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<title>Shorewall Logging</title>
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2003-07-16 20:59:33 +02:00
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2002-12-29 19:23:07 +01:00
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<meta http-equiv="content-type"
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content="text/html; charset=ISO-8859-1">
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2003-07-16 20:59:33 +02:00
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2002-12-29 19:23:07 +01:00
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<meta name="author" content="Tom Eastep">
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</head>
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<body>
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<table border="0" cellpadding="0" cellspacing="0"
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style="border-collapse: collapse;" bordercolor="#111111" width="100%"
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<tbody>
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<tr>
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<td width="100%">
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<h1 align="center"><font color="#ffffff">Logging</font></h1>
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</td>
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</tr>
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</tbody>
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</table>
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<br>
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By default, Shorewall directs NetFilter to log using syslog (8). Syslog
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classifies log messages by a <i>facility</i> and a <i>priority</i> (using
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the notation <i>facility.priority</i>). <br>
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<br>
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The facilities defined by syslog are <i>auth, authpriv, cron, daemon,
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kern, lpr, mail, mark, news, syslog, user, uucp</i> and <i>local0</i> through
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<i>local7</i>.<br>
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<br>
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Throughout the Shorewall documentation, I will use the term <i>level</i>
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rather than <i>priority</i> since <i>level</i> is the term used by NetFilter.
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The syslog documentation uses the term <i>priority</i>.<br>
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<h3>Syslog Levels<br>
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</h3>
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Syslog levels are a method of describing to syslog (8) the importance
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of a message and a number of Shorewall parameters have a syslog level
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as their value.<br>
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<br>
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Valid levels are:<br>
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<br>
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7
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debug<br>
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6
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info<br>
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5
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notice<br>
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4
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warning<br>
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3
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err<br>
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2
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crit<br>
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1
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alert<br>
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0
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emerg<br>
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<br>
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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
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the <i>kern</i> facility and the level that you specify. If you are unsure
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of the level to choose, 6 (info) is a safe bet. You may specify levels
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by name or by number.<br>
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<br>
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Syslogd writes log messages to files (typically in /var/log/*) based
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on their facility and level. The mapping of these facility/level pairs
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to log files is done in /etc/syslog.conf (5). If you make changes to this
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file, you must restart syslogd before the changes can take effect.<br>
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<h3>Configuring a Separate Log for Shorewall Messages</h3>
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There are a couple of limitations to syslogd-based logging:<br>
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<ol>
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<li>If you give, for example, kern.info it's own log destination then
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that destination will also receive all kernel messages of levels 5 (notice)
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through 0 (emerg).</li>
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<li>All kernel.info messages will go to that destination and not just
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those from NetFilter.<br>
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</li>
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</ol>
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Beginning with Shorewall version 1.3.12, if your kernel has ULOG
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target support (and most vendor-supplied kernels do), you may also specify
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a log level of ULOG (must be all caps). When ULOG is used, Shorewall will
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direct netfilter to log the related messages via the ULOG target which
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will send them to a process called 'ulogd'. The ulogd program is available
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from http://www.gnumonks.org/projects/ulogd and can be configured to log
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all Shorewall message to their own log file.<br>
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<br>
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<b>Note: </b>The ULOG logging mechanism is <u>completely separate</u> from
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syslog. Once you switch to ULOG, the settings in /etc/syslog.conf have absolutely
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no effect on your Shorewall logging (except for Shorewall status messages
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which still go to syslog).<br>
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<br>
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You will need to have the kernel source available to compile ulogd.<br>
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<br>
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Download the ulod tar file and:<br>
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<ol>
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<li>Be sure that /usr/src/linux is linked to your kernel source tree<br>
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</li>
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<li>cd /usr/local/src (or wherever you do your builds)</li>
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<li>tar -zxf <i>source-tarball-that-you-downloaded</i></li>
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<li>cd ulogd-<i>version</i><br>
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</li>
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<li>./configure</li>
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<li>make</li>
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<li>make install<br>
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</li>
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</ol>
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If you are like me and don't have a development environment on your
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firewall, you can do the first six steps on another system then either
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NFS mount your /usr/local/src directory or tar up the /usr/local/src/ulogd-<i>version</i>
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directory and move it to your firewall system.<br>
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<br>
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Now on the firewall system, edit /usr/local/etc/ulogd.conf and set:<br>
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<ol>
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<li>syslogfile <i><file that you wish to log to></i></li>
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<li>syslogsync 1</li>
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</ol>
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I also copied the file /usr/local/src/ulogd-<i>version</i>/ulogd.init
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to /etc/init.d/ulogd. I had to edit the line that read "daemon /usr/local/sbin/ulogd"
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to read daemon /usr/local/sbin/ulogd -d". On a RedHat system, a simple "chkconfig
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--level 3 ulogd on" starts ulogd during boot up. Your init system may need
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something else done to activate the script.<br>
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<br>
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You will need to change all instances of log levels (usually 'info') in
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your configuration files to 'ULOG' - this includes entries in the policy,
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rules and shorewall.conf files. Here's what I have:<br>
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<pre> [root@gateway shorewall]# grep ULOG *<br> policy:loc fw REJECT ULOG<br> policy:net all DROP ULOG 10/sec:40<br> policy:all all REJECT ULOG<br> rules:REJECT:ULOG loc net tcp 6667<br> shorewall.conf:TCP_FLAGS_LOG_LEVEL=ULOG<br> shorewall.conf:RFC1918_LOG_LEVEL=ULOG<br> [root@gateway shorewall]#<br></pre>
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Finally edit /etc/shorewall/shorewall.conf and set LOGFILE=<i><file
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that you wish to log to></i>. This tells the /sbin/shorewall program
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where to look for the log when processing its "show log", "logwatch" and "monitor"
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commands.<br>
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<p><font size="2"> Updated 1/11/2003 - <a href="support.htm">Tom Eastep</a>
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</font></p>
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<p><a href="copyright.htm"><font size="2">Copyright</font> ©
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<font size="2">2001, 2002, 2003 Thomas M. Eastep</font></a><br>
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</p>
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<br>
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</html>
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