Different options for Crontab
crontab -e Edit your crontab file, or create one if it doesn’t already exist.
crontab -r Remove your crontab file.
crontab -v Display the last time you edited your crontab file. (This option is only available on a few systems.)
Understanding and Setting crontab environment
An active line in a crontab will be either an environment setting or a cron command. An environment setting is of the form,
The MLS_LEVEL environment variable provides support for multiple per- job SELinux security contexts in the same crontab.
Few environment variable can be defined in the cronfile. By default cron jobs do not consider USER defined variables, but you can explicitly tell it to use user defined variables.
0 5 * * * . $HOME/.profile; /path/to/command/to/run
Cron expression and fields
Field Allowed Values ----- -------------- Minute 0-59 Hour 0-23 Day of Month 1-31 Month 1-12, jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec Day of Week 0-7, sun, mon, tue, wed, thu, fri, sat (0 and 7 are "sun")