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The service provided by timed is based on a master-slave scheme. When timed(ADMN) 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(S) to perform the needed corrections on the host's clock.
It also communicates with rdate(ADMN) to set the date globally, and with timedc(ADMN), a timed control program. If the machine running the master crashes, then the slaves will elect a new master from among slaves running with the -M flag. A timed running without the -M, -F, or -G flags will remain a slave. The -t flag enables timed to trace the messages it receives in the file /usr/adm/timed.log. Tracing can be turned on or off by the program timedc(ADMN).
timed normally detaches from the console and runs in the background. The -d flag can be used to force timed to remain in the foreground.
Normally, timed checks for a master time server on each network to which it is connected, except as modified by the options described below. It will request synchronization service from the first master server located. If permitted by the -M flag, it will provide synchronization service on any attached networks on which no current master server was detected. Such a server propagates the time computed by the top-level master. The -n flag, followed by the name of a network which the host is connected to (see networks(SFF)), overrides the default choice of the network addresses made by the program. Each time the -n flag appears, that network name is added to a list of valid networks. All other networks are ignored.
The -i flag, followed by the name of a network to which the host is connected (see networks(SFF)), overrides the default choice of the network addresses made by the program. Each time the -i flag appears, that network name is added to a list of networks to ignore. All other networks are used by the time daemon.
NOTE: The -n and -i flags will be meaningless if used together.
It is possible to use timed in an NTP environment. In this case, use the -M and -N flags in conjunction. timed will act as a master to other timed nodes, but will slave itself to the local clock updates performed by NTP.
The -F flag can be used for a similar purpose; it instructs timed to only trust the specified hosts. -N and -F local-host-name are functionally equivalent.
On systems which are running NIS, the -G option can be used to specify a ``net group'' of trusted hosts. This is a convenient short-hand for -F.
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 associated with ``multi-homed'' machines that looked for time masters on more than one network and eventually chose to become a slave on the other network.
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.