Script produces different result when executed by Bash than by cron

Question

Please consider following crontab (root):

SHELL=/bin/bash
...
...
0 */3 * * * /var/maintenance/raid.sh

And the bash script /var/maintenance/raid.sh:

#!/bin/bash

echo -n "Checking /dev/md0... "
if ! [ $(mdadm --detail /dev/md0 | grep -c "active sync") -eq 2 ]; then
    mdadm --detail /dev/md0 | mail -s "Raid problem /dev/md0" "my@email.com";
    echo "ERROR"
else 
    echo "ALL OK"
fi;

#-------------------------------------------------------

echo -n "Checking /dev/md1... "
...

And this is what happen when...

...executed from shell prompt (bash):

Mail with mdadm --detail /dev/md0 output is sent to my email (proper behaviour)

...executed by cron:

Blank mail is sent to my email (subject is there, but there is no message)

Why such difference and how to fix it?

What if you put the full path of all the commands? Crontab does have different environment variables than the normal user (root in this case). — fedorqui, Sep 20 '13 at 08:25

score 5 · Accepted Answer · edited Jun 02 '19 at 01:07

5

As indicated in the comments, do use full paths on crontab scripts, because crontab does have different environment variables than the normal user (root in this case).

In your case, instead of mdadm, /sbin/mdadm makes it.

How to get the full path of a command? Using the command command -v:

$ command -v rm
/bin/rm

edited Jun 02 '19 at 01:07

jww

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answered Sep 20 '13 at 08:38

fedorqui

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1

If the command is not already in a directory listed in `PATH`, `which` will not find it for you. – chepner Sep 20 '13 at 16:28

score 3 · Answer 2 · edited Sep 20 '13 at 08:35

3

cron tasks run in a shell that is started without your login scripts being run, which set up paths, environment variables etc.

When building cron tasks, prefer things like absolute paths and explicit options etc

edited Sep 20 '13 at 08:35

fedorqui

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answered Sep 20 '13 at 08:25

Bohemian

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score 3 · Answer 3 · answered Jun 02 '19 at 01:06

3

Before running your script as a cron job, you can test it with no environment variables using env -i

env -i /var/maintenance/raid.sh

answered Jun 02 '19 at 01:06

Cole Tierney

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`cron` jobs are usually executed as a different user than when the script is developed. It seems like you would need something like `env -u root -i /var/maintenance/raid.sh` to accurately test it. – jww Jun 02 '19 at 01:10

Script produces different result when executed by Bash than by cron

3 Answers3

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