Cron python job not running

Question

I tried to automate the launch of a python script. After having tested it works in thonny, I moved to Cron and I got quite lost.

I started from calling 12 21 * * * /usr/bin/python3 /home/pi/main.py to 12 21 * * * /usr/bin/python3.5 /home/pi/main.py(with minute and hour value to change accordingly to the time of test) but nothing happens.

I ultimately tried to add the following line: 12 21 * * * (echo "hi" >>/var/log/it_runs.txt) and that indeed print an "hi" in a "it_runs" txt file. That makes me think the problem is with calling python. Do I call python in the wrong way? When debugging with Thonny i set python as 3.5.

Pls and advice is more than accepted Ale

Answer 1

You didn't tell us what your Python script did - or was supposed to do. We try to answer RPi-related questions here, but all of our mind-readers are currently on strike for better wages. So you're left to depend on people like me who need some information to provide answers.

All that said, I'm going to take a guess. I'll answer your question in this way - by a working example that is as similar to yours as I know how to make it:

1. Create a Python script in user pi's home directory;

   $ nano hello.py
   

2. Enter a single line in the editor:

   print("Hello from Python Script Launched run under cron")
   

3. Save & close the editor - check to ensure the file /home/pi/hello.py exists

4. Open your crontab for editing:

   $ crontab -e
   

5. Make the following entry at the bottom of your crontab:

   * * * * * /usr/bin/python3 /home/pi/hello.py >> hellopy.txt 2>&1
   

6. Save & exit the crontab editor - it should confirm that a new crontab has been installed

7. You can see the once-per-minute output as it goes to the output file using tail:

   $ $ tail -f -n 10 hellopy.txt
   Hello from Python Script Launched run under cron
   Hello from Python Script Launched run under cron
   etc, etc, etc
   

   control + c to end the listing (or just use cat instead of tail if you prefer)

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EDIT/ADDENDUM:

To view your user environment:

$ printenv

To view your "cron user's environment", add the following line to your crontab:

@reboot sleep 10; /usr/bin/printenv > /home/pi/cronenv.txt 2>&1

Review the differences between these two environments in light of your Python program.