Restrict at and cron to Authorized Users if Necessary

Remove the cron.deny file:

$ sudo rm /etc/cron.deny

Edit /etc/cron.allow, adding one line for each user allowed to use the crontab command to create cron jobs.

Remove the at.deny file:

$ sudo rm /etc/at.deny

Edit /etc/at.allow, adding one line for each user allowed to use the at command to create at jobs.