but due to a number of reasons I need to run very large job via monthly cron initiated script. How do I avoid the need to supply credentials? cron job will be run as root
Have you considered dividing and conquering your very large job using Summary Indexing? This may remove the need for a monthly cron job altogether.
See http://answers.splunk.com/questions/10123/splunk-add-user-non-interactive-without-logging-in-on-comm...
