TIMED(8) | System Manager's Manual | TIMED(8) |
timed
—
timed |
[-dMt ] [-F
host ...] [-G
netgroup] [-i
network | -n
network] |
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
-F
host ...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-M
flag. This option may only
be specified once.-i
networktimed
. This option may be specified multiple times
to add more than one network to the list.-M
timed
master if
necessary.-n
networktimed
. This option may be specified multiple times
to add more than one network to the list.-t
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 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.
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.
timed
timed
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX 4.3BSD.
timed
utility appeared in
4.3BSD.
May 11, 1993 | NetBSD 9.4 |