Example:
MAILTO="your email@youremail.com"
0 */6 * * * root apt-get update && apt install upgrade -y && apt-get -y -d full-upgrade && apt-get autoremove -y
or
sudo apt-get update && sudo apt-get full-upgrade -y && sudo apt autoremove -y
The email address and command lines should take up two lines, with the email being on the first and the command being on the second. You can use https://crontab-generator.org/ to help generate your command.
Default layout format:
[minute] [hour] [day_of_month] [month] [day_of_week] [user] [command_to_run]
Setting things up
Bring your system up to date
sudo apt-get update
sudo apt-get upgrade -y
Install the corn apt service
sudo apt install cron cron-apt -y
Edit the /etc/crontab file
sudo nano /etc/crontab
Restart the cron system service
sudo systemctl enable cron