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RSYSLOGD(8)                        Linux System Administration                        RSYSLOGD(8)

NAME
       rsyslogd - reliable and extended syslogd

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

DESCRIPTION
       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 docu‐
       mentation at http://www.rsyslog.com/doc

       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 defi‐
       nition  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  stan‐
       dard  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.

OPTIONS
       -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 information.

       -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  cor‐
              rectness.   This  option  is  meant to verify a config file. To do so, run rsyslogd
              interactively in foreground, specifying -f  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).  rsyslogd is started and controlled by init(8).

       -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.

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

              kill -SIGNAL $(cat /var/run/rsyslogd.pid)

       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/rsyslogd.pid)

       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.

SECURITY THREATS
       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  sys‐
       tem 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 percent‐
              age 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
              socket.

       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 mes‐
       sages 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.

DEBUGGING
       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  speci‐
       fied using the RSYSLOG_DEBUGLOG environment variable.

FILES
       /etc/rsyslog.conf
              Configuration file for rsyslogd.  See rsyslog.conf(5) for exact information.
       /dev/log
              The Unix domain socket to from where local syslog messages are read.
       /var/run/rsyslogd.pid
              The file containing the process id of rsyslogd.
       prefix/lib/rsyslog
              Default  directory for rsyslogd modules. The prefix is specified during compilation
              (e.g. /usr/local).
ENVIRONMENT
       RSYSLOG_DEBUG
              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.
              DebugOnDemand
                     Enables  debugging  but turns off debug output. The output can be toggled by
                     sending SIGUSR1. Mutually exclusive with Debug.
              LogFuncFlow
                     Print out the logical flow of functions (entering and exiting them)
              FileTrace
                     Specifies which files to trace LogFuncFlow. If not set (the default), a Log‐
                     FuncFlow trace is provided for all files. Set to limit it to the files spec‐
                     ified.FileTrace may be specified multiple times, one file each (e.g.  export
                     RSYSLOG_DEBUG="LogFuncFlow FileTrace=vm.c FileTrace=expr.c"
              PrintFuncDB
                     Print  the content of the debug function database whenever debug information
                     is printed (e.g. abort case)!
              PrintAllDebugInfoOnExit
                     Print all debug information immediately before rsyslogd exits (currently not
                     implemented!)
              PrintMutexAction
                     Print mutex action as it happens. Useful for finding deadlocks and such.
              NoLogTimeStamp
                     Do not prefix log lines with a timestamp (default is to do that).
              NoStdOut
                     Do  not  emit debug messages to stdout. If RSYSLOG_DEBUGLOG is not set, this
                     means no messages will be displayed at all.
              Help   Display a very short list of commands - hopefully a life saver if you  can't
                     access the documentation...

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

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

Further Information
       Please visit http://www.rsyslog.com/doc for additional information, tutorials and  a  sup‐
       port forum.

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

COLLABORATORS
       rsyslogd  is  derived from sysklogd sources, which in turn was taken from the BSD sources.
       Special  thanks  to   Greg   Wettstein   (greg@wind.enjellic.com)   and   Martin   Schulze
       (joey@linux.de) for the fine sysklogd package.

       Rainer Gerhards
       Adiscon GmbH
       Grossrinderfeld, Germany
       rgerhards@adiscon.com

Version 8.6.0                              02 Dec 2014                                RSYSLOGD(8)

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