Cron: Only get errors in emails?

Question

I finally set up a realistic backup schedule on my data through a shell script, which are handled by cron on tight intervals. Unfortunately, I keep getting empty emails each time the CRON has been executed and not only when things go wrong.

Is it possible to only make CRON send emails when something goes wrong, ie. my TAR doesn't execute as intended?

Here's how my crontab is setup for the moment;

0 */2 * * * /bin/backup.sh 2>&1 | mail -s "Backup status" email@example.com

Thanks a lot!

Answer 1

Ideally you'd want your backup script to output nothing if everything goes as expected and only produce output when something goes wrong. Then use the MAILTO environment variable to send any output generated by your script to your email address.

MAILTO=email@example.com
0 */2 * * * /bin/backup.sh

If your script normally produces output but you don't care about it in cron, just sent it to /dev/null and it'll email you only when something is written to stderr.

MAILTO=email@example.com
0 */2 * * * /bin/backup.sh > /dev/null

Answer 2

You are specifically instructing cron to always send email, even when /bin/backup.sh (don't put it there btw) succeeds. Just omit the | mail -s "Backup status" email@example.com part and email will only be sent when there is output. You can probably (depending on your cron) explicitly set the email address to mail to as an assignment in the crontab file.

For details, see

man 5 crontab

Answer 3

You should be directing the stderr anmd not both stdout and stderr.

Use 1> /dev/null not 2>&1 and it should be fine. Also, you may need to report the error correctly in your backup script.

Answer 4

Cronic (http://habilis.net/cronic/) looks like a good idea; to use it you don't have to change your scripts.