crontab still sending emails even with > /dev/null

Question

I have a crontab (root) that runs a script and output is set to > /dev/null but I always get the emails whenever it runs. I only want to receive error emails.

# Rackspace driveclient update (12pm MST)
0 12 * * * /root/scripts/driveclient-update > /dev/null

The only way I can get it to turn off is to use > /dev/null 2>&1 but then I won't get error emails. This is happening on three different CentOS servers, two are 6.3 and one is 6.4.

NOTE: I have read over and over that > /dev/null is supposed to send stdout there and prevent the email if there is nothing but stdout from the script, so at works for at least some people; I cannot figure out why it is not working on these servers.

Here's an example of where > /dev/null is supposed to work:

Using the MAILTO variable

The MAILTO variable allows you to set the email address that the notification emails from Cron are sent to. You can suppress all emails from your Cron jobs by setting this to an empty string like so:

$ crontab -e

Now on the top of the file, add:

MAILTO=""

Then save and close the file.

Sending output to /dev/null

The /dev/null location in Linux is a "black hole" for data: any output sent here is gone, which makes it a great candidate for suppressing output from Cron jobs.

To suppress all output (STDOUT and STDERR) from your Cron job, append > /dev/null 2>&1 to the end of your job:

$ crontab -e

Example:

*/30 * * * * command  > /dev/null 2>&1

The number 2 represents the STDERR (standard error) stream, while 1 is the STDOUT (standard out) stream.

If you want to receive emails about errors only but not successes, append > /dev/null to your job to suppress output from STDOUT only:

*/30 * * * * command > /dev/null

Originally from alphadevx.com - Suppressing Cron Job Email Notifications (link is now dead)

Answer 1

Set MAILTO="[email protected]" in the crontab file. And let your script 'echo' stderr or stderr when exceptions are thrown by a $(subshell). Anything can happen, so work with return values (0 is OK, anything else is an exception) like in this example:

#!/bin/bash
return=$(/usr/bin/curl --silent --show-error --fail "http://server/somestate" 2>&1)
exitcode=$?
if [ $exitcode != 0 ]
then
    echo "ERROR $HOSTNAME $0 $exitcode $return"
    logger "ERROR $HOSTNAME $0 $exitcode $return"
    exit $exitcode
else
    logger "INFO $HOSTNAME $0 $exitcode $return"
    exit 0
fi

Answer 2

> only redirects std out/err, email is an internal function to the script most like. check the script -h for optional parameters or rackspace utility documents

Answer 3

I discovered wget and yum send stdout to stderr so I had to pipe everything to log files.

Answer 4

For later referance. You don't have to send everything to a logfile. It is possible to tell bash to also send output on STDERR to /dev/null.

# Rackspace driveclient update (12pm MST)
0 12 * * * /root/scripts/driveclient-update > /dev/null 2>&1

Note that all I did was append 2>&1 to the end of the file.

Answer 5

This is a solution I found a long time ago, use the following in crontab. This assumes you only want an email when the script returns non-zero.

# Rackspace driveclient update (12pm MST)
0 12 * * * if ! out="$(/root/scripts/driveclient-update 2>&1)"; then echo "$out"; fi