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TIMED(8) BSD System Manager's Manual TIMED(8)
NAME
timed -- time server daemon
SYNOPSIS
timed [-dtM] [-i network | -n network] [-F host ...]
DESCRIPTION
The timed utility is a time server daemon which may be invoked at boot time via launchd(8). (See
launchd.plist(5) for more information about configuring daemons to run at boot.) 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 net-works. networks.
works.
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 synchro-nization synchronization
nization messages periodically sent by the master and calls adjtime(2) to perform the needed correc-tions corrections
tions on the host's clock.
It also communicates with date(1) in order to set the date globally, and with timedc(8), a timed con-trol control
trol utility. If the machine running the master becomes unreachable, the slaves will elect a new mas-ter master
ter 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 synchroniza-tion synchronization
tion 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), 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.
BSD February 11, 2008 BSD
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