UNIX for Dummies Questions & Answers

Dear *nix users.

I'm on Mac OS 10.6 / Terminal and try to use crontab to schedule two scripts every 30 minutes and every 41 minutes.

I followed the man instructions and created / installed a crontab file for the current user:crontab -e

with the following content

Code:

*/30 * * * * /usr/local/bin/Script1.sh
*/41 * * * * /usr/local/bin/Script2.sh

Here is the problem: Script1 runs every half hour and Script2 runs every 41th minute of each hour. But both scripts run at each full hour. I don't understand why. What's going wrong?

Best wishes, M.

Step values (like your /41) don't cross hourly (or daily, monthly, etc.) boundaries, so come the next hour it starts over. So there's often little point in having a step value greater than 30 which also isn't nicely divisible into 60 (for minutes) if you want a job to run at a fixed interval.

For example, using /25

Code:

$ crontab -l
*/25 * * * * /bin/date >> /tmp/date.txt

$ tail -f /tmp/date.txt 
Fri Dec  7 12:25:00 CET 2012
Fri Dec  7 12:50:00 CET 2012
Fri Dec  7 13:00:00 CET 2012
Fri Dec  7 13:25:00 CET 2012

Ah, this is the problem. I've just assumed: every 41 minutes is what it says.
I try to figure out a better scheduling approach. Thank you Scott.

For odd times like this, what is sometimes done is running the job more often than needed, and having the job check the time itself. If it's not what you wanted, quit early.

Thank you for your hint Corona688.
This time, however, I content myself with easy solution.
Not perfect, but acceptable

Code:

0,30 * * * * /usr/local/bin/Script1.sh
15,45 * * * * /usr/local/bin/Script2.sh