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386 lines
14 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<refentry>
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<refmeta>
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<refentrytitle>shorewall-logging</refentrytitle>
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<manvolnum>5</manvolnum>
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<refmiscinfo>Configuration Files</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>logging</refname>
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<refpurpose>Shorewall logging</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command><replaceable>action</replaceable>:<replaceable>level</replaceable></command>
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</cmdsynopsis>
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<cmdsynopsis>
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<command>NFLOG(<replaceable>nflog-parameters</replaceable>)</command>
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</cmdsynopsis>
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<cmdsynopsis>
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<command>ULOG(<replaceable>ulog-parameters</replaceable>)</command>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>The disposition of packets entering a Shorewall firewall is
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determined by one of a number of Shorewall facilities. Only some of these
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facilities permit logging.</para>
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<orderedlist>
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<listitem>
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<para>The packet is part of an established connection. While the
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packet can be logged using LOG rules in the ESTABLISHED section of
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<ulink
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url="manpages/shorewall-rules.html">/etc/shorewall/rules</ulink>, that
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is not recommended because of the large amount of information that may
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be logged.</para>
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</listitem>
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<listitem>
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<para>The packet represents a connection request that is related to an
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established connection (such as a <ulink url="FTP.html">data
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connection associated with an FTP control connection</ulink>). These
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packets may be logged using LOG rules in the RELATED section of <ulink
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url="manpages/shorewall-rules.html">shorewall-rules(5)</ulink>.</para>
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</listitem>
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<listitem>
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<para>The packet is rejected because of an option in <ulink
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url="manpages/shorewall.conf.html">shorewall.conf</ulink>(5) or <ulink
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url="manpages/shorewall-interfaces.html">shorewall-interfaces(5)</ulink>.
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These packets can be logged by setting the appropriate logging-related
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option in <ulink
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url="manpages/shorewall.conf.html">/etc/shorewall/shorewall.conf</ulink>.</para>
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</listitem>
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<listitem>
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<para>The packet matches a rule in <ulink
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url="manpages/shorewall-rules.html">shorewall-rules</ulink>(5). By
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including a syslog level (see below) in the ACTION column of a rule
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(e.g., <quote>ACCEPT<emphasis role="bold">:info</emphasis> net $FW tcp
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22</quote>), the connection attempt will be logged at that
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level.</para>
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</listitem>
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<listitem>
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<para>The packet doesn't match a rule so it is handled by a policy
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defined in <ulink
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url="manpages/shorewall-policy.html">shorewall-policy(5)</ulink>.
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These may be logged by specifying a syslog level in the LOG LEVEL
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column of the policy's entry (e.g., <quote>loc net ACCEPT <emphasis
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role="bold">info</emphasis></quote>).</para>
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</listitem>
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</orderedlist>
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</refsect1>
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<refsect1>
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<title>Default Logging</title>
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<para>By default, Shorewall directs Netfilter to log using syslog (8).
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Syslog classifies log messages by a <emphasis>facility</emphasis> and a
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<emphasis>priority</emphasis> (using the notation
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<emphasis>facility.priority</emphasis>).</para>
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<para>The facilities defined by syslog are <emphasis>auth, authpriv, cron,
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daemon, kern, lpr, mail, mark, news, syslog, user, uucp</emphasis> and
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<emphasis>local0</emphasis> through <emphasis>local7.</emphasis></para>
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<para>Throughout the Shorewall documentation, the term
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<emphasis>level</emphasis> rather than <emphasis>priority is used,
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</emphasis>since <emphasis>level</emphasis> is the term used by Netfilter.
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The syslog documentation uses the term
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<emphasis>priority</emphasis>.</para>
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</refsect1>
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<refsect1>
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<title>Syslog Levels</title>
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<para>Syslog levels are a method of describing to syslog (8) the
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importance of a message. A number of Shorewall parameters have a syslog
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level as their value.</para>
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<para>Valid levels are:</para>
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<simplelist>
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<member>7 - <emphasis role="bold">debug</emphasis> (Debug-level
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messages)</member>
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<member>6 - <emphasis role="bold">info</emphasis>
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(Informational)</member>
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<member>5 - <emphasis role="bold">notice</emphasis> (Normal but
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significant Condition)</member>
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<member>4 - <emphasis role="bold">warning</emphasis> (Warning
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Condition)</member>
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<member>3 - <emphasis role="bold">err</emphasis> (Error
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Condition)</member>
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<member>2 - <emphasis role="bold">crit</emphasis> (Critical
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Conditions)</member>
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<member>1 - <emphasis role="bold">alert</emphasis> (must be handled
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immediately)</member>
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<member>0 - <emphasis role="bold">emerg</emphasis> (System is
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unusable)</member>
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</simplelist>
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<para>For most Shorewall logging, a level of 6 (info) is appropriate.
