Radix cross Linux

Index: netdate.8
===================================================================
--- netdate.8	(nonexistent)
+++ netdate.8	(revision 5)
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+.TH NETDATE 8L 85/08/21
+.UC 4
+.SH NAME
+netdate \- set date and time by ARPA Internet RFC 868
+.SH SYNOPSIS
+.B
+netdate
+[ \-v ] [ \-l limit ] [ protocol ] hostname...
+.SH DESCRIPTION
+\fINetdate\fP takes a list of names of Internet hosts as arguments,
+selects the one which supplies the best time, and sets
+the system time accordingly.
+The invoker must be the super-user for the time to be set.
+Protocol names (either \fBudp\fP or \fBtcp\fP) may be
+interspersed with the host names, and determine the
+protocol which will be used to connect to the hosts
+whose names follow, up to the next protocol name or
+the end of the arguments.
+The default protocol is \fBudp\fP.
+.PP
+The ``best'' time is chosen by polling the named hosts
+once each to find their times and taking their differences
+from the local host's time.
+These differences are used to find the largest group of hosts
+whose times agree with each other within a certain limit.
+The first host in the largest group is picked as the best host.
+(The assumption is that the hosts which are usually most accurate
+will be named first.)
+That host is polled again and the local host's time is set to the result.
+The chosen host's time is checked on this second poll to insure that
+its difference from the local host's time has not varied more than the limit
+from its difference at the first poll.
+.PP
+The default limit is five seconds.  It may be set with the \fB\-l\fP option.
+The \fB\-v\fP option causes the groups to be shown.
+The host name \fBlocalhost\fP is recognized as a synonym for the name
+of the local host, no network connection is made for it, and its
+time difference is always zero.
+If \fBlocalhost\fP is chosen as having the best time,
+the system time will not be set.
+Hosts which do not respond are not counted in the groups.
+If the limit is set to zero, the time is set to that of the
+first host to respond and no other checking is done.
+Supplying only one host name argument also sets the limit to zero.
+.PP
+While the RFC868 protocol only returns 32\ bits of data, containing
+the time in seconds, \fInetdate\fP will accept an extra 32\ bits,
+containing microseconds (expected to be accurate to no more than milliseconds).
+Delays on long haul networks may make this extra precision useless,
+but it is useful on local area networks.
+The extra precision is not used on the first poll of a host,
+but it is used on the second poll of the chosen host,
+if that host supplies it.
+.SH EXAMPLE
+The most accurate hosts are named first in each example.
+Some such call on \fInetdate\fP should be put at the end of
+\fB/etc/rc.d/rc.local\fP,
+so that the time will be set properly on system startup.
+It is also useful to have a shell script, e.g., \fB/sbin/timehosts\fP,
+which contains a call on \fInetdate\fP with arguments appropriate
+to the local system, so that it is easy to set the time manually.
+.SH "netdate -l 30 udp dcn\-gate tcp neighbor"
+\fIDcn\-gate\fP is a hypothetical host which usually keeps time
+accurate to within milliseconds of Coordinated Universal Time,
+but may occasionally be eight hours off.
+\fINeighbor\fP is a neighbor of the local host which keeps time
+with moderate accuracy.
+The time will be set to that of \fIdcn\-gate\fP if that and \fIneighbor\fP
+agree to within thirty seconds, else it will not be set at all.
+This is almost good enough for most circumstances, but won't do
+when the local host's time is known to be wrong (e.g., after
+a long downtime or a bad crash) and must be set to something.
+If one of the hosts named is inaccurate or not responding, there is a problem.
+.SH "netdate -l 30 udp dcn\-gate tcp neighbor neighbor2"
+Only two of the three hosts named must agree on the time.
+The time will still be set (to that of the first neighbor),
+even if \fIdcn\-gate\fP is far off as long as the two neighbors agree.
+This is probably good enough for most cases.
+One can arbitrarily gerrymander the vote for more insurance
+(and less clarity), as in the following example.
+.SH "netdate\ udp\ dcn\-gate\ dcn1\ tcp\ bbn\-unix\ localhost\ neighbor"
+Here \fIdcn1\fP and \fIbbn\-unix\fP are more hypothetical very accurate
+timekeepers, at least one of which keeps time independently from
+\fIdcn\-gate\fP, one hopes.
+It is very likely that the time will be set to that one of those three
+very accurate hosts, as long as at least two of them agree, or at least
+one of them agrees with the neighbor or the local host's time.
+If all the foreign hosts disagree, the time will not be set,
+since \fBlocalhost\fP will be chosen as best.
+.SH "netdate\ \-l\ 3\ localhost\ localhost\ udp\ dcn\-gate\ dcn1\ tcp\ bbn\-unix"
+This example gives \fBlocalhost\fP two votes and declares it to usually
+have the most accurate time.
+All three foreign hosts must agree within three seconds
+and also differ from \fBlocalhosts\fP by more than three seconds
+for the time to be set.
+Thus the time will be set only if it really needs to be.
+.SH FILES
+.nf
+/etc/services	for the time service port number
+/etc/protocols	for the protocol numbers
+/var/log/wtmp	to record time-setting
+.SH SEE ALSO
+ARPANET Request for Comments 868, gettimeofday(2), date(1),
+WWV (USA):
+2.5,5,10,15 MHz AM for Coordinated Universal Time (UCT).
+.SH DIAGNOSTICS