SYSKLOGD(8)               Linux System Administration              SYSKLOGD(8)
       sysklogd - Linux system logging utilities.

       syslogd  [ -a socket ] [ -d ] [ -f config file ] [ -h ] [ -l hostlist ]
       [ -m interval ] [ -n ] [ -p socket ] [ -r ] [ -s domainlist ] [ -S ]  [
       -v ] [ -x ]

       Sysklogd provides two system utilities which provide support for system
       logging and kernel message trapping.  Support of both internet and unix
       domain  sockets  enables this utility package to support both local and
       remote logging.

       System logging is provided by a version of syslogd(8) derived from  the
       stock  BSD  sources.   Support  for  kernel  logging is provided by the
       klogd(8) utility which allows kernel logging to be conducted in  either
       a standalone fashion or as a client of syslogd.

       Syslogd  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.

       While the syslogd sources have been heavily modified a couple of  notes
       are  in  order.   First  of  all there has been a systematic attempt to
       insure that syslogd follows its default, standard  BSD  behavior.   The
       second important concept to note is that this version of syslogd inter-
       acts 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  behav-

       The  main  configuration  file /etc/syslog.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 whole line is ignored.

       -a socket
              Using this argument you can specify additional sockets from that
              syslogd 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

       -d     Turns  on  debug mode.  Using this the daemon will not proceed a
              fork(2) to set itself 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 information.

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

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

       -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.

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

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

       -p socket
              You can specify an alternative unix  domain  socket  instead  of

       -r     This option will enable the facility to receive message from the
              network using an internet domain socket with the syslog  service
              (see  services(5)).   The default is to not receive any messages
              from the network.

              This option is introduced in version 1.3 of the  sysklogd  pack-
              age.   Please  note that the default behavior is the opposite of
              how older versions behave, so you might have to turn this on.

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

       -S     Verbose logging. If specified once,  the  numeric  facility  and
              priority are logged with each locally-written message. If speci-
              fied more than once, the names of the facility and priority  are
              logged with each locally-written message.

       -v     Print version and exit.

       -x     Disable  name  lookups  when  receiving  remote  messages.  This
              avoids deadlocks when the nameserver  is  running  on  the  same
              machine that runs the syslog daemon.

       Syslogd  reacts  to  a set of signals.  You may easily send a signal to
       syslogd using the following:

              kill -SIGNAL 'cat /var/run/'

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

              The syslogd will die.

              If debugging is enabled these  are  ignored,  otherwise  syslogd
              will die.

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

              Wait for childs if some were born, because of wall'ing messages.

       Syslogd  uses  a  slightly  different syntax for its configuration file
       than the original BSD sources.  Originally all messages of  a  specific
       priority and above were forwarded to the log file.

              For  example  the  following line caused ALL output from daemons
              using the daemon facilities (debug is the  lowest  priority,  so
              every higher will also match) to go into /usr/adm/daemons:

                   # Sample syslog.conf
                   daemon.debug             /usr/adm/daemons

       Under the new scheme this behavior remains the same.  The difference is
       the addition of four new specifiers, the  asterisk  (*)  wildcard,  the
       equation sign (=), the exclamation mark (!), and the minus sign (-).

       The  * specifies that all messages for the specified facility are to be
       directed to the destination.  Note that  this  behavior  is  degenerate
       with  specifying  a priority level of debug.  Users have indicated that
       the asterisk notation is more intuitive.

       The = wildcard is used to restrict logging to  the  specified  priority
       class.  This allows, for example, routing only debug messages to a par-
       ticular logging source.

              For example the following line in syslog.conf would direct debug
              messages from all sources to the /usr/adm/debug file.

                   # Sample syslog.conf
                   *.=debug            /usr/adm/debug

       The  !  is  used  to exclude logging of the specified priorities.  This
       affects all (!) possibilities of specifying priorities.

              For example the following lines would log all  messages  of  the
              facility  mail  except  those  with  the  priority  info  to the
              /usr/adm/mail file.  And all messages from (including)
              to  news.crit  (excluding)  would be logged to the /usr/adm/news

                   # Sample syslog.conf
                   mail.*;mail.!=info       /usr/adm/mail
         ;news.!crit     /usr/adm/news

       You may use it intuitively as an exception specifier.  The  above  men-
       tioned interpretation is simply inverted.  Doing that you may use


       to  skip  every message that comes with a mail facility.  There is much
       room to play with it. :-)

       The - may only be used to  prefix  a  filename  if  you  want  to  omit
       sync'ing the file after every write to it.

       This  may  take  some acclimatization for those individuals used to the
       pure BSD behavior but testers have indicated that this syntax is  some-
       what  more  flexible  than  the  BSD behavior.  Note that these changes
       should not affect standard syslog.conf(5) files.  You must specifically
       modify the configuration files to obtain the enhanced behavior.

       These  modifications  provide  network support to the syslogd facility.
       Network support means that messages can be forwarded from one node run-
       ning  syslogd  to another node running syslogd where they will be actu-
       ally logged to a disk file.

       To enable this you have to specify the -r option on the  command  line.
       The default behavior is that syslogd won't listen to the network.

