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Run as root, it can correct the system clock to this offset as +well. It can be run as an interactive command or from a cron job. + + <p>This document applies to version 4.2.8p1 of <code>sntp</code>. + + <p>The program implements the SNTP protocol as defined by RFC 5905, the NTPv4 +IETF specification. + + <div class="shortcontents"> +<h2>Short Contents</h2> +<ul> +<a href="#Top">Simple Network Time Protocol User Manual</a> +</ul> +</div> + +<ul class="menu"> +<li><a accesskey="1" href="#sntp-Description">sntp Description</a>: Description +<li><a accesskey="2" href="#sntp-Invocation">sntp Invocation</a>: Invoking sntp +<li><a accesskey="3" href="#Usage">Usage</a>: Usage +</ul> + +<div class="node"> +<p><hr> +<a name="sntp-Description"></a> +<br> +</div> + +<!-- node-name, next, previous, up --> +<h3 class="section">Description</h3> + +<p>By default, <code>sntp</code> writes the local data and time (i.e., not UTC) to the +standard output in the format: + +<pre class="example"> 1996-10-15 20:17:25.123 (+0800) +4.567 +/- 0.089 secs +</pre> + <p>where +YYYY-MM-DD HH:MM:SS.SUBSEC is the local date and time, +(+0800) is the local timezone adjustment (so we would add 8 hours and 0 minutes to convert the reported local time to UTC), +and +the +4.567 +/- 0.089 secs indicates the time offset and +error bound of the system clock relative to the server clock. + +<div class="node"> +<p><hr> +<a name="sntp-Invocation"></a> +<br> +</div> + +<h3 class="section">Invoking sntp</h3> + +<p><a name="index-sntp-1"></a><a name="index-standard-Simple-Network-Time-Protocol-client-program-2"></a> + + <p><code>sntp</code> +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 +<code>cron</code> +job. + + <p>NTP (the Network Time Protocol) and SNTP (the Simple Network Time Protocol) +are defined and described by RFC 5905. + + <p>The default is to write the estimated correct local date and time (i.e. not +UTC) to the standard output in a format like: + + <p><code>'1996-10-15 20:17:25.123 (+0800) +4.567 +/- 0.089 [host] IP sN'</code> + + <p>where the +<code>'(+0800)'</code> +means that to get to UTC from the reported local time one must +add 8 hours and 0 minutes, +the +<code>'+4.567'</code> +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. +<code>'+/- 0.089'</code> +is the reported +<em>synchronization</em> <em>distance</em> +(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 +<code>'+/- ?'</code>. +If the +<em>host</em> +is different from the +<em>IP</em>, +both will be displayed. +Otherwise, only the +<em>IP</em> +is displayed. +Finally, the +<em>stratum</em> +of the host is reported. + + <p>This section was generated by <strong>AutoGen</strong>, +using the <code>agtexi-cmd</code> template and the option descriptions for the <code>sntp</code> program. +This software is released under the NTP license, <http://ntp.org/license>. + +<ul class="menu"> +<li><a accesskey="1" href="#sntp-usage">sntp usage</a>: sntp help/usage (<span class="option">--help</span>) +<li><a accesskey="2" href="#sntp-ipv4">sntp ipv4</a>: ipv4 option (-4) +<li><a accesskey="3" href="#sntp-ipv6">sntp ipv6</a>: ipv6 option (-6) +<li><a accesskey="4" href="#sntp-authentication">sntp authentication</a>: authentication option (-a) +<li><a accesskey="5" href="#sntp-broadcast">sntp broadcast</a>: broadcast option (-b) +<li><a accesskey="6" href="#sntp-concurrent">sntp concurrent</a>: concurrent option (-c) +<li><a accesskey="7" href="#sntp-gap">sntp gap</a>: gap option (-g) +<li><a accesskey="8" href="#sntp-kod">sntp kod</a>: kod option (-K) +<li><a accesskey="9" href="#sntp-keyfile">sntp keyfile</a>: keyfile option (-k) +<li><a href="#sntp-logfile">sntp logfile</a>: logfile option (-l) +<li><a href="#sntp-steplimit">sntp steplimit</a>: steplimit option (-M) +<li><a href="#sntp-ntpversion">sntp ntpversion</a>: ntpversion option (-o) +<li><a href="#sntp-usereservedport">sntp usereservedport</a>: usereservedport option (-r) +<li><a href="#sntp-timeout">sntp timeout</a>: timeout option (-t) +<li><a href="#sntp-wait">sntp wait</a>: wait option +<li><a href="#sntp-config">sntp config</a>: presetting/configuring sntp +<li><a href="#sntp-exit-status">sntp exit status</a>: exit status +<li><a href="#sntp-Usage">sntp Usage</a>: Usage +<li><a href="#sntp-Authors">sntp Authors</a>: Authors +</ul> + +<div class="node"> +<p><hr> +<a name="sntp-usage"></a>Next: <a rel="next" accesskey="n" href="#sntp-ipv4">sntp