TIMED(8) BSD System Manager's Manual TIMED(8)NAMEtimed - time server daemon
SYNOPSIStimed [-dMt] [-i network | -n network] [-F host ...] [-G netgroup]
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.
-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 ac-
cept 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 con-
nected networks are treated as trustworthy.
-G netgroup
Specify a netgroup of trustworthy hosts, in addition to any mas-
ters specified with the -M flag. This option may only be speci-
fied 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 start-
ed 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 mes-
sages 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 mas-
ter 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 pro-
vide 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 re-
ceiver 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 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 asso-
ciated with "multi-homed" machines that looked for time masters on more
than one network and eventually chose to become a slave on the other net-
work.
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 can-
not 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 timedSEE ALSOdate(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.
HISTORY
The timed utility appeared in 4.3BSD.
MirOS BSD #10-current May 11, 1993 1
