clockdiff (8) - Linux Manuals

clockdiff: measure clock difference between hosts

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.

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 <kuznet [at] ms2.inr.ac.ru>. It was based on code borrowed from BSD timed daemon. It is now maintained by YOSHIFUJI Hideaki <yoshfuji [at] skbuff.net>.

SECURITY

clockdiff requires CAP_NET_RAW 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.