syslog-ng reference manual

Balázs Scheidler

   Copyright © 1999-2000 by Balázs Scheidler
   
   This manual is free software; you may redistribute it and/or modify it
   under the terms of the GNU General Public License as published by the
   Free Software Foundation; either version 2, or (at your option) any
   later version.
   
   This is distributed in the hope that it will be useful, but without
   any warranty; without even the implied warranty of merchantability or
   fitness for a particular purpose. See the GNU General Public License
   for more details.
     _________________________________________________________________
   
   Table of Contents
   1. Introduction to syslog-ng
   2. Message paths
          
        Sources
        Filters
        Destinations
        Log paths
        Options
                
   3. Reference
          
        Source drivers
                
              internal()
              unix-stream() and unix-dgram()
              tcp() and udp()
              file()
              pipe()
              sun-streams() driver
                      
        Destination drivers
                
              file()
              pipe()
              unix-stream() & unix-dgram()
              udp() & tcp()
              usertty()
              program()
                      
        Filter functions
        Options
                
   4. Performance tuning in syslog-ng
          
        Setting garbage collector parameters
                
              gc_idle_threshold()
              gc_busy_threshold()
                      
        Setting output queue size
        Setting sync parameter
     _________________________________________________________________
   
Chapter 1. Introduction to syslog-ng

   One of the most neglected area of Unix is handling system events.
   Daily checks for system messages is crucial for the security and
   health conditions of a computer system.
   
   System logs contain much "noise" - messages which have no importance -
   and on the contrary important events, which should not be lost in the
   load of messages. With current tools it's difficult to select which
   messages we are interested in.
   
   A message is sent to different destinations based on the assigned
   facility/priority pair. There are 12+8 (12 real and 8 local)
   predefined facilities (mail, news, auth etc.), and 8 different
   priorities (ranging from alert to debug).
   
   One problem is that there are facilities which are too general
   (daemon), and these facilities are used by many programs, even if they
   do not relate each other. It is difficult to find the interesting bits
   from the enourmous amount of messages.
   
   A second problem is that there are very few programs which allow
   setting their "facility code" to log under. It's at best a compile
   time parameter.
   
   So using facilities as a means of filtering is not the best way. For
   it to be a good solution would require runtime option for all
   applications, which specifies the log facility to log under, and the
   ability to create new facilities in syslogd. Neither of these are
   available, and the first is neither feasible.
   
   One of the design principles of syslog-ng was to make message
   filtering much more finegrained. syslog-ng is able to filter messages
   based on the contents of messages in addition to the priority/facility
   pair. This way only the messages we are really interested in get to a
   specific destination. Another design principle was to make
   logforwarding between firewalled segments easier: long hostname
   format, which makes it easy to find the originating and chain of
   forwarding hosts even if a log message traverses several computers.
   And last principle was a clean and powerful configuration file format.
     _________________________________________________________________
   
Chapter 2. Message paths

   In syslog-ng a message path (or message route) consist of one or more
   sources, one or more filtering rules and one or more destinations
   (sinks). A message is entered to syslog-ng in one of its sources, if
   that message matches the filtering rules it goes out using one of the
   destinations.
     _________________________________________________________________
   
Sources

   A source is a collection of source drivers, which collect messages
   using a given method. For instance there's a source driver for
   AF_UNIX, SOCK_STREAM style sockets, which is used by the Linux
   syslog() call.
   
   To declare a source, you'll need to use the source statement in the
   configuration file with the following syntax:
   
          source <identifier> { source-driver(params); source-driver(params); .
.. };
        
   The identifier has to uniquely identify this given source and of
   course may not clash with any of the reserved words (in case you had a
   nameclash, simply enclose the identifier in quotation marks)
   
   You can control exactly which drivers are used to gather log messages,
   thus you'll have to know how your system and its native syslogd
   communicate. Here's a introduction to the inner workings of syslogd on
   some of the platforms I tested:
   
   Table 2-1. Communication method between syslogd and its clients
   Platform Method
   Linux A SOCK_STREAM unix socket named /dev/log
   BSD flavors A SOCK_DGRAM unix socket named /var/run/log
   Solaris (2.5 or below) An SVR4 style STREAMS device named /dev/log
   Solaris (2.6 or above) In addition to the STREAMS device used in
   versions below 2.6, uses a new multithreaded IPC method called door.
   By default the door used by syslogd is /etc/.syslog_door
   
   Each possible communication mechanism has the corresponding source
   driver in syslog-ng. For instance to open a unix socket with
   SOCK_DGRAM style communication you use the driver unix-dgram, the same
   with SOCK_STREAM style - as used under Linux - is called unix-stream.
   
