timed.8

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH timed 8
.SH Name
timed \- time server daemon
.SH Syntax
.B /usr/etc/timed
[ 
.B \-i | \-n
.I network 
][ 
.B \-E
][
.B \-M 
][
.B \-t
]
.SH Description
The 
.PN timed
.NXR "timed" "daemon"
daemon synchronizes a host's time with the time of other
machines in a local area network running
.PN timed .
It is normally invoked
at boot time from the
.PN /etc/rc.local
file.  
.PP
Servers running
.PN timed
slow down the clocks of some machines
and speed up the clocks of others to bring them all
to the average network time.
The average network time is computed from measurements of clock differences
with the Internet Communication Message Protocol (ICMP)
timestamp request message.
.PP
The service provided by 
.PN timed
is based on a master-slave scheme.
When
.PN 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 the 
.PN adjtime 
or
.PN settimeofday
routine to perform any corrections on the host's clock.
.PP
It also communicates with the
.PN date
command to set the date globally,
and with the 
.PN timed 
control program,
.PN timedc .
If the machine running the master crashes, then the slaves elect
a new master from among slaves running with the 
.PN \-M
flag set.  The
.PN \-M
flag provides time synchronization on any attached networks
where no current master server is detected.
Such a server propagates the time computed by the top-level master.
At least one 
.PN timed
daemon on each network must run with the
.PN \-M
option set to
allow it to become a 
.PN timed 
master.
.SH Options
.IP \-E 
Overrides the input of slaves.  Use the
.PN \-E
flag in conjunction with the 
.PN \-M
flag.  It specifies that a master
.PN timed
should not average the times of the slaves to calculate the network time but
should distribute the time of its local host as the network time.  This flag
allows a master 
.PN timed 
to distribute time to a network while the network time is controlled by an
outside agent such as the Network Time Protocol.
.IP "[\-i | \-n] \fInetwork\fP"
.RS
.IP \-i 
Specifies a network to ignore.  Each network that appears as an
argument to the 
.PN \-i
flag is added to the list of networks that
.PN timed
will ignore.  If the 
.PN \-i
flag is used,
.PN timed
accesses all networks to which the host is connected except for those 
networks specified as arguments to the
.PN \-i
flag.  
.IP \-n 
Specifies a network to use.  When the
.PN timed
is started, it gathers
information about all the network devices connected to the local
host.  If neither the 
.PN \-n
flag nor the 
.PN \-i
flag is used,
.PN timed
tries to access all the network devices connected to the local host.
The network argument to the
.PN \-n
flag is the name of a network that
.PN timed
should access.  
.IP
If the
.PN \-n
switch is used, only those networks specified by the 
.PN \-n
flag are accessed. 
.IP
Do not use the
.PN \-i
and
.PN \-n
flags together.
.RE
.IP \-M 
Allows a slave time server to become a master time server if the
master server crashes.  A system running the
.PN timed
daemon without the 
.PN \-M
flag set remains a slave.
The 
.PN timed
daemon checks for a master time server on each network to which
it is connected.  It requests synchronization service from the first
master server it locates.
.IP \-t 
Enables 
.PN timed
to trace the messages it receives in the
file 
.PN /usr/adm/timed.log .
Tracing can be enabled or disabled with the 
.PN timedc 
program.
.SH Restrictions
Any system running
.PN timed
with the
.PN \-E
and
.PN \-M
options set is eligible to become the 
.PN timed
master, and distribute its local time to all systems
running 
.PN timed
on its network.  Run the Network Time Protocol daemon,
.PN ntpd ,
instead of 
.PN timed
to prevent this behavior.
.SH Files
./".ta \w'/usr/adm/timed.masterlog     'u
.TP 35
.PN /etc/rc.local
Invokes the 
.PN timed
daemon each time the system boots
.TP 35
.PN /usr/adm/timed.log		
Tracing file for 
.PN timed
.TP 35
.PN /usr/adm/timed.masterlog	
Log file for master 
.PN timed 
.SH See Also
date(1), adjtime(2), gettimeofday(2), 
networks(5), ntpd(8), timedc(8)
.br
.I "Introduction to Networking and Distributed System Services"