I recently came across a tough to debug issue where I was calling a shell script from python using the subprocess module, this shell script called rsync, no matter what I would always run into a timeout situation. I fired up strace and noticed that the process was in a timeout state.
select(4, NULL, [3], [3], {60, 0}) = 0 (Timeout)
I looked at the subprocess documentation and apparently using pipes will fill the system pipe buffer.
Warning
This will deadlock when using stdout=PIPE and/or stderr=PIPE and the child process generates enough output to a pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use communicate() to avoid that.
I was baffled, I finally took the approach to eliminate stderr and stdout and just check the return status of the command using run(). Here is what I finally came up with, and all was well.
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stdbuf -oL -e0 /usr/local/bin/rsync --outbuf=N -avz |
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def execute_jobs(cmd): try: logger.info('Start Command: [%s]' % cmd) subprocess.run(shlex.split(cmd), check=True) logger.info('Command Success: [%s]' % cmd) except subprocess.CalledProcessError as e: logger.critical('[%s] FATAL: Command failed with error [%s]' % (cmd,e)) |
Hope you find this and it helps you.
run() is less flexible, it just does the following for you under the hood.
proc = subprocess.Popen([
arg1,
arg2
], stdout=subprocess.PIPE)
proc_stdout, proc_stderr = proc.communicate()