       The  strategy  is  to  have  syslogd listen on a unix domain socket for
       locally generated log messages.  This behavior will  allow  syslogd  to
       inter-operate  with the syslog found in the standard C library.  At the
       same time syslogd listens on the standard syslog port for messages for-
       warded  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 syslogd neither can  receive  remote  messages
       nor  send  them,  because the UDP port cant be opened.  Instead syslogd
       will die immediately, blowing out an error message.

       To cause messages to be forwarded to another host  replace  the  normal
       file  line  in  the syslog.conf file with the name of the host to which
       the messages is to be sent prepended with an @.

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

                   # Sample syslogd configuration file to
                   # messages to a remote host forward all.
                   *.*            @hostname

              To  forward  all kernel messages to a remote host the configura-
              tion file would be as follows:

                   # Sample configuration file to forward all kernel
                   # messages to a remote host.
                   kern.*         @hostname

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

       With normal syslogds you would get syslog-loops if you  send  out  mes-
       sages  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).   In  my domain (Infodrom Oldenburg) we accidently got one and our
       disks filled up with the same single message. :-(

       To avoid this in further times no messages that were  received  from  a
       remote  host are sent out to another (or the same) remote host anymore.
       If there are scenarios where this doesn't make sense,  please  drop  me
       (Joey) a line.

       If  the  remote host is located in the same domain as the host, syslogd
       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 quali-
       fied names instead of simple hostnames.  You may want to use the strip-
       domain  feature  -s  of this server.  You can tell the syslogd 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 machines.  This, too, results in  logging  only  their  simple
       hostnames and not the fqdns.

       The  UDP  socket used to forward messages to remote hosts or to receive
       messages from them is only opened when it is needed.  In releases prior
       to  1.3-23  it was opened every time but not opened for reading or for-
       warding respectively.

       This version of syslogd 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 syslogd 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

       There is probably one important consideration when installing this ver-
       sion of syslogd.  This version of syslogd is dependent on  proper  for-
       matting  of  messages  by  the syslog function.  The functioning of the
       syslog function in the shared libraries changed somewhere in the region
       of[2-4].n.   The  specific change was to null-terminate the
       message before transmitting it to the /dev/log  socket.   Proper  func-
       tioning  of this version of syslogd is dependent on null-termination 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 removed.  Relinking
       these binaries to newer versions of the shared libraries  will  correct
       this problem.

       Both  the syslogd(8) and the klogd(8) can either 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 daemons
       started.  This is because init(8) depends on the process ID.

       There is the potential for the syslogd daemon to be used as  a  conduit
       for  a  denial  of  service  attack.  Thanks go to John Morrison (jmor- for alerting me to this potential.  A rogue  pro-
       gram(mer)  could  very easily flood the syslogd daemon with syslog mes-
       sages 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 syslogd to be run as a non-root pro-
              cess.  ALSO NOTE that this will prevent usage of remote  logging
              since syslogd will be unable to bind to the 514/UDP socket.

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

       5.     Use step 4 and if the problem persists and is not secondary to a
              rogue  program/daemon  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 West-
              ern 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  bel-
              ligerent individual.

       When  debugging  is turned on using -d option then syslogd will be very
       verbose by writing much of what it does on stdout.  Whenever  the  con-
       figuration  file  is  reread and re-parsed you'll see a tabular, corre-
       sponding to the internal data structure.  This tabular consists of four

       number This field contains a serial number starting by zero.  This num-
              ber 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/syslog.conf.

              This field is  tricky  and  represents  the  internal  structure
              exactly.   Every  column  stands  for  a facility (refer to sys-
              log(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.

              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 console-log-
              ging this is the used console; for tty-logging this is the spec-
              ified tty; wall has no additional arguments.

              Configuration  file  for  syslogd.  See syslog.conf(5) for exact
              The Unix domain socket to from where local syslog  messages  are
              The file containing the process id of syslogd.

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

       Syslogd Syslogd  doesn't change the filemode of opened logfiles at any
       stage of process.  If a file is created it is world readable,  however,
       the syslog init script in Red Hat Enterprise Linux sets umask to 077 so
       only root has read permissions.  You can also change the permissions on
       your  own.  This could be done in combination  with  rotating  logfiles
       using  the savelog(8) program that is shipped in the smail 3.x  distri-
       bution.  Remember that it might be a security hole if everybody is able
       to read auth.* messages as these might contain passwords.

       syslog.conf(5), klogd(8), logger(1), syslog(2), syslog(3), services(5),

       Syslogd  is  taken  from  BSD sources, Greg Wettstein (greg@wind.enjel- performed the port to Linux,  Martin  Schulze  (
       fixed  some  bugs and added several new features.  Klogd was originally
       written by  Steve  Lord  (,  Greg  Wettstein  made  major

       Dr. Greg Wettstein
       Enjellic Systems Development
       Oncology Research Division Computing Facility
       Roger Maris Cancer Center
       Fargo, ND

       Stephen Tweedie
       Department of Computer Science
       Edinburgh University, Scotland

       Juha Virtanen

       Shane Alderton

       Martin Schulze
       Infodrom Oldenburg

Version 1.3                     12 October 1998                    SYSKLOGD(8)