ipv4</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">sntp help/usage (<span class="option">--help</span>)</h4> + +<p><a name="index-sntp-help-3"></a> +This is the automatically generated usage text for sntp. + + <p>The text printed is the same whether selected with the <code>help</code> option +(<span class="option">--help</span>) or the <code>more-help</code> option (<span class="option">--more-help</span>). <code>more-help</code> will print +the usage text by passing it through a pager program. +<code>more-help</code> is disabled on platforms without a working +<code>fork(2)</code> function. The <code>PAGER</code> environment variable is +used to select the program, defaulting to <span class="file">more</span>. Both will exit +with a status code of 0. + +<pre class="example">sntp - standard Simple Network Time Protocol client program - Ver. 4.2.8p1 +Usage: sntp [ -<flag> [<val>] | --<name>[{=| }<val>] ]... \ + [ hostname-or-IP ...] + Flg Arg Option-Name Description + -4 no ipv4 Force IPv4 DNS name resolution + - prohibits the option 'ipv6' + -6 no ipv6 Force IPv6 DNS name resolution + - prohibits the option 'ipv4' + -a Num authentication Enable authentication with the key auth-keynumber + -b Str broadcast Listen to the address specified for broadcast time sync + - may appear multiple times + -c Str concurrent Concurrently query all IPs returned for host-name + - may appear multiple times + -d no debug-level Increase debug verbosity level + - may appear multiple times + -D Num set-debug-level Set the debug verbosity level + - may appear multiple times + -g Num gap The gap (in milliseconds) between time requests + -K Fil kod KoD history filename + -k Fil keyfile Look in this file for the key specified with -a + -l Fil logfile Log to specified logfile + -M Num steplimit Adjustments less than steplimit msec will be slewed + - it must be in the range: + greater than or equal to 0 + -o Num ntpversion Send int as our NTP protocol version + - it must be in the range: + 0 to 7 + -r no usereservedport Use the NTP Reserved Port (port 123) + -S no step OK to 'step' the time with settimeofday(2) + -s no slew OK to 'slew' the time with adjtime(2) + -t Num timeout The number of seconds to wait for responses + no wait Wait for pending replies (if not setting the time) + - disabled as '--no-wait' + - enabled by default + opt version output version information and exit + -? no help display extended usage information and exit + -! no more-help extended usage information passed thru pager + -> opt save-opts save the option state to a config file + -< Str load-opts load options from a config file + - disabled as '--no-load-opts' + - may appear multiple times + +Options are specified by doubled hyphens and their name or by a single +hyphen and the flag character. + + +The following option preset mechanisms are supported: + - reading file $HOME/.ntprc + - reading file ./.ntprc + - examining environment variables named SNTP_* + +Please send bug reports to: <http://bugs.ntp.org, bugs@ntp.org> +</pre> + <div class="node"> +<p><hr> +<a name="sntp-ipv4"></a>Next: <a rel="next" accesskey="n" href="#sntp-ipv6">sntp ipv6</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-usage">sntp usage</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">ipv4 option (-4)</h4> + +<p><a name="index-sntp_002dipv4-4"></a> +This is the “force ipv4 dns name resolution” option. + +<p class="noindent">This option has some usage constraints. It: + <ul> +<li>must not appear in combination with any of the following options: +ipv6. +</ul> + + <p>Force DNS resolution of the following host names on the command line +to the IPv4 namespace. +<div class="node"> +<p><hr> +<a name="sntp-ipv6"></a>Next: <a rel="next" accesskey="n" href="#sntp-authentication">sntp authentication</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-ipv4">sntp ipv4</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">ipv6 option (-6)</h4> + +<p><a name="index-sntp_002dipv6-5"></a> +This is the “force ipv6 dns name resolution” option. + +<p class="noindent">This option has some usage constraints. It: + <ul> +<li>must not appear in combination with any of the following options: +ipv4. +</ul> + + <p>Force DNS resolution of the following host names on the command line +to the IPv6 namespace. +<div class="node"> +<p><hr> +<a name="sntp-authentication"></a>Next: <a rel="next" accesskey="n" href="#sntp-broadcast">sntp