RSYSLOGD(8)                Linux System Administration               RSYSLOGD(8)

       rsyslogd - reliable and extended syslogd

       rsyslogd [ -d ] [ -D ] [ -f config file ] [ -i pid file ] [ -n ] [ -N
       level ] [ -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 logging.

       Note that this version of rsyslog ships with extensive documentation in
       html format.  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
       documentation, because the man pages only covers basic aspects of
       operation.  For details and configuration examples, see the rsyslog.conf
       (5) man page and the online documentation at

       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 programs 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 writing
       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 couple 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
       configuration file changes are necessary in order to support the template
       system. However, rsyslogd should be able to use a standard syslog.conf
       and act like the original syslogd. However, an original syslogd will not
       work correctly with a rsyslog-enhanced configuration file. At best, it
       will generate funny looking file names.  The second important concept to
       note is that this version of rsyslogd interacts transparently 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 example of the anomalous behavior.

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

       -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).

       -C     This prevents rsyslogd from changing to the root directory. This
              is almost never a good idea in production 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 messages.

       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 logging
       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 machine.

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

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

   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 stdout. An additional output file can be specified using the
       RSYSLOG_DEBUGLOG environment variable.

              Configuration file for rsyslogd.  See rsyslog.conf(5) for exact
              The Unix domain socket to from where local syslog messages are
              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):

              Debug  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 DebugOnDemand.
                     Enables debugging but turns off debug output. The output
                     can be toggled by sending SIGUSR1. Mutually exclusive with
                     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 FileTrace=expr.c"
                     Print the content of the debug function database whenever
                     debug information is printed (e.g. abort case)!
                     Print all debug information immediately before rsyslogd
                     exits (currently not implemented!)
                     Print mutex action as it happens. Useful for finding
                     deadlocks and such.
                     Do not prefix log lines with a timestamp (default is to do
                     Do not emit debug messages to stdout. If RSYSLOG_DEBUGLOG
                     is not set, this means no messages will be displayed at
              Help   Display a very short list of commands - hopefully a life
                     saver if you can't access the documentation...

              If set, writes (almost) all debug message to the specified log
              file in addition to stdout.
              Provides the default directory in which loadable modules reside.

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

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

Version 8.6.0                      02 Dec 2014                       RSYSLOGD(8)