timed -- time server daemon
timed [-dtM] [-i network | -n network] [-F host ...]
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.
Add network to the list of networks to ignore. All other networks
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. The timed utility 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.
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 master
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 provide
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 synchronize
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 interrupts
disabled. This means that the clock stops while they are printing.
A machine with many disk or network hardware problems and consequent messages
cannot keep good time by itself. Each message typically causes the
clock to lose a dozen milliseconds. A time daemon can correct the
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.
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.
/var/log/timed.log tracing file for timed
/var/log/timed.masterlog log file for master timed
date(1), adjtime(2), gettimeofday(2), icmp(4), networks(5), ntpd(8),
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX
The timed utility appeared in 4.3BSD.
FreeBSD 5.2.1 June 6, 1993 FreeBSD 5.2.1 [ Back ]