401 lines
14 KiB
Groff
401 lines
14 KiB
Groff
.TH SNTP 1 2009-12-08 "( 4.2.4p8)" "Programmer's Manual"
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.\" EDIT THIS FILE WITH CAUTION (sntp.1)
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.\"
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.\" It has been AutoGen-ed Tuesday December 8, 2009 at 08:14:50 AM EST
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.\" From the definitions sntp-opts.def
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.\" and the template file agman1.tpl
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.\"
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.SH NAME
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sntp \- standard SNTP program
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.SH SYNOPSIS
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.B sntp
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.\" Mixture of short (flag) options and long options
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.RB [ \-\fIflag\fP " [\fIvalue\fP]]... [" \--\fIopt-name\fP " [[=| ]\fIvalue\fP]]..."
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.PP
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All arguments must be options.
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.SH "DESCRIPTION"
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This manual page documents, briefly, the \fBsntp\fP command.
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.I sntp
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can be used as a SNTP client to query a NTP or SNTP server and either display
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the time or set the local system's time (given suitable privilege). It can be
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run as an interactive command or in a
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.I cron
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job.
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NTP is the Network Time Protocol (RFC 1305) and SNTP is the
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Simple Network Time Protocol (RFC 2030, which supersedes RFC 1769).
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.SS Options
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.PP
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.I sntp
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recognizes the following options:
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.TP
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.B \-v
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indicates that diagnostic messages for non-fatal errors and a limited amount of
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tracing should be written to standard error. Fatal ones always produce a
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diagnostic. This option should be set when there is a suspected problem with
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the server, network or the source.
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.TP
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.B \-V
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requests more and less comprehensible output, mainly for investigating problems
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with apparently inconsistent timestamps. This option should be set when the
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program fails with a message indicating that is the trouble.
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.TP
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.B \-W
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requests very verbose debugging output, and will interfere with the timing
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when writing to the terminal (because of line buffered output from C). Note
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that the times produced by this are the corrections needed, and not the error
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in the local clock. This option should be set only when debugging the source.
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.TP
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.B \-q
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indicates that it should query a daemon save file being maintained by it.
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This needs no privilege and will change neither the save file nor the clock.
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.PP
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The default is that it should behave as a client, and the following options
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are then relevant:
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.TP
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.B \-r
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indicates that the system clock should be reset by
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.IR settimeofday .
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Naturally, this will work only if the user has enough privilege.
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.TP
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.B \-a
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indicates that the system clock should be reset by
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.IR adjtime .
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Naturally, this will work only if the user has enough privilege.
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.PP
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The default is to write the estimated correct local date and time (i.e. not
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UTC) to the standard output in a format like
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.BR "'1996 Oct 15 20:17:25.123 + 4.567 +/- 0.089 secs'" ,
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where the
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.B "'+ 4.567 +/- 0.089 secs'"
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indicates the estimated error in the time on the local system.
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.TP
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.BI \-l " lockfile"
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sets the name of the lock file to ensure that there is only
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one copy of
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.I sntp
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running at once. The default is installation-dependent, but will usually be
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.IR /etc/sntp.pid .
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.TP
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.BI \-e " minerr"
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sets the maximum ignorable variation between the clocks to
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.IR minerr .
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Acceptable values are from 0.001 to 1, and the default is 0.1 if a NTP host is
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is specified and 0.5 otherwise.
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.TP
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.BI \-E " maxerr"
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sets the maximum value of various delays that are deemed acceptable to
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.IR maxerr .
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Acceptable values are from 1 to 60, and the default is 5. It should sometimes
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be increased if there are problems with the network, NTP server or system
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clock, but take care.
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.TP
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.BI \-P " prompt"
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sets the maximum clock change that will be made automatically to
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.IR maxerr .
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Acceptable values are from 1 to 3600 or
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.IR no ,
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and the default is 30. If the program is being run interactively in ordinary
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client mode, and the system clock is to be changed, larger corrections will
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prompt the user for confirmation. Specifying
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.I no
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will disable this and the correction will be made regardless.
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.TP
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.BI \-c " count"
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sets the maximum number of NTP packets required to
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.IR count .
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Acceptable values are from 1 to 25 if a NTP host is specified and from 5 to 25
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otherwise, and the default is 5. If the maximum isn't enough, the system needs
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a better consistency algorithm than this program uses.
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.TP
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.BI \-d " delay"
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sets a rough limit on the total running time to
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.I delay
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seconds. Acceptable values are from 1 to 3600, and the default is 15 if a NTP
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host is specified and 300 otherwise.
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.TP
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.B \-4
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force IPv4 DNS resolution.
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.TP
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.B \-6
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force IPv6 DNS resolution.
