Bash – Is this redirecting to /dev/null

Make the line this:

* * * * *       root    /usr/local/sbin/mycommand.sh > /dev/null 2>&1

This will capture both STDOUT (1) and STDERR (2) and send them to /dev/null.

MAILTO

You can also disable the email by setting and then resetting the MAILTO="" which will disable the sending of any emails.

Example

MAILTO=""
* * * * *       root    /usr/local/sbin/mycommand.sh > /dev/null 2>&1

MAILTO="admin@somedom.com"
 * * * * *      root    /usr/local/sbin/myothercommand.sh

Additional messaging

Often times you'll get the following types of messages in /var/log/syslog:

Nov 11 08:17:01 manny CRON[28381]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)

These are simply notifications via cron that a directory of cronjobs was executed. This message has nothing to do directly with these jobs, instead it's coming from the crond daemon directly. There isn't really anything you can do about these, and I would encourage you to not disable these, since they're likely the only window you have into the goings on of crond via the logs.

If they're very annoying to you, you can always direct them to an alternative log file to get them out of your /var/log/syslog file, through the /etc/syslog.conf configuration file for syslog.

There are two streams of output from a process that are generally sent to the terminal: standard output (which is bound to file descriptor 1), and standard error (which is bound to file descriptor 2). This allows for easily separated capture of expected output, and error messages or other diagnostic information that is not generally expected to be output.

When you use the redirect (>), that only kicks standard output to the specified file or location, leaving standard error untouched. This allows you to see if there are errors (like those you are seeing).

If you want to send all output, including standard error, you need to redirect both streams:

/path/to/program arg1 arg2 > /dev/null 2>&1

Or, alternatively but more explicitly:

/path/to/program arg1 arg2 > /dev/null 2> /dev/null

The syntax 2>&1 means "Send output currently going to file descriptor 2 to the same place that output going to file descriptor 1 is going to". > is omitting the default of FD1, so it is semantically the same as 1>, which might make 2> make more sense.