This thread may be of use:

You can create a config file in /etc/newssyslog.d to rotate logs in OS X.

On Fri, Dec 13, 2013 at 9:37 AM, Tom Hendrikx <tom@whyscream.net> wrote:
On 12/13/2013 03:25 PM, USMC Guy wrote:
> I have fail2ban installed on my mac OS X 10.9 Mavericks.  the current
> version of OS X logs ssh attempts to /var/log/system.log. I am running
> fail2ban 0.8.11.  At midnight, when the system.log rolls over making the
> file unavailable for a few seconds, the jail goes into idle and stays
> there.  How can I resolve this?

You should look into the logrotate snippets in the source. You should
configure OS X to do the same thing when it roattaes the logfile. I
don't know how syslog and log rotation is provided on OS X, so can't
really help with that.

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