Provided by: sysklogd_1.5-6ubuntu1_i386 bug


       sysklogd - Linux system logging utilities.


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


       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.


       -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/syslog.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
              interval 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
              syslogd 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
              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
              is   specified   and    the    host    logging    resolves    to
      no domain would be cut, you will have to
              specify two domains like: -s

       -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.
              However,  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.


       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
              syslogd 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
       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 (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
       mentioned 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
       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.


       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

                   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 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
       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 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
       qualified 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
       forwarding 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
       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[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.


       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
       ( 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

       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
              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.


       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.

              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

       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-
              logging this is the used console; for tty-logging  this  is  the
              specified 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),


       The system log daemon syslogd is originally  taken  from  BSD  sources,
       Greg  Wettstein  <>  performed the port to Linux,
       Martin Schulze <> fixed some bugs, added  several  new
       features and took over maintenance.