Using the python logging module in a systemd service script

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1

I’ve developed this Python script that uses the logging module to log output. The idea is that it is supposed to output to stdout as well as to a log file.

I start with a basic config by setting the logging level and format:

logging.basicConfig(format='[%(levelname)s] %(asctime)s %(message)s', level=logging.INFO)
logger = logging.getLogger()

Then I add the file handler (in a try block):

logger.addHandler(logging.FileHandler('/var/log/file.log', mode='a'))

The script runs an infinite while loop (e.g. ‘while True:’) until terminated.

When I run this from an active console, it works exactly as anticipated. But if I run it as a systemd service, I get nothing for output. The log file never records anything, and journald never captures any of the standard output.

On the systemd side, I’m running the script as a “simple” service. I’m not using any special parameters for logging. In the past this has worked for me, so I’m not sure why it doesn’t work now. I am running it on Debian 11. I’ve looked through the docs for both python’s logging module and systemd, but a lot of what I’m reading doesn’t seem to answer my question.

Any thoughts, ideas or other suggestions? I’m happy to share more code if that helps.

2

If you are going to have systemd log your stdout/stderr to the journal you do not need the log file.

This is what I tried that worked on my Fedora 39 system.
debian 11 should be the same.

:  19:25:19   armf39  ~
:  [1] root $ cat /usr/local/bin/logging_service.py
#!/usr/bin/python3
import logging

logging.basicConfig(format='[%(levelname)s] %(asctime)s %(message)s', level=logging.INFO)
logger = logging.getLogger()

logger.info('example service starting')
logger.error('example service error')

:  19:25:27   armf39  ~
: [1] root $ cat /etc/systemd/system/logging_example.service
[Unit]
Description=logging example

[Service]
Type=oneshot
ExecStart=/usr/local/bin/logging_service.py
RemainAfterExit=yes

:  19:25:43   armf39  ~
: [1] root $ systemctl start logging_example

:  19:26:02   armf39  ~
: [1] root $ systemctl status logging_example
● logging_example.service - logging example
     Loaded: loaded (/etc/systemd/system/logging_example.service; static)
    Drop-In: /usr/lib/systemd/system/service.d
             └─10-timeout-abort.conf
     Active: active (exited) since Mon 2023-12-04 19:24:37 GMT; 1min 28s ago
    Process: 3140 ExecStart=/usr/local/bin/logging_service.py (code=exited, status=0/SUCCESS)
   Main PID: 3140 (code=exited, status=0/SUCCESS)
        CPU: 26ms

Dec 04 19:24:37 armf39.chelsea.private systemd[1]: Starting logging_example.service - logging example...
Dec 04 19:24:37 armf39.chelsea.private logging_service.py[3140]: [INFO] 2023-12-04 19:24:37,928 example service starting
Dec 04 19:24:37 armf39.chelsea.private logging_service.py[3140]: [ERROR] 2023-12-04 19:24:37,928 example service error
Dec 04 19:24:37 armf39.chelsea.private systemd[1]: Finished logging_example.service - logging example.

:  19:26:06   armf39  ~
: [1] root $ journalctl -u logging_example
2023-12-04T19:24:37+0000 systemd[1]: Starting logging_example.service - logging example...
2023-12-04T19:24:37+0000 logging_service.py[3140]: [INFO] 2023-12-04 19:24:37,928 example service starting
2023-12-04T19:24:37+0000 logging_service.py[3140]: [ERROR] 2023-12-04 19:24:37,928 example service error
2023-12-04T19:24:37+0000 systemd[1]: Finished logging_example.service - logging example.

:  19:26:18   armf39  ~
: [1] root $