Cron is a Linux system process that will execute a program at a preset time. To use cron you must prepare a text file that describes the program that you want executed and the times that cron should execute them. Then you use the crontab program to load the text file that describes the cron jobs into cron. via Using cron
crontab -e to edit the crontab file.
[min] [hour] [day of month] [month] [day of week] [program to be run]
10 3 * * * /usr/bin/foo==> Will run /usr/bin/foo at 3:10am on every day.
12 3 * * * root tar czf /usr/local/backups/daily/etc.tar.gz /etc >> /dev/null 2>&1via Cron Help Guide