1. Monday, October 31, 2011 12:00 AM
2. Tuesday, November 1, 2011 12:00 AM ---- (This is immediate day after 31)
3. Thursday, December 1, 2011 12:00 AM
4. Saturday, December 31, 2011 12:00 AM
5. Sunday, January 1, 2012 12:00 AM
I've never seen a slash in a crontab entry. I'm surprised that's not an error.
But...I don't think you can schedule a cron job to run every 30 days. You can pick a day of week or day of the month...but every 30 days requires something to remember the last time it ran. I don't think cron does that.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
I didn't know there was such a class. If you read the api carefully, "1/30" means "run it on the 1st and 30 days after the first" - NOT 'run every 30 days'. I still don't see how to schedule it like you want. It doesn't work that way.
I don't know of a way to do it with cron. You may be able to do it by having a dummy file. When you run, you first check to see if the file is 30 days old or not. If not, shut down. If it is, run the job, then touch the file.