Become superuser.
Edit the /etc/cron.d/at.deny file and add the names of users, one per line, who will be prevented from using at commands.
daemon bin smtp nuucp listen nobody noaccess username1 username2 username3 . . . |
The following example shows an at.deny file that has been edited so that the users smith and jones may not access the at command.
$ cat at.deny daemon bin smtp nuucp listen nobody noaccess jones smith |