path: root/rsyslogd.8

RSYSLOGD(8)                        Linux System Administration                        RSYSLOGD(8)

NAME
       rsyslogd - reliable and extended syslogd

SYNOPSIS
       rsyslogd [ -4 ] [ -6 ] [ -A ] [ -a socket ] [ -d ] [ -e ]
       [ -f config file ] [ -g port,max-nbr-of-sessions ] [ -h ]
       [ -i pid file ] [ -l hostlist ] [ -n ]
       [ -q ] [ -Q ] [ -r [port] ] [ -s domainlist ]
       [ -t port,max-nbr-of-sessions ] [ -v ] [ -w ] [ -x ]

DESCRIPTION
       Rsyslogd  is  a system utility providing support for message logging.  Support of both in-
       ternet and unix domain sockets enables this utility to support both local and remote  log-
       ging (via UDP and TCP).

       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 MySQL 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  de-
       fault,  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 orginal 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.

       For details and configuration examples, see the rsyslog.conf (5) man page.

OPTIONS
       -A     When sending UDP messages, there are potentially multiple pathes to the target des-
              tination. By default, rsyslogd only sends to the first target it  can  successfully
              send  to. If -A is given, messages are sent to all targets. This may improve relia-
              bility, but may also cause message duplicaton. This option should enabled  only  if
              it is fully understood.

       -4     Causes  rsyslogd  to listen to IPv4 addresses only.  If neither -4 nor -6 is given,
              rsyslogd listens to all configured addresses of the system.

       -6     Causes rsyslogd to listen to IPv6 addresses only.  If neither -4 nor -6  is  given,
              rsyslogd listens to all configured addresses of the system.

       -a socket
              Using  this  argument  you can specify additional sockets from that rsyslogd has to
              listen to.  This is needed if you're going to let some daemon run within a chroot()
              environment.   You  can use up to 19 additional sockets.  If your environment needs
              even more, you have to increase the symbol MAXFUNIX  within  the  syslogd.c  source
              file.   An example for a chroot() daemon is described by the people from OpenBSD at
              http://www.psionic.com/papers/dns.html.

       -d     Turns on debug mode.  Using this the daemon will not proceed a fork(2) to  set  it-
              self  in the background, but opposite to that stay in the foreground and write much
              debug information on the current tty.  See the DEBUGGING section for more  informa-
              tion.

       -e     Set  the  default  of $RepeatedMsgReduction config option to "off".  Hine: "e" like
              "every message". For further information, see there.

       -f config file
              Specify an alternative configuration file instead of  /etc/rsyslog.conf,  which  is
              the default.

       -g     Identical  to  -t  except  that every tcp connection is authenticated using gss-api
              (kerberos 5). Service name may be set using $GssListenServiceName  or  the  default
              "host"  will  be  used.  Encryption can be used if specified by the client and sup-
              ported by both sides.

       -h     By default rsyslogd will not forward messages it receives from remote hosts.  Spec-
              ifying this switch on the command line will cause the log daemon to forward any re-
              mote messages it receives to forwarding hosts which have been defined.

       -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.

       -l hostlist
              Specify  a hostname that should be logged only with its simple hostname and not the
              fqdn.  Multiple hosts may be specified using the colon (``:'') separator.

       -n     Avoid auto-backgrounding.  This is needed especially if the rsyslogd is started and
              controlled by init(8).

       -q add hostname if DNS fails during ACL processing
              During  ACL  processing, hostnames are resolved to IP addreses for performance rea-
              sons. If DNS fails during that process, the hostname is  added  as  wildcard  text,
              which results in proper, but somewhat slower operation once DNS is up again.

       -Q do not resolve hostnames during ACL processing
              Do not resolve hostnames to IP addresses during ACL processing.

       -r ["port"]
              Activates  the  syslog/udp listener service. The listener will listen to the speci-
              fied port.  If no port is specified, 0 is used as port number, which in  turn  will
              lead  to a lookup of the system default syslog port. If there is no system default,
              514 is used. Please note that the port must immediately follow the -r option.  Thus
              "-r514" is valid while "-r 514" is invalid (note the space).

