<refentry id="clockdiff">

<refmeta>
<refentrytitle>clockdiff</refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo>iputils-&snapshot;</refmiscinfo>
</refmeta>

<refnamediv>
<refname>clockdiff</refname>
<refpurpose>measure clock difference between hosts</refpurpose>
</refnamediv>

<refsynopsisdiv>
<cmdsynopsis>
<command>clockdiff</command>
<arg choice="opt"><option>-o</option></arg>
<arg choice="opt"><option>-o1</option></arg>
<arg choice="req"><replaceable/destination/</arg>
</cmdsynopsis>
</refsynopsisdiv>

<refsect1><title>DESCRIPTION</title>
<para>
<command/clockdiff/ Measures clock difference between us and
<replaceable/destination/ with 1 msec resolution using ICMP TIMESTAMP
<link linkend="clockdiff.icmp-timestamp">[2]</link>
packets or, optionally, IP TIMESTAMP option
<link linkend="clockdiff.ip-timestamp">[3]</link>
option added to ICMP ECHO.
<link linkend="clockdiff.icmp-echo">[1]</link>
</para>
</refsect1>

<refsect1><title>OPTIONS</title>

<variablelist>

 <varlistentry>
  <term><option/-o/</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/</term>
  <listitem><para>
Slightly different form of <option/-o/, 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/ is better for Linux.
  </para></listitem>
 </varlistentry>

</variablelist>

</refsect1>

<refsect1><title>WARNINGS</title>
<itemizedlist>
 <listitem><para>
Some nodes (Cisco) use non-standard timestamps, which is allowed
by RFC, but makes timestamps mostly useless.
 </para></listitem>
 <listitem><para>
Some nodes generate messed timestamps (Solaris&gt;2.4), when
run <command/xntpd/. 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>
 <listitem><para>
<command/clockdiff/ shows difference in time modulo 24 days.
 </para></listitem>
</itemizedlist>

</refsect1>

<refsect1><title>SEE ALSO</title>
<para>
<link linkend="ping">
<citerefentry><refentrytitle/ping/<manvolnum/8/</citerefentry></link>,
<link linkend="arping">
<citerefentry><refentrytitle/arping/<manvolnum/8/</citerefentry></link>,
<link linkend="tracepath">
<citerefentry><refentrytitle/tracepath/<manvolnum/8/</citerefentry></link>.
</para>
</refsect1>

<refsect1><title>REFERENCES</title>
<para>
[1] <anchor id="clockdiff.icmp-echo">ICMP ECHO,
<ulink url="http://tools.ietf.org/rfc/rfc792.txt">
RFC0792, page 14</ulink>.
</para>
<para>
[2] <anchor id="clockdiff.icmp-timestamp">ICMP TIMESTAMP,
<ulink url="http://tools.ietf.org/rfc/rfc792.txt">
RFC0792, page 16</ulink>.
</para>
<para>
[3] <anchor id="clockdiff.ip-timestamp">IP TIMESTAMP option,
<ulink url="http://tools.ietf.org/rfc/rfc791.txt">
RFC0791, 3.1, page 16</ulink>.
</para>
</refsect1>

<refsect1><title>AUTHOR</title>
<para>
<command/clockdiff/ was compiled by
<ulink url="mailto:kuznet@ms2.inr.ac.ru">Alexey Kuznetsov
&lt;kuznet@ms2.inr.ac.ru&gt;</ulink>. It was based on code borrowed
from BSD <command/timed/ daemon.
It is now maintained by
<ulink url="mailto:yoshfuji@skbuff.net">YOSHIFUJI Hideaki
&lt;yoshfuji@skbuff.net&gt;</ulink>.
</para>
</refsect1>

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

<refsect1><title>AVAILABILITY</title>
<para>
<command/clockdiff/ is part of <filename/iputils/ package
and the latest versions are  available in source form at
<ulink url="http://www.skbuff.net/iputils/iputils-current.tar.bz2">
http://www.skbuff.net/iputils/iputils-current.tar.bz2</ulink>.
</para>
</refsect1>

<![IGNORE[
<refsect1><title>COPYING</title>
<para>
<literallayout>
This documentation is free software; you can redistribute
it and/or modify it under the terms of the GNU General Public
License Version 2.

This program is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.
 
For more details see the file COPYING in the source
distribution of Linux kernel of version 2.4.
</literallayout>
</para>
</refsect1>
]]>


</refentry>