TIMED(8)                             BSD                              TIMED(8)



NAME
     timed - time server daemon

SYNOPSIS
     /etc/timed [ -t ] [ -M ] [ -n network ] [ -i network ]

DESCRIPTION
     timed is the time server daemon and is normally invoked at boot time from
     the rc(8) file. It synchronizes the host's time with the time of other
     machines in a local area network running timed(8).  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.  timed also communicates with date(1) in order
     to set the date globally, and with timedc(8), a timed control program.

     The service provided by timed is based on a master-slave scheme.  Started
     with or without the -M option, timed checks the local area network for a
     master.  It becomes a slave if a master already exists or if it was
     started without the -M option.  A newly created slave asks the master for
     the network time and uses adjtime(2) to set the host's clock to that
     time.  After that, the slave accepts synchronization messages
     periodically sent by the master and uses adjtime(2) to perform the needed
     corrections on the host's clock. Since the correction is expressed as a
     time difference rather than an absolute time, transmission delays do not
     interfere with the accuracy of the synchronization.

     A slave whose clock is ahead of the master of a set of participating
     machines adjusts itself backward before joining the set.  No time
     synchronization is done over the period of time it takes the
     participating machines to adjust themselves to an earlier time specified
     with date(1).  timed logs an error under conditions that require it to
     set its machine's clock backwards in excess of ADJTIME_MAX_DELTA
     (<sys/time.h>).  If the machine is a slave, timed exits.  If the machine
     is a master, timed continues.

     Specifying -t enables trace mode, in which timed logs messages it
     receives in /usr/adm/timed.log.  Use timedc(8) to turn trace mode on or
     off.

     A machine that starts timed with the -M option becomes the master if none
     already exists.  A master may control up to 254 slaves.  If the master
     crashes, then the slaves having been started with the -M option elect a
     new master from among themselves.  Use timedc(8) to find out who's
     master.

     A time daemon running on a gateway may act as a submaster.  A submaster
     classifies each network to which it is connected as one of three types.
     A slave network is a network on which the submaster acts as a slave.
     There can be only one slave network.  A master network is a network on
     which the submaster acts as a master.  An ignored network is any other
     network which already has a valid master.  The submaster tries
     periodically to become master on ignored networks, but gives up
     immediately if a master already exists.

     The -n network option tells the time daemon running on a gateway to
     attend only to network, and ignore all others.  The -i network option
     tells the time daemon running on a gateway to ignore only network, and to
     attend to all others.  In each case, network must be a legitimate address
     (see networks(5)).  A time daemon running on a gateway typically would be
     instructed to ignore all but the networks belonging to the local

     administrative control.

     There's a pathological condition that can arise in the case where, let's
     say, machines A and B are both gateways between networks X and Y.  If
     time daemons were started on both A and B without constraints, it would
     be possible for submaster time daemon A to be a slave on network X and
     the master on network Y, while submaster time daemon B is a slave on
     network Y and the master on network X.  This loop of master time daemons
     will not function properly or guarantee a unique time on both networks,
     and will cause the submasters to use large amounts of system resources in
     the form of network bandwidth and CPU time.  This kind of loop can also
     be generated with more than two master time daemons, when several local
     area networks are interconnected.

FILES
     /usr/adm/timed.log           tracing file for timed
     /usr/adm/timed.masterlog     log file for master timed

SEE ALSO
     date(1), adjtime(2), gettimeofday(2), icmp(4P), timedc(8).