clockdiff



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


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 for anonymous ftp ftp://ftp.inr.ac.ru/ip-rout-
       ing/iputils-current.tar.gz.



iputils-020927                   07 April 2005                    CLOCKDIFF(8)

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