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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 ] [ -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:

       -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
	      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

       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	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.

       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)


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