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 proba-
       bly  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  rsys-
       log.conf (5) man page and the online documentation 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 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 sup-
       port 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 stan-
       dard  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. 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 be-
              haviour. 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.

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 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 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 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.

DEBUGGING

       When debugging is turned on using the -d option, rsyslogd produces debugging information according to the RSYSLOG_DEBUG  environment  vari-
       able  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.

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 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="Log-
                     FuncFlow 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 support 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.enjel-
       lic.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)