   Example 2-1. Source statement on a Linux based operating system
          source src { unix-stream("/dev/log"); internal(); udp(ip(0.0.0.0) por
t(514)); };
        
   Each driver may take parameters, some of them required, some of them
   optional. The required parameters are usually positional, which means
   that they have to come first. See the unix-stream driver specification
   above, as it refers to the file /dev/log.
   
   Table 2-2. Available source drivers in syslog-ng
   Name Description
   internal Messages generated internally in syslog-ng
   unix-stream Opens the specified unix socket in SOCK_STREAM mode, and
   listens for messages.
   unix-dgram Opens the specified unix socket in SOCK_DGRAM mode, and
   listens for messages.
   file Opens the specified file, and reads messages.
   pipe, fifo Opens the specified named pipe and reads messages
   udp Listens on the specified UDP port for messages.
   tcp Listens on the specified TCP port for messages.
   sun-stream, sun-streams Opens the specified STREAMS device on Solaris
   systems, and reads messages.
   
   For a complete descriptions on the above drivers, see the reference
   section.
     _________________________________________________________________
   
Filters

   Filters perform log routing inside syslog-ng. You can write a boolean
   expression using internal functions, which has to evaluate to true for
   the message to pass.
   
   Filters have also a uniquely identifying name, so you can refer to
   filters in your log statements. Syntax for the filter statement:
          filter <identifier> { expression; };
        
   An expression may contain the operators "and", "or" and "not", and any
   of the functions listed below.
   
   Example 2-2. A filter statement finding the messages containing the
   word deny coming from the host blurp
          filter f_blurp_deny { host("blurp") and match("deny"); };
        
   Table 2-3. Available filter functions in syslog-ng
   Function Description
   facility() Selects messages based on their facility code
   level() or priority() Selects messages based on their priority
   program() Tries to match a regular expression to the program name
   field of log messages
   host() Tries to match a regular expression to the hostname field of
   log messages
   match() Tries to match a regular expression to the message itself.
   filter() Call another filter rule and evaluate its value
   
   For a complete description on the above functions, see the Reference
   chapter.
   
   There's a special filter identifier "DEFAULT" which allows you to
   catch not-yet-handled messages. For example, consider the following
   configuration:
          options { keep_hostname(yes); };

          source src { unix-stream("proba2"); internal(); };
        
          destination ftpd { file("ftplog"); };
          destination named { file("namedlog"); };
          destination daemon { file("daemonlog"); };
        
          filter f_ftpd { match("ftp"); };
          filter f_named { match("named"); };
          filter f_daemon { facility(daemon); };
        
          log { source(src); filter(f_ftpd); destination(ftpd); };
          log { source(src); filter(f_named); destination(named); };
          log { source(src); filter(f_daemon); filter(DEFAULT); destination(dae
mon); };
        
           The default filter above catches all facility=daemon messages
   which are not caught by the filter f_ftpd and f_named.
     _________________________________________________________________
   
Destinations

   A destination is a message sink, where log is sent if filtering rules
   match. Similarly to sources, destinations may include several drivers
   which define how messages are dispatched. To declare a destination in
   the configuration file, you'll need a destination statement, whose
   syntax is as following:
          destination <identifier> { destination-driver(params); destination-dr
iver(params); ... };
        
   Table 2-4. Available destination drivers in syslog-ng
   Name Description>
   file Writes messages to the given file
   fifo, pipe Writes messages to the given named pipe
   unix-stream Sends messages to the given unix socket in SOCK_STREAM
   style (Linux)
   unix-dgram Sends messages to the given unix socket in SOCK_DGRAM style
   (BSD)
   udp Sends messages to specified host and UDP port
   tcp Sends messages to specified host and TCP port
   usertty Sends messages to specified user if logged in
   program Forks and launches given program, and sends messages to its
   standard input.
   For detailed list of the supported drivers, see the Reference chapter.
     _________________________________________________________________
   
Log paths

   In the previous chapters we learnt how to define sources, filters and
   destinations. We'll need to connect those together, which is
   accomplished by the log statement. Any message coming from one of the
   listed sources, matching the filters (each of them) are sent to the
   listed destinations. The needed syntax is here:
          log { source(s1); source(s2); ...
          filter(f1); filter(f2); ...
          destination(d1); destination(d2); ... };
        
   Members on the logpath are evaluated in order, e.g. the only filter
   invokations applied to a source are those which are after the source
   reference.
     _________________________________________________________________
   
Options

   There are several options you can specify, which modifies the
   behaviour of syslog-ng. For an exact list of possible options see the
   chapter Reference. The general syntax is here:
          options { option1(params); option2(params); ... };
        
   Each option may have parameters, just like in driver specification.
   
