Jenkins: how to run task every 30 days

Question

Jenkins version is 2.235.5 (I should update it to next LTS version 2.249).

I configured Jenkins to run a job periodically every 30 days: Build Triggers → Build periodically → Schedule:

H 3 */30 * *

And now I see:

Would last have run at Saturday, October 31, 2020 3:20:39 AM EDT; would next run at Sunday, November 1, 2020 3:20:39 AM EST.

So it will be started again after 1 day, not 30 days…

How to run a job periodically every 30 days?

Update: history of Jenkins "predictions" for schedule above (job was created October 28):

Would last have run at Thursday, October 1, 2020 3:20:06 AM EDT; would next run at Saturday, October 31, 2020 3:20:06 AM EDT.

Would last have run at Saturday, October 31, 2020 3:20:39 AM EDT; would next run at Sunday, November 1, 2020 3:20:39 AM EST.

Would last have run at Sunday, November 1, 2020 3:20:43 AM EST; would next run at Tuesday, December 1, 2020 3:20:43 AM EST.

Answer 1

In short, it's not practically possible. This S/O answer is quite detailed.

Jenkins used a cron expression, and the different fields are:

MINUTES Minutes in one hour (0-59)
HOURS Hours in one day (0-23)
DAYMONTH Day in a month (1-31)
MONTH Month in a year (1-12)
DAYWEEK Day of the week (0-7) where 0 and 7 are sunday

cron syntax simply does not support every n days.

An impractical option wuld be to have a daily job with a Conditional BuildStep to calculate if this day is n × 30 days from a given fixed day and abort if not..

But every 30 days doesn't really align w/calendar anyways, so is that really the intent?

Answer 2

Jenkins- scheduled tab change syntax like...

. 30 * * * *

Example for understanding.... similar to cron job