broadcast</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-ipv6">sntp ipv6</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">authentication option (-a)</h4> + +<p><a name="index-sntp_002dauthentication-6"></a> +This is the “enable authentication with the key <var>auth-keynumber</var>” option. +This option takes a number argument <span class="file">auth-keynumber</span>. +Enable authentication using the key specified in this option's +argument. The argument of this option is the <span class="option">keyid</span>, a +number specified in the <span class="option">keyfile</span> as this key's identifier. +See the <span class="option">keyfile</span> option (<span class="option">-k</span>) for more details. +<div class="node"> +<p><hr> +<a name="sntp-broadcast"></a>Next: <a rel="next" accesskey="n" href="#sntp-concurrent">sntp concurrent</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-authentication">sntp authentication</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">broadcast option (-b)</h4> + +<p><a name="index-sntp_002dbroadcast-7"></a> +This is the “listen to the address specified for broadcast time sync” option. +This option takes a string argument <span class="file">broadcast-address</span>. + +<p class="noindent">This option has some usage constraints. It: + <ul> +<li>may appear an unlimited number of times. +</ul> + + <p>If specified <code>sntp</code> will listen to the specified address +for NTP broadcasts. The default maximum wait time +can (and probably should) be modified with <span class="option">-t</span>. +<div class="node"> +<p><hr> +<a name="sntp-concurrent"></a>Next: <a rel="next" accesskey="n" href="#sntp-gap">sntp gap</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-broadcast">sntp broadcast</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">concurrent option (-c)</h4> + +<p><a name="index-sntp_002dconcurrent-8"></a> +This is the “concurrently query all ips returned for host-name” option. +This option takes a string argument <span class="file">host-name</span>. + +<p class="noindent">This option has some usage constraints. It: + <ul> +<li>may appear an unlimited number of times. +</ul> + + <p>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 +<code>ntpd</code>, and therefore <code>sntp</code> will send queries to these IPs +one after another, with a 2-second gap in between each query. + + <p>The <span class="option">-c</span> or <span class="option">--concurrent</span> 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. +<div class="node"> +<p><hr> +<a name="sntp-gap"></a>Next: <a rel="next" accesskey="n" href="#sntp-kod">sntp kod</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-concurrent">sntp concurrent</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">gap option (-g)</h4> + +<p><a name="index-sntp_002dgap-9"></a> +This is the “the gap (in milliseconds) between time requests” option. +This option takes a number argument <span class="file">milliseconds</span>. +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. +<div class="node"> +<p><hr> +<a name="sntp-kod"></a>Next: <a rel="next" accesskey="n" href="#sntp-keyfile">sntp keyfile</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-gap">sntp gap</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">kod option (-K)</h4> + +<p><a name="index-sntp_002dkod-10"></a> +This is the “kod history filename” option. +This option takes a file argument <span class="file">file-name</span>. +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. +<div class="node"> +<p><hr> +<a name="sntp-keyfile"></a>Next: <a rel="next" accesskey="n" href="#sntp-logfile">sntp logfile</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-kod">sntp kod</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">keyfile option (-k)</h4> + +<p><a name="index-sntp_002dkeyfile-11"></a> +This is the “look in this file for the key specified with <span class="option">-a</span>” option. +This option takes a file argument <span class="file">file-name</span>. +This option specifies the keyfile. +<code>sntp</code> will search for the key specified with <span class="option">-a</span> +<span class="file">keyno</span> in this file. See <span class="command">ntp.keys(5)</span> for more +information. +<div class="node"> +<p><hr> +<a name="sntp-logfile"></a>Next: <a rel="next" accesskey="n" href="#sntp-steplimit">sntp steplimit</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-keyfile">sntp keyfile</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">logfile