Theres a product called 'logrotate' that performs this task. Though not related to syslog-ng in any way.

-Patrick

Sent: Wed Nov 10 2010 09:58:23 GMT-0700 (Mountain Standard Time)
From: vijay <bhaskarpeddi@gmail.com>
To: Syslog-ng users' and developers' mailing list <syslog-ng@lists.balabit.hu>
Subject: [syslog-ng] clearing log files 
hi all,
    In my system /var/log all syslog files are accumulating.Is there
any way to delete files automatically.


                                                            vijay
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