timed(8)

NAME

timed - time server daemon

SYNOPSIS

timed [-M] [-t] [-d] [-i network]  [-n  network]  [-F  host1
host2 ...]

DESCRIPTION

This is a time server daemon and is normally invoked at boot

time from
the rc(8) file. It synchronizes the host's time with the

time of other
machines in a local area network running timed 8. 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 aver

age network
time is computed from measurements of clock differences us

ing the ICMP
timestamp request message.

The service provided by timed is based on a master-slave

scheme. When
timed 8 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 ac

cepts synchro
nization 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 crashes, then the slaves will elect a new master from

among slaves
running with the -M flag. A timed running without the -M or

-F flags
will remain a slave. The -t flag enables timed to trace the

messages it
receives in the file /var/log/timed.log. Tracing can be

turned on or off
by the program timedc(8). The -d flag is for debugging the

daemon. It
causes the program to not put itself into the background.

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 syn
chronization 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, fol
lowed by the name of a network which the host is connected

to (see
networks(5)), 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(5)), overrides the default choice of the net

work 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. The -n and -i flags are meaningless if

used together.

Timed checks for a master time server on each network to

which it is con
nected, except as modified by the -n and -i options de

scribed above. If
it finds masters on more than one network, it chooses one

network on
which to be a "slave," and then periodically checks the oth

er networks to
see if the masters there have disappeared.

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 typi

cally causes the
clock to lose a dozen milliseconds. A time daemon can cor

rect the
result.

Messages in the system log about machines that failed to re

spond usually
indicate machines that crashed or were turned off. Com

plaints 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 slaves on

other networks.

WARNINGS

If two or more time daemons, whether timed or ntp, try to

adjust the same
clock, temporal chaos will result. If both timed and anoth

er 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 us

ing 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), timedc(8)

R. Gusella and S. Zatti, TSP: The Time Synchronization

Protocol for UNIX
4.3BSD.

HISTORY

The timed daemon appeared in 4.3BSD.

Linux NetKit (0.17) May 11, 1993 Linux

NetKit (0.17)