On opensuse 13.2, checking /var/log/messages, there are hundreds of these log
entries

    "pam_unix(crond:session): session closed/open for user root"

    grep "pam_unix(crond:session): session" /var/log/messages | egrep
"open|closed" | grep " for user root" | wc -l
        1094

This, at ubuntu

    Thousands of pam_unix log entries in logwatch
   
https://askubuntu.com/questions/250105/thousands-of-pam-unix-log-entries-in-logwatch

suggests editing

    /etc/pam.d/common-session-noninteractive
        ...
+        session [success=1 default=ignore] pam_succeed_if.so service in cron
quiet use_uid
        session required pam_unix.so
        ...

On opensuse 13.2 there's no such file.

This is useless noise.  How do you quiet that logging down?