freebsd/usr.sbin/ntp/doc/sntp.8

.Dd February 4 2015
.Dt SNTP 8 User Commands
.Os
.\"  EDIT THIS FILE WITH CAUTION  (sntp-opts.mdoc)
.\"
.\" $FreeBSD$
.\"
.\"  It has been AutoGen-ed  February  4, 2015 at 02:34:20 AM by AutoGen 5.18.5pre4
.\"  From the definitions    sntp-opts.def
.\"  and the template file   agmdoc-cmd.tpl
.Sh NAME
.Nm sntp
.Nd standard Simple Network Time Protocol client program
.Sh SYNOPSIS
.Nm
.\" Mixture of short (flag) options and long options
.Op Fl flags
.Op Fl flag Op Ar value
.Op Fl \-option\-name Ns Oo Oo Ns "=| " Oc Ns Ar value Oc
[ hostname\-or\-IP ...]
.Pp
.Sh DESCRIPTION
.Nm
can be used as an SNTP client to query a NTP or SNTP server and either display
the time or set the local system's time (given suitable privilege).  It can be
run as an interactive command or from a
.Ic cron
job.
NTP (the Network Time Protocol) and SNTP (the Simple Network Time Protocol)
are defined and described by RFC 5905.
.Pp
The default is to write the estimated correct local date and time (i.e. not
UTC) to the standard output in a format like:
.Ic "'1996\-10\-15 20:17:25.123 (+0800) +4.567 +/\- 0.089 [host] IP sN'"
where the
.Ic "'(+0800)'"
means that to get to UTC from the reported local time one must
add 8 hours and 0 minutes,
the
.Ic "'+4.567'"
indicates the local clock is 4.567 seconds behind the correct time
(so 4.567 seconds must be added to the local clock to get it to be correct).
Note that the number of decimals printed for this value will change
based on the reported precision of the server.
.Ic "'+/\- 0.089'"
is the reported
.Em synchronization distance
(in seconds), which represents the maximum error due to all causes.
If the server does not report valid data needed to calculate the
synchronization distance, this will be reported as
.Ic "'+/\- ?'" .
If the
.Em host
is different from the
.Em IP ,
both will be displayed.
Otherwise, only the 
.Em IP
is displayed.
Finally, the
.Em stratum
of the host is reported.
.Sh "OPTIONS"
.Bl -tag
.It  Fl 4 , Fl \-ipv4 
Force IPv4 DNS name resolution.
This option must not appear in combination with any of the following options:
ipv6.
.sp
Force DNS resolution of the following host names on the command line
to the IPv4 namespace.
.It  Fl 6 , Fl \-ipv6 
Force IPv6 DNS name resolution.
This option must not appear in combination with any of the following options:
ipv4.
.sp
Force DNS resolution of the following host names on the command line
to the IPv6 namespace.
.It  Fl a Ar auth\-keynumber , Fl \-authentication Ns = Ns Ar auth\-keynumber 
Enable authentication with the key \fBauth\-keynumber\fP.
This option takes an integer number as its argument.
.sp
Enable authentication using the key specified in this option's
argument.  The argument of this option is the \fBkeyid\fP, a
number specified in the \fBkeyfile\fP as this key's identifier.
See the \fBkeyfile\fP option (\fB\-k\fP) for more details.
.It  Fl b Ar broadcast\-address , Fl \-broadcast Ns = Ns Ar broadcast\-address 
Listen to the address specified for broadcast time sync.
This option may appear an unlimited number of times.
.sp
If specified \fBsntp\fP will listen to the specified address
for NTP broadcasts.  The default maximum wait time
can (and probably should) be modified with \fB\-t\fP.
.It  Fl c Ar host\-name , Fl \-concurrent Ns = Ns Ar host\-name 
Concurrently query all IPs returned for host\-name.
This option may appear an unlimited number of times.
