How to log a Python crash?

Question

I am running a python code in a raspberry Pi. The code is supposed to last forever. However, after a few hours it crashes. Since it is running on a remote machine, I cannot see the message it gives during the crash.

How can I store this message on a file so I can see what was the problem? is this does autonomously in linux? or should I write some function to export the error during crash. How can I do that?

• John Zwinck: How are you launching your Python program exactly?
• johnsyweb: "Since it is running on a remote machine, I cannot see the message it gives during the crash." That really shouldn't be a restriction.
• alandalusi: i ssh the raspberrypi and run the python code : sudo python file.py

Answer 1

You can have a main function and log in case if main function crashes

def main():
 ...
 raise ValueError("Crashed because I'm a bad exception")
 ...
if __name__ == "__main__":
 try:
 main()
 except Exception as e:
 logger.exception("main crashed. Error: %s", e)

This is better in case if you're using something like logstash and want to see the error and the time on your UI.

Thanks to Eric for improving the answer

• Eric: Use logger.exception('main crashed'), which will print the stack trace too
• Ahmed: Feel free to edit my answer to include logger.exception
• PythoNic: Make sure, to setup the logging at some point. Python 3.9: logger.basicConfig(filename=..., encoding='utf-8', level=logger.DEBUG). Also the library is called logging, not logger. (So for the upper code, you would need import logging as logger.)
• PythoNic: 3.8 without parameter encoding, so logger.basicConfig(filename=..., level=logger.DEBUG). See Python docs for details (in your language :)

Answer 2

You can store the output in a file, if the process is started like this:

python script.py >> /logdir/script.py.log 2>&1

• alandalusi: is it possible to view the log on the terminal and log it on script.py.log at the same time?
• Markus Unterwaditzer: @alandalusi use tail -f /logdir/script.py.log to watch the log.
• alandalusi: It is funny that unlike running the script on terminal, the results are not put on the log file on real-time. any reason for this?
• kaspernj: This is probably because of tail's sleep interval. You can set that like this: "tail -s 0.1 -f /logdir/script.py.log"
• alandalusi: Its probably because of the buffering stackoverflow.com/questions/107705/python-output-buffering need to test this solution though

Answer 3

I had tried many attempts myself, but they all seemed weird...Until I figured it out! Simply write this code around your python file, and all should be well! By the way, I will be naming the crashlogs CRASH- and then the python time (e.g. CRASH-1607012036.015824.txt)

try:
 <your program here>
except Exception as e:
 crash=["Error on line {}".format(sys.exc_info()[-1].tb_lineno),"\n",e]
 print(crash)
 timeX=str(time.time())
 with open("monstergame/crashlogs/CRASH-"+timeX+".txt","w") as crashLog:
 for i in crash:
 i=str(i)
 crashLog.write(i)

Note: This is Python 3 code, not Python 2