UNIX cron

Every user can have its own list of cron jobs which can be viewed using 

crontab -l

In order to add or edit a cron job , you need to execute the following commands

export EDITOR=vi
crontab -e

Now , you can edit the file as you do while working on a vi editor .

For more tips on vi editor , you can follow the below link authored by me .
http://middlewareplay.appspot.com/kbhtml/Vi_editor.html

Note for new unix users , refrain from running the command crontab -r as this will remove your existing crontab file ( list of all cron jobs ) and there is no way of getting it back until you have the backup of crontab file  ,somewhere .

Below is the list of important  cron files

 /etc/cron.d main cron directory
/etc/cron.d/cron.allow list of allowed users
/etc/default/cron contains cron default settings
/etc/cron.d/cron.deny list of denied users
/var/cron/log accounting information
/var/spool/cron/crontabs spool area for crontab has crontab files for each user.