328 lines
9.9 KiB
Plaintext
328 lines
9.9 KiB
Plaintext
/* -*- Mode: Text -*- */
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autogen definitions options;
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#include autogen-version.def
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copyright = {
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date = "1970-2006";
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owner = "ntp.org";
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eaddr = "http://bugs.ntp.isc.org, bugs@ntp.org";
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type = note;
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text = `cat COPYRIGHT`;
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};
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prog-name = "sntp";
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prog-title = "standard SNTP program";
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homerc = $HOME, ".";
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long-opts;
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config-header = "config.h";
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#ifndef __windows__
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rcfile = ".ntprc";
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#else
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rcfile = "ntp.ini";
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#endif
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environrc;
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#include version.def
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test-main;
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flag = {
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name = ipv4;
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value = 4;
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equivalence = ipv4;
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descrip = "Force IPv4 DNS name resolution";
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doc = <<- _EndOfDoc_
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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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_EndOfDoc_;
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};
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flag = {
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name = ipv6;
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value = 6;
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equivalence = ipv4;
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descrip = "Force IPv6 DNS name resolution";
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doc = <<- _EndOfDoc_
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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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_EndOfDoc_;
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};
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flag = {
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name = unprivport;
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value = u;
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descrip = "Use an unprivileged port";
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doc = <<- _EndOfDoc_
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Use an unprivilegded UDP port for our queries.
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_EndOfDoc_;
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};
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flag = {
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name = normalverbose;
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value = v;
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flags-cant = extraverbose, megaverbose;
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descrip = "Slightly verbose";
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doc = <<- _EndOfDoc_
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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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_EndOfDoc_;
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};
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flag = {
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name = extraverbose;
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value = V;
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flags-cant = normalverbose, megaverbose;
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descrip = "Extra verbose";
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doc = <<- _EndOfDoc_
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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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_EndOfDoc_;
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};
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flag = {
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name = megaverbose;
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value = W;
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flags-cant = normalverbose, extraverbose;
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descrip = "Mega verbose";
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doc = <<- _EndOfDoc_
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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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_EndOfDoc_;
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};
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flag = {
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name = settimeofday;
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value = r;
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flags-cant = adjtime;
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descrip = "Set (step) the time with settimeofday()";
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doc = <<- _EndOfDoc_
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_EndOfDoc_;
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};
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flag = {
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name = adjtime;
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value = a;
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flags-cant = settimeofday;
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descrip = "Set (slew) the time with adjtime()";
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doc = <<- _EndOfDoc_
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_EndOfDoc_;
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};
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detail = <<- _END_DETAIL
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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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_END_DETAIL;
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prog-man-descrip = <<- _END_PROG_MAN_DESCRIP
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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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_END_PROG_MAN_DESCRIP;
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