KeyboardInterrupt raises an exception which results in a zero exit code

[Amar Civgin]

Bug description

During training whenever there is a keyboard interrupt the fit loop raises a SIGTERMException

pytorch-lightning/src/lightning/pytorch/loops/fit_loop.py

Lines 397 to 398 in 98005bb

 if trainer.received_sigterm: 
     raise SIGTERMException 

which results in a 0 exit code. Other scripts relying on the exit code of the training script pick this up as if the training script has exited normally.

The issue comes from here:

pytorch-lightning/src/lightning/pytorch/utilities/exceptions.py

Lines 19 to 28 in 98005bb

 class SIGTERMException(SystemExit): 
     """Exception used when a :class:`signal.SIGTERM` is sent to a process. 
  
     This exception is raised by the loops at specific points. It can be used to write custom logic in the 
     :meth:`lightning.pytorch.callbacks.callback.Callback.on_exception` method. 
  
     For example, you could use the :class:`lightning.pytorch.callbacks.fault_tolerance.OnExceptionCheckpoint` callback 
     that saves a checkpoint for you when this exception is raised. 
  
     """ 

raising a SystemExit in python without specifying the exit code, has the code set to None which gets converted to 0. The fix would be to have:

 class SIGTERMException(SystemExit): 
     """Exception used when a :class:`signal.SIGTERM` is sent to a process. 
  
     This exception is raised by the loops at specific points. It can be used to write custom logic in the 
     :meth:`lightning.pytorch.callbacks.callback.Callback.on_exception` method. 
  
     For example, you could use the :class:`lightning.pytorch.callbacks.fault_tolerance.OnExceptionCheckpoint` callback 
     that saves a checkpoint for you when this exception is raised. 
  
     """
     code = 128 + 15  # see https://tldp.org/LDP/abs/html/exitcodes.html

What version are you seeing the problem on?

v2.0, v2.1, v2.2, master

How to reproduce the bug

Start a training and then send a keyboard interrupt signal to it, and run echo $? to see the exit code.