CLOCKDIFF(8) - Linux man page online | Administration and privileged commands

Measure clock difference between hosts.

28 June 2019
CLOCKDIFF(8) System Manager's Manual: iputils CLOCKDIFF(8)


clockdiff - measure clock difference between hosts


clockdiff [-o] [-o1] destination


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]


-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 prespec‐ ified hop addresses instead of four term one. What flavor works better depends on target host. Particularly, -o is better for Linux.


· Some nodes (Cisco) use non-standard timestamps, which is allowed by RFC, but makes time‐ stamps 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.


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


[1] ICMP ECHO, RFC0792, page 14. [2] ICMP TIMESTAMP, RFC0792, page 16. [3] IP TIMESTAMP option, RFC0791, 3.1, page 16.


clockdiff was compiled by Alexey Kuznetsov <>. It was based on code borrowed from BSD timed daemon. It is now maintained by YOSHIFUJI Hideaki <yosh‐>.


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


clockdiff is part of iputils package and the latest versions are available in source form at
iputils-161105 28 June 2019 CLOCKDIFF(8)
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clockdiff(8) referred by arping(8)
refer to arping(8) | ping(8) | tracepath(8)
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