option (-l)</h4> + +<p><a name="index-sntp_002dlogfile-12"></a> +This is the “log to specified logfile” option. +This option takes a file argument <span class="file">file-name</span>. +This option causes the client to write log messages to the specified +<span class="file">logfile</span>. +<div class="node"> +<p><hr> +<a name="sntp-steplimit"></a>Next: <a rel="next" accesskey="n" href="#sntp-ntpversion">sntp ntpversion</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-logfile">sntp logfile</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">steplimit option (-M)</h4> + +<p><a name="index-sntp_002dsteplimit-13"></a> +This is the “adjustments less than <var>steplimit</var> msec will be slewed” option. +This option takes a number argument. +If the time adjustment is less than <span class="file">steplimit</span> milliseconds, +slew the amount using <span class="command">adjtime(2)</span>. Otherwise, step the +correction using <span class="command">settimeofday(2)</span>. The default value is 0, +which means all adjustments will be stepped. This is a feature, as +different situations demand different values. +<div class="node"> +<p><hr> +<a name="sntp-ntpversion"></a>Next: <a rel="next" accesskey="n" href="#sntp-usereservedport">sntp usereservedport</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-steplimit">sntp steplimit</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">ntpversion option (-o)</h4> + +<p><a name="index-sntp_002dntpversion-14"></a> +This is the “send <var>int</var> as our ntp protocol version” option. +This option takes a number argument. +When sending requests to a remote server, tell them we are running +NTP protocol version <span class="file">ntpversion</span> . +<div class="node"> +<p><hr> +<a name="sntp-usereservedport"></a>Next: <a rel="next" accesskey="n" href="#sntp-timeout">sntp timeout</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-ntpversion">sntp ntpversion</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">usereservedport option (-r)</h4> + +<p><a name="index-sntp_002dusereservedport-15"></a> +This is the “use the ntp reserved port (port 123)” option. +Use port 123, which is reserved for NTP, for our network +communications. +<div class="node"> +<p><hr> +<a name="sntp-timeout"></a>Next: <a rel="next" accesskey="n" href="#sntp-wait">sntp wait</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-usereservedport">sntp usereservedport</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">timeout option (-t)</h4> + +<p><a name="index-sntp_002dtimeout-16"></a> +This is the “the number of seconds to wait for responses” option. +This option takes a number argument <span class="file">seconds</span>. +When waiting for a reply, <code>sntp</code> will wait the number +of seconds specified before giving up. The default should be +more than enough for a unicast response. If <code>sntp</code> is +only waiting for a broadcast response a longer timeout is +likely needed. +<div class="node"> +<p><hr> +<a name="sntp-wait"></a>Next: <a rel="next" accesskey="n" href="#sntp-config">sntp config</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-timeout">sntp timeout</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">wait option</h4> + +<p><a name="index-sntp_002dwait-17"></a> +This is the “wait for pending replies (if not setting the time)” option. + +<p class="noindent">This option has some usage constraints. It: + <ul> +<li>can be disabled with –no-wait. +<li>It is enabled by default. +</ul> + + <p>If we are not setting the time, wait for all pending responses. + +<div class="node"> +<p><hr> +<a name="sntp-config"></a>Next: <a rel="next" accesskey="n" href="#sntp-exit-status">sntp exit status</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-wait">sntp wait</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">presetting/configuring sntp</h4> + +<p>Any option that is not marked as <i>not presettable</i> may be preset by +loading values from configuration ("rc" or "ini") files, and values from environment variables named <code>SNTP</code> and <code>SNTP_<OPTION_NAME></code>. <code><OPTION_NAME></code> must be one of +the options listed above in upper case and segmented with underscores. +The <code>SNTP</code> variable will be tokenized and parsed like +the command line. The remaining variables are tested for existence and their +values are treated like option arguments. + +<p class="noindent"><code>libopts</code> will