.sp
Requests from an NTP "client" to a "server" should never be sent
more rapidly than one every 2 seconds.  By default, any IPs returned
as part of a DNS lookup are assumed to be for a single instance of
\fBntpd\fP, and therefore \fBsntp\fP will send queries to these IPs
one after another, with a 2\-second gap in between each query.
.sp
The \fB\-c\fP or \fB\-\-concurrent\fP flag says that any IPs
returned for the DNS lookup of the supplied host\-name are on
different machines, so we can send concurrent queries.
.It  Fl d , Fl \-debug\-level 
Increase debug verbosity level.
This option may appear an unlimited number of times.
.sp
.It  Fl D Ar number , Fl \-set\-debug\-level Ns = Ns Ar number 
Set the debug verbosity level.
This option may appear an unlimited number of times.
This option takes an integer number as its argument.
.sp
.It  Fl g Ar milliseconds , Fl \-gap Ns = Ns Ar milliseconds 
The gap (in milliseconds) between time requests.
This option takes an integer number as its argument.
The default
.Ar milliseconds
for this option is:
.ti +4
 50
.sp
Since we're only going to use the first valid response we get and
there is benefit to specifying a good number of servers to query,
separate the queries we send out by the specified number of
milliseconds.
.It  Fl K Ar file\-name , Fl \-kod Ns = Ns Ar file\-name 
KoD history filename.
The default
.Ar file\-name
for this option is:
.ti +4
 /var/db/ntp\-kod
.sp
Specifies the filename to be used for the persistent history of KoD
responses received from servers.  If the file does not exist, a
warning message will be displayed.  The file will not be created.
.It  Fl k Ar file\-name , Fl \-keyfile Ns = Ns Ar file\-name 
Look in this file for the key specified with \fB\-a\fP.
.sp
This option specifies the keyfile.
\fBsntp\fP will search for the key specified with \fB\-a\fP
\fIkeyno\fP in this file.  See \fBntp.keys(5)\fP for more
information.
.It  Fl l Ar file\-name , Fl \-logfile Ns = Ns Ar file\-name 
Log to specified logfile.
.sp
This option causes the client to write log messages to the specified
\fIlogfile\fP.
.It  Fl M Ar number , Fl \-steplimit Ns = Ns Ar number 
Adjustments less than \fBsteplimit\fP msec will be slewed.
This option takes an integer number as its argument.
The value of
.Ar number
is constrained to being:
.in +4
.nf
.na
greater than or equal to 0
.fi
.in -4
.sp
If the time adjustment is less than \fIsteplimit\fP milliseconds,
slew the amount using \fBadjtime(2)\fP.  Otherwise, step the
correction using \fBsettimeofday(2)\fP.  The default value is 0,
which means all adjustments will be stepped.  This is a feature, as
different situations demand different values.
.It  Fl o Ar number , Fl \-ntpversion Ns = Ns Ar number 
Send \fBint\fP as our NTP protocol version.
This option takes an integer number as its argument.
The value of
.Ar number
is constrained to being:
.in +4
.nf
.na
in the range  0 through 7
.fi
.in -4
The default
.Ar number
for this option is:
.ti +4
 4
.sp
When sending requests to a remote server, tell them we are running
NTP protocol version \fIntpversion\fP .
.It  Fl r , Fl \-usereservedport 
Use the NTP Reserved Port (port 123).
.sp
Use port 123, which is reserved for NTP, for our network
communications.
.It  Fl S , Fl \-step 
OK to 'step' the time with \fBsettimeofday(2)\fP.
.sp
.It  Fl s , Fl \-slew 
OK to 'slew' the time with \fBadjtime(2)\fP.
.sp
.It  Fl t Ar seconds , Fl \-timeout Ns = Ns Ar seconds 
The number of seconds to wait for responses.
This option takes an integer number as its argument.
The default
.Ar seconds
for this option is:
.ti +4
 5
.sp
When waiting for a reply, \fBsntp\fP will wait the number
of seconds specified before giving up.  The default should be
more than enough for a unicast response.  If \fBsntp\fP is
only waiting for a broadcast response a longer timeout is
likely needed.
