Below are the tips I keep in mind with respect to crontab file format / configuration on Linux and Unix systems.
- crontab file line layout is:
minute hour day month dayofweek command
- For any one of columns you can use a “*” to match every instance
e.g. * for hour column means every hour (at the exact specified minutes)
- For any one of columns you can use more than one value comma separated
e.g. 1,3,25 is 1,3 or 25 matched
- For any one of columns you can use range of values with hyphen “-”
e.g. 4-7 is 4,5,6,7
- For any one of columns you can define steps.
e.g. */3 in for “day” means once in every three days
- For any one of columns you can combine ranges and values
e.g. 1-3,7,9-12 is actually 1,2,3,7,9,10,11,12
- For any one of “minute hour day month dayofweek” you can define steps in custom ranges
e.g. 2-11/3 is actually 2,5,8,11
For more information you can check the manpages below:
- man crontab ~ for the command usage
- man 5 crontab ~ for the file format & configuration
