systemd中的Python脚本：虚拟环境还是真实环境

Question

I have been trying to run a python script on start-up (on a Pi). I initially did this via an .sh script triggered by cron.

Posting with a problem on StackExchange Pi ( https://raspberrypi.stackexchange.com/questions/110868/parts-of-code-not-running-when-autostarting-script-in-crontab ) the suggestion is to use systemd.

The person helping me there has suggested not using a virtual environment when executing the Python script (they note their limited familiarity with Python), and using the real environment instead. But other resources strongly suggest the use of a virtual environment (eg https://docs.python.org/3/tutorial/venv.html ).

In the hope of setting this up correctly could anyone weigh in on the correct approach?

Answer 1

systemd is going to try to run your script on startup so your virtual environment will not have been activated yet. You can (maybe) avoid that issue by telling systemd to use the python in the virtualenv's bin, with the appropriate environment variables. Or you can activate as a pre-run step for that script's launch in systemd. Maybe.

But on balance I'd make it easy on systemd and your OS and ignore the virtualenv absolutists. Get the script to work on your dev machine using virtualenv all you want, but then prep systemd to use the global python, with suitable packages installed. You can always use virtualenvs on that pi, for scripts that don't have to work with systemd. Systemd doesn't always have the clearest error messages.

This answer is certainly opinion-based.

Answer 2

Use the virtual environment. I don't see any reason not to. At some point you might want to have multiple Python applications run at the same time on that system, and these applications might require different versions of the same dependency and then you would be back to square one, so... Use the virtual environment.

When configuring systemd , crontab , or whatever, make sure to use the python binary that is placed inside the virtual environment's bin directory, so that there is no need to activate the virtual environment:

/path/to/venv/bin/python -m my_executable_module

/path/to/venv/bin/python /path/to/my_script.py

/path/to/venv/bin/my_executable_script