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 fails with sh with following error:

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

Having googled the problem it seems like stand shell doesn't have the same maths operators like % (modulus) like bash. Not sure why the cron job is failing in the script? i am assumming its because its 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.

script causing the problems

#!/bin/bash
echo Running the jmeter-cron-randomiser script


script="/home/xxxxxxx/jmeter/VerificationService-0.0.1-SNAPSHOT/jmeter-cron.sh"    

min=$(( 1 * 1 ))
rmin=$(( $RANDOM % $min ))

echo  "min = ${min}";
echo  "rmin = ${rmin}"

at -f "$script" now+${rmin}min

Solution

I note in the crontab(5) man page, this:

The ``sixth'' field (the rest of the line) specifies the command to be run. The entire command portion of the line will be executed by /bin/sh or by the shell specified in the SHELL variable of the cronfile.

So, you may want to specify bash either with

SHELL=/bin/bash

or, as the above affects all cron scripts, this

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

Comments

[MGodby]

Does your script begin with a shebang, i.e. #!/bin/bash ?

[kal]

yes it does #!/bin/bash

[kal]

i think the key is the difference between running the sh and the bash script and why there is an arithmetic exception with sh but not with bash from the command line. I think thats where its failing when its fired from cron.

[MGodby]

This will probably require more information about your script if you want help troubleshooting its behavior.

[kal]

#!/bin/bash echo Running the jmeter-cron-randomiser script script="/home/xxxxx/jmeter/VerificationService-0.0.1-SNAPSHO‌​T/jmeter-cron.sh" min=$(( 1 * 1 )) rmin=$(( $RANDOM % $min )) echo "min = ${min}"; echo "rmin = ${rmin}" at -f "$script" now+${rmin}min '

[MGodby]

Please update your original question and use appropriate formatting for readability.

[kal]

i am varying the times for testing purposes but it basically something i picked up from net for randomly firing off another script in the next x mins/hours etc

[MGodby]

Upon further inspection, I think that $RANDOM does not exist in your script because cron launched from a non-bash shell like you said.

[kal]

yes thats the crux of the problem. when I run from sh $RANDOM is not resolved but is from bash

[Volker Siegel]

What is the exact name of the crontab file? /etc/crontab?

[Alaa Ali]

If you're using root's crontab (that is, if you're editing it using crontab -e while logged in as root), you shouldn't put the username in the cronjob command. Remove the word root before the command. You should only put a username when adding cronjobs in /etc/crontab. And there are a lot of troubleshooting steps you can do here mate. Comment out everything on the script and just put some echo lines that append to a file, like echo $SHELL > /home/xxxxx/tesfile just to see if it actually works. Then add in your script lines but remove the $RANDOM var to see if it works. Troubleshoot.

[kal]

already tried the SHELL=/bin/bash in the crontab entry and also and but no luck.

[kal]

meant to say that i tried the SHELL=/bin/bash in the crontab entry and also the * * * * 1-5 root bash /home/xxxxxx/jmeter/Verif.. but no luck

[kal]

after debugging a little further the problem is with $RANDOM (see above)

[MGodby]

He is running a different script with at, jmeter-cron.sh vs jmeter-cron-randomise.sh

[kal]

yes there are 2 scripts involved here. the flow is cron --> jmeter-cron-randomise.sh ---> jmeter-cron.sh

[Volker Siegel]

@MGodby I see, didn't notice - so he should post that script. By the way, that explains the wrong line number in the error: the % is iin line 8, not 7. So I suspect the other script is similar, with an % expression in line 7.

[Volker Siegel]

@kal can you confirm the line number? Maybe we do not need the other script actually.

[kal]

hurray! the problem is resolved by directly editing the /etc/crontab to use SHELL=/bin/bash

[kal]

thanks for your time guys but i am not sure why its worked with the system wide crontab file?

[Volker Siegel]

Oh, I thought you had said you tried that already a while ago?! But looking closely at the comments on the other question, you did not confirm with "i tried the SHELL=/bin/bash in the crontab", but "i tried the SHELL=/bin/bash in the crontab entry"... tricky...

[Volker Siegel]

You can not use the user column in a different crontab - only in the system crontab.

[Volker Siegel]

@kal So it was the personal crontab of usere root? But then, it should have failed before even starting your script, when trying ro run the command root, right?

[kal]

@VolkerSiegel you can have root user in the root user's crontab file (ie. crontab -e once your logged in as root) but the root user also uses the /etc/crontab or thats what i understands from the docs at link. For some reason the $RANDOM was not being resolved because the root users crontab entry for bash shell etc. were not being honoured and the /etc/crontab are.

[Andrea Corbellini]

@kal: you should include the output you get from cron. By reading the question, it seems like the error you are getting is arithmetic expression: expecting primary. But by reading your comments, it seems you are getting another error

[Andrea Corbellini]

FWIW, the crontab manpage doesn't say that the script is executed by /bin/sh; it says that the command is executed by /bin/sh