/etc/logrotate.d is subsidiary to /etc/logrotate.conf itself. The "defaults" are defined in /etc/logroate.conf but can be overriden in the specific /etc/logroate.d file.
In RHEL /etc/cron.daily calls the logrotate each day but since the logroate.conf starts with "weekly" the files are usually only actually rotated once a week.
You can override time and size by adding them to /etc/logrotate.d/syslog. For example on our mail server we keep a month's worth of log at a time and keep them for a year so we modified the file to include "monthly" and "rotate 12". You could put size there if you wanted:
Code:
/var/log/cron
/var/log/maillog
/var/log/messages
/var/log/secure
/var/log/spooler
{
monthly
rotate 12
sharedscripts
compress
postrotate
/bin/kill -HUP `cat /var/run/syslogd.pid 2> /dev/null` 2> /dev/null || true
endscript
}