File structure with tasks for CronTab:
* * * * * command - - - - - | | | | | | | | | +----- Day (0 - 6) (Sunday=0) | | | +------- Month (1 - 12) | | +--------- Day of month (1 - 31) | +----------- Hour (0 - 23) +------------- Minute (0 - 59)
01 * * * * command - launch a program or script every hour in one minute
* 6 * * * command - launch a program or script each day at 6 o'clock in the morning
Values can be a number, three letters name, as well as a range such as "1-5" in the day field will mean "Monday through Friday.
Values can be separated by commas: "1,15,31" in the field day will run the specified command the 1st, 15th and 31th of each month.
All five time fields allow you to use "*", which refers to "use any valid value for this field.
To create jobs, use the commands listed below:
crontab -e - change your crontab file or creates a new
crontab -l - displays content of the existing crontab file
crontab -r - remove your crontab file
crontab -v - display the last time you changed your crontab file
Files with the tasks can be found here:
/usr/lib/cron - main catalog of commands associated with time
/usr/spool/cron/crontabs - catalog of files regular action
/usr/lib/cron/log - logs
/usr/lib/cron/cron.allow - users who are allowed to run the crontab
/usr/lib/cron/cron.deny - users who are banned to run the crontab