Become superuser.
Using the editor of your choice, edit the /etc/cron.d/cron.deny file to add user names, one per line, who will be prevented from using crontab commands.
daemon bin smtp nuucp listen nobody noaccess username1 username2 username3 . . . |
Verify the /etc/cron.d/cron.deny file.
# cat /etc/cron.d/cron.deny |