       -s domainlist
              Specify  a domainname that should be stripped off before logging.  Multiple domains
              may be specified using the colon (``:'') separator.  Please be advised that no sub-
              domains  may  be  specified but only entire domains.  For example if -s north.de is
              specified and the host logging resolves to satu.infodrom.north.de no  domain  would
              be cut, you will have to specify two domains like: -s north.de:infodrom.north.de.

       -t port,max-nbr-of-sessions
              Activates  the  syslog/tcp listener service. The listener will listen to the speci-
              fied port. If max-nbr-of-sessions is specified, that becomes the maximum number  of
              concurrent  tcp  sessions.  If  not specified, the default is 200. Please note that
              syslog/tcp is not standardized, but the implementation in rsyslogd  follows  common
              practice  and  is  compatible  with e.g. Cisco PIX, syslog-ng and MonitorWare (Win-
              dows).  Please note that the port must  immediately  follow  the  -t  option.  Thus
              "-t514" is valid while "-t 514" is invalid (note the space).

       -v     Print version and exit.

       -w     Supress  warnings  issued  when  messages are received from non-authorized machines
              (those, that are in no AllowedSender list).

       -x     Disable DNS for remote messages.

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

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

       HUP    This lets rsyslogd perform a re-initialization.  All open  files  are  closed,  the
              configuration file (default is /etc/rsyslog.conf) will be reread and the rsyslog(3)
              facility is started again.

       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.

SUPPORT FOR REMOTE LOGGING
       Rsyslogd  provides  network  support  to the syslogd facility.  Network support means that
       messages can be forwarded from one node running rsyslogd to another node running  rsyslogd
       (or a compatible syslog implementation) where they will be actually logged to a disk file.

       To  enable this you have to specify one of -g , -r or -t options on the command line.  The
       default behavior is that rsyslogd won't listen to the network. You can also combine  these
       options  if  you want rsyslogd to listen to both TCP and UDP messages. Only one of the TCP
       listener options can be used.  The last one specified will take effect.

       The strategy is to have rsyslogd listen on a unix domain socket for locally generated  log
       messages.  This behavior will allow rsyslogd to inter-operate with the syslog found in the
       standard C library.  At the same time rsyslogd listens on the  standard  syslog  port  for
       messages  forwarded  from  other hosts.  To have this work correctly the services(5) files
       (typically found in /etc) must have the following entry:

                   syslog          514/udp

       If this entry is missing rsyslogd will use the well known port of 514 (so in  most  cases,
       it's not really needed).

       To  cause  messages  to  be  forwarded to another host replace the normal file line in the
       rsyslog.conf file with the name of the host to which the messages is to be sent  prepended
       with an @ (for UDP delivery) or the sequence @@ (for TCP delivery). The host name can also
       be followed by a colon and a port number, in which case the message is sent to the  speci-
       fied port on the remote host.

              For  example,  to  forward  ALL  messages  to a remote host use the following rsys-
              log.conf entry:

                   # Sample rsyslogd configuration file to
                   # messages to a remote host forward all.
                   *.*            @hostname
              More samples can be found in sample.conf.

              If the remote hostname cannot be resolved at startup, because the name-server might
              not  be  accessible  (it  may  be  started after rsyslogd) you don't have to worry.
              Rsyslogd will retry to resolve the name ten times and then complain.  Another  pos-
              sibility to avoid this is to place the hostname in /etc/hosts.

              With  normal syslogds you would get syslog-loops if you send out messages that were
              received from a remote host to the same host (or more complicated to a  third  host
              that sends it back to the first one, and so on).

              To avoid this no messages that were received from a remote host are sent out to an-
              other (or the same) remote host. You can disable this feature by the -h option.

              If the remote host is located in the same domain as the host, rsyslogd  is  running
              on, only the simple hostname will be logged instead of the whole fqdn.

              In  a  local network you may provide a central log server to have all the important
              information kept on one machine.  If the network consists of different domains  you
              don't  have to complain about logging fully qualified names instead of simple host-
              names.  You may want to use the strip-domain feature -s of this  server.   You  can
              tell rsyslogd to strip off several domains other than the one the server is located
              in and only log simple hostnames.

