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TIMED(8)		FreeBSD	System Manager's Manual		      TIMED(8)

NAME
     timed -- time server daemon

SYNOPSIS
     timed [-dtM] [-i network] [-n network] [-F	host ...]

DESCRIPTION
     The timed daemon is a time	server daemon which is normally	invoked	at
     boot time from the	rc.network(8) file.  It	synchronizes the host's	time
     with the time of other machines, which are	also running timed, in a local
     area network.  These time servers will slow down the clocks of some
     machines and speed	up the clocks of others	to bring them to the average
     network time.  The	average	network	time is	computed from measurements of
     clock differences using the ICMP timestamp	request	message.

     The following options are available:

     -d	     Enable debugging mode; do not detach from the terminal.

     -i	network
	     Add network to the	list of	networks to ignore.  All other net-
	     works to which the	machine	is directly connected are used by
	     timed.  This option may be	specified multiple times to add	more
	     than one network to the list.

     -F	host ...
	     Create a list of trusted hosts.  timed will only accept trusted
	     hosts as masters.	If it finds an untrusted host claiming to be
	     master, timed will	suppress incoming messages from	that host and
	     call for a	new election.  This option implies the -M option.  If
	     this option is not	specified, all hosts on	the connected networks
	     are treated as trustworthy.

     -M	     Allow this	host to	become a timed master if necessary.

     -n	network
	     Add network to the	list of	allowed	networks.  All other networks
	     to	which the machine is directly connected	are ignored by timed.
	     This option may be	specified multiple times to add	more than one
	     network to	the list.

     -t	     Enable tracing of received	messages and log to the	file

     /var/log/timed.log.
	     Tracing can be turned on or off while timed is running with the
	     timedc(8) utility.

     The -n and	-i are mutually	exclusive and require as arguments real	net-
     works to which the	host is	connected (see networks(5)).  If neither flag
     is	specified, timed will listen on	all connected networks.

     A timed running without the -M nor	-F flags will always remain a slave.
     If	the -F flag is not used, timed will treat all machines as trustworthy.

     timed is based on a master-slave scheme.  When timed is started on	a
     machine, it asks the master for the network time and sets the host's
     clock to that time.  After	that, it accepts synchronization messages
     periodically sent by the master and calls adjtime(2) to perform the
     needed corrections	on the host's clock.

     It	also communicates with date(1) in order	to set the date	globally, and
     with timedc(8), a timed control program.  If the machine running the mas-
     ter becomes unreachable, the slaves will elect a new master from among
     those slaves which	are running with at least one of the -M	and -F flags.

     At	startup	timed normally checks for a master time	server on each network
     to	which it is connected, except as modified by the -n and	-i options
     described above.  It will request synchronization service from the	first
     master server located.  If	permitted by the -M or -F flags, it will pro-
     vide synchronization service on any attached networks on which no trusted
     master server was detected.  Such a server	propagates the time computed
     by	the top-level master.  timed will periodically check for the presence
     of	a master on those networks for which it	is operating as	a slave.  If
     it	finds that there are no	trusted	masters	on a network, it will begin
     the election process on that network.

     One way to	synchronize a group of machines	is to use an NTP daemon	to
     synchronize the clock of one machine to a distant standard	or a radio
     receiver and -F hostname to tell its timed	daemon to trust	only itself.

     Messages printed by the kernel on the system console occur	with inter-
     rupts disabled.  This means that the clock	stops while they are printing.
     A machine with many disk or network hardware problems and consequent mes-
     sages cannot keep good time by itself.  Each message typically causes the
     clock to lose a dozen milliseconds.  A time daemon	can correct the
     result.

     Messages in the system log	about machines that failed to respond usually
     indicate machines that crashed or were turned off.	 Complaints about
     machines that failed to respond to	initial	time settings are often	asso-
     ciated with "multi-homed" machines	that looked for	time masters on	more
     than one network and eventually chose to become a slave on	the other net-
     work.

WARNINGS
     Temporal chaos will result	if two or more time daemons attempt to adjust
     the same clock.  If both timed and	another	time daemon are	run on the
     same machine, ensure that the -F flag is used, so that timed never
     attempts to adjust	the local clock.

     The protocol is based on UDP/IP broadcasts.  All machines within the
     range of a	broadcast that are using the TSP protocol must cooperate.
     There cannot be more than a single	administrative domain using the	-F
     flag among	all machines reached by	a broadcast packet.  Failure to	follow
     this rule is usually indicated by complaints concerning "untrusted"
     machines in the system log.

FILES
     /var/log/timed.log	       tracing file for	timed
     /var/log/timed.masterlog  log file	for master timed

SEE ALSO
     date(1), adjtime(2), gettimeofday(2), icmp(4), networks(5), timedc(8)

     R.	Gusella	and S. Zatti, TSP: The Time Synchronization Protocol for UNIX
     4.3BSD.

HISTORY
     The timed daemon appeared in 4.3BSD.

FreeBSD	9.2			 June 6, 1993			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | WARNINGS | FILES | SEE ALSO | HISTORY

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