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<refentry id='clockdiff8'>
<refmeta>
  <refentrytitle>CLOCKDIFF</refentrytitle>
  <manvolnum>8</manvolnum>
  <refmiscinfo class='manual'>iputils</refmiscinfo>
</refmeta>
<refnamediv>
  <refname>clockdiff</refname>
  <refpurpose>measure clock difference between hosts</refpurpose>
</refnamediv>
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<refsynopsisdiv id='synopsis'>
  <cmdsynopsis>
    <command>clockdiff</command>
    <arg choice='opt'>-o </arg>
    <arg choice='opt'>-o1 </arg>
    <arg choice='plain'><replaceable>destination</replaceable></arg>
    <sbr/>
  </cmdsynopsis>
</refsynopsisdiv>


<refsect1 id='description'>
  <title>DESCRIPTION</title>
  <para><command>clockdiff</command> Measures clock difference between us and
<emphasis remap='I'>destination</emphasis> with 1 msec resolution using ICMP TIMESTAMP [2] packets or, optionally, IP TIMESTAMP option [3] option added to ICMP ECHO.
[1]</para>
</refsect1>

<refsect1 id='options'>
  <title>OPTIONS</title>
  <variablelist remap='TP'>
    <varlistentry>
    <term><option>-o</option></term>
    <listitem>
<para>Use IP TIMESTAMP with ICMP ECHO instead of ICMP TIMESTAMP
messages. It is useful with some destinations, which do not support
ICMP TIMESTAMP (f.e. Solaris &lt;2.4).</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-o1</option></term>
  <listitem>
<para>Slightly different form of <option>-o</option>, namely it uses three-term
IP TIMESTAMP with prespecified hop addresses instead of four term one.
What flavor works better depends on target host. Particularly,
<option>-o</option> is better for Linux.</para>
  </listitem>
  </varlistentry>
</variablelist>
</refsect1>

<refsect1 id='warnings'>
  <title>WARNINGS</title>
<variablelist remap='TP'>
  <varlistentry>
  <listitem><para>&bull; Some nodes (Cisco) use non-standard timestamps, which is allowed by RFC, but makes timestamps mostly useless.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <listitem><para>&bull; Some nodes generate messed timestamps (Solaris&gt;2.4), when run <emphasis remap='B'>xntpd</emphasis>. Seems, its IP stack uses a corrupted clock source, which is synchronized to time-of-day clock periodically and jumps
randomly making timestamps mostly useless. Good news is that you can use NTP in this case, which is even better.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <listitem><para>&bull; <command>clockdiff</command> shows difference in time modulo 24 days.</para>
  </listitem>
  </varlistentry>
</variablelist>
</refsect1>

<refsect1 id='see_also'>
  <title>SEE ALSO</title>
<para><citerefentry><refentrytitle>ping</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>arping</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>tracepath</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</refsect1>

<refsect1 id='references'>
  <title>REFERENCES</title>
  <para>[1] ICMP ECHO, RFC0792, page 14.</para>
  <para>[2] ICMP TIMESTAMP, RFC0792, page 16.</para>
  <para>[3] IP TIMESTAMP option, RFC0791, 3.1, page 16.</para>
</refsect1>

<refsect1 id='author'>
  <title>AUTHOR</title>
  <para><command>clockdiff</command> was compiled by
Alexey Kuznetsov
&lt;kuznet@ms2.inr.ac.ru&gt;. It was based on code borrowed
from BSD <emphasis remap='B'>timed</emphasis> daemon.</para>
</refsect1>

<refsect1 id='security'>
  <title>SECURITY</title>
  <para><command>clockdiff</command> requires CAP_NET_RAW capability
to be executed. It is safe to be used as set-uid root.</para>
</refsect1>

<refsect1 id='availability'>
  <title>AVAILABILITY</title>
  <para><command>clockdiff</command> is part of <emphasis remap='I'>iputils</emphasis> package.</para>
</refsect1>
</refentry>