The cron facility consists of crond, the cron daemon, and crontab files containing job-scheduling information.
cron is intended for the execution of commands on a periodic basis.
crond examines all crontab files every minute.
Each system user has access to cron through a personal crontab file.
The crontab command allows the crontab file to be viewed and, with the –e option, edited.
Entries in the crontab file are in the form of:
minute hour day month dayofweek command
Asterisks in any of the time fields match all possible values.
In addition to personal crontab files, the system has its own crontab files in /etc/crontab, as well as files in /etc/cron.d.