Limiting the size of system.log and exception.log files
http://linux.die.net/man/8/logrotate
Follow this i think it will help you to solve your issue :-
cd /etc/logrotate.d/
vim magento-logrotate.conf
now add the following to the magento-logrotate.conf
file:
/path/to/magento/var/log/*log {
rotate 7
daily
compress
missingok
notifempty
}
execute your configuration now:
logrotate -f /etc/logrotate.d/magento-logrotate.conf