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<!-- $Id: ulogd.sgml 5846 2005-07-12 15:33:23Z laforge $ -->

<article>

<title>ULOGD - the Userspace Logging Daemon</title>
<author>Harald Welte &lt;laforge@gnumonks.org&gt</author>
<date>Revision $Revision: 5846 $, $Date: 2005-07-12 17:33:23 +0200 (Tue, 12 Jul 2005) $</date>

<abstract>
This is the documentation for <tt>ulogd</tt>, the Userspace logging daemon.
ulogd makes use of the Linux &gt;= 2.4.x packet filter subsystem (iptables) and
the ULOG target for iptables.
</abstract>

<toc>

<sect>DESIGN

<sect1>CONCEPT
<p>
I want to provide a flexible, almost universal logging daemon for my netfilter 
ULOG target. It is not optimized in any way, the goal is to keep as simple as 
possible. These are my thoughts about how the architecture which is most 
capable of doing that:
<p>
<descrip>
<tag>Interpreter plugins</tag>
It should be possible to add plugins / runtime modules for new protocols, etc.
For example the standard logging daemon provides source-ip, dest-ip, 
source-port, dest-port, etc. Logging for various other protocols (GRE, 
IPsec, ...) may be implemented as modules.

<tag>Output plugins</tag>
... describe how and where to put the information gained by logging plugins. 
The easiest way is to build a line per packet and fprint it to a file. 
Some people might want to log into a SQL database or want an output 
conforming to the intrusion detection systems communication draft from the
IETF.

</descrip>

<sect1>DETAILS
<p>
The major clue is providing a framework which is as flexible as possible. 
Nobody knows what strange network protocols are out there :) Flexibility
depends on the communication between the output of the logging plugins 
and input of the output plugins.
<p>
Rusty advised me to use some kind of type-key-value triples, which is in fact
what I implemented.
<p>
One issue is, of course, performance. Up to ulogd 0.3, ulogd did several
linked list iterations and about 30 malloc() calls _per packet_. This 
changed with the new &gt;= 0.9 revisions:
<itemize>
<item>Not a single dynamic allocation in the core during runtime. 
Everything is pre-allocated at start of ulogd to provide the highest
possible throughput.
<item>Hash tables in addition to the linked lists. Linked lists are only
traversed if we really want to access each element of the list.
</itemize>

<sect>INSTALLATION
<p>
<sect1>Linux kernel
<p>
First you will need a recent 2.4.x kernel.  If you have a kernel &gt;=
2.4.18-pre8, it already has the kernel support for ULOG (ipt_ULOG.o).
<p>
If you have an older kernel version (between 2.4.0 and 2.4.18-pre6), you
can use the patch-o-matic system of netfilter/iptables, as described in
the following section.

<sect1>ipt_ULOG from netfilter/iptables patch-o-matic
<p>
You only need to read this chapter if you have a 2.4.x kernel &lt;=
2.4.18-pre6.
<p>
In order to put the ipt_ULOG module into your kernel source,you need the latest
iptables package, or even better: the latest CVS snapshot. A description how to
obtain this is provided on the netfilter
homepage <URL URL="http://www.netfilter.org/">.
<p>
To run patch-o-matic, just type 
<tscreen><verb>
make patch-o-matic
</verb></tscreen>
in the userspace directory of netfilter CVS.

<sect1>ulogd
<sect2>Recompiling the source
<p>
Download the ulogd package from <URL URL="http://ftp.netfilter.org/pub/ulogd/"> and
untar it. 
<p>
If you want to build ulogd with MySQL support, type './configure --with-mysql'. You may also have to specify the path of the mysql libraries using '--with-mysql=path'. To build ulogd without MySQL support, just use './configure'.
<p>
To compile and install the program, call 'make install'.

<sect2>Using a precompiled package
<p>
I also provide a SRPM, which should compile on almost any rpm-based distribution. It is available at <URL URL="http://ftp.netfilter.org/pub/ulogd/">
<p>
Just download the package and do the usual 'rpm --rebuild &lt;file&gt;'.