search in 2 places for configuration files: + <ul> +<li>$HOME +<li>$PWD +</ul> + The environment variables <code>HOME</code>, and <code>PWD</code> +are expanded and replaced when <span class="file">sntp</span> runs. +For any of these that are plain files, they are simply processed. +For any that are directories, then a file named <span class="file">.ntprc</span> is searched for +within that directory and processed. + + <p>Configuration files may be in a wide variety of formats. +The basic format is an option name followed by a value (argument) on the +same line. Values may be separated from the option name with a colon, +equal sign or simply white space. Values may be continued across multiple +lines by escaping the newline with a backslash. + + <p>Multiple programs may also share the same initialization file. +Common options are collected at the top, followed by program specific +segments. The segments are separated by lines like: +<pre class="example"> [SNTP] +</pre> + <p class="noindent">or by +<pre class="example"> <?program sntp> +</pre> + <p class="noindent">Do not mix these styles within one configuration file. + + <p>Compound values and carefully constructed string values may also be +specified using XML syntax: +<pre class="example"> <option-name> + <sub-opt>...&lt;...&gt;...</sub-opt> + </option-name> +</pre> + <p class="noindent">yielding an <code>option-name.sub-opt</code> string value of +<pre class="example"> "...<...>..." +</pre> + <p><code>AutoOpts</code> does not track suboptions. You simply note that it is a +hierarchicly valued option. <code>AutoOpts</code> does provide a means for searching +the associated name/value pair list (see: optionFindValue). + + <p>The command line options relating to configuration and/or usage help are: + +<h5 class="subsubheading">version (-)</h5> + +<p>Print the program version to standard out, optionally with licensing +information, then exit 0. The optional argument specifies how much licensing +detail to provide. The default is to print just the version. The licensing infomation may be selected with an option argument. +Only the first letter of the argument is examined: + + <dl> +<dt><span class="samp">version</span><dd>Only print the version. This is the default. +<br><dt><span class="samp">copyright</span><dd>Name the copyright usage licensing terms. +<br><dt><span class="samp">verbose</span><dd>Print the full copyright usage licensing terms. +</dl> + +<div class="node"> +<p><hr> +<a name="sntp-exit-status"></a>Next: <a rel="next" accesskey="n" href="#sntp-Usage">sntp Usage</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-config">sntp config</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">sntp exit status</h4> + +<p>One of the following exit values will be returned: + <dl> +<dt><span class="samp">0 (EXIT_SUCCESS)</span><dd>Successful program execution. +<br><dt><span class="samp">1 (EXIT_FAILURE)</span><dd>The operation failed or the command syntax was not valid. +<br><dt><span class="samp">66 (EX_NOINPUT)</span><dd>A specified configuration file could not be loaded. +<br><dt><span class="samp">70 (EX_SOFTWARE)</span><dd>libopts had an internal operational error. Please report +it to autogen-users@lists.sourceforge.net. Thank you. +</dl> + <div class="node"> +<p><hr> +<a name="sntp-Usage"></a>Next: <a rel="next" accesskey="n" href="#sntp-Authors">sntp Authors</a>, +Previous: <a rel="previous" accesskey="p" href="#sntp-exit-status">sntp exit status</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">sntp Usage</h4> + +<div class="node"> +<p><hr> +<a name="sntp-Authors"></a>Previous: <a rel="previous" accesskey="p" href="#sntp-Usage">sntp Usage</a>, +Up: <a rel="up" accesskey="u" href="#sntp-Invocation">sntp Invocation</a> +<br> +</div> + +<h4 class="subsection">sntp Authors</h4> + +<div class="node"> +<p><hr> +<a name="Usage"></a> +<br> +</div> + +<!-- node-name, next, previous, up --> +<h3 class="section">Usage</h3> + +<p>The simplest use of this program is as an unprivileged command to +check the current time, offset, and error in the local clock. +For example: + +<pre class="example"> sntp ntpserver.somewhere +</pre> + <p>With suitable privilege, it can be run as a command or in a +<code>crom</code> job to reset the local clock from a reliable server, like +the <code>ntpdate</code> and <code>rdate</code> commands. +For example: + +<pre class="example"> sntp -a ntpserver.somewhere +</pre> + </body></html> + |