              Using the -l option there's also a possibility to define single hosts as local  ma-
              chines.   This,  too,  results  in  logging only their simple hostnames and not the
              fqdns.

OUTPUT TO DATABASES
       Rsyslogd has support for writing data to MySQL database tables. The  exact  specifics  are
       described in the rsyslog.conf (5) man page. Be sure to read it if you plan to use database
       logging.

       While it is often handy to have the data in a database, you must be aware of the  implica-
       tions.  Most importantly, database logging takes far longer than logging to a text file. A
       system that can handle a large log volume when writing to text files can most  likely  not
       handle a similar large volume when writing to a database table.

OUTPUT TO NAMED PIPES (FIFOs)
       Rsyslogd  has support for logging output to named pipes (fifos).  A fifo or named pipe can
       be used as a destination for log messages by prepending a pipy symbol (``|'') to the  name
       of  the  file.   This is handy for debugging.  Note that the fifo must be created with the
       mkfifo command before rsyslogd is started.

              The following configuration file routes debug messages from the kernel to a fifo:

                   # Sample configuration to route kernel debugging
                   # messages ONLY to /usr/adm/debug which is a
                   # named pipe.
                   kern.=debug              |/usr/adm/debug

INSTALLATION CONCERNS
       There is probably one important consideration when installing rsyslogd.  It  is  dependent
       on  proper  formatting  of messages by the syslog function.  The functioning of the syslog
       function in the shared libraries changed somewhere in  the  region  of  libc.so.4.[2-4].n.
       The  specific  change  was  to  null-terminate  the  message before transmitting it to the
       /dev/log socket.  Proper functioning of this version of rsyslogd is dependent on null-ter-
       mination of the message.

       This  problem  will  typically manifest itself if old statically linked binaries are being
       used on the system.  Binaries using old versions of the syslog function will  cause  empty
       lines  to  be  logged  followed by the message with the first character in the message re-
       moved.  Relinking these binaries to newer versions of the shared  libraries  will  correct
       this problem.

       The  rsyslogd(8)  can be run from init(8) or started as part of the rc.*  sequence.  If it
       is started from init the option -n must be set, otherwise you'll get tons of  syslog  dae-
       mons started.  This is because init(8) depends on the process ID.

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

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

       5.     Use step 4 and if the problem persists and is not secondary to a rogue program/dae-
              mon  get  a 3.5 ft (approx. 1 meter) length of sucker rod* and have a chat with the
              user in question.

              Sucker rod def. -- 3/4, 7/8 or 1in. hardened steel rod, male threaded on each  end.
              Primary use in the oil industry in Western North Dakota and other locations to pump
              'suck' oil from oil wells.  Secondary uses are for the construction of cattle  feed
              lots and for dealing with the occasional recalcitrant or belligerent individual.

   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 reply 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 -d option then rsyslogd will be very verbose by  writing
       much  of  what it does on stdout.  Whenever the configuration file is reread and re-parsed
       you'll see a tabular, corresponding to the internal data structure.  This tabular consists
       of four fields:

       number This  field  contains a serial number starting by zero.  This number represents the
              position in the internal data structure (i.e. the array).  If one  number  is  left
              out then there might be an error in the corresponding line in /etc/rsyslog.conf.

       pattern
              This  field  is tricky and represents the internal structure exactly.  Every column
              stands for a facility (refer to syslog(3)).  As you can see, there are  still  some
              facilities left free for former use, only the left most are used.  Every field in a
              column represents the priorities (refer to syslog(3)).

       action This field describes the particular action that takes place whenever a  message  is
              received  that  matches  the  pattern.  Refer to the syslog.conf(5) manpage for all
              possible actions.

       arguments
              This field shows additional arguments to the actions in the last field.  For  file-
              logging  this  is  the filename for the logfile; for user-logging this is a list of
              users; for remote logging this is the hostname of the machine to log to;  for  con-
              sole-logging  this  is the used console; for tty-logging this is the specified tty;
              wall has no additional arguments.

          templates
              There will also be a second internal structure which lists  all  defined  templates
              and  there contents. This also enables you to see the internally-defined, hardcoded
              templates.

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.

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

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 3.11.3 (devel)                   16 February 2008                             RSYSLOGD(8)