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SYSKLOGD(8)		  Linux System Administration		   SYSKLOGD(8)

NAME
       sysklogd - Linux system logging utilities.

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

DESCRIPTION
       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‐
       ior.

       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.

OPTIONS
       -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 <http://www.guides.sk/psionic/dns/>.

       -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.	This can cause
	      syslog loops that fill up hard disks quite fast and  thus	 needs
	      to be used with caution.

       -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.  Depending on other log messages  generated	 these
	      lines may not be written consecutively.

       -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
	      /dev/log.

       -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 north.de is speci‐
	      fied 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.

       -u user
	      The syslogd daemon runs with full root privileges by default. If
	      you  specify this option, the daemon will drop its privileges to
	      the given user (and the  primary	group  of  this	 user)	before
	      starting	up  logging. This greatly reduces the potential impact
	      of exploitable security holes in syslogd.

	      syslogd will still open all log files as root at startup.	  How‐
	      ever,  after  receiving a SIGHUP signal (which causes the daemon
	      to restart) the log files will be reopened as the non-privileged
	      user which fails if the log files are only writeable by root. If
	      you need to restart the daemon using the signal, then  you  have
	      to  adapt	 the  permissions of your log files to be writeable by
	      the specified user (or its primary group).

       -v     Print version and exit.

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

	      kill -SIGNAL `cat /var/run/syslogd.pid`

       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.

       SIGTERM
	      The syslogd will die.

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

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

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

CONFIGURATION FILE SYNTAX DIFFERENCES
       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 news.info (including)
	      to  news.crit  (excluding)  would be logged to the /usr/adm/news
	      file.

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

	    mail.none
       or
	    mail.!*
       or
	    mail.!debug

       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.

SUPPORT FOR REMOTE LOGGING
       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 no messages received from a remote host are sent  out  to
       another (or the same) remote host anymore.  If you experience are setup
       in which you need this  behaviour,  please  use	the  -h	 command  line
       switch.	 However, this option needs to be handled with caution since a
       syslog loop can fill up hard disks quite fast.

       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.

OUTPUT TO NAMED PIPES (FIFOs)
       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

INSTALLATION CONCERNS
       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 libc.so.4.[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.

SECURITY THREATS
       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‐
       riso@rflab.ee.ubc.ca)  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
	      process.	 ALSO NOTE that this will prevent usage of remote log‐
	      ging since syslogd 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/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.

DEBUGGING
       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
       fields:

       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.

       pattern
	      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.

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

FILES
       /etc/syslog.conf
	      Configuration file for syslogd.  See  syslog.conf(5)  for	 exact
	      information.
       /dev/log
	      The  Unix	 domain socket to from where local syslog messages are
	      read.
       /var/run/syslogd.pid
	      The file containing the process id of syslogd.

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

       Syslogd 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 logfiles using the
       savelog(8) program that is  shipped  in	the  smail  3.x	 distribution.
       Remember	 that it might be a security hole if everybody is able to read
       auth.* messages as these might contain passwords.

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

AUTHORS
       The  system  log	 daemon syslogd is originally  taken from BSD sources,
       Greg Wettstein <greg@wind.enjellic.com> performed the  port  to	Linux,
       Martin  Schulze	<joey@infodrom.org> fixed some bugs, added several new
       features and took over maintenance.

Version 1.5			  27 May 2007			   SYSKLOGD(8)
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