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.PP
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.B address(es)
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are the DNS names or IP numbers of hosts to use for the challenge and response
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protocol; if no names are given, the program waits for broadcasts. Polling a
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server is vastly more reliable than listening to broadcasts. Note that a
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single component numeric address is not allowed, to avoid ambiguities. If
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more than one name is give, they will be used in a round-robin fashion.
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.PP
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Constraints:
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.IP
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.B minerr
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must be less than
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.B maxerr
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which must be less than
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.B delay
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(or, if a NTP host is not specified
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.BR delay / count "),"
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and
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.B count
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must be less than half of
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.BR delay .
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.IP
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In update mode,
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.B maxerr
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must be less than
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.BR prompt.
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.PP
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Note that none of the above values are closely linked to the limits described
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in the NTP protocol (RFC 1305).
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.SH USAGE
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The simplest use of this program is as an unprivileged command to check the
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current time and error in the local clock. For example:
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.IP
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.B sntp ntpserver.somewhere
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.PP
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With suitable privilege, it can be run as a command or in a
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.I cron
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job to reset the local clock from a reliable server, like the
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.I ntpdate
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and
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.I rdate
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commands. For example:
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.IP
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.B sntp \-a ntpserver.somewhere
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.PP
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More information on how to use this utility is given in the
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.I README
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file in the distribution. In particular, this
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.I man
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page does not describe how to set it up as a server, which needs special care
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to avoid propagating misinformation.
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.SH RETURN VALUE
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When used as a client in non-daemon mode, the program returns a zero exit
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status for success, and a non-zero one otherwise. When used as a daemon
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(either client or server), it does not return except after a serious error.
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.SH BUGS
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The program implements the SNTP protocol, and does not provide all NTP
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facilities. In particular, it contains no checks against any form of spoofing.
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If this is a serious concern, some network security mechanism (like a firewall
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or even just
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.IR tcpwrappers )
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should be installed.
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.PP
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There are some errors, ambiguities and inconsistencies in the RFCs, and this
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code may not interwork with all other NTP implementations. Any unreasonable
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restrictions should be reported as bugs to whoever is responsible. It may
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be difficult to find out who that is.
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.PP
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The program will stop as soon as it feels that things have got out of control.
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In client daemon mode, it will usually fail during an extended period of
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network or server inaccessibility or excessively slow performance, or when the
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local clock is reset by another process. It will then need restarting
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manually. Experienced system administrators can write a shell script, a
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.I cron
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job or put it in
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.IR inittab ,
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to do this automatically.
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.PP
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The error cannot be estimated reliably with broadcast packets or for the drift
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in daemon mode (even with client-server packets), and the guess made by the
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program may be wrong (possibly even very wrong). If this is a problem, then
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setting the
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.B \-c
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option to a larger value may help. Or it may not.
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.SH AUTHOR
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.I sntp
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was developed by N.M. Maclaren of the University of Cambridge Computing
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Service.
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.SH OPTIONS
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.TP
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.BR \-4 ", " \--ipv4
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Force IPv4 DNS name resolution.
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This option is a member of the ipv4 class of options.
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.sp
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Force DNS resolution of following host names on the command line
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to the IPv4 namespace.
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.TP
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.BR \-6 ", " \--ipv6
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Force IPv6 DNS name resolution.
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This option is a member of the ipv4 class of options.
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.sp
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Force DNS resolution of following host names on the command line
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to the IPv6 namespace.
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.TP
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.BR \-u ", " \--unprivport
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Use an unprivileged port.
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.sp
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Use an unprivilegded UDP port for our queries.
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.TP
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.BR \-v ", " \--normalverbose
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Slightly verbose.
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This option must not appear in combination with any of the following options:
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extraverbose, megaverbose.
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.sp
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Diagnostic messages for non-fatal errors and a limited amount of
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tracing should be written to standard error. Fatal ones always
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produce a diagnostic. This option should be set when there is a
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suspected problem with the server, network or the source.
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.TP
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.BR \-V ", " \--extraverbose
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Extra verbose.
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This option must not appear in combination with any of the following options:
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normalverbose, megaverbose.
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.sp
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Produce more and less comprehensible output, mainly for investigating
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problems with apparently inconsistent timestamps. This option should
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be set when the program fails with a message indicating that is the
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trouble.
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.TP
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.BR \-W ", " \--megaverbose
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Mega verbose.
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This option must not appear in combination with any of the following options:
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normalverbose, extraverbose.
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.sp
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Very verbose debugging output that will interfere with the timing
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when writing to the terminal (because of line buffered output from C).
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Note that the times produced by this are the corrections needed, and
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not the error in the local clock. This option should be set only when
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debugging the source.
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.TP
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.BR \-r ", " \--settimeofday
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Set (step) the time with settimeofday().
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This option must not appear in combination with any of the following options:
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adjtime.
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.sp
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.TP
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.BR \-a ", " \--adjtime
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Set (slew) the time with adjtime().
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This option must not appear in combination with any of the following options:
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settimeofday.
