to edit the crontab of a user
sudo crontab -u username -e
root crontab:
sudo crontab -e
send ALL (even errors) to null:
* * * * * root /usr/local/sbin/mycommand.sh > /dev/null 2>&1
send only normal output to null (will still email errors):
* * * * * root /usr/local/sbin/mycommand.sh > /dev/null
