Certain processes must be run at a specific time, over and over again. An example of this might be a backup process that is kicked off each night, or a log analyzer that must be run every minute. These processes are run at specific times or on specific days; the rest of the time, they are not running.
cron starts from either rc or rc.local, forks, and puts itself in the background. There is no need to background this command. cron searches /var/spool/cron for entries that match users in the /etc/passwd file; found entries are loaded into memory. cron also searches /etc/crontab for system entries.
cron "wakes up" once a minute and does several things:
It checks the entries that it knows about and runs any ...