The Linux firewall is a great way to secure a server, especially one that is Internet facing. Together with ipset and an appropriate blacklist, it can protect your server from the worst the Internet can throw at it. However, netfilter (aka iptables), can generate a lot of messages. By default they go to the kernel logging channel, flooding out log files such as messages, syslog and kern.log.
It is important to keep log files clear so that system issues are not missed. For example, a hardware or memory error message might be written to kern.log, but could be difficult to notice due to many thousands of firewall messages. Worse, over time, the important message will be moved into a historical log files due to the action of logrotate.
This article explains how to send firewall messages to their own log file, using the example of a Raspberry Pi running Raspbian 9 (Debian Stretch). After a small configuration change, netfilter messages go to their own file instead of clogging up the general logs.Continue reading