Cron can be used to schedule the scripts that are to be executed periodically which allows Linux and Unix users to run commands or scripts at a given date and time. It is one of the most useful tools in Linux or UNIX-like operating systems. It is usually used for sysadmin jobs such as backups or cleaning /tmp/ directories and more. Servers can automatically perform tasks otherwise have to perform yourself, such as running scripts. On Linux servers, the cron utility is the preferred way to automate the running of scripts.
Command to list all cronjob as root user
crontab -l