service()
    # Instead of running forever, simulate a SIGTERM after 1 second
    import threading
    timer = threading.Timer(1.0, service.mock_signal, args=[signal.SIGTERM])
    timer.start()
    service.run()
    timer.join()

Output

stdout

Service started, press Ctrl+C to stop
Received signal 15, shutting down gracefully...
Service stopped

How it works

The signal.signal calls register the shutdown method as the handler for both SIGTERM (15) and SIGINT (2). The mock_signal method directly calls the same handler, simulating what happens when the OS delivers a signal. The threading.Timer fires after one second, exercising the shutdown path without actually killing the process. The main loop checks the running flag every 0.5 seconds, so it exits cleanly after the mock signal flips it to False. This pattern is critical for production services that must flush data or close resources before exiting.

Common mistakes

Calling `signal.signal` inside the loop instead of once at startup
Forgetting to pass both `signum` and `frame` arguments to the handler
Using `sys.exit()` directly instead of setting a running flag
Creating the timer without joining it, leaving threads dangling

Variations

Use `signal.signal(signal.SIGTERM, lambda s, f: service.shutdown())` to wrap the handler
Replace the Timer with `asyncio.get_event_loop().call_later(1, service.mock_signal, signal.SIGTERM)` for async services

Real-world use cases

Web servers like Flask or Django that need to close database connections before pod termination.
Kubernetes-managed containers that must respond to SIGTERM within a grace period.
Data pipeline workers that must finish in-flight batch jobs before exiting.

How to Mock a SIGTERM Handler in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

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How it works

Common mistakes

Variations

Real-world use cases

More from Production deployment patterns

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