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

NAME
     timed — time server daemon

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

DESCRIPTION
     The timed utility 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.
	     - Can take one or more parameters.
	     - 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.
	     - Use real host names (resolvable by RDNS) not aliases (eg in
	       named(8) parlance: use A names, not C names).
	     - Use full names eg time1.domain.com not time1.
	     - -F automatically includes the functionality of -M ( so -M does
	       not need to asserted).
	     - If -F is not specified, all hosts on 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 flags are mutually exclusive and require as arguments real
     networks 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.

     The timed utility 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 utility.  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.  The timed utility 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 ntpd(8) to synchro‐
     nize the clock of one machine to a distant standard or a radio receiver
     and -F hostname to tell its timed 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), ntpd(8),
     timedc(8)

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

HISTORY
     The timed utility appeared in 4.3BSD.

BSD			       February 11, 2008			   BSD
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