NAME
timed —
time server daemon
SYNOPSIS
timed |
[-dMt]
[-F host
...] [-G
netgroup]
[-i network |
-n network] |
DESCRIPTION
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.
-
-
- -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.
-
-
- -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.
-
-
- -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.
WARNINGS
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.
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),
netgroup(5),
networks(5),
ntpd(8),
timedc(8)
R. Gusella and S.
Zatti, TSP: The Time Synchronization Protocol for
UNIX 4.3BSD.
HISTORY
The
timed utility appeared in
4.3BSD.