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.conf(5)
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.
- Can take one or more parameters.
timed
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.
- Use real host names (resolvable by RDNS) not aliases (eg in
named(8)
parlance: use A names, not C names).
- Use full names eg time1.domain.com not time1.
-F
automatically includes the functionality of -M
(so -M
does not need to asserted).
- If
-F
is not specified, all hosts on connected
networks are treated as trustworthy.
-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
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.
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
The timed
utility appeared in
4.3BSD.