Does your cron script run in a bash shell, but not while running under crontab?

This is the scenario: you want to set a cron job and the script you want to use runs correctly when called from the command line, but when you run the same script with crontab, it does not work.

More than likely, this problem is caused by the default shell environment variables setup by crontab. Cron supplies a default (bare) environment for every shell:

HOME=user's-home-directory
LOGNAME=user's-login-id
PATH=/usr/bin:/usr/sbin:.
SHELL=/usr/bin/sh

Here are a few solutions:

• Explicitly enter the needed environment variables.
• Load your .profile in the crontab or in the script called by crontab.
• Use the absolute path for every command run in the script.

Here is a simple test to know exactly what variables are different, or even missing, in the crontab environment:

From the shell prompt, enter:

$ env > /tmp/myenv.log

Then set a cron job to do the same from the crontab.

$crontab -e
* * * * * env > /tmp/crontabenv.log
:wq

This line in the crontab will execute every minute, and store the environment variables in /tmp/crontabenv.log . diff both files to find the differences.

For more info about how to edit and use the crontab do: $man crontab

• Crontab - Quick reference
• crontab - schedule periodic background work
• Crontab command descriptions

tags: linux  crontab  command line  

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