Syslog.conf return to default when I restart the service

[clebersleite]

I want to add this line on my syslog.conf

kern.warning /var/log/iptables.log

but when i put and restart syslog:

/etc/init.d/syslog restart

it is ok, after a quick time syslog.conf back to original

any ideas how to fix it to permanent?