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 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. 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. It is now maintained by YOSHIFUJI Hideaki <>.

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 rent.tar.bz2.

iputils-071127 17 September 2013 CLOCKDIFF(8)