CLOCKDIFF

Index · Directives iputils s20180629

## 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 <kuznet@ms2.inr.ac.ru>. It was based on code borrowed from BSD timed daemon.

## 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.