CLOCKDIFF(8)			    iputils			  CLOCKDIFF(8)

NAME
       clockdiff - measure clock difference between hosts

SYNOPSIS
       clockdiff [-o] [-o1] [--time-format ctime iso] [-V] {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] 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.

       -T, --time-format ctime iso
	   Print time stamp in output either ISO-8601 format or classical
	   ctime format. The ctime format is default. The ISO time stamp
	   includes timezone, and is easier to parse.

       -I
	   Alias of --time-format iso  option and argument.

       -h, --help
	   Print help and exit.

       -V, --version
	   Print version and exit.

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 and CAP_SYS_NICE capabilities to be
       executed. It is safe to be used as set-uid root.

AVAILABILITY
       clockdiff is part of iputils package.

iputils 20250605						  CLOCKDIFF(8)