   Table 2-5. List of supported global options in syslog-ng
   Name Accepted values Description
   time_reopen() number The time to wait before a died connection is
   reestablished
   time_reap() number The time to wait before an idle destination file is
   closed.
   sync_freq() number The number of lines buffered before written to file
   mark_freq() number The number of seconds between two MARK lines. NOTE:
   not implemented yet.
   log_fifo_size() number The number of lines fitting to the output queue
   chain_hostnames() yes or no Enable or disable the chained hostname
   format.
   use_time_recvd() yes or no Use the time a message is received instead
   of the one specified in the message.
   use_dns() yes or no Enable or disable DNS usage. syslog-ng blocks on
   DNS queries, so enabling DNS may lead to a Denial of Service attack.
   To prevent DoS, protect your syslog-ng network endpoint with firewall
   rules, and make sure that all hosts, which may get to syslog-ng is
   resolvable.
   use_fqdn() yes or no Add Fully Qualified Domain Name instead of short
   hostname.
   gc_idle_threshold() number Sets the threshold value for the garbage
   collector, when syslog-ng is idle. GC phase starts when the number of
   allocated objects reach this number. Default: 100.
   gc_busy_threshold() number Sets the threshold value for the garbage
   collector, when syslog-ng is busy. GC phase starts when the number of
   allocated objects reach this number. Default: 3000.
     _________________________________________________________________
   
Chapter 3. Reference

   This chapter documents the drivers and options you may specify in the
   configuration file.
     _________________________________________________________________
   
Source drivers

   The following drivers may be used in the source statement, as
   described in the previous chapter.
     _________________________________________________________________
   
internal()

   All internally generated messages "come" from this special source. If
   you want warnings, errors and notices from syslog-ng itself, you have
   to include this source in one of your source statement.
          Declaration: internal()
        
   Syslog-ng will print you a warning, if this driver is not referenced.
   
   Example 3-1. Using the internal() driver
            source s_local { internal(); };
        
     _________________________________________________________________
   
unix-stream() and unix-dgram()

   This two drivers behave similarly: they open the given AF_UNIX socket,
   and start listening on them for messages. unix-stream() is primarily
   used on Linux, and uses SOCK_STREAM semantics (connection oriented, no
   messages are lost), unix-dgram() is used on BSDs, and uses SOCK_DGRAM
   semantics, this may result in lost local messages, if the system is
   overloaded.
   
   To avoid denial of service attacks when using connection-oriented
   protocols, the number of simoultaneously accepted connections should
   be limited. This can be achieved using the max-connections()
   parameter.
          Declaration:
            unix-stream(filename [options]);
            unix-dgram(filename [options]);
        
   The following options can be specified:
   
   Table 3-1. Available options for unix-stream & unix-dgram
   Name Type Description Default
   owner() string Set the uid of the socket. root
   group() string Set the gid of the socket. Default: root. root
   perm() number Set the permission mask. For octal numbers prefix the
   number with '0', e.g. use 0755 for rwxr-xr-x. 0666
   keep-alive() yes or no Selects whether to keep connections opened when
   syslog-ng is restarted, can be used only with unix-stream(). Default:
   yes. yes
   max-connections() number Limits the number of simoultaneously opened
   connections. Can be used only with unix-stream(). 10
   
   Example 3-2. Using the unix-stream() and unix-dgram() drivers
            source s_stream { unix-stream("/dev/log" max-connections(10)); };
            source s_dgram { unix-dgram("/var/run/log"); };
        
     _________________________________________________________________
   
tcp() and udp()

   These drivers let you receive messages from the network, and as the
   name of the drivers show, you can use both UDP and TCP.
   
   UDP is a simple datagram protocol, which provides "best possible
   service" to transfer messages between hosts. It may lose messages, and
   no attempt is made to retransmit such lost messages at the protocol
   level.
   
   TCP provides connection-oriented service, which basically means
   flow-controlled message pipeline. In this pipeline, each message is
   acknowledged, and retransmission is done for each lost packet.
   Generally it's safer to use TCP, because lost connections can be
   detected, and no messages get lost, but traditionally syslogd protocol
   uses UDP.
   
