Python Signals, Timeouts and Process Termination

OS and Process Automation / Guide 21 of 39 / Intermediate

• Control nodeUbuntu 26.04 LTS
• Python3.14.4
• requests2.34.2
• paramiko5.0.0
• TimeAbout 20 min

signal.Signals as an enum needs Python 3.5, and signal.raise_signal 3.8. Signal handlers only run in the main thread of the main interpreter, which has always been true.

• pytest9.1.1
• PyYAML6.0.3
• boto3 / botocore1.43.78

This guide includes

Use this because a script that can hang for ever is worse than one that fails. This matters because a timeout on Popen.wait does not stop the child - it only stops you waiting for it.

• timing out a child with subprocess.run, then meeting the timeout that does not stop it
• sending terminate then kill, and reading what a return code says about a signal
• handling a signal in your own script
• seeing what a bare kill -9 costs you, and which signals cannot be caught
• enforcing a timeout on yourself, not only on children

Before you start

• guide 18 - the runner this adds a timeout to.
• guide 5 - what an exit status means.

1. 1

   A child that takes too long

2. 2

   The timeout that does not stop the child

3. 3

   terminate, then kill

4. 4

   What a return code says about a signal

5. 5

   Handling a signal in your own script

6. 6

   And what a bare kill -9 costs you

7. 7

   The one signal you cannot catch

8. 8

   A timeout you enforce on yourself

Official sources

• CertGrid - Python Automation for IT
• Python documentation - The Python Standard Library