RSYSLOGD(8)               (28 May 2014)               RSYSLOGD(8)

          rsyslogd - reliable and extended syslogd

          rsyslogd [ -d ] [ -D ] [ -f config file ] [ -i pid file ] [
          -n ] [ -N level ] [ -o fullconf ] [ -C ] [ -v ]

          Rsyslogd is a system utility providing support for message
          logging.  Support of both internet and unix domain sockets
          enables this utility to support both local and remote log-

          Note that this version of rsyslog This is provided in the
          ./doc subdirectory and probably in a separate package if you
          installed rsyslog via a packaging system.  To use rsyslog's
          advanced features, you need to look at the HTML documenta-
          tion, because the man pages only covers basic aspects of
          operation.  For details and configuration examples, see man
          page and the online documentation

          Rsyslogd(8) is derived from the sysklogd package which in
          turn is derived from the stock BSD sources.

          Rsyslogd provides a kind of logging that many modern pro-
          grams use.  Every logged message contains at least a time
          and a hostname field, normally a program name field, too,
          but that depends on how trusty the logging program is. The
          rsyslog package supports free definition of output formats
          via templates. It also supports precise timestamps and writ-
          ing directly to databases. If the database option is used,
          tools like phpLogCon can be used to view the log data.

          While the rsyslogd sources have been heavily modified a cou-
          ple of notes are in order.  First of all there has been a
          systematic attempt to ensure that rsyslogd follows its
          default, standard BSD behavior. Of course, some configura-
          tion file changes are necessary in order to support the tem-
          plate system. However, rsyslogd should be able to use a
          standard syslog.conf and act like the original syslogd. How-
          ever, an original syslogd will not work correctly with a
          rsyslog-enhanced configuration file. At best, it will gener-
          ate funny looking file names.  The second important concept
          to note is that this version of rsyslogd interacts transpar-
          ently with the version of syslog found in the standard
          libraries.  If a binary linked to the standard shared
          libraries fails to function correctly we would like an exam-
          ple of the anomalous behavior.

          The main configuration file /etc/rsyslog.conf or an

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          alternative file, given with the -f option, is read at
          startup.  Any lines that begin with the hash mark (``#'')
          and empty lines are ignored.  If an error occurs during
          parsing the error element is ignored. It is tried to parse
          the rest of the line.

          -D   Runs the Bison config parser in debug mode. This may
               help when hard to find syntax errors are reported.
               Please note that the output generated is deeply techni-
               cal and orignally targeted towards developers.

          -d   Turns on debug mode. See the DEBUGGING section for more

          -f config file
               Specify an alternative configuration file instead of
               /etc/rsyslog.conf, which is the default.

          -i pid file
               Specify an alternative pid file instead of the default
               one.  This option must be used if multiple instances of
               rsyslogd should run on a single machine. To disable
               writing a pid file, use the reserved name "NONE" (all
               upper case!), so "-iNONE".

          -n   Avoid auto-backgrounding.  This is needed especially if
               the rsyslogd is started and controlled by init(8).

          -N  level
               Do a config check. Do NOT run in regular mode, just
               check configuration file correctness.  This option is
               meant to verify a config file. To do so, run rsyslogd
               interactively in foreground, specifying -f <config-
               file> and -N level.  The level argument modifies
               behaviour. Currently, 0 is the same as not specifying
               the -N option at all (so this makes limited sense) and
               1 actually activates the code. Later, higher levels
               will mean more verbosity (this is a forward-
               compatibility option).

          -o  fullconf
               Generates a consolidated config file fullconf that con-
               tains all of rsyslog's configuration in a single file.
               Include files are exploded into that file in exactly
               the way rsyslog sees them.  This option is useful for
               troubleshooting, especially if problems with the order
               of action processing is suspected. It may also be used
               to check for "unexepectedly" included config content.

          -C   This prevents rsyslogd from changing to the root

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               directory. This is almost never a good idea in produc-
               tion use. This option was introduced in support of the
               internal testbed.

          -v   Print version and exit.

          Rsyslogd reacts to a set of signals.  You may easily send a
          signal to rsyslogd using the following:

               kill -SIGNAL $(cat /var/run/

          Note that -SIGNAL must be replaced with the actual signal
          you are trying to send, e.g. with HUP. So it then becomes:

               kill -HUP $(cat /var/run/

          HUP  This lets rsyslogd perform close all open files.