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Shorewall log messages are generated by Netfilter and are logged using the
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<emphasis>kern</emphasis> facility and the level that you specify. If you
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are unsure of the level to choose, 6 (info) is a safe bet. You may specify
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levels by name or by number.</para>
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<para>Beginning with Shorewall 4.5.5, the <replaceable>level</replaceable>
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name or number may be optionally followed by a comma-separated list of one
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or more<replaceable> log options</replaceable>. The list is enclosed in
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parentheses. Log options cause additional information to be included in
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each log message.</para>
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<para>Valid log options are:</para>
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<variablelist>
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<varlistentry>
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<term><emphasis role="bold">ip_options</emphasis></term>
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<listitem>
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<para>Log messages will include the option settings from the IP
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header.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">macdecode</emphasis></term>
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<listitem>
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<para>Decode the MAC address and protocol.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">tcp_sequence</emphasis></term>
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<listitem>
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<para>Include TCP sequence numbers.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">tcp_options</emphasis></term>
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<listitem>
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<para>Include options from the TCP header.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">uid</emphasis></term>
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<listitem>
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<para>Include the UID of the sending program; only valid for packets
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originating on the firewall itself.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Example: <emphasis
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role="bold">info(tcp_options,tcp_sequence)</emphasis></para>
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<para>Syslogd writes log messages to files (typically in <filename
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class="directory">/var/log/</filename>*) based on their facility and
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level. The mapping of these facility/level pairs to log files is done in
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/etc/syslog.conf (5). If you make changes to this file, you must restart
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syslogd before the changes can take effect.</para>
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<para>Syslog may also write to your system console. See <ulink
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url="FAQ.htm#faq16">Shorewall FAQ 16</ulink> for ways to avoid having
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Shorewall messages written to the console.</para>
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</refsect1>
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<refsect1>
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<title>Configuring a Separate Log for Shorewall Messages (ulogd)</title>
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<para>There are a couple of limitations to syslogd-based logging:</para>
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<orderedlist>
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<listitem>
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<para>If you give, for example, kern.info its own log destination then
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that destination will also receive all kernel messages of levels 5
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(notice) through 0 (emerg).</para>
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</listitem>
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<listitem>
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<para>All kernel.info messages will go to that destination and not
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just those from Netfilter.</para>
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</listitem>
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<listitem>
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<para>Netfilter (Shorewall) messages show up in
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<command>dmesg</command>.</para>
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</listitem>
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</orderedlist>
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<para>If your kernel has NFLOG target support (and most vendor-supplied
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kernels do), you may also specify a log level of NFLOG (must be all caps).
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When NFLOG is used, Shorewall will direct Netfilter to log the related
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messages via the NFLOG target which will send them to a process called
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<quote>ulogd</quote>. The ulogd program is included in most
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distributions.</para>
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<note>
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<para>The NFLOG logging mechanism is <emphasis
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role="underline">completely separate</emphasis> from syslog. Once you
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switch to NFLOG, the settings in <filename>/etc/syslog.conf</filename>
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have absolutely no effect on your Shorewall logging (except for
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Shorewall status messages which still go to syslog).</para>
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</note>
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<para>You will need to change all instances of log levels (usually
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<quote>info</quote>) in your Shorewall configuration files to
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<quote>NFLOG</quote> - this includes entries in the policy, rules and
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shorewall.conf files. If you initially installed using Shorewall 5.1.2 or
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later, you can simply change the setting of LOG_LEVEL in
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shorewall.conf.</para>
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</refsect1>
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<refsect1>
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<title>Understanding the Contents of Shorewall Log Messages</title>
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<para>For general information on the contents of Netfilter log messages,
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see <ulink
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url="http://logi.cc/en/2010/07/netfilter-log-format/">http://logi.cc/en/2010/07/netfilter-log-format/</ulink>.</para>
