*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->Linux man pages -> sysklogd (8)              
Title
Content
Arch
Section
 

SYSKLOGD(8)

Contents


NAME    [Toc]    [Back]

       sysklogd - Linux system logging utilities.

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

       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 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/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    [Toc]    [Back]

       -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.psionic.com/papers/dns.html.

       -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
	      /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 package.
  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 (``:'')  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.

       -v     Print version and exit.

SIGNALS    [Toc]    [Back]

       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    [Toc]    [Back]
	      The syslogd will die.

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

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

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

CONFIGURATION FILE SYNTAX DIFFERENCES    [Toc]    [Back]

       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 particular
 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  mentioned
 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  somewhat
  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    [Toc]    [Back]

       These  modifications  provide  network support to the syslogd facility.
       Network support means that messages can be forwarded from one node running
  syslogd  to another node running syslogd where they will be actually
 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 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 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 configuration
 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 nameserver
  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  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).   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 qualified
 names instead of simple hostnames.	You may want to use the stripdomain
  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 forwarding
 respectively.

OUTPUT TO NAMED PIPES (FIFOs)    [Toc]    [Back]

       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    [Toc]    [Back]

       There is probably one important consideration when installing this version
 of syslogd.  This version of syslogd 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 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    [Toc]    [Back]

       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 (jmorriso@rflab.ee.ubc.ca) for alerting me to this potential.  A rogue  program(mer)
  could  very easily flood the syslogd 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 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  logging
 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  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.

DEBUGGING    [Toc]    [Back]

       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 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/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-logging
 this is the used console; for tty-logging this is the specified
 tty; wall has no additional arguments.

FILES    [Toc]    [Back]

       /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    [Toc]    [Back]

       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    [Toc]    [Back]

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

COLLABORATORS    [Toc]    [Back]

       Syslogd	is  taken  from  BSD sources, Greg Wettstein (greg@wind.enjellic.com)
 performed the port to Linux,  Martin  Schulze  (joey@linux.de)
       fixed  some  bugs and added several new features.  Klogd was originally
       written by  Steve  Lord	(lord@cray.com),  Greg	Wettstein  made  major
       improvements.

       Dr. Greg Wettstein
       Enjellic Systems Development
       Oncology Research Division Computing Facility
       Roger Maris Cancer Center
       Fargo, ND
       greg@wind.enjellic.com

       Stephen Tweedie
       Department of Computer Science
       Edinburgh University, Scotland
       sct@dcs.ed.ac.uk

       Juha Virtanen
       jiivee@hut.fi

       Shane Alderton
       shane@ion.apana.org.au

       Martin Schulze
       Infodrom Oldenburg
       joey@linux.de



Version 1.3			12 October 1998 		   SYSKLOGD(8)
[ Back ]
 Similar pages
Name OS Title
linprocfs FreeBSD Linux process file system
mkdosfs Linux create an MS-DOS file system under Linux
mkfs Linux build a Linux file system
fsck.minix Linux a file system consistency checker for Linux
fsck.ext3 Linux check a Linux second extended file system
e2fsck Linux check a Linux second extended file system
mke2fs Linux create a Linux second extended file system
fsck.ext2 Linux check a Linux second extended file system
mkfs.ext2 Linux create a Linux second extended file system
mkfs.ext3 Linux create a Linux second extended file system
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service