TIMED(8) BSD System Manager's Manual TIMED(8)NAMEtimed — time server daemon
SYNOPSIStimed [-dtM] [-i network] [-n network] [-F host ...]
DESCRIPTION
The timed utility is a time server daemon, it is invoked at boot time by
setting the timed_enable variable in rc.conf(5). 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 mes‐
sage.
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 net‐
works 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.
-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 are mutually exclusive and require as arguments real net‐
works 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 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
receiver 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 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 timedSEE ALSOdate(1), adjtime(2), gettimeofday(2), icmp(4), networks(5), rc.conf(5),
timedc(8)
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX
4.3BSD.
HISTORY
The timed utility appeared in 4.3BSD.
BSD June 6, 1993 BSD
