clockdiff — measure clock difference between hosts
clockdiff  [
        -o
      ] [
        -o1
      ] [
        --time-format
        
      ] [
        ctime iso-V
      ] {destination}
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]
-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  option and argument.iso
          
-h
        , 
          --help
        Print help and exit.
-V
        , 
          --version
        Print version and exit.
• 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.
[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 <kuznet@ms2.inr.ac.ru>. It was based on code borrowed from BSD timed daemon.