bionic (8) rsyslogd.8.gz

Provided by: rsyslog_8.32.0-1ubuntu4.2_amd64 bug

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 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 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.

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 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.

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  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.

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="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 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.enjellic.com)  and  Martin  Schulze (joey@linux.de) for the fine sysklogd
       package.

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