<sect>Configuration
<sect1>iptables ULOG target
<sect2>Quick Setup
<p>
Just add rules using the ULOG target to your firewalling chain. A very basic
example:
<tscreen><verb>
iptables -A FORWARD -j ULOG --ulog-nlgroup 32 --ulog-prefix foo 
</verb></tscreen>
<p>
To increase logging performance, try to use the
<tscreen><verb>
--ulog-qthreshold N
</verb></tscreen>
option (where 1 &lt; N &lt;= 50). The number you specify is the amount of packets
batched together in one multipart netlink message. If you set this to 20, the
kernel schedules ulogd only once every 20 packets. All 20 packets are then 
processed by ulogd. This reduces the number of context switches between kernel
and userspace.
<p>
Of course you can combine the ULOG target with the different netfilter match
modules.  For a more detailed description, have a look at the netfilter
HOWTO's, available on the netfilter homepage.
<sect2>ULOG target reference
<p>
<descrip>
<tag>--ulog-nlgroup N</tag>
The number of the netlink multicast group to which ULOG'ed packets are sent.
You will have to use the same group number in the ULOG target and ulogd in
order to make logging work.
<tag>--ulog-cprange N</tag>
Copyrange.  This works like the 'snaplen' parameter of tcpdump.  You can specify
a number of bytes up to which the packet is copied.  If you say '40', you will
receive the first fourty bytes of every packet. Leave it to <tt>0</tt>
<tag>--ulog-qthreshold N</tag>
Queue threshold.  If a packet is matched by the iptables rule, and already N
packets are in the queue, the queue is flushed to userspace.  You can use this
to implement a policy like: Use a big queue in order to gain high performance,
but still have certain packets logged immediately to userspace.
<tag>--ulog-prefix STRING</tag>
A string that is associated with every packet logged by this rule.  You can use
this option to later tell from which rule the packet was logged.
</descrip>

<sect2>ipt_ULOG module parameters
<p>
The ipt_ULOG kernel module has a couple of module loadtime parameters which can
(and should) be tuned to accomodate the needs of the application:
<descrip>
<tag>nlbufsiz N</tag>
Netlink buffer size. A buffer of the specified size N is allocated for every
netlink group that is used.  Please note that due to restrictions of the kernel
memory allocator, we cannot have a buffer size &gt; 128kBytes.  Larger buffer
sizes increase the performance, since less kernel/userspace context switches
are needed for the same amount of packets.  The backside of this performance
gain is a potentially larger delay. The default value is 4096 bytes, which is
quite small.
<tag>flushtimeout N</tag> 
The flushtimeout determines, after how many clock ticks (on alpha: 1ms, on
x86 and most other platforms: 10ms time units) the buffer/queue is to be
flushed, even if it is not full.  This can be used to have the advantage of a
large buffer, but still a finite maximum delay introduced.  The default value
is set to 10 seconds.
</descrip>
Example:
<tscreen><verb>
modprobe ipt_ULOG nlbufsiz=65535 flushtimeout=100
</verb></tscreen>
This would use a buffer size of 64k and a flushtimeout of 100 clockticks (1 second on x86).

<sect1>ulogd
<p>
ulogd is what this is all about, so let's describe it's configuration...
<sect2>ulogd configfile syntax reference
<p>
All configurable parameters of ulogd are in the configfile, typically located
at '/etc/ulogd.conf'.
<p>
The following configuration parameters are available:
<descrip>
<tag>nlgroup</tag>
The netlink multicast group, which ulgogd should bind to. This is the same as
given with the '--ulog-nlgroup' option to iptables.
<tag>logfile</tag>
The main logfile, where ulogd reports any errors, warnings and other unexpected conditions. Apart from a regular filename, the following special values can be used; ``syslog'' to log via the unix syslog(3) mechanism.  ``stdout'' to log to stdout.
<tag>loglevel</tag>
This specifies, how verbose the logging to logfile is. Currently defined
loglevels are: 1=debug information, 3=informational messages, 5=noticable
exceptional conditions, 7=error conditions, 8=fatal errors, program abort.
<tag>plugin</tag>
This option is followed by a filename of a ulogd plugin, which ulogd shold load
upon initialization. This option may appear more than once.
<tag>rmem</tag>
Size of the netlink socket receive memory.  You should set this to at least the
size of the kernel buffer (nlbufsiz parameter of the ipt_ULOG module).  Please
note that there is a maximum limit in /proc/sys/net/core/rmem_max which you
cannot exceed by increasing the ``rmem'' parameter.  You may need to raise the
system-wide maximum limit before.
<tag>bufsize</tag>
Size of the receive buffer. You should set this to at least the socket receive buffer (rmem).
</descrip>
<sect2>ulogd commandline option reference
<p>
Apart from the configfile, there are a couple of commandline options to ulogd:
<descrip>
<tag>-h --help</tag>
Print a help message about the commandline options.
<tag>-V --version</tag>
Print version information about ulogd.
<tag>-d --daemon</tag> 
For off into daemon mode.  Unless you are debugging, you will want to use this
most of the time.
<tag>-c --configfile</tag>
Using this commandline option, an alternate config file can be used.  This is
important if multiple instances of ulogd are to be run on a single machine.
</descrip>