.It  Fl \-wait , " Fl \-no\-wait"
Wait for pending replies (if not setting the time).
The \fIno\-wait\fP form will disable the option.
This option is enabled by default.
.sp
If we are not setting the time, wait for all pending responses.
.It Fl \&? , Fl \-help
Display usage information and exit.
.It Fl \&! , Fl \-more\-help
Pass the extended usage information through a pager.
.It Fl > Oo Ar cfgfile Oc , Fl \-save\-opts Oo Ns = Ns Ar cfgfile Oc
Save the option state to \fIcfgfile\fP.  The default is the \fIlast\fP
configuration file listed in the \fBOPTION PRESETS\fP section, below.
The command will exit after updating the config file.
.It Fl < Ar cfgfile , Fl \-load\-opts Ns = Ns Ar cfgfile , Fl \-no\-load\-opts
Load options from \fIcfgfile\fP.
The \fIno\-load\-opts\fP form will disable the loading
of earlier config/rc/ini files.  \fI\-\-no\-load\-opts\fP is handled early,
out of order.
.It Fl \-version Op Brq Ar v|c|n
Output version of program and exit.  The default mode is `v', a simple
version.  The `c' mode will print copyright information and `n' will
print the full copyright notice.
.El
.Sh "OPTION PRESETS"
Any option that is not marked as \fInot presettable\fP may be preset
by loading values from configuration ("RC" or ".INI") file(s) and values from
environment variables named:
.nf
  \fBSNTP_<option\-name>\fP or \fBSNTP\fP
.fi
.ad
The environmental presets take precedence (are processed later than)
the configuration files.
The \fIhomerc\fP files are "\fI$HOME\fP", and "\fI.\fP".
If any of these are directories, then the file \fI.ntprc\fP
is searched for within those directories.
.Sh USAGE
.Bl -tag -width indent
.It Li "sntp ntpserver.somewhere"
is the simplest use of this program
and can be run as an unprivileged command
to check the current time and error in the local clock.
.It Li "sntp \-Ss \-M 128 ntpserver.somewhere"
With suitable privilege,
run as a command
or from a
.Xr cron 8
job,
.Ic "sntp \-Ss \-M 128 ntpserver.somewhere"
will request the time from the server,
and if that server reports that it is synchronized
then if the offset adjustment is less than 128 milliseconds
the correction will be slewed,
and if the correction is more than 128 milliseconds
the correction  will be stepped.
.It Li "sntp \-S ntpserver.somewhere"
With suitable privilege,
run as a command
or from a
.Xr cron 8
job,
.Ic "sntp \-S ntpserver.somewhere"
will set (step) the local clock from a synchronized specified server,
like the (deprecated)
.Xr ntpdate 8 ,
or
.Xr rdate 8
commands.
.El
.Sh "ENVIRONMENT"
See \fBOPTION PRESETS\fP for configuration environment variables.
.Sh "FILES"
See \fBOPTION PRESETS\fP for configuration files.
.Sh "EXIT STATUS"
One of the following exit values will be returned:
.Bl -tag
.It 0 " (EXIT_SUCCESS)"
Successful program execution.
.It 1 " (EXIT_FAILURE)"
The operation failed or the command syntax was not valid.
.It 66 " (EX_NOINPUT)"
A specified configuration file could not be loaded.
.It 70 " (EX_SOFTWARE)"
libopts had an internal operational error.  Please report
it to autogen\-users@lists.sourceforge.net.  Thank you.
.El
.Sh AUTHORS
.An "Johannes Maximilian Kuehn"
.An "Harlan Stenn"
.An "Dave Hart"
.Sh "COPYRIGHT"
Copyright (C) 1992\-2015 The University of Delaware and Network Time Foundation all rights reserved.
This program is released under the terms of the NTP license, <http://ntp.org/license>.
.Sh "BUGS"
Please send bug reports to: http://bugs.ntp.org, bugs@ntp.org
.Sh "NOTES"
This manual page was \fIAutoGen\fP\-erated from the \fBsntp\fP
option definitions.