clockdiff(8) — Linux manual page


CLOCKDIFF(8)                       iputils                      CLOCKDIFF(8)

NAME         top

       clockdiff - measure clock difference between hosts

SYNOPSIS         top

       clockdiff [-o] [-o1] [--time-format ctime iso] [-V] {destination}

DESCRIPTION         top

       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         top

           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).

           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.

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

       -h, --help
           Print help and exit.

       -V, --version
           Print version and exit.

WARNINGS         top

           · 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         top

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

REFERENCES         top

       [1] ICMP ECHO, RFC0792, page 14.

       [2] ICMP TIMESTAMP, RFC0792, page 16.

       [3] IP TIMESTAMP option, RFC0791, 3.1, page 16.

AUTHOR         top

       clockdiff was compiled by Alexey Kuznetsov <>. It
       was based on code borrowed from BSD timed daemon.

SECURITY         top

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

AVAILABILITY         top

       clockdiff is part of iputils package.

COLOPHON         top

       This page is part of the iputils (IP utilities) project.  Information
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iputils s20200821                                               CLOCKDIFF(8)

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