Why crontab scripts are not working? Different environment

Cron passes a minimal set of environment variables to your jobs. To see the difference, add a dummy job like this:

* * * * * env > /tmp/env.output

Wait for /tmp/env.output to be created, then remove the job again. Now compare the contents of /tmp/env.output with the output of env run in your regular terminal.

A common "gotcha" here is the PATH environment variable being different. Maybe your cron script uses the command somecommand found in /opt/someApp/bin, which you've added to PATH in /etc/environment? cron ignores PATH from that file, so runnning somecommand from your script will fail when run with cron, but work when run in a terminal. It's worth noting that variables from /etc/environment will be passed on to cron jobs, just not the variables cron specifically sets itself, such as PATH.

To get around that, just set your own PATH variable at the top of the script. E.g.

#!/bin/bash
PATH=/opt/someApp/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

# rest of script follows

Some prefer to just use absolute paths to all the commands instead. I recommend against that. Consider what happens if you want to run your script on a different system, and on that system, the command is in /opt/someAppv2.2/bin instead. You'd have to go through the whole script replacing /opt/someApp/bin with /opt/someAppv2.2/bin instead of just doing a small edit on the first line of the script.

You can also set the PATH variable in the crontab file, which will apply to all cron jobs. E.g.

PATH=/opt/someApp/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

15 1 * * * backupscript --incremental /home /root

HOW TO LOG CRON JOBS

* * * * * myjob.sh >> /var/log/myjob.log 2>&1

will log all output from the cron job to /var/log/myjob.log