timed - time server daemon
timed [-dMt] [-i network | -n network] [-F host ...] [-G
netgroup]
The timed utility is a time server daemon which is normally
invoked at
boot time from the rc(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 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.
-G netgroup
Specify a netgroup of trustworthy hosts, in addition
to any masters
specified with the -M flag. This option may
only be specified
once.
-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 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 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 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 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 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), netgroup(5),
networks(5),
ntpd(8), rdate(8), timedc(8)
R. Gusella and S. Zatti, TSP: The Time Synchronization
Protocol for UNIX
4.3BSD.
The timed utility appeared in 4.3BSD.
OpenBSD 3.6 May 11, 1993
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