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.sp
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.TP
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.BR \-? , " \--help"
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Display usage information and exit.
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.TP
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.BR \-! , " \--more-help"
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Extended usage information passed thru pager.
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.TP
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.BR \-> " [\fIrcfile\fP]," " \--save-opts" "[=\fIrcfile\fP]"
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Save the option state to \fIrcfile\fP. The default is the \fIlast\fP
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configuration file listed in the \fBOPTION PRESETS\fP section, below.
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.TP
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.BR \-< " \fIrcfile\fP," " \--load-opts" "=\fIrcfile\fP," " \--no-load-opts"
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Load options from \fIrcfile\fP.
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The \fIno-load-opts\fP form will disable the loading
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of earlier RC/INI files. \fI--no-load-opts\fP is handled early,
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out of order.
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.TP
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.BR \-v " [{\fIv|c|n\fP}]," " \--version" "[=\fI{v|c|n}\fP]"
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Output version of program and exit. The default mode is `v', a simple
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version. The `c' mode will print copyright information and `n' will
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print the full copyright notice.
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.SH OPTION PRESETS
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Any option that is not marked as \fInot presettable\fP may be preset
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by loading values from configuration ("RC" or ".INI") file(s) and values from
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environment variables named:
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.nf
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\fBSNTP_<option-name>\fP or \fBSNTP\fP
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.fi
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.aj
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The environmental presets take precedence (are processed later than)
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the configuration files.
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The \fIhomerc\fP files are "\fI$HOME\fP", and "\fI.\fP".
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If any of these are directories, then the file \fI.ntprc\fP
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is searched for within those directories.
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.SH AUTHOR
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ntp.org
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.br
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Please send bug reports to: http://bugs.ntp.org, bugs@ntp.org
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.PP
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.nf
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.na
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General Public Licence for the software known as MSNTP
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\------------------------------------------------------
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(c) Copyright, N.M. Maclaren, 1996, 1997, 2000
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(c) Copyright, University of Cambridge, 1996, 1997, 2000
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Free use of MSNTP in source and binary forms is permitted, provided that this
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entire licence is duplicated in all copies, and that any documentation,
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announcements, and other materials related to use acknowledge that the software
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was developed by N.M. Maclaren (hereafter refered to as the Author) at the
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University of Cambridge. Neither the name of the Author nor the University of
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Cambridge may be used to endorse or promote products derived from this material
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without specific prior written permission.
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The Author and the University of Cambridge retain the copyright and all other
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legal rights to the software and make it available non-exclusively. All users
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must ensure that the software in all its derivations carries a copyright notice
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in the form:
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(c) Copyright N.M. Maclaren,
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(c) Copyright University of Cambridge.
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NO WARRANTY
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Because the MSNTP software is licensed free of charge, the Author and the
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University of Cambridge provide absolutely no warranty, either expressed or
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implied, including, but not limited to, the implied warranties of
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merchantability and fitness for a particular purpose. The entire risk as to
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the quality and performance of the MSNTP software is with you. Should MSNTP
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prove defective, you assume the cost of all necessary servicing or repair.
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In no event, unless required by law, will the Author or the University of
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Cambridge, or any other party who may modify and redistribute this software as
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permitted in accordance with the provisions below, be liable for damages for
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any losses whatsoever, including but not limited to lost profits, lost monies,
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lost or corrupted data, or other special, incidental or consequential losses
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that may arise out of the use or inability to use the MSNTP software.
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COPYING POLICY
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Permission is hereby granted for copying and distribution of copies of the
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MSNTP source and binary files, and of any part thereof, subject to the
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following licence conditions:
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1. You may distribute MSNTP or components of MSNTP, with or without additions
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developed by you or by others. No charge, other than an "at-cost" distribution
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fee, may be charged for copies, derivations, or distributions of this material
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without the express written consent of the copyright holders.
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2. You may also distribute MSNTP along with any other product for sale,
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provided that the cost of the bundled package is the same regardless of whether
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MSNTP is included or not, and provided that those interested only in MSNTP must
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be notified that it is a product freely available from the University of
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Cambridge.
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3. If you distribute MSNTP software or parts of MSNTP, with or without
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additions developed by you or others, then you must either make available the
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source to all portions of the MSNTP system (exclusive of any additions made by
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you or by others) upon request, or instead you may notify anyone requesting
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source that it is freely available from the University of Cambridge.
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4. You may not omit any of the copyright notices on either the source files,
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the executable files, or the documentation.
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5. You may not omit transmission of this License agreement with whatever
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portions of MSNTP that are distributed.
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6. Any users of this software must be notified that it is without warranty or
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guarantee of any nature, express or implied, nor is there any fitness for use
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represented.
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October 1996
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April 1997
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October 2000
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.fi
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.ad
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.PP
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This manual page was \fIAutoGen\fP-erated from the \fBsntp\fP
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option definitions.
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