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man pages section 8: System Administration Commands

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Updated: Wednesday, July 27, 2022

rsyslogd (8)


rsyslogd - reliable and extended syslogd


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


Linux System Administration                                        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 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 docu-
       mentation, because the man pages only covers basic  aspects  of  opera-
       tion.  For details and configuration examples, see the rsyslog.conf (5)
       man page and the online documentation at https://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 con-
       figuration 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

       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 informa-

       -f config file
              Specify  an alternative configuration file instead of /etc/rsys-
              log.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  con-
              figuration  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 actu-
              ally 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 contains 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  prob-
              lems  with  the  order of action processing is suspected. It may
              also be used to check for "unexepectedly" included  config  con-

       -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/rsyslogd.pid)

       Note that -SIGNAL must be replaced with the actual signal you are  try-
       ing 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 rsys-
              logd 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  log-
              ging  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

   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 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.

              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  pro-
                     cessed  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 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  File-
                     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 that).
                     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 annoyances.

Further Information
       Please visit https://www.rsyslog.com/doc/ for  additional  information,
       tutorials and a support forum.

       See attributes(7) for descriptions of the following attributes:

       |Availability   | system/rsyslog   |
       |Stability      | Uncommitted      |

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

       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 pack-

       Rainer Gerhards
       Adiscon GmbH
       Grossrinderfeld, Germany

       Compared to syslogd(8), rsyslogd cannot be forced to reread its config-
       uration file with the SIGHUP signal and because of that svcadm  refresh
       command doesn't do that either.

       To do that, you must restart rsyslogd with svcadm restart.

       When  the  service is enabled the first time, an attempt is made to see
       if  any  /etc/syslog.conf  (see  syslog.conf(5)),  entries  might  need
       migrating and if so rsyslog is brought up in a degraded SMF state.

       Please  visit /etc/rsyslog.conf (see rsyslog.conf(5)), and customize as

       Then clear the service:

       # svcadm clear svc:/system/system-log:rsyslog

       Source code for open source software components in Oracle  Solaris  can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source   was   downloaded   from    https://www.rsyslog.com/files/down-

       Further information about this software can be found on the open source
       community website at https://www.rsyslog.com/.

Version 8.1905.0                  28 May 2014                      RSYSLOGD(8)