Python进程在Ubuntu上消亡：错误代码是什么意思，是否有修复程序？

Question

I am running multiple copies of the same python script on an Amazon EC2 Ubuntu instance. Each copy in turn launches the same child Python script using the solution proposed here

From time to time some of these child processes die. subprocess.check_output throws an exception and returns the error code -9 . I ran the child process directly from the prompt and after running for some time, the process dies with a not-so-detailed message Killed .

Questions:

• What does -9 mean?
• How can I find out more about what went wrong? Specifically, my suspicion is that it might be caused by the machine getting overloaded by the several copies of the same script running at the same time. At the same time, the specific child process that I ran directly appears to be dying every time it's launched, directly or not, and more or less at the same moment (ie after processing more or less the same amount of input data). Python is not producing any error messages.
• Assuming I have no bugs in the Python code, what can I do to try to prevent the crashes?

Answer 1

check_output() accumulates output from the subprocess in memory. If the process generates enough output it might be killed by oom killer due to the large RAM consumption.

If you don't need the output, you could use check_call() instead and discard the output:

import os
from subprocess import check_call, STDOUT

DEVNULL = open(os.devnull, "r+b")

check_call([command], stdout=DEVNULL, stderr=STDOUT)

Answer 2

-9 means kill signal that is not catchable or ignorable, or just quit immediately.

For example if you're trying to kill a process you could enter in your terminal:

ps aux | grep processname

or just this to get a list of all processes: ps aux

Once you have the pid of the process you want to terminate, you'd type kill -9 followed by the pid:

kill -9 1234 

My memory is a little foggy when it comes to logs, but I'd cat around in /var/log/ and see if you find anything, or dmesg.

As far as preventing crashes in your Python code, have you tried any exception handling?

Exceptions in Python