<sect>Available plugins
<p>
It is important to understand that ulogd without plugins does nothing.  It will receive packets, and do nothing with them.
<p>
There are two kinds of plugins, interpreter and output plugins.  Interpreter
plugins parse the packet, output plugins write the interpreted information to
some logfile/database/...

<sect1>Interpreter plugins
<p>
ulogd comes with the following interpreter plugins:
<sect2>ulogd_BASE.so
<p>
Basic interpreter plugin for nfmark, timestamp, mac address, ip header, tcp
header, udp header, icmp header, ah/esp header... Most people will want to load
this very important plugin.
<sect2>ulogd_PWSNIFF.so
<p>
Example interpreter plugin to log plaintext passwords as used with FTP and
POP3. Don't blame me for writing this plugin! The protocols are inherently
insecure, and there are a lot of other tools for sniffing passwords... it's
just an example.
<sect2>ulogd_LOCAL.so
<p>
This is a 'virtual interpreter'.  It doesn't really return any information on
the packet itself, rather the local system time and hostname.  Please note that
the time is the time at the time of logging, not the packets receive time.

<sect1>Output plugins
<p>
ulogd comes with the following output plugins:

<sect2>ulogd_OPRINT.so
<p>
A very simple output module, dumping all packets in the format
<tscreen><verb>
===>PACKET BOUNDARY
key=value
key=value
...
===>PACKET BOUNDARY
...
</verb></tscreen>
to a file.  The only useful application is debugging.
<p>The module defines the following configuration directives:
<descrip>
<tag>dumpfile</tag>
The filename where it should log to. The default is
<tt>/var/log/ulogd.pktlog</tt>
</descrip>

<sect2>ulogd_LOGEMU.so
<p>
An output module which tries to emulate the old syslog-based LOG targed as far
as possible. Logging is done to a seperate textfile instead of syslog, though.
<p>
The module defines the following configuration directives:
<descrip>
<tag>file</tag>The filename where it should log to. The default is
<tt>/var/log/ulogd.syslogemu</tt>
<tag>sync</tag>Set this to 1 if you want to have your logfile written
synchronously. This may reduce performance, but makes your log-lines appear
immediately.  The default is <tt>0</tt>
</descrip>

<sect2>ulogd_MYSQL.so
<p>
An output plugin for logging into a mysql database. This is only compiled if
you have the mysql libraries installed, and the configure script was able to
detect them. (that is: --with-mysql was specified for ./configure)

<p>
The plugin automagically inserts the data into the configured table; It
connects to mysql during the startup phase of ulogd and obtains a list of the
columns in the table. Then it tries to resolve the column names against keys of
interpreter plugins. This way you can easily select which information you want
to log - just by the layout of the table.

<p>
If, for example, your table contains a field called 'ip_saddr', ulogd will
resolve this against the key 'ip.saddr' and put the ip address as 32bit
unsigned integer into the table.

<p>
You may want to have a look at the file '<tt>doc/mysql.table</tt>' as an
example table including fields to log all keys from ulogd_BASE.so. Just delete
the fields you are not interested in, and create the table.