   None of tcp() and udp() drivers require positional parameters. By
   default they bind to 0.0.0.0:514, which means that syslog-ng will
   listen on all available interfaces. To limit accepted connections to
   one interface only, use the localip() parameter as described below.
   
   NOTE: the tcp port 514 is reserved for use with rshell, so you have to
   pick another port if you intend to use syslog-ng and rshell at the
   same time.
          Declaration:
            tcp([options]);
            udp([options]);
        
   The following options are valid for udp() and tcp()
   
   Table 3-2. Available options for unix-stream & unix-dgram
   Name          Type   Description                Default
   ip or localip string The IP address to bind to. 0.0.0.0
   
   Example 3-3. Using the udp() and tcp() drivers
            source s_tcp { tcp(ip(127.0.0.1) port(1999); max-connections(10));
};
            source s_udp { udp(); };
        
     _________________________________________________________________
   
file()

   Usually the kernel presents its messages in a special file (/dev/kmsg
   on BSDs, /proc/kmsg on Linux), so to read such special files, you'll
   need the file() driver. Please note that you can't use this driver to
   follow a file like tail -f does. To feed a growing logfile into
   syslog-ng (HTTP access.log for instance), use a script like this:
   
   Example 3-4. example script to feed a growing logfile into syslog-ng
            #!/bin/sh
            tail -f | logger -p local4.info
        

   NOTE: on Linux, the klogd daemon reads kernel messages, and forwards
   them to the syslogd process. klogd preprocesses kernel messages and
   replaces addresses with symbolic names (from /boot/System.map). If you
   don't want to lose this functionality you'll have to run klogd with
   syslog-ng as well.
          Declaration:
            file(filename);
        
   Example 3-5. Using the file() driver
            source s_file { file("/proc/kmsg"); };
        
     _________________________________________________________________
   
pipe()

   The pipe driver opens a named pipe with the specified name, and
   listens for messages. It's used as the native message getting protocol
   on HP-UX.
          Declaration:
            pipe(filename);
        
   NOTE: you'll need to create this pipe using mkfifo(1).
   
   Example 3-6. Using the pipe() driver
            source s_pipe { pipe("/dev/log"); };
        
     _________________________________________________________________
   
sun-streams() driver

   Solaris uses its STREAMS API to send messages to the syslogd process.
   You'll have to compile syslog-ng with this driver compiled in (see
   ./configure --help).
   
   Newer versions of Solaris (2.5.1 and above), in addition to STREAMS
   uses a new IPC called door to confirm delivery of a message. Syslog-ng
   supports this new IPC mechanism with the door() option (see below).
     _________________________________________________________________
   
Destination drivers

   Destination drivers output log messages to somewhere outside
   syslog-ng: a file or a network socket.
     _________________________________________________________________
   
file()

   The file driver is one of the most important destination drivers in
   syslog-ng. It allows you to output logmessages to the named file, or
   as you'll see to a set of files.
   
   The destination filename may include macros which gets expanded when
   the message is written, thus a simple file() driver may result in
   several files to be created. Macros can be included by prefixing the
   macro name with a '$' sign (without the quotes), just like in
   Perl/PHP.
   
   If the expanded filename refers to a directory which doesn't exist,
   it'll be created depending on the create_dirs() setting (both global
   and a per destination option)
   
   Warning: since the state of each created file must be tracked by
   syslog-ng, it consumes some memory for each file. If no new messages
   are written to a file within 60 seconds (controlled by the time_reap
   global option), it's closed, and its state is freed.
   
   Exploiting this a DoS attack can be mounted against your system. If
   the number of possible destination files and its needed memory is more
   than the amount your logserver has.
   
   The most suspicious macro is $PROGRAM, where the possible variations
   is quite high, so in untrusted environments $PROGRAM usage should be
   avoided.
   
   Table 3-3. Available macros in filename expansion
   Name Description
   HOST The name of the source host where the message is originated from.
   If the message traverses several hosts, and chain_hostnames() is on,
   the first one is used.
   FACILITY The name of the facility, the message is tagged as coming
   from.
   PRIORITY or LEVEL The priority of the message.
   PROGRAM The name of the program the message was sent by.
   YEAR The year the message was sent. Time expansion macros can either
   use the time specified in the log message, e.g. the time the log
   message is sent, or the time the message was received by the log
   server. This is controlled by the use_time_recvd() option.
   MONTH The month the message was sent.
   DAY The day of month the message was sent.
   HOUR The hour of day the message was sent.
   MIN The minute the message was sent.
   SEC The second the message was sent.
   
