path: root/rsyslogd.8

RSYSLOGD(8)                        Linux System Administration                        RSYSLOGD(8)

NAME
       rsyslogd - reliable and extended syslogd

SYNOPSIS
       rsyslogd  [ -a socket ] [ -d ] [ -f config file ] [ -h ] [ -i pid file ] [ -l hostlist ] [
       -m interval ] [ -n ] [ -o ] [ -p socket ] [ -r port ]
       [ -s domainlist ] [ -t port ] [ -v ]

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 insure 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 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.

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

       -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.

              Note:  At  the moment, this option is only available for command line comptability.
              It has, however, NO effect and is ignored.

       -m interval
              The rsyslogd logs a mark timestamp regularly.  The default interval between two  --
              MARK  --  lines  is 20 minutes.  This can be changed with this option.  Setting the
              interval to zero turns it off entirely.

              Note: At the moment, this option is only available for command  line  comptability.
              It has, however, NO effect and is ignored.

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

       -o     Omit reading the standard local log socket. This option is most useful for  running
              multiple  instances  of  rsyslogd on a single machine. When specified, no local log
              socket is opened at all.

       -p socket
              You can specify an alternative unix domain socket instead of /dev/log.

       -r port
              Activates the syslog/udp listener service. The listener will listen to  the  speci-
              fied port. Please note that a port must be specified in any case. This is different
              from the stock sysklogd package. If you would like  to  use  the  system's  default
              port, specify 0 as the port number. That will result in an /etc/services lookup for
              the actual port number. If the "-r" option is not given, no syslog/udp  listner  is
              available.

       -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
              Activates  the  syslog/tcp listener service. The listener will listen to the speci-
              fied port. 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 (Windows).

       -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`

       SIGHUP 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.

       SIGTERM
              Rsyslogd will die.

       SIGINT, SIGQUIT
              If debugging is enabled these are ignored, otherwise rsyslogd will die.

       SIGUSR1
              Switch  debugging on/off.  This option can only be used if rsyslogd is started with
              the -d debug option.

       SIGCHLD
              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 either the -r or -t option on the  command  line.   The
       default  behavior is that rsyslogd won't listen to the network. You can also combine these
       two options if you want rsyslogd to listen to both TCP and UDP messages.

       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 preception of system activity. 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
       This  is  an  early  release  of Rsyslogd .  As such, there are probably a number of bugs.
       Those that I know are described in the file BUGS that came with the package.  Be  sure  to
       review it.

       If an error occurs in one line the whole rule is ignored.

       Rsyslogd  doesn't  change  the  filemode of opened logfiles at any stage of process.  If a
       file is created it is world readable.  If you want to avoid this, you have  to  create  it
       and  change permissions on your own.  This could be done in combination with rotating log-
       files using the savelog(8) program that is shipped in the smail 3.x distribution.   Remem-
       ber that it might be a security hole if everybody is able to read auth.* messages as these
       might contain passwords.

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

       Michael Meckelein
       Adiscon GmbH
       mmeckelein@adiscon.com

Version 0.9.6                             08 August 2005                              RSYSLOGD(8)