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<para>For Shorewall-specific information, see <ulink
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url="/FAQ.htm#faq17">FAQ #17</ulink>.</para>
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</refsect1>
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<refsect1>
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<title>Customizing the Content of Shorewall Log Messages</title>
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<para>In a Shorewall logging rule, the log level can be followed by a
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<firstterm>log tag</firstterm> as in "DROP:NFLOG:junk". The generated log
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message will include "<emphasis>chain-name</emphasis> junk DROP".</para>
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<para>By setting the LOGTAGONLY option to Yes in <ulink
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url="/manpages/shorewall.conf.html">shorewall.conf(5)</ulink> or <ulink
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url="/manpages6/shorewall6.conf.html">shorewall6.conf(5)</ulink>, the
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disposition ('DROP' in the above example) will be omitted. Consider the
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following rule:</para>
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<programlisting>#ACTION SOURCE DEST PROTO
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REJECT(icmp-proto-unreachable):notice:IPv6 loc net 41 # who's using IPv6 tunneling</programlisting>
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<para>This rule generates the following warning at compile time:</para>
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<simplelist>
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<member>WARNING: Log Prefix shortened to "Shorewall:IPv6:REJECT(icmp-p "
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/etc/shorewall/rules (line 212)</member>
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</simplelist>
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<para>and produces the rather ugly prefix "Shorewall:IPv6:REJECT(icmp-p
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".</para>
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<para>Now consider this similar rule:</para>
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<programlisting>#ACTION SOURCE DEST PROTO
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REJECT(icmp-proto-unreachable):notice:IPv6,tunneling loc net 41 # who's using IPv6 tunneling</programlisting>
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<para>With LOGTAGONLY=Yes, no warning is generated and the prefix becomes
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"Shorewall:IPv6:tunneling:"</para>
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<para>See the <ulink url="shorewall.conf.html">shorewall[6].conf man
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page</ulink> for further information about how LOGTAGONLY=Yes can be
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used.</para>
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</refsect1>
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<refsect1>
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<title>Log Backends</title>
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<para>Netfilter logging allows configuration of multiple backends. Logging
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backends provide the The low-level forward of log messages. There are
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currently three backends:</para>
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<variablelist>
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<varlistentry>
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<term>LOG (ipt_LOG and ip6t_LOG).</term>
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<listitem>
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<para>Normal kernel-based logging to a syslog daemon.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>ULOG (ipt_ULOG)</term>
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<listitem>
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<para>ULOG logging as described ablve. Only available for
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IPv4.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>netlink (nfnetlink_log)</term>
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<listitem>
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<para>The logging backend behind NFLOG, defined above.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>The currently-available and currently-selected IPv4 and IPv6
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backends are shown in /proc/sys/net/netfilter/nf_log:</para>
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<programlisting>cat /proc/net/netfilter/nf_log
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0 NONE (nfnetlink_log)
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1 NONE (nfnetlink_log)
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2 ipt_ULOG (ipt_ULOG,ipt_LOG,nfnetlink_log)
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3 NONE (nfnetlink_log)
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4 NONE (nfnetlink_log)
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5 NONE (nfnetlink_log)
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6 NONE (nfnetlink_log)
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7 NONE (nfnetlink_log)
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8 NONE (nfnetlink_log)
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9 NONE (nfnetlink_log)
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10 ip6t_LOG (ip6t_LOG,nfnetlink_log)
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11 NONE (nfnetlink_log)
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12 NONE (nfnetlink_log)</programlisting>
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<para>The magic numbers (0-12) are Linux address family numbers (AF_INET
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is 2 and AF_INET6 is 10).</para>
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<para>The name immediately following the number is the currently-selected
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backend, and the ones in parentheses are the ones that are available. You
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can change the currently selected backend by echoing it's name into
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/proc/net/netfilter/nf_log.<replaceable>number</replaceable>.</para>
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<para>Example - change the IPv4 backend to LOG:</para>
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<programlisting>sysctl net.netfilter.nf_log.2=ipt_LOG</programlisting>
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<para>Beginning with Shorewall 4.6.4, you can configure the backend using
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the LOG_BACKEND option in <ulink
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url="manpages/shorewall.conf.html">shorewall.conf(5)</ulink> and <ulink
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url="manpages6/shorewall6.conf.html">shorewall6.conf(5)</ulink>.</para>
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</refsect1>
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<refsect1>
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<title>SEE ALSO</title>
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<para><ulink
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url="/shorewall_logging.htm">http://www.shorewall.net/shorewall_logging.html</ulink></para>
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</refsect1>
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</refentry>
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