Python: What is the default handling of SIGTERM?
Building on the answer of Thomas Wouters, python does not register a handler for the SIGTERM signal. We can see this by doing:
In[23]: signal.SIG_DFL == signal.signal(signal.SIGTERM,signal.SIG_DFL)Out[23]: True
That means that the system will take the default action. On linux, the default action (according to the signal man page) for a SIGTERM is to terminate the process.
Terminating a process means that:
the process will simply not be allocated any more time slices during which it can execute code.
- This means that it will not raise an exception, or call the code in try: finally: blocks, or the
__exit__
method of context managers. It will not do those things because that particular python interpreter will never get the chance to execute another instruction.
- This means that it will not raise an exception, or call the code in try: finally: blocks, or the
The process's memory and other resources (open files, network sockets, etc...) will be released back to the rest of the system.
Nothing. Python itself does not register a signal handler for it. You can check this in the interactive interpreter:
>>> import signal>>> signal.signal(signal.SIGTERM, signal.SIG_DFL)0>>> signal.SIG_DFL0
That shows signal.signal()
returning signal.SIG_DFL for signal.SIGTERM
. Contrast it with signal.SIGINT
, which does have a default signal handler (which raises KeyboardInterrupt
):
>>> signal.signal(signal.SIGINT, signal.SIG_DFL)<built-in function default_int_handler>
Look at this example:
import timeclass A: def __init__(self): print("A.__init__()") def __del__(self): print("A.__del__()")a = A()b = A()time.sleep(10)
Under normal circumstances, the output would be:
A.__init__()A.__init__()A.__del__()A.__del__()
But if you kill it with SIGTERM you get:
A.__init__()A.__init__()Terminated
Thus the program does not terminate cleanly (the destructors are not called).