Cronjob to run in every 40 days

Question

HI,
I want to schedule one cronjob to run once in every 40 days.
Please suggest what would be exact cronscript for this.
Thanks,
Saurabh

Answer 1

Yeah, an "at" job sitting out there running itself every 40 days isn't going to be easy to keep track of.
On Linux the "date" utility supports the "+%s" format, which is seconds since the epoch. Divide that by 86400 and you have days since the epoch. Something like this:
#!/bin/bash
now=`date "+%s"`
today=$(( $now / 86400 ))
rem=$(( $today % 40 ))Put that in a cron job, and if the remainder is whatever single value you pick, run your job. Else do nothing.
That will run every 40 days.
The "%s" format specification to the date utility is a non-POSIX extension, so it's not available on strictly POSIX-compliant systems. Though it's pretty trivial to write something in C that will emit the current time in seconds since epoch. Perl probably can be used, too.