cron - Cannot run bash script from crontab when it works from command line bash

Question

I have a strange problem of being to able to run a bash script from commandline but not from the crontab entry for root. I am running Ubuntu 12.04.

* * * * 1-5 root /home/xxxxxx/jmeter/VerificationService-0.0.1-SNAPSHOT/jmeter-cron-randomise.sh >> /home/xxxxxxx/jmeter/VerificationService-0.0.1-SNAPSHOT/cron.log

If I run the script from the cmd line using bash, it works fine but sh fails with following error:

> jmeter-cron-randomise.sh: 7: jmeter-cron-randomise.sh: arithmetic
> expression: expecting primary: "  % 1 "

Having googled the problem, it seems like standard shell doesn't have the same math operators, like % (modulus), as bash. I'm Not sure why the cron job is failing in the script? I am assuming it is because it's not using the bash shell? It's definitely being fired by the cron daemon (can see it in /var/log/syslog). Any help much appreciated.

Answer 1

You likely need to tell cron that the shell to use is the bash shell as it defaults to sh. You can do that for all crontab entries by putting this line in your crontab:

SHELL=/bin/bash

Note that this will cause all scripts in the crontab to be run under bash which may not be what you want. If you want to change the crontab line itself to just run bash, change it to this:

* * * * 1-5 root /bin/bash /home/xxxxxx/jmeter/VerificationService-0.0.1-SNAPSHOT/jmeter-cron-randomise.sh >> /home/xxxxxxx/jmeter/VerificationService-0.0.1-SNAPSHOT/cron.log 2>&1

Note that I have also caused stderr to be written to the cron.log file (2>&1) which may not be what you want but is pretty common practice. This may help you further diagnose errors from the script.