          TERM ,  INT ,  QUIT
               Rsyslogd will die.

          USR1 Switch debugging on/off.  This option can only be used
               if rsyslogd is started with the -d debug option.

          CHLD Wait for childs if some were born, because of wall'ing

          There is the potential for the rsyslogd daemon to be used as
          a conduit for a denial of service attack.  A rogue
          program(mer) could very easily flood the rsyslogd daemon
          with syslog messages resulting in the log files consuming
          all the remaining space on the filesystem.  Activating log-
          ging over the inet domain sockets will of course expose a
          system to risks outside of programs or individuals on the
          local machine.

          There are a number of methods of protecting a machine:

          1.   Implement kernel firewalling to limit which hosts or
               networks have access to the 514/UDP socket.

          2.   Logging can be directed to an isolated or non-root
               filesystem which, if filled, will not impair the

          3.   The ext2 filesystem can be used which can be configured
               to limit a certain percentage of a filesystem to usage
               by root only.  NOTE that this will require rsyslogd to
               be run as a non-root process.  ALSO NOTE that this will
               prevent usage of remote logging on the default port

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               since rsyslogd will be unable to bind to the 514/UDP

          4.   Disabling inet domain sockets will limit risk to the
               local machine.

        Message replay and spoofing
          If remote logging is enabled, messages can easily be spoofed
          and replayed.  As the messages are transmitted in clear-
          text, an attacker might use the information obtained from
          the packets for malicious things. Also, an attacker might
          replay recorded messages or spoof a sender's IP address,
          which could lead to a wrong perception of system activity.
          These can be prevented by using GSS-API authentication and
          encryption. Be sure to think about syslog network security
          before enabling it.

          When debugging is turned on using the -d option, rsyslogd
          produces debugging information according to the
          RSYSLOG_DEBUG environment variable and the signals received.
          When run in foreground, the information is written to std-
          out. An additional output file can be specified using the
          RSYSLOG_DEBUGLOG environment variable.

               Configuration file for rsyslogd.  See rsyslog.conf(5)
               for exact information.
               The Unix domain socket to from where local syslog mes-
               sages are read.
               The file containing the process id of rsyslogd.
               Default directory for rsyslogd modules. The prefix is
               specified during compilation (e.g. /usr/local).

               Controls runtime debug support. It contains an option
               string with the following options possible (all are
               case insensitive):

                    Turns on debugging and prevents forking. This is
                    processed earlier in the startup than command line
                    options (i.e. -d) and as such enables earlier
                    debugging output. Mutually exclusive with Debu-

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                    Enables debugging but turns off debug output. The
                    output can be toggled by sending SIGUSR1. Mutually
                    exclusive with Debug.

                    Print out the logical flow of functions (entering
                    and exiting them)

                    Specifies which files to trace LogFuncFlow. If not
                    set (the default), a LogFuncFlow trace is provided
                    for all files. Set to limit it to the files
                    specified.FileTrace may be specified multiple
                    times, one file each (e.g. export
                    RSYSLOG_DEBUG="LogFuncFlow FileTrace=vm.c

                    Print the content of the debug function database
                    whenever debug information is printed (e.g. abort

                    Print all debug information immediately before
                    rsyslogd exits (currently not implemented!)

                    Print mutex action as it happens. Useful for find-
                    ing deadlocks and such.

                    Do not prefix log lines with a timestamp (default
                    is to do that).

                    Do not emit debug messages to stdout. If
                    RSYSLOG_DEBUGLOG is not set, this means no mes-
                    sages will be displayed at all.

               Help Display a very short list of commands - hopefully
                    a life saver if you can't access the documenta-

               If set, writes (almost) all debug message to the speci-
               fied log file in addition to stdout.

               Provides the default directory in which loadable mod-
               ules reside.

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          Please review the file BUGS for up-to-date information on
          known bugs and annoyances.

     Further Information
          Please visit for additional
          information, tutorials and a support forum.

          rsyslog.conf(5), logger(1), syslog(2), syslog(3),
          services(5), savelog(8)

          rsyslogd is derived from sysklogd sources, which in turn was
          taken from the BSD sources. Special thanks to Greg Wettstein
          ( and Martin Schulze (
          for the fine sysklogd package.

          Rainer Gerhards
          Adiscon GmbH
          Grossrinderfeld, Germany

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