CLOCKDIFF

Section: System Manager's Manual: iputils (8)
Updated: 19 July 2011
Index Return to Main Contents
 

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 messages. It is useful with some destinations, which do not support 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. Particularly, -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 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.
*
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 <[email protected]>. It was based on code borrowed from BSD timed daemon. It is now maintained by YOSHIFUJI Hideaki <[email protected]>.  

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 at http://www.skbuff.net/iputils/iputils-current.tar.bz2.


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
WARNINGS
SEE ALSO
REFERENCES
AUTHOR
SECURITY
AVAILABILITY

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