<p>
The module defines the following configuration directives:
<descrip>
<tag>table</tag>
Name of the table to which ulogd should log.
<tag>ldb</tag>
Name of the mysql database.
<tag>host</tag>
Name of the mysql database host.
<tag>port</tag>
TCP port number of mysql database server.
<tag>user</tag>
Name of the mysql user.
<tag>pass</tag>
Password for mysql.
</descrip>

<sect2>ulogd_PGSQL.so
<p>
An output plugin for logging into a postgresql database. This is only compiled
if you have the mysql libraries installed, and the configure script was able to
detect them. (that is: --with-pgsql was specified for ./configure)

<p>
The plugin automagically inserts the data into the configured table; It
connects to pgsql during the startup phase of ulogd and obtains a list of the
columns in the table. Then it tries to resolve the column names against keys of
interpreter plugins. This way you can easily select which information you want
to log - just by the layout of the table.

<p>
If, for example, your table contains a field called 'ip_saddr', ulogd will
resolve this against the key 'ip.saddr' and put the ip address as 32bit
unsigned integer into the table.

<p>
You may want to have a look at the file '<tt>doc/mysql.table</tt>' as an
example table including fields to log all keys from ulogd_BASE.so. Just delete
the fields you are not interested in, and create the table.

<p>
The module defines the following configuration directives:
<descrip>
<tag>table</tag>
Name of the table to which ulogd should log.
<tag>db</tag>
Name of the database.
<tag>host</tag>
Name of the mysql database host.
<tag>port</tag>
TCP port number of database server.
<tag>user</tag>
Name of the sql user.
<tag>pass</tag>
Password for sql user.
</descrip>

<sect2>ulogd_PCAP.so
<p>
An output plugin that can be used to generate libpcap-style packet logfiles.
This can be useful for later analysing the packet log with tools like tcpdump
or ethereal.

The module defines the following configuration directives:
<descrip>
<tag>file</tag>
The filename where it should log to.  The default is:
<tt>/var/log/ulogd.pcap</tt>
<tag>sync</tag>
Set this to <tt>1</tt> if you want to have your pcap logfile written
synchronously.  This may reduce performance, but makes your packets appear
immediately in the file on disk.  The default is <tt>0</tt>
</descrip>

<sect2>ulogd_SQLITE3.so
<p>
An output plugin for logging into a SQLITE v3 database. This is only compiled
if you have the sqlite libraries installed, and the configure script was able to
detect them. (that is: --with-sqlite3 was specified for ./configure)

<p>
The plugin automagically inserts the data into the configured table; It
opens the sqlite db during the startup phase of ulogd and obtains a list of the
columns in the table. Then it tries to resolve the column names against keys of
interpreter plugins. This way you can easily select which information you want
to log - just by the layout of the table.

<p>
If, for example, your table contains a field called 'ip_saddr', ulogd will
resolve this against the key 'ip.saddr' and put the ip address as 32bit
unsigned integer into the table.

<p>
You may want to have a look at the file '<tt>doc/sqlite3.table</tt>' as an
example table including fields to log all keys from ulogd_BASE.so. Just delete
the fields you are not interested in, and create the table.

<p>
The module defines the following configuration directives:
<descrip>
<tag>table</tag>
Name of the table to which ulogd should log.
<tag>db</tag>
Name of the database.
<tag>buffer</tag>
Size of the sqlite buffer.
</descrip>
</sect2>

<sect2>ulogd_SYSLOG.so
<p>
An output plugin that really logs via syslogd. Lines will look exactly like printed with traditional LOG target.

<p>
The module defines the following configuration directives:
<descrip>
<tag>facility</tag>
The syslog facility (LOG_DAEMON, LOG_KERN, LOG_LOCAL0 .. LOG_LOCAL7, LOG_USER)
<tag>level</tag>
The syslog level (LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO, LOG_DEBUG)
</descrip>
</sect2>

<sect> QUESTIONS / COMMENTS
<p>
All comments / questions / ... are appreciated.
<p>
Just drop me a note to laforge@gnumonks.org
<p>
Please note also that there is now a mailinglist, ulogd@lists.gnumonks.org. 
You can subscribe at
<URL URL="http://lists.gnumonks.org/mailman/listinfo/ulogd/">.
<p> 
The preferred method for reporting bugs is the netfilter bugzilla system,
available at <URL URL="http://bugzilla.netfilter.org/">.

</article>
