Third cron field doesn't seem to work (job runs when I don't want it to)

Question

I scheduled a job like this:

*   *    6-8  *  1-5  echo "test" >>/tmp/test.log 2>&1

I expect this job to run only on 6th,7th,8th, these 3 days. but today is 18th, it still runs. What is wrong with this job? What shall I do if I want it to run a some specific days?

Answer 1

The day-of-month and day-of-week positions are OR'd, so in your example, the cron will run on the 6th, 7th, or 8th or Monday through Friday. Since the 18th is a Monday, it runs. It's not exactly intuitive.

To get the behavior I think you desire (run on the 6th, 7th, and 8th if they are a weekday), then you can do something like this:

* * * * 1-5 date '+%d' | grep '[678]' && echo "test" >>/tmp/test.log 2>&1

Answer 2

The day-of-the-month specification (field-3; one-relative) and the day-of-the-month field (5) are both specified. In this case, a match for either means that your crontab runs.