   Table 3-4. Available options for file()
   Name Type Description Default
   log_fifo_size() number The number of entries in the output fifo. Use
   global setting.
   sync_freq() number The logfile is synced when this number of messages
   has been written to it. Use global setting.
   encrypt() yes or no Encrypt the resulting file. NOTE: this is not
   implemented as of 1.3.14. Use global setting.
   compress() yes or no Compress the resulting logfile using zlib. NOTE:
   this is not implemented as of 1.3.14. Use global setting.
   owner() string Set the owner of the created filename to the one
   specified. root
   group() string Set the group of the created filename to the one
   specified. root
   perm() number The permission mask of the file if it is created by
   syslog-ng. 0600
   dir_perm() number The permission mask of directories created by
   syslog-ng. Log directories are only created if a file after macro
   expansion refers to a non-existing directory, and dir creation is
   enabled using create_dirs(). 0600
   create_dirs() yes or no Enable creating non-existing directories. no
     _________________________________________________________________
   
pipe()

   This driver sends messages to a named pipe like /dev/xconsole
     _________________________________________________________________
   
unix-stream() & unix-dgram()

   This driver sends messages to a unix socket in either SOCK_STREAM or
   SOCK_DGRAM mode.
     _________________________________________________________________
   
udp() & tcp()

   This driver sends messages to another host on the local intranet or
   internet using either UDP or TCP protocol.
     _________________________________________________________________
   
usertty()

   This driver writes messages to the terminal of a logged-in user.
     _________________________________________________________________
   
program()

   This driver fork()'s executes the given program with the given
   arguments and sends messages down to the stdin of the child.
     _________________________________________________________________
   
Filter functions

   The following functions may be used in the filter statement, as
   described in the previous chapter.
     _________________________________________________________________
   
Options

   The following options can be specified in the options statement, as
   described in the previous chapter.
     _________________________________________________________________
   
Chapter 4. Performance tuning in syslog-ng

   There are several settings available you can finetune the behaviour of
   syslog-ng. The defaults should be adequate for a single server or
   workstation installation, but for a central loghost receiving the logs
   from multiple computers it may not be enough.
     _________________________________________________________________
   
Setting garbage collector parameters

   Syslog-ng uses a garbage collector internally, and while the garbage
   collector is running it does not accept messages. This may cause
   problems if some non-connection oriented transport protocol is used,
   like unix-dgram() or udp(). There are two settings which control the
   garbage collection phase:
     _________________________________________________________________
   
gc_idle_threshold()

   With this option you can specify the idle threshold of the gc. If the
   number of allocated objects reach this number, and the system is idle
   (no message arrived within 100msec), a gc phase starts. Since the
   system is idle, presumably no messages will be lost if the gc is ran.
   Therefore this value should be low, but higher than the minimally
   allocated objects. The minimum number of objects allocated depends on
   your configuration, but you can get exact numbers by specifying the -v
   command line option.
     _________________________________________________________________
   
gc_busy_threshold()

   This threshold is used when syslog-ng is busy accepting messages (this
   means that within 100msec an I/O event occured), however to prevent
   syslog-ng eating all your memory, gc should be ran in these cases as
   well. Set this value high, so that your log bursts don't get
   interrupted by the gc.
     _________________________________________________________________
   
Setting output queue size

   Syslog-ng always reads its incoming log channels to prevent your
   running daemons from blocking. This may result in lost messages if the
   output queue is full. It's therefore important to set the output queue
   size (termed in number of messages), which you can do globally, or on
   a per destination basis.
          options { log_fifo_size(1000); };
        
   or
          destination d_messages { file("/var/log/messages" log_fifo_size(1000)
; };
        
   You should set your fifo size to the estimated number of messages in a
   message burst. If bursts extend the bandwidth of your destination
   pipe, syslog-ng can feed messages into the destination pipe after the
   burst has collapsed.
   
   Of course syslog-ng cannot widen your network bandwidth, so if your
   destination host lives on a noisy network, and your logtraffic extends
   the bandwidth of this network, syslog-ng can't do anything. It'll do
   its best however.
     _________________________________________________________________
   
Setting sync parameter

   The sync parameter doesn't exactly do what you might expect. As you
   have seen messages to be sent are buffered in an output queue. The
   sync parameter specifies the number of messages held in this buffer
   before anything is written.
   
   Note that it doesn't write all buffered messages in one single chunk,
   it writes each distinct message with a single write() system call.