Cron and At Daemons

$ sudo systemctl enable cron.service

$ sudo systemctl mask --now atd.service

• 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.