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 ] [ -w ]

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.

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

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 1.10.2 (unstable)               27 September 2005                             RSYSLOGD(8)