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Linux 2.6 - man page for ntpd (linux section 8)

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NTPD(8) 		   The Network Time Protocol (NTP) Distribution 		  NTPD(8)

NAME
       ntpd - Network Time Protocol (NTP) daemon

SYNOPSIS
       ntpd [ -46aAbgLmnNqx ] [ -c conffile ] [ -f driftfile ] [ -i jaildir ] [ -k keyfile ] [ -l
       logfile ] [ -p pidfile ] [ -P priority ] [ -r broadcastdelay ] [ -s statsdir ] [ -t key	]
       [ -u user[:group] ] [ -U interface_update_interval ] [ -v variable ] [ -V variable ]

DESCRIPTION
       The ntpd program is an operating system daemon which sets and maintains the system time of
       day in synchronism with Internet standard time servers.	It is a  complete  implementation
       of  the Network Time Protocol (NTP) version 4, but also retains compatibility with version
       3, as defined by RFC-1305, and version 1 and 2,	as  defined  by  RFC-1059  and	RFC-1119,
       respectively.   ntpd  does  most computations in 64-bit floating-point arithmetic and does
       relatively clumsy 64-bit fixed-point operations only when necessary to preserve the  ulti-
       mate  precision,  about	232  picoseconds.  While the ultimate precision is not achievable
       with ordinary workstations and networks of today, it may be required with future gigahertz
       CPU clocks and gigabit LANs.

       The  daemon  can  operate  in  any  of  several modes, including symmetric active/passive,
       client/server broadcast/multicast and manycast.	A broadcast/multicast or manycast  client
       can  discover  remote  servers, compute server-client propagation delay correction factors
       and configure itself automatically.  This makes it possible to deploy a fleet of  worksta-
       tions without specifying configuration details specific to the local environment.

       Ordinarily,  ntpd reads the ntp.conf configuration file at startup time in order to deter-
       mine the synchronization sources and operating modes.  It is also possible  to  specify	a
       working,  although  limited configuration entirely on the command line, obviating the need
       for a configuration file.  This may be particularly appropriate when the local host is  to
       be  configured  as  a  broadcast/multicast client or manycast client, with all peers being
       determined by listening to broadcasts at run time.

       Various internal ntpd variables can be displayed and configuration options  altered  while
       the daemon is running using the ntpq and ntpd utility programs.

       When ntpd starts it looks at the value of umask, and if it is zero ntpd will set the umask
       to 0222.

OPTIONS
       -a     Require cryptographic authentication for broadcast  client,  multicast  client  and
	      symmetric passive associations.  This is the default.

       -A     Do  not require cryptographic authentication for broadcast client, multicast client
	      and symmetric passive associations.  This is almost never a good idea.

       -b     Enable the client to synchronize to broadcast servers.

       -c conffile
	      Specify the name and path of the configuration file, default /etc/ntp.conf.

       -f driftfile
	      Specify the name and path of the frequency file, default /etc/ntp.drift.	 This  is
	      the same operation as the driftfile driftfile configuration command.

       -g     Normally,  ntpd  exits  with  a message to the system log if the offset exceeds the
	      panic threshold, which is 1000 s by default.  This option allows the time to be set
	      to  any  value  without  restriction;  however,  this can happen only once.  If the
	      threshold is exceeded after that, ntpd will exit with a message to the system  log.
	      This option can be used with the -q and -x options.

       -i jaildir
	      Chroot  the  server  to  the  directory jaildir.	This option also implies that the
	      server attempts to drop root privileges at startup (otherwise,  chroot  gives  very
	      little additional security).  You may need to also specify a -u option.

       -I [address | interface name]
	      Open  the  network  address  given,  or all the addresses associated with the given
	      interface name.  This option may appear multiple times.  This option  also  implies
	      not  opening other addresses, except wildcard and localhost.  This option is depre-
	      cated.  Please consider using the configuration file interface  command,	which  is
	      more versatile.

       -k keyfile
	      Specify  the  name and path of the symmetric key file, default /etc/ntp.keys.  This
	      is the same operation as the keys keyfile configuration command.

       -l logfile
	      Specify the name and path of the log file.  The default is  the  system  log  file.
	      This is the same operation as the logfile logfile configuration command.

       -L     Do not listen to virtual IPs.  The default is to listen.

       -n     Don't fork.

       -N     To the extent permitted by the operating system, run the ntpd at the highest prior-
	      ity.

       -p pidfile
	      Specify the name and path of the file used to record the ntpd process ID.  This  is
	      the same operation as the pidfile pidfile configuration command.

       -P priority
	      To the extent permitted by the operating system, run the ntpd at the specified pri-
	      ority.

       -q     Exit the ntpd just after the first time the clock is  set.   This  behavior  mimics
	      that  of the ntpdate program, which is to be retired.  The -g and -x options can be
	      used with this option.  Note: The kernel time  discipline  is  disabled  with  this
	      option.

       -r broadcastdelay
	      Specify  the  default propagation delay from the broadcast/multicast server to this
	      client.  This is necessary only if the delay cannot be  computed	automatically  by
	      the protocol.

       -s statsdir
	      Specify  the  directory path for files created by the statistics facility.  This is
	      the same operation as the statsdir statsdir configuration command.

       -t key Add a key number to the trusted key list.  This option can occur more than once.

       -u user[:group]
	      Specify a user, and optionally a group, to switch to.

       -U interface_update_interval
	      Number of seconds to wait between interface list scans to pick up  new  and  delete
	      network  interface.   Set  to  0	to  disable dynamic interface list updating.  The
	      default is to scan every 5 minutes.

       -v variable, -V variable
	      Add a system variable listed by default.

       -x     Normally, the time is slewed if the offset is less than the step	threshold,  which
	      is  128  ms  by  default, and stepped if above the threshold.  This option sets the
	      threshold to 600 s, which is well within the accuracy window to set the clock manu-
	      ally.   Note:  Since  the slew rate of typical Unix kernels is limited to 0.5 ms/s,
	      each second of adjustment requires an amortization interval of 2000  s.	Thus,  an
	      adjustment  as much as 600 s will take almost 14 days to complete.  This option can
	      be used with the -g and -q options.  Note: The kernel time discipline  is  disabled
	      with this option.

FILES
       /etc/ntp.conf
	      default name of the configuration file

       /etc/ntp.drift
	      default name of the drift file

SEE ALSO
       ntp.conf(5), ntpdate(8)

       The  complete  documentation  can be found at /usr/share/doc/ntp-doc/html/ntpd.html in the
       package ntp-doc.

Debian					    2007-12-07					  NTPD(8)
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