Ubuntu Cron Logs – How to Check Cron Logs in Ubuntu

Here's what I did, and it seems to work in this situation. At least, it shows me an error, whereas running from the command line as the user doesn't show the error.

Step 1: I put this line temporarily in the user's crontab:

* * * * *   /usr/bin/env > /home/username/tmp/cron-env

then took it out once the file was written.

Step 2: Made myself a little run-as-cron bash script containing:

#!/bin/bash
/usr/bin/env -i $(cat /home/username/tmp/cron-env) "$@"

So then, as the user in question, I was able to

run-as-cron /the/problematic/script --with arguments --and parameters

This solution could obviously be expanded to make use of sudo or such for more flexibility.

Hope this helps others.

Ideally you'd want your backup script to output nothing if everything goes as expected and only produce output when something goes wrong. Then use the MAILTO environment variable to send any output generated by your script to your email address.

MAILTO=email@example.com
0 */2 * * * /bin/backup.sh

If your script normally produces output but you don't care about it in cron, just sent it to /dev/null and it'll email you only when something is written to stderr.

MAILTO=email@example.com
0 */2 * * * /bin/backup.sh > /dev/null