CLOCKDIFF(8)	       System Manager's Manual: iputils		 CLOCKDIFF(8)



NAME
       clockdiff - measure clock difference between hosts

SYNOPSIS
       clockdiff [ -o]	[ -o1]	destination


DESCRIPTION
       clockdiff  Measures clock difference between us and destination with 1
       msec resolution using ICMP TIMESTAMP [2] packets	 or,  optionally,  IP
       TIMESTAMP option [3] option added to ICMP ECHO.	[1]

OPTIONS
       -o     Use  IP TIMESTAMP with ICMP ECHO instead of ICMP TIMESTAMP mes-
	      sages. It is useful with some destinations, which do  not	 sup-
	      port ICMP TIMESTAMP (f.e. Solaris <2.4).

       -o1    Slightly	different  form	 of  -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. Particu-
	      larly, -o is better for Linux.

WARNINGS
       ? Some nodes (Cisco) use non-standard timestamps, which is allowed  by
	 RFC, but makes timestamps mostly useless.

       ? Some nodes generate messed timestamps (Solaris>2.4), when run xntpd.
	 Seems, its IP stack uses a corrupted clock source, which is synchro-
	 nized	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.

       ? clockdiff shows difference in time modulo 24 days.

SEE ALSO
       ping(8), arping(8), tracepath(8).

REFERENCES
       [1] ICMP ECHO, RFC0792, page 14.

       [2] ICMP TIMESTAMP, RFC0792, page 16.

       [3] IP TIMESTAMP option, RFC0791, 3.1, page 16.

AUTHOR
       clockdiff  was compiled by Alexey Kuznetsov . It
       was based on code borrowed from BSD timed daemon.

SECURITY
       clockdiff requires CAP_NET_RAWIO capability to be executed. It is safe
       to be used as set-uid root.

AVAILABILITY
       clockdiff  is  part  of	iputils	 package  and the latest versions are
       available in source form	 for  anonymous	 ftp  ftp://ftp.inr.ac.ru/ip-
       routing/iputils-current.tar.gz.



iputils-020927		      27 September 2002			 CLOCKDIFF(8)

UNIX/Linux commands referenced on this page:

1. clock
2. which
3. addresses
4. time
5. as
6. ftp