A checklist for debugging cronjobs

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This is a non-exhaustive list of gotchas that I’ve found myself run into time and again when I have to put a scraper or a model on a cron job. By following these steps you should be able to debug your cronjob and get it to work as expected.

So, let’s say you have set a Python script as a cron-job,

  1. First, make sure the shebang is the first line to your script:

    #!/usr/bin/env

  2. Check if the script has execution rights, if not, run:

    chmod +x <script-name>.py

  3. Now, check if script runs with just the script name:

    ./<script-name>.py

  4. Use this command to go into the bash prompt and try step 3: env -i /bin/bash --noprofile --norc

    This should give you an fair idea of why your script is not running. Cron executes commands in a different shell and within an empty environment, so without absolute paths it wouldn’t even have access to the user’s version of Python. Hence, its always a better idea to use absolute paths to refer to the script in the cron job and for every file that the Python script uses.

  5. Oftenly, in bash environment the python keyword is aimed at the local version of Python. At this point, it can be a good idea to add the output of $PATH as the first line of the crontab. Make sure to leave no gap between the “=” sign, like so: SHELL=/bin/sh PATH=/home/user/anaconda3/bin

If the problem still persists, take a long break and head out to stackoverflow.

All the best.

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