Actually, the 'best' (one could claim) solution is a combination of what @DaveCheney suggested and what user7321 did eventually, plus a third action which I would recommend:
- Preventing syslogd from appending cron-related log messages to /var/log/syslog
- Ensuring cron log messages do get logged somewhere (specifically, in /var/log/cron) + ensuring log rotation for the cron log.
- Preventing syslogd from appending cron-related log messages to /var/log/messages as well
/etc/syslog.conf, the combination of these changes something like
And don't forget to force-reload (or restart) both the cron and syslogd services, e.g. using:
Note: This works with rsyslog.d as well, and probably also with syslog-ng (possibly with some minor tweaking for syntax).