Python stdout goes where under systemd? (Was: Example of python service running under systemd?)
travisgriggs at gmail.com
Fri Sep 12 23:45:42 CEST 2014
On Sep 12, 2014, at 12:05 PM, Travis Griggs <travisgriggs at gmail.com> wrote:
> Thanks all for the help/advice. I’m getting there.
> To experiment/learn, I made a simple python program (/Foo/cyclic.py):
> #!/usr/bin/env python3
> import time
> while True:
> with open('sound', 'r') as file:
> currentValue = file.read()
> otherValue = 'tick' if currentValue == 'tock' else 'tock'
> with open('sound', 'w') as file:
> print(currentValue, '->', otherValue)
> Run from the command line, this tick-tocks nicely, both outputting, as well as updating the ‘/Foo/sound’ file on a 5 second period.
> I then created a simple .service file:
> Description=Foo for learning service
> I chose to be “explicit” with some of the default options (Type and StandardOutput).
> I finally executed:
> systemctl --system daemon-reload
> systemctl enable foo
> systemctl start foo
> It seems to work. Almost. The file is being updated regularly (watch cat /Foo/sound shows the change happening). But I can’t seem to find the output from my print() statement. journalctl -f doesn’t show anything. Nor does tail -f /var/log/syslog or any of the others. It just seems to be going nowhere? Is there something I need to do special to get the print() output going somewhere logable?
Arghhh… I’ll answer my own question here. I wasn’t patient enough, when I checked after lunch, I found I had a mountain of tick/tock entries in journalctl -f. Python print() is buffered, so it wasn’t showing up except in huge blocks. Changed the .service